With the research methods and principles determined in the previous chapter, we can now carry out substantive research. The first thing we must study here is the largest problem humanity is facing, as well as the large problems we may face soon.
The two factors that act upon human beings are external and internal. This chapter focuses on the external elements that may threaten or influence human beings.
SECTION ONE: THREATS FROM THE UNIVERSE
When we stand on Earth and look towards the towering mountains, mighty rivers, and magnificent oceans, we are often amazed by the mightiness of our planet. However, from the perspective of the universe, the earth is miniscule. It is only one small member within the sun’s stellar system. Its mass is three-hundred-and-forty-thousandth of the solar system, and it is completely subject to the sun’s control.
In the vast universe, the role of the sun is much smaller compared to that of the earth within its star system. As a star system, the solar system is two-hundred-billionth of the entire Milky Way, and the Milky Way only occupies three-hundred-billionth of the universe. The solar system is nothing more than a drop of water or a speck of dust within the vastness of the universe.
When considering threats to mankind from the universe, we will first consider humans and the earth together, since humans cannot survive without the earth. Then we will consider the earth and sun together, since the earth is subject to the sun and will be influenced by it, thus influencing humans as well. Lastly, we will consider the solar system as one point, since that is what it signifies within the universe at large.
One: Gravity and Star History
There is one force in nature that cannot be obstructed by any object or distance, and that is the gravitational force between substances. Humans have weight while standing on Earth because the earth has gravitational pull on humans. That gravitational force is equal to one’s weight; the moon orbits the earth without fail because the earth’s gravity attracts the moon; similarly, the earth orbits the sun due to the sun’s gravitational pull. The sun rotates around the center of the Milky Way due to the Milky Way’s gravitational force.
Gravity was first discovered when Isaac Newton observed apples falling from the tree instead of flying to the sky. In our daily life, many natural phenomena are caused by gravity. The rise and fall of ocean tides are caused by the gravity of the sun and moon. The sun’s gravity not only acts on the side of the earth facing it, but the other side is affected by the sun’s gravity as well. Two planets tens of thousands of light-years apart have gravity between them as well.
In addition to gravity, there are three other forces in the natural world: electromagnetic force, and the strong and weak forces within the nucleus. The strong force is the strongest among the four natural forces, but it only acts within the nucleus. The second strongest force is electromagnetic force; it is only one- hundredth times the strength of strong force, but its scope is much larger. It is electromagnetic force that stops nuclei from touching and prevents the strong force from being released. In addition, the release of the strong force is dependent on neutrons; weak force is the force that causes protons to decay into neutrons, making it a necessary aid in the release of strong force. Gravitational force is the weakest force in nature; it is millions of billions of times weaker than electromagnetic force, and weaker still than strong force. However, gravitational force is not subject to restraint from any sort of distance or object. It is omnipresent and all encompassing, allowing its weaknesses to unite into incredible power, overcoming all other forces to rule our universe.
A star is a planet that produces heat and light through the use of nuclear energy. Nuclear energy is produced when a planet is large enough to exert gravitational force on its core temperature until it reaches more than ten million degrees. When this happens, the hydrogen nuclei that make up the star will produce violent movement, eventually breaking through the exclusion of electromagnetic force and colliding with each other, resulting in nuclear fusion and the release of strong force.
The nuclear fusion of hydrogen is a process that combines four hydrogen atoms into one helium atom; 0.7 percent of its mass is lost in the process. That is the cost of releasing nuclear strong force; a very small amount of loss in mass can produce huge amounts of energy. For other stars similar in size to our sun, nuclear fusion occurs twice: once as hydrogen fusion, and once as helium fusion.
When hydrogen fusion produces light and heat, the helium it produces is deposited into the core of the star. Once large amounts of hydrogen become helium through fusion, the hydrogen levels at the star’s core will be exhausted with mainly helium atoms left, but hydrogen will continue to burn outside the star’s core. Two forces will occur at the same time in the star’s core: one is the gravitational force of the star, and the other is the expansion pressure caused by hydrogen fusion outside the core. When the combined strength of these two forces causes the core’s temperature to reach one hundred million degrees, the helium nuclei will break through the electromagnetic force and collide, resulting in helium fusion and strong force release.
When helium burns, it transforms into oxygen and carbon, and since it releases even more energy than hydrogen fusion, it will be as if another star ignited within the star’s interior. This inner star will force the outer star to expand, making the star’s diameter a hundred times bigger, and its volume a million times larger. The new star will be very large, but its surface temperature will be lower than the original star’s surface temperature, and it will appear red in color; it is called a red giant.
Helium fusion does not last as long as hydrogen fusion. During the later stages of helium fusion the star will enter an unstable state. The material in the star’s periphery will be thrown out, while the core—composed mainly of carbon and oxygen—will collapse into a highly dense, very hot white dwarf star.
White dwarfs are dead stars, and although they have a high temperature, that temperature is just remnant heat from the original star. No more thermonuclear reactions can take place within this star. After tens of billions of years of slow cooling, it will become an ice-cold planet. According to human standards, white dwarfs are priceless materials. The materials inside it are arranged in a lattice-like structure, just like the structure of a diamond; sadly, this huge diamond would be difficult to obtain.
Since hydrogen fusion is more stable and lasting in comparison to other fusions, the hydrogen fusion stage is known as the main star sequence of a star in astronomy. The time a star stays in the main star sequence decreases rapidly as its mass grows. A star like the sun stays in the main star sequence for about ten billion years; however, a star 0.3 times the mass of the sun burns for thousands of billions of years, while a star five times the mass of the sun only burns for tens of millions of years. This is because a star will have stronger gravitational force the larger its mass. This gravitational force will speed up the internal nuclear fusion speed of the star. Once the star’s mass reaches a certain extent, the extreme violence of nuclear fusions will destabilize the star, causing it to explode. That is why stars cannot be infinitely large. So far, the largest star we have observed is the R136α1 star; its mass is about three hundred times that of the sun.
A star’s mass cannot be too small, either. The smallest star will generally not be less than 8 percent of the sun’s mass, because a star would not have sufficient gravitational force to ignite hydrogen atoms and create nuclear fusion if it were too small. If it cannot produce light and heat, it cannot be called a star.
The final fate of a star is largely determined by its mass. A star with mass less than 0.7 times that of the sun will not have strong enough gravity; it will only burn hydrogen. Its helium will never be ignited. A star with mass 0.7–8 times that of the sun would share in the sun’s fate. Within this mass interval, smaller stars will burn hydrogen first and helium later, while larger stars will also burn carbon. After these stars cease to burn, they will quietly evolve into white dwarves.
A star whose mass is greater than eight to ten times that of the sun will explode violently after its star death. Once a star has mass eight to ten times the mass of the sun, the great force of gravity within it will continue to ignite other elements after hydrogen, helium, and carbon are exhausted. These other elements in order are: oxygen, neon, silicon, and iron. Every time a new heavy element is ignited, another inner star with even bigger energy will be produced, continuously enlarging the outer star from within until its diameter reaches tens of billions of kilometers. When this ignition process reaches the element iron, iron’s nuclear combustion not only releases energy, but it also absorbs energy. Once the star’s interior loses the support of energy, a catastrophic result occurs. This star that had reached tens of billions of kilometers in diameter will suddenly collapses towards its center, causing an extremely violent explosion. The material of the star will be tossed hundreds of billions of kilometers away. This explosion is known as a supernova.
When a supernova occurs, the core of a star will be brutally compressed, and electrons will be pressed into protons. Since electrons are negatively charged and electrons are positively charged, this compression of electron into protons will cancel out the positive and negative charges, producing neutrons. The newly formed neutron star will be extremely dense; it can reach up to hundreds of millions of tons per cubic centimeter in density.
Neutron stars have very strong magnetic fields; they are 108 to 1,015 times stronger than that of Earth, and they rotate very quickly, reaching up to several hundred rotations every second. Neutron stars can emit strong electromagnetic waves (light) through its two magnetic poles. Since a neutron star’s magnetic axis and its axis of rotation does not coincide, the electromagnetic waves it emits during rotation will circulate space regularly; this is the lighthouse effect of the neutron star. A neutron star’s lighthouse effect can indicate direction in space. The many spacecrafts we send into the universe carrying information to aliens are directed by the position of neutron stars.
When a star with even bigger mass explodes, the violent collapse will crush the nuclei within it, forming an even more compact and dense celestial object—so dense that even light cannot escape its gravity. This is the black hole. The existence of black holes in the universe has already been confirmed.
Two: Black Hole Swallowing
When we stand on earth and throw an object towards the sky, this object will eventually fall back to the ground because Earth’s gravity is acting on it. Without Earth’s gravitational force, this object will fly out into space in the same direction it was thrown, never to return. Even though the Earth has gravity, once the speed of the thrown object reaches a certain extent, it will escape Earth’s gravitational force and travel forward ceaselessly. This speed is called the escape velocity. The escape velocity of Earth’s surface is 11.2 kilo- meters per second. In other words, when we throw an object towards space at a speed of 11.2 kilometers per second from Earth, this object will no longer fall back to the ground but fly into space. Escape velocity is different on the surface of different planets. The escape velocity of the sun is 617 kilometers per second; the escape velocity of the moon’s surface is 2.38 kilometers per second. The escape velocity of the sun’s surface is much bigger than that of the earth’s, because the sun’s gravitational force is larger than that of Earth’s. The moon’s surface escape velocity is smaller because the moon’s gravity is smaller than Earth’s gravity.
Light has the fastest speed in nature; it can travel three hundred thousand kilometers per second. When a planet’s gravity is exceedingly large and its surface escape velocity reaches the speed of light, it becomes a black hole. Even light cannot escape from a black hole. If the earth were compressed into a little ball one centimeter in radius, tinier even than a ping-pong ball, it would become a black hole. Black holes are not rare in the universe. Could our solar system fall into one such a black hole? If that were to happen, it would undoubtedly be the end of mankind.
The largest black hole in the Milky Way lies in the Galactic Center. Let us first analyze the threat this black hole poses to us. We know that the sun rotates around the Galactic Center once every 250 million years. Since the sun has been formed for five billion years, it should have rotated thus twenty times. From what we observe today, there is no indication of irregularity in the rotation of the solar system. The black hole in the center of the Milky Way swallows the planets within the Galactic Center; in order for other stars to be swallowed, they must first enter this range. The solar system is located relatively far from the Galactic
Center on the outer edge of the Milky Way; it is 270,000 light-years away from the Galactic Center. While rotating around the Galactic Center, as long as the sun does not change its trajectory drastically, it should not reach the Galactic Center within the next tens of billions of years. In order for the sun’s trajectory to change drastically, a planet equivalent in size to the sun would have to collide with it. If such a collision took place, the devastation of humanity would not be caused by black hole swallowing, but by this collision instead.
From another point of view, this also illustrates that the sun will not be swallowed by the Galactic Center black hole until its star death. The universe has a history of 12.8 billion years; scientists generally believe that the Milky Way formed not long after the formation of the universe, though the specific numbers differ. The European Southern Observatory (ESO) estimates the Milky Way to have formed 13.6 billion years ago and the Galactic Center’s black hole to have a mass about 2.6 million times that of the sun. The Milky Way’s mass totals about two hundred billion times the mass of the sun, which means that the black hole at the Galactic Center swallowed eighty thousandth of the stars in the Milky Way in 13.6 billion years. With this speed, it would take about a trillion years for the entire Milky Way to be swallowed. The sun will only remain in its main star sequence for five billion more years, so there is no need to worry about being swallowed by the Galactic Center black hole.
In addition to the black hole at the Galactic Center, would there be any other black holes that could swallow the sun? Apart from the Galactic Center, black holes are also likely to appear in the heart of globular star clusters. As a globular cluster will have tens of thousands to millions of stars clustered in a relatively small concentrated area, its center is likely to produce a black hole. Of course, such black holes would be much smaller than the black hole in the center of the Milky Way; it would only be hundreds of thousands of times the mass of the sun. At present, astronomers have observed X-rays emitting from the center of some globular clusters; this is evidence that black holes do indeed exist within globular clusters.
There are about five hundred globular clusters in the Milky Way, but they are all far away from us. The brightest globular cluster we can see is the Centaurus. It has about one million stars and is sixteen thousand light- years away from us. The globular cluster nearest to us is M4; it has about one hundred thousand stars and is 7,200 light-years away from us, which of course is a very safe distance.
Apart from the black hole in the Galactic Center and the ones in the centers of globular clusters, other black holes formed through the death of larger independent stars also exist. Astronomers have already observed such black holes in the universe, but they are all very far away from us. The most famous among them is the Cygnus X-1. This is a black hole relatively close to us at 10,000 light-years away from the solar system. To date, the nearest black hole observed from us is located in Sagittarius; it forms a binary system with an ordinary star numbered V4641SGR. This black hole is 1,200 light-years away from the solar system. Both 10,000 and 1,600 light-years are a safe enough distance away, as neither could affect the safety of the solar system.
In fact, a medium-sized black hole poses about the same threat to the solar system as a star. At best, a black hole will have a slightly larger threat range, but since the distance between stars is so great, such a range is almost negligible. At the same time, stars large enough to form black holes are few and far between in the universe. Only about one in ten thousand stars has the ability to form a black hole. The possibility of the sun encountering a black hole is only one-ten-thousandth that of it encountering stellar collision.
Three: Stars, Rogue Planet Collision, and Supernovas
1. Stars and Rogue Planet Collision
Today’s universe is the domain of stars. Stars not only occupy a great proportion of the universe, but they are also readily visible. The sun is a star, and we humans rely on its glory to survive. There are hundreds of billions of stars in the Milky Way. Could the sun collide with or be seriously disturbed by one such star, causing the overall ecological destruction of Earth and the extinction of humanity?
Let us first analyze the regional environment in which the solar system is located. The solar system is located on the outer edge of the Milky Way; the planet concentration in this area is much sparser compared to the Galactic Center and galactic nucleus. The star nearest to the solar system is the Alpha Centauri, a triple star system consisting of three stars. Within the Alpha Centauri, the Alpha Centauri C is closer to us at 4.25 light-years; it is thus also known as the Proxima Centauri. A little farther away from us than the Alpha Centauri is the Barnard’s Star, 5.96 light-years away, and the Wolf 359, 7.8 light-years away. All other stars are more than eight light-years away from us, and only seven-star systems exist within ten light-years of us. According to our observation of the Alpha Centauri, it is currently approaching us at a slightly fixed angle and will reach a minimum distance of three light-years from us in many years before moving away again.
Regarding the possibility of stellar collision, this set of data can best illustrate the situation: if we shrink the 139.2 kilometer in diameter sun into a small speck of sand one mm in diameter, the star nearest to us would be29.2 kilometers away, and the average star distance to us would be fifty-two kilometers, making the chance of collision very minimal.
More importantly, the little specks of “sand” sparsely distributed in the three-dimensional space are not randomly arranged and rocketing around; they are moving very slowly in regular patterns. Take the star’s operation as an example: this grain of sand only moves 4.92 meters every year. On top of that, all stars are orbiting the Galactic Center on their own trajectories without exception. They respect each other and follow a strict order. In the universe, the larger in mass a celestial object is, the more regular it is and the less likely it will be disturbed by external forces. A celestial object on the level of a star rarely changes trajectory; the gravitational force of the Galactic Center is one of the only forces strong enough to act on it. For a star like the sun that exists in the sparsely populated edge of the galaxy, stellar collision and stellar disturbance are both extremely unlikely to occur, even once in hundreds of billions of years.
There are also some planets in the universe that do not emit heat or light; they are not affiliated to stars or star systems and thus cannot be counted as ordinary planets. These planets only exist because they were too small when they first formed, so they were only able to ignite the hydrogen atoms in their center. These planets can only form independent systems rotating around their own centers; we may call them rogue planets. Are they likely to collide with the sun or cause disturbances?
Because the number of naturally formed small objects will always be higher than the number of naturally formed large objects in the universe, rogue planets will outnumber stars. Such planets may likely exist around the solar system; they are merely undiscovered. However, the number of such planets will still be quite small. If we apply the previous metaphor, the danger of one such planet colliding with or seriously disturbing the sun is similar to the addition of two or three slow-moving, even smaller specks of sand within a range dozens of kilometers in radius.
Moreover, rogue planets move along a set trajectory just like stars; they are also ruled by the gravitational force of the Milky Way’s center and orbit the Galactic Center in an orderly manner. Rogue planets each have their own orbit, and the disturbance among them is minimal... thus the possibility of collision between these sparsely distributed sand specks is even smaller. In fact, even if two galaxies merged, the possibility of collision—even in the center intersection area where planets are most concentrated—would be small at less than one in a hundred billionth. This is because relative to the size of stars, the distance between stars is much too big.
Some people will ask: If the possibility of celestial body collision is so small, why do we still observe such occurrences happening? Celestial body collision or interference generally only happens in three situations: one is within the center of a star system; the second is within the center of a star cluster; and the third is between companion stars. The center area of any star system will have the most material and star concentration. From the very beginning of a star system’s formation, a gravitational center will occur and attract as much material as possible, creating a center in the star system. At the same time, once a star system is formed, material and celestial bodies close to the center area will be pulled towards the center due to gravitational force. However, the attraction of celestial bodies toward the center of the galaxy happens very slowly. For peripheral stars like our solar system, this will not be an issue for at least hundreds of billions of years.
The same holds true for star clusters. During the formation of star systems, certain areas with higher density formed star clusters where tens of thousands or millions of stars cluster in one small space. Star clusters must have their own centers as well; this center will have an even higher concentration of stars and material, so the possibility of stellar collision will be greater. Fortunately, our solar system is far from any star cluster and will not join their crowded ranks.
Many stars in the universe are binary or triple stars, meaning they are two or three stars wound closely together. In systems like this, due to gravity, any star will have great influence on its companions and will also be greatly influenced by their companions. That is why such companion systems are often very unstable. Our solar system is obviously not one such star system.
2. Supernovas
Supernovas are the most violent eruptions known to happen in the stellar world, increasing the brightness of the star tens of thousands or even hundreds of millions of times in a very short time. Stellar material is thrown out at a rate of up to ten thousand kilometers per second, and the powerful radiation can strongly affect a very large area. In terms of threats in the universe, the threat of supernovas is far larger than that of stellar and rogue planet collision or disturbance, and even more so than that of black holes. Supernovas are the threats that really should be paid attention to in the universe.
There are two types of supernovas, type I and type II. Type I supernovas are the result of closely orbiting binary stars. The principle is this: if two stars are grouped closely together in a binary system and one is larger in mass, the larger star will evolve into a denser white dwarf star first while the other star is still burning. Since stars are gas planets that have flow, the white dwarf star will attract material from its neighbor with its gravitational force, forming a layer of hydrogen around the white dwarf star. Once this hydrogen layer builds to a certain extent, its temperature will rise to a great height under the white dwarf’s gravity. Once that temperature reached ten million degrees, the hydrogen nuclei will ignite and nuclear fusion will occur. If the white dwarf star accretes enough material from its companion star, helium fusion will occur after the hydrogen fusion, and carbon fusion will also follow. Since a white dwarf is mainly composed of carbon, carbon fusion will not ignite in the external layer, but rather in the center of the star. Carbon fusion will spread from the center towards the outer edges of the star, culminating in a huge explosion that will throw the crushed remnants of the white dwarf star and all its peripheral material into space. Type II supernovas are stellar explosion of large stars after they evolve into their later period; we have already discussed this.
It is estimated that a supernova occurs every twenty-five to seventy-five years in the Milky Way, but few are ever observed because the solar system is located on the galactic disk and is blocked by other stars and interstellar material when observing the Milky Way.
Supernovas can threaten humans in two ways. On the one hand, when a supernova happens, its thermal radiation will raise the earth’s temperature, damaging the planet’s ecological balance. So far, humans have observed seven supernovas in the Milky Way, but they all occurred far away from us. The nearest supernova happened in 1006, and it was 4,006 light-years away, thus posing no threat to us at that time. However, close-up supernovas would be a different situation altogether. According to our calculations, if a supernova were to explode where the Alpha Centauri is located close by us, it would be like an additional sun one-sixth the size of the actual sun, appearing atop Earth for a month and a half; the earth’s average temperature would rise four to five degrees.
On the other hand, a supernova can harm us through the radiation emitted by gamma rays and other harmful rays. This problem is much more serious than thermal radiation because the strong gamma rays and other harmful rays emitted by a supernova can threaten life within a very wide range. According to a specialized study conducted by NASA Goddard Space Flight Center’s astrophysicist Neil Grace and his colleagues, only a supernova occurring within twenty-five light-years of space could weaken the ozone layer enough to double Earth’s surface UV, thus seriously affecting the survival of mankind.
To sum up, the supernovas we must beware of are the ones within a twenty-five-light-year range of us. According to astronomical observations, there are no stars capable of producing supernovas within this range. The conditions for supernovas are fairly obvious. A type I supernova requires a pair of closely orbiting medium large stars, and a type II supernova requires a star with mass more than eight times larger than the sun. Stars like this are very easy to discover at close range, and there are no such stars nearby.
Even though there is no possibility for a supernova occurrence close to the solar system today, the sun itself is not static. It rotates the Galactic Center at 220 kilometers per second. The other stars that orbit near the sun’s trajectory follow a certain pattern as well, so we may line up with a supernova within twenty-five light-years in the near future. Scientists have calculated that a supernova takes place within one hundred light-years of us every 750 million years. According to this projection, a supernova will happen within twenty-five light-years of us every forty-eight billion years. Our sun has only been formed for five billion years and will become a red giant in another five billion years. Humans will no longer be able to survive on Earth at that time; thus, such occurrences pose minimal endangerment to us.
Even if we do catch up with a supernova, there is nothing to fear. There are obvious signs before a supernova happens, and these signs will provide us with at least one million years of preparation time. Once we observe the possibility of a supernova in our vicinity, we will have ample time to take a series of effective precautions. In extreme circumstances, we can develop measures to discharge large amounts of ozone into the atmosphere in order to counteract the destruction of the ozone layer; we can develop anti-UV radiation skin care products and radiation-resistant clothing to protect from strong ultraviolet radiation; we can stay in radiation-proof buildings or air- raid shelters during the first twenty days of the most intense gamma ray radiation; and the few people who must work outdoors can wear radiation- proof space suits. If the supernova were even closer, we would also have to prevent against thermal radiation. The sea level would rise due to melting glaciers, so we would have to move some coastal residents; we would also have to take appropriate precautions against epidemics that may occur from floods and frequent hurricanes. In short, such encounters would be extremely troublesome but would not pose a threat to the overall survival of humanity.
Four: The Threat of Micro Black Holes and Antimatter Planets
Today’s understanding of the universe is based on quantum mechanics and general relativity, both of which have only been established for a century, so our understanding of the universe cannot reflect the essence of the universe. According to analysis based on existing cosmological theory, there are two types of celestial bodies whose existence remains unproven. If they do exist, the threat they pose to the solar system and humanity would be devastating. They are micro black holes and antimatter planets.
1. The Threat of Micro Black Holes
According to the Big Bang theory, after the initial explosion, enormous pressure may have compressed material in different areas into small black holes. These black holes range from tens of thousands of kilograms to the size of small stars. We call them micro black holes or quantum mechanical black holes.
If such micro black holes existed, what kind of situation would they be in after 13.8 billion years? According to the laws of nature, the smaller, more irregularly formed objects are more likely to exist in great numbers, and vice versa. The same rule should apply to the micro black holes formed in the Big Bang. Most would be small in size with very few ones reaching the size of the moon or Earth. How would these micro black holes threaten us? To answer that question, we must first understand some of the characteristics of black holes. Even though black holes swallow even light, they are not completely insulated. Black holes also evaporate, and the smaller a black hole is, the faster it evaporates. Larger black holes evaporate slower. The evaporation period of a black hole the mass of the Milky Way is 10100 years (one hundred zeros after 1); the evaporation period of a black hole with mass equivalent to the sun is 1065 years. Such large black holes take very long time to evaporate, perhaps longer than the universe would exist. However, a one-billion-ton black hole would only need ten billion years to evaporate; a one-million-ton black hole would only need ten years; and a one-ton black hole would evaporate in 10-10 seconds—less than a blink of an eye.
Considering that a black hole will swallow at least some material in the process of its existence, people generally use one billion tons as the mass divider line. It is generally believed that black holes with less mass than this have already evaporated, while black holes larger than one billion tons still exist. This mass is roughly equivalent to that of a large mountain.
The vast majority of black holes formed by the Big Bang were very small; few would have surpassed one billion tons in mass; thus, most black holes should have evaporated in the past 13.8 billion years. The opposite would apply to the larger micro black holes; they evaporated very slowly to begin with and constantly swallowed material close to them, making them larger and larger and more difficult to evaporate. If such black holes lived until this day, their mass should be even larger than they were 13.8 billion years ago.
The distribution density of micro black holes should be roughly the same as other material in the universe; as ancient celestial objects, they would most likely be concentrated in the centers of star systems if they still existed today. At the same time, if the estimates concerning micro black holes are correct, the Milky Way would have such micro black holes as well, and the majority of them would be concentrated in the center of the Milky Way. The micro black holes in the center of the Milky Way are far away from the sun and will not endanger its safety, but other micro black holes will exist in other parts of the Milky Way. Could these micro black holes threaten the safety of the solar system?
Let us use a micro black hole with mass equivalent to the moon colliding with the sun as an example. A micro black hole whose mass equals the moon is already fairly large, but it would only be about 0.1 millimeters in size—about as big as a speck of barely recognizable sand. If a celestial body the size of the moon collided with the sun, there would first be an earth-shattering impact and then the moon would be swallowed by the sun. However, the situation would be completely different if a micro black hole equivalent in mass to the moon but only sand sized collided with the sun. When a speck of sand so small has a great deal of mass, its kinetic energy will be very large as long as a certain degree of speed is reached. Since the cross section of this speck of sand is so small, it will receive little resistance and easily penetrate the sun from one side and emerge from the other, continuing on into space. The micro black hole will not evaporate but will instead absorb some of the sun’s mass and radiate some of its own energy, thus increasing its own mass. Since the absorption capacity of such a micro black hole is limited, the sun will continue burning like nothing happened.
If this speck of sand moved very slowly and stayed inside after penetrating the sun due to gravity and resistance, something else would happen. In this situation, the micro black hole would slowly absorb the sun’s material into itself and increase continuously in mass while the sun’s mass decreased. At first no change would be seen on the surface of the sun, but after millions of years of absorption the nuclear fusion system inside the sun would be completely destroyed, and the sun would fall into the micro black hole. Next this micro black hole would become a black hole with mass equivalent to that of the sun. The earth and all other planets would continue to rotate around this celestial body. Since the sun’s light and heat would no longer exist, the temperature on Earth’s surface would drop quickly and Earth would become an uninhabitable freezing world.
Of course, a micro black hole may also directly impact with Earth, and it would create conditions similar to that of a micro black hole colliding with the sun. The micro black hole would either penetrate through the earth or stay inside and slowly absorb the planet until the earth fell into the black hole.
The threat of micro black holes should be considered in two cases: one treats the existence of micro black holes as a hypothesis, and the other will analyze the authenticity of micro black hole existence. If we assume that micro black holes do exist, after 13.8 billion years of evaporation, the possibility of us meeting one of the few surviving larger micro black holes cannot exceed one in a hundred billion. Even if there were an encounter, three results might occur. In the first case, the micro black hole would go through the sun with no lasting damage; in the second case, it would penetrate into the sun and absorb its material until the sun collapsed and was destroyed. Both of these results have been illustrated already.
In the third case, the micro black hole might be captured by the gravity of the sun and become a member of the solar system family. Micro black holes are smaller than the sun, so if they enter the sun’s gravitational range at a certain speed (as long as they do not collide with the sun), it would be perfectly natural that they be captured instead.
In the above three possibilities, the third possibility is the greatest. It takes great precision to collide with the sun, while being captured only requires entering of the gravitational range. The first possibility is probably the second most likely to occur, since the relative velocity between one celestial body relative to that of another is generally high, especially under strong gravitational pull; the second possibility is least likely because the probability of one celestial body slowly colliding into another celestial body is too small. In the above three possibilities, the second one is the only one that poses a real threat to the sun, which means that the threat of micro black holes is pretty insignificant.
Now let us examine the authenticity of micro black holes existing. According to a theory by the famous scientist Stephen Hawking, micro black holes are widely present in the universe. If this were the case, there would have to be situations in which micro black holes swallowed stars. There are trillions of stars in the universe, so if micro black holes were ubiquitous, it would be impossible for there to be no stars swallowed by them. It follows that there would be sudden collapses of stars accompanied by the emission of X-rays. If micro black holes existed around us, they would swallow objects and emit X-rays as well. In all our observations of the vast universe, we have never found traces indicating the existence of micro black holes.
2. The Threat of Antimatter Planets
Antimatter is inferred from Big Bang cosmology. We know that the basic unit that forms matter is the atom, which consists of the nucleus and electrons. The nucleus is composed of protons and neutrons. Electrons are negatively charged, protons are positively charged, and neutrons are not charged. The water we drink is actually water molecules composed of two hydrogen atoms and one oxygen atom, and the salt we eat is actually sodium chloride molecules composed of one sodium atom and one chloride atom. Everything we see and feel is made of matter; countless electrons, protons, neutrons, and the atoms and molecules they compose are present in the universe.
According to Big Bang cosmology principles, when the Big Bang formed matter in the universe, it should have also formed the same amount of anti- matter. The so-called antimatter includes the positively charged antielectron corresponding to the negatively charged electron, the negatively charged anti- proton corresponding to the positively charged proton, and the antineutron that is still not charged but has all the opposite properties of the neutron. The antielectron, antiproton, and antineutron combine to form anti-atoms, which in turn form anti-molecules, thus forming the world of antimatter.
Scientists obtained antielectrons, antiprotons, and antineutrons early on in the laboratory, but they are annihilated when they come into contact with matter and release energy and gamma rays. If the sun were to meet a sun-sized antimatter planet, it would become a huge fireball and strong gamma rays before disappearing to become energy floating in the universe. Therefore, if the sun ever met a large antimatter object, the result would be catastrophic for humans.
If, judging by Big Bang cosmology, antimatter did exist in the universe in roughly equal amount to matter, the universe would be filled with anti- matter. This would mean that antimatter planets would inevitable encounter material planets and be annihilated. But what is the actual situation?
Over the years, scientists have devoted much effort to the search of anti- matter. In 1979, American scientists placed a balloon roughly sixty stories high, thirty-five kilometers above ground, and managed to capture twenty- eight antiprotons, which is a very small amount. Later, the Chinese-American scientist Ding Zhaozhong (Samuel Chao Chung Ting) organized a space study that captured a small number of antiprotons as well. Antimatter particles have also been obtained in scientific laboratories. A number of studies have shown that large antimatter does not exist in the universe; there are no antimatter celestial bodies within thirty million light-years. That means that there will be no antimatter celestials in our Milky Way, or even in the Local Group. The study principle of scientists is not difficult to understand. Let us take the determination of the sun’s matter/antimatter status as an example. Solar winds are constantly blowing over Earth; the main component of solar wind is protons. If the sun were antimatter, all the protons it produced would be antiprotons instead of just a few antiprotons (this number of antiprotons could not light a 100-watt light bulb for one billionth of a second through annihilation), and the earth would be annihilated by these antiprotons. As that is not the case, we can positively confirm that the sun is composed of matter instead of antimatter.
The same method can be applied to the Milky Way and the Local Group. In the Milky Way and neighboring galaxies, cosmic rays fly everywhere in particle form without annihilating any celestial bodies, thus demonstrating that there is no large antimatter in our Milky Way or in the Local Group. However, we do not have enough basis for judgment when it comes to farther galaxies. Today’s astronomical observations can only receive light from distant celestial objects; matter radiates photons, so antimatter would radiate anti-photons. Since photons are neutral, anti-photons are actually the same particles as photons, making it impossible to distinguish with current technology whether distant celestial objects are made of matter or antimatter. Of course, celestial objects also radiate neutrinos; neutrinos radiated by matter and antimatter will certainly not be the same. Interaction between neutrinos and any other material is always weak, so neutrinos radiated by the sun can penetrate through Earth with minimal damage, making it difficult to design a device capable of receiving them.
In conclusion, it does not matter for the time being whether there are large numbers of antimatter celestial objects in the distance, just the fact that no such objects exist within thirty million light-years of the solar system is enough to placate us. Even if antimatter celestial bodies did exist over thirty million light-years away, it would take tens of billions of years for them to collide with the sun, and the sun will have long ceased existing by then.
Five: The End of the Universe
The end of the universe would undoubtedly be the end of mankind as well; in fact, conditions for human survival would cease to exist long before the end of the universe. So how and when will the universe finally end?
Our universe is a rapidly expanding universe; its expansion is propelled by the Big Bang from 13.8 billion years ago; however, there is also a ubiquitous force in the universe that constrains its expansion, namely the gravitational attraction between matter. The strength of gravitational force depends on the mass of objects and the distance between objects.
Will the expansion force of the universe eventually overcome the gravitational pull between objects, or will gravitational pull between objects win out over the universe’s expansion force? This will decide the ultimate fate of the universe. f the expansion force of the universe outweighs the gravitational pull between matter, the universe will continue expanding. This is known as the open universe theory. On the other hand, if gravitational pull between cosmic matter wins out in the end, the universe’s expansion will reach its maximum in several billion years before contracting under the weight of gravity, ultimately returning to the starting point of the universe. This is the closed universe theory. The cosmic model established by the Big Bang only allows for these two possible end results. Which one will be the ultimate end of the universe?
If we could accurately obtain the average density of matter in the universe, it would not difficult to determine this outcome. Unfortunately, apart from the visible matter that we do not fully understand, there are also large amounts of dark matter and dark energy that we know nothing about in the universe. This makes it impossible to formulate a clear judgment on the end of the universe. Our discussion can only be divided into two assumptions.
The first assumption undertakes that our universe is an open universe, and the galaxies around us will continue to move away. In a few thousand million years, the only universe we see will be the thirty or so galaxies located in the Local Group. All other galaxies will have moved out of our line of sight, invisible even to the most advance observation tools. When that time comes, the universe we would observe would only be ten billionth that of what we see today.
The same would be true for the other galaxy clusters (groups). As independent celestial systems in the universe, galaxy clusters (groups) link their internal galaxies together while moving away from all other galaxies; eventually, all the other galaxies would be obscured.
Galaxy clusters (groups) are not static. The galaxies within them merge constantly to enlarge the galaxies, forming a series of super galaxies. Since stars rely on nuclear fusion to emit light and heat, once all hydrogen elements in the universe are exhausted, only brown dwarfs, neutron stars, and black holes will be left. These are all remnants of stars that have already died. Once this happens, the universe will end its Stellar Era and enter the Degenerate Era; this era will happen in hundreds of trillions of years.
The Degenerate Era will be much longer than the Stellar Era; it will last at least 1037 years. During this time, the remnants of dead stars will collide with each other, and black holes will swallow remaining celestial bodies and each other during collision, thus increasing the mass of black holes over time. After a period of 1037 years, the universe will enter the Black Hole Era.
The Black Hole Era will last even longer than the Degenerate Era and will be dominated by black hole evaporation. The bigger in mass a black hole is, the lower its surface temperature will be and the slower its evaporation will be. It is not possible to calculate how long the Black Hole Era will take; we have only one concept as reference. A black hole with mass equivalent to the sun will take 1065 years to evaporate, while a black hole whose mass equals the Milky Way will take 10100 years to evaporate. Once all black holes have evaporated, the universe will enter its last era, the Dark Era. At this time the universe will only have energy, and no more celestial bodies will be left.
If we take the second assumption and believe our universe to be a closed, it will reach its maximum after billions of years to stop expanding and start contracting instead. At this time, when we observe the galaxies from the Milky Way, they will no longer be moving away, but moving towards us instead. When this day comes is dependent on the energy and matter levels of the universe. At least from today’s observation, the universe has shown no signs of stopping its expansion. Not only that, but according to observation in recent years, the universe shows signs of accelerating its expansion. This indicates that there still exists large amounts of dark matter and dark energy that we do not understand in the universe. We can extrapolate that the universe will not stop expanding in the next billion years, and that the possibility of the universe ending as an open universe is higher.
There is one thing we can be quite certain about: if the universe is a closed universe, its expansion and contraction will be essentially symmetrical; however long the universe took to expand, it will take the same time to contract.
When the contraction of the universe is 13.8 billion years away from its end point, the background radiation temperature of the universe should be roughly the same as today’s, which is about three K; when it is one billion years away from its end point, background radiation should rise to thirty K, and galaxy clusters should start to merge; when it is one hundred million years from its end point, the universe’s background radiation should reach three hundred K, which is higher than the average temperature of Earth today. Life will have difficulty surviving in the universe; after that, as the universe continues to expand and background radiation rises accordingly, the universe sky will brighten from the darkness it is today and turn a fiery red. When the universe is 300,000 years away from its end point, background radiation will reach three thousand K, and all atoms will disintegrate. Matter will exist in the form of nucleons, electrons, photons, and neutrinos; the sky will no longer be transparent after that. When the universe is one hour away from ending, its temperature will reach one hundred million K and be mainly composed of photons and neutrinos. Three minutes away from end point, the universe’s temperature will reach one billion K and will be filled with electrons, neutrinos, and their anti-particles, with a small number of protons and neutrons; 10-4 seconds away from end point the universe will reach a temperature of one thousand billion K, and only protons, neutrons, and their anti-particles will be left; 10-35 seconds from end point, the universe’s temperature will reach 1027 K, and the four natural forces will unite; 10-43 seconds from end point, the universe’s temperature will reach 1032 K, and then the universe will shrink rapidly and reach its end.
Since the end of the universe is too distant a threat to mankind, discussing these issues right now has no direct implications. However, as one of the factors that affect humans’ survival, the elaborating of it is necessary to comprehensively explain the problem.
While studying the universe, scientists found that the more we discover about the universe, the more unknowns we encounter. What is a singularity? What happens inside a black hole? What is dark matter? None of these questions can be answered by our current levels of research; however, the discussion in this section can clearly answer one thing: the universe will not bring catastrophic disaster to humanity in the next billion years. This conclusion is enough; that is the whole intention of this section.
SECTION TWO: THREATS FROM THE SOLAR SYSTEM
In the vast universe, the solar system only takes up one small corner. Nevertheless, it is the homeland of humans; the earth we live on is one small planet within the sun’s star system.
Standing above the sun’s north pole, we can see that all eight planets of the solar system rotate around the sun in the same counterclockwise direction. Their orbits almost align onto one plane, called the ecliptic. The orbit of the planets is described as oval, but in reality it is almost round.
The composition of these eight planets vary greatly, but they can be divide into two categories. The terrestrial planets—Mercury, Venus, Earth, and Mars—are solid planets composed of rock and metal. They are dense, they rotate slowly, and they have few satellites, similar to Earth. The Jovian planets—Jupiter, Saturn, Uranus, and Neptune—are bulky, heavy, low-density planets composed mainly of liquid hydrogen, liquid helium, and other substances. They wander space like “water balls,” rotate fast, and have many satellites and rings.
The satellites of each planet are also important celestial bodies in the solar system. There are over 150 confirmed satellites in the solar system, and many more await confirmation. Although the earth is a relatively small planet, its satellite—the moon—is a large satellite, ranking fifth among the solar system satellites.
There are also many smaller celestial bodies in the solar system, such as dwarf planets, asteroids, comets, and meteoroids; they are too numerous to count. In addition, interstellar dust and interstellar rays are also components of the solar system.
As the third planet in the solar system, the earth is 150 million kilometers from the sun; the furthest planet, Neptune, is 3.5 billion kilometers away. That is far from the boundaries of the solar system. Dwarf planets (such as Pluto), many smaller celestial bodies, and interstellar material all exist beyond Neptune.
One: Threats from the Sun
1. The Sun Turns into a Red Giant
The sun’s mass is 2×1030 kilograms; its diameter is 1.39 million kilometers, and it is composed of 71 percent hydrogen, 27 percent helium, and 2 percent carbon, oxygen, silicon, iron, and other elements. Humans’ survival depends primarily on the sun; its light shines upon Earth and warms us. Without the sun’s light and heat, the earth would be a cold, dead planet. If the sun went through any big change, it would be a catastrophe for Earth and mankind.
The sun relies on nuclear energy to emit light and heat; the energy it pro- duces every second is equivalent to that of twelve billion tons of coal. Earth only receives less than 2.2 billion of that light and heat, but it is enough to maintain the earth’s ecology and turn it into a beautiful and pleasant planet. The energy source of the sun has always been a topic of concern to scientists.
Since ancient times, humans’ experience with ignition has never strayed from the concept of chemical combustion. Whether it is coal, oil, or trees, burning has always been generated through the atomic shift of chemical energy. According to calculations done with the highest combustion value fuels, if the sun continues to burn, it cannot last more than thousands of years; the most optimistic estimates do not exceed hundreds of thousands of years. On this basis, people have come to many erroneous conclusions, such as the belief that Earth’s history as well as human and biological history are both significantly shorter than their actual length. The further inference from that views the future of mankind extremely pessimistically. Since the sun’s fate determines the fate of Earth and mankind, if the sun were to burn up in a few thousand years, humans would be extinct in a few thousand years as well.
However, the study of the earth’s crust as well as the study of paleontology showed that both Earth and life on Earth have existed for far longer than people imagine. We also learned through astronomical observations that the actual history of stars was very different from past understandings, so people began to doubt the sun’s energy source.
As early as the 1860s, scientists learned from optical analysis that the sun’s main component was hydrogen. With the discovery of elemental radioactivity at the end of the nineteenth century, scientists recognized that there was a previously unknown energy in nature—nuclear energy. Significant breakthroughs in the understanding of nuclear energy followed quickly; in particular, Einstein’s famous mass-energy equation theoretically proved the existence of nuclear energy, as well as the relationship between energy and mass. Further observations and studies show that the sun’s internal energy is over ten million degrees, which means that in the extreme temperatures of the sun’s core, the violent movement of the nuclei can break through the electromagnetic force. Scientists finally concluded that there was thermonuclear reaction happening inside the sun’s interior and that the sun’s light and heat were provided by nuclear energy. Moreover, the energy of other stars is also derived from nuclear energy.
Today, our understanding of the sun has reached a very high level, enough to ascertain the following: Our sun was born as a star about five billion years ago; its predecessor was a large hot air mass. We can confidently determine that this hot air mass was the remains of a second- or third-generation large star exploding in the universe. Through hundreds of millions of years of evolution, this hot air mass formed its own mass-intensive central area through gravity, then formed a primitive planet that continued to absorb the material around it through strong gravitational force, ultimately igniting the hydro- gen atoms at the core. This was the birth of the sun as a star.
The sun can burn hydrogen elements for about ten billion years; at present, it has burned five billion years with five billion more remaining. This is the stable and mild period of the sun; however, in five billion years, the helium atoms inside the sun will ignite and the sun will become a huge red giant. Helium will continue to burn for one billion years, but once helium is exhausted, the sun will quietly become a white dwarf. Although this white dwarf will have some remnant heat, there will be no nuclear combustion inside of it and it will naturally cool with time. Once the sun evolves into a red giant, the diameter of the new sun will be more than one hundred times that of the original sun, so it will quickly swallow Mercury, Venus, and eventually Earth. Once Earth ceases to exist, the homeland of humanity will disappear into the universe.
Standing on a billion-year perspective to consider the external forces that threaten the survival of mankind, the evolution of the sun into a red giant in five billion years is undoubtedly a threat. In fact, the sun will no longer be stable a few hundreds of millions of years before this. In this transition period, the Earth will suffer constant pressure from the sun.
When the sun evolves into a red giant, its flames will spread out. Not only will Earth be swallowed, but Mars will also become inhabitable. Humans will need to migrate even farther out. At this time, Jupiter or one or more of Saturn’s satellites might be transformed into a place for human habitation, but the external environment will be abysmal.
Once the sun finally evolves into a white dwarf, it will no longer be possible for humans to survive in the solar system. Even though a hot white dwarf can radiate light and heat during its cooling process, its radiation energy will be extremely limited. Perhaps Mercury’s position today would be close enough to enjoy such light and heat, but Mercury would have been swallowed when the sun turned into a red giant. Unless humans could move a planet closer to the white dwarf or live on an artificial celestial body, we would have to move out of the solar system. Moreover, white dwarf planets are not reliable long term, as they will slowly cool until all light and heat are completely lost.
Humans would not be able to survive in the solar system once the transition period began. During this period, the sun would be very unstable as it constantly underwent dramatic change, meaning that it would be impossible to accurately determine its movement pattern. One violent change would be enough to destroy humanity.
2. Threats from Solar Activity
Can we fully trust the sun in the billions of years before it becomes a red giant? Will it suddenly malfunction one day and greatly endanger humans? Do we really understand the sun and have a basis to say that there is no problem there?
The sun is a gas planet divided into the core, the radiation zone, the convection zone, and its atmosphere from the inside out. This atmosphere can be divided into the photosphere, the chromosphere, and the corona. These three layers are not cleanly divided but infiltrate each other. The sun’s convection zone and what lies beneath cannot be directly seen through telescopes; their properties can only be determined through observational data and related theoretical calculations. The most direct impact the sun has on the earth comes from its surface activity; these solar phenomena mainly include sunspots, sun flares, prominences, and solar winds.
Even without the use of observational instruments we can observe that black spots appear frequently on the sun. These black spots are sunspots. Sunspots often exist in pairs and rotate around the sun from west to east in the same direction as solar rotation. They last a few days or as long as a few weeks from formation to disappearance. The central temperature of sunspots is about 4,500 K–1,200 K less than the surface of the photosphere, making them appear black in comparison. Sunspots are generally oval in shape; small sunspots are a few kilometers in diameter while larger ones can reach a diameter of tens of thousands of kilometers. Sometimes they appear in groups that span several hundred thousand kilometers. It is generally believed that the appearance of sunspots is a result of the sun’s magnetic field. The activities of sunspots have obvious cycles; sometimes they appear frequently, and other times they rarely occur. The average cycle is eleven years.
Solar flares are sudden flashes of increased brightness on the chromo- sphere; they are concentrated outbreaks of solar energy within a very short period of time. When a solar flare breaks out, it can throw out a large number of charged particles in a very short time, and it can accelerate solar winds a hundredfold.
Prominences are strong flows of hydrogen that burst out from the chr- mosphere. These bursts of hydrogen ignite into red flames and surge up hundreds of thousands of kilometers. It is generally believed that prominences are a result of sudden changes in the sun’s magnetic field or are produced by the constant fluctuation of hydrogen flows. The activities of solar flares and prominences are closely related to the activity of sunspots; the movement of sunspots is considered to be the main sign in determining the strength of solar activity.
Earth’s ecology is closely related to solar activity. When solar flares break out, strong solar winds interfere greatly with the earth’s magnetic fields; these are known as magnetic storms. Shortwave communication on Earth relies on the ionosphere fifty or sixty kilometers above surface to reflect and disseminate information. Once magnetic storms occur, the ionosphere’s degree of dissociation increases and electromagnetic waves are absorbed or fail to reflect normally, thus weakening the signal and interrupting short- wave communication.
Magnetic storms also affect the chemical structure and dynamics of the earth’s upper atmosphere. Prolonged exposure to magnetic storms may greatly affect the earth’s climate and cause floods or droughts. According to global climate analysis, the climate change cycle is twenty-two years, which is consistent with the sun’s magnetic cycle. Solar activity is also associated with earthquakes. Through analysis of global seismicity cycles over the years, we have determined the earth’s seismic cycle to be eleven years—completely consistent with sunspot activity cycles. Some scientists believe that the energy impact of solar winds on Earth increases during solar activity peak years, leading Earth’s rock layer to discharge under pressure. In addition, the rock layer also stretches and vibrates under the alternating electromagnetic field, causing the rocks that had already accumulated tension to fracture and dislocate, leading to earthquakes.
In the study of old trees, we have learned that when solar activity is frequent, the growth rings of tress are wider, meaning they grow faster. Contrarily, in slower solar activity years, the growth rings of trees tend to be narrower, indicating slower growth. This confirms the impact of solar activity on Earth’s biology. According to historical statistics, the growth of crops also conforms to this pattern.
Solar activity is also closely related to human health. For example, during solar activity, ultraviolet light is significantly enhanced, and the earth’s magnetic field experiences strong disturbance, which can affect cardiovascular functions. During solar activity peak years, bacteria also breeds faster, causing the flu, diphtheria, and other epidemics to occur at higher rates. According to Russian scientists, the biggest cholera pandemics in history generally took place during solar activity peak years.
While it is certain that solar activity influences the earth’s ecology, and that the sun can both nurture and harm life on Earth, none of the above factors can endanger the overall survival of mankind. This conclusion is not deduced by decades or centuries of observation, nor is it summarized through thousands or tens of thousands of years’ experience, but it is proven by five billion years of history. In the past five billion years, the sun has transformed the earth from a barren planet into a beautiful and pleasant planet. It woke the earth from its dead silence and enabled the first batch of life to be hatched 4.28 billion years ago; those were the simplest microbes. From then on, life evolved, continually basked in the glory of the sun, and never stopped until large complex life formed in the ocean 530 million years ago. Then, four hundred million years ago, life moved on land. Apes entered the threshold of man more than four million years ago, and humans completed their evolution nearly 100,000 years ago.
In five billion years the sun has never forsaken us, which is why we have every reason to believe that it will continue to nurture us for the next five billion years of its main star sequence. This conclusion can be confirmed by astronomical observations of other stars similar to the sun in the universe, and by existing scientific theories.
Two: Extraterrestrial Body Collision
In July of 1994, astronomy enthusiasts from all over the world witnessed the astronomical marvel through their telescopes of a comet colliding with Jupiter. While over Jupiter, comet Shoemaker-Levy 9 was torn into twenty- one pieces by Jupiter’s huge gravitational force. These pieces crashed into Jupiter at a speed of sixty kilometers per second, exploding into a huge fireball and flashes of light while also producing a series of dark spots in Jupiter’s atmosphere. The impact of such a collision is equivalent in strength to 100,000 nuclear bombs. If it happened on Earth, our entire ecology would suffer great damage, and humans’ survival would be seriously threatened.
The 1994 Jupiter collision is not the largest impact Earth has suffered. Many people consider the extinction of Earth’s dinosaurs 6,500 years ago to have been caused by an asteroid colliding with Earth. It is believed that an asteroid fifteen kilometers in diameter hit what is today Mexico’s Yucatan Peninsula. Scientists have long been studying an impact pit buried deep under the Yucatan Peninsula; it is estimated to be 180 kilometers in diameter and 900 meters deep. If humans had lived in that era, we would have suffered a huge catastrophe. In fact, a large enough extraterrestrial body would be more than enough to destroy humanity. Therefore, we must study extraterrestrial body collisions in order to research the overall survival of mankind.
Within the solar system, celestial bodies that may collide with us include asteroids, comets, meteorites, and meteors. Since meteorites and meteors are too small to pose a threat to humans, we will only discuss the collision of asteroids and comets here.
1. Asteroid Collision
Asteroids revolve around the sun, just like Earth, but they are merely much smaller in size. There are many asteroids in the solar system, concentrated mainly in two areas. One is the vicinity of Pluto’s Kuiper belt, and the other is the asteroid belt between Mars and Jupiter. As the Kuiper belt is far away from us, the asteroids there are not a threat to Earth. When studying the threat of asteroids, scientist generally do not consider the asteroids of the Kuiper belt.
The total number of asteroids in the solar system is estimated to be more than 500,000 (excluding the Kuiper belt and its outer asteroids). They are mostly small in size, and though they exist in great numbers, their total mass does not reach five ten thousandths that of Earth. Most of these asteroids are located on the asteroid belt in an area that measures roughly 2.17–3.64 astronomical units. (An astronomical unit refers to the distance between the earth and the sun; one astronomical unit is about 150 million kilometers.) The asteroids in the asteroid belt are very far away from us and generally do not pose a threat; however, due to their small size, light mass, and vulnerability to planetary influence, asteroids are highly probable to change trajectory, requiring us to give the distant asteroid belt considerable attention.
Many scientists believe that most of the asteroids in the solar system are concentrated between Mars and Jupiter because Jupiter’s gravity attracted the asteroids originally located in the inner ring. Since Jupiter is the largest planet in the solar system, its gravity is much greater than the planets of the inner ring.
There are also a few very unique asteroids that have strayed from the asteroid belt and approached the inner orbit of Earth, while some others have progressed to the outer side of Saturn’s orbit. Since these asteroids are very close to Earth, we call them near-Earth asteroids. These are the asteroids that truly concern us, as they pose a much bigger threat to Earth than do the asteroids in the asteroid belt.
Although there is no written record of an asteroid hitting Earth, the number of asteroids around us, as well as our observational experience of celestial bodies, make asteroids a very real threat. Compared to threats from the universe and the threat of the sun evolving into a red giant, the threat of asteroids seems much more immediate. The numerous records of meteorites impacting Earth are a warning themselves, seeing as meteorites are just smaller versions of asteroids.
On February 15, 2013, a meteorite penetrated the atmosphere above Russia’s Chelyabinsk and exploded into pieces, forming meteorite rain. The shock waves produced by friction between the meteorite and the atmosphere caused many buildings’ windows to explode, injuring more than a thousand people. This event was filmed by a number of people.
If a large enough asteroid were to hit Earth, it could destroy humanity; even a relatively large asteroid colliding with Earth could greatly damage humanity. Due to this, several major countries have devoted considerable effort into observing and studying asteroids. For example, the US congress requires NASA to record and classify any asteroids that are more than one kilometer in diameter.
At present, we have discovered close to thirty thousand near-Earth asteroids, 1,100 of those are larger than one kilometer in diameter, and the largest of them all is the famous 433 Eros asteroid. Eros’ orbit lies between Earth and Mars; its diameter is twenty-two kilometers. If an asteroid this size hit Earth, it would greatly affect global ecology; many species would go extinct, humans would suffer great destruction, and human cultural achievements would be damaged significantly. Fortunately, we have a very thorough under- standing of this asteroid. The NEAR-Shoemaker unmanned probe launched by NASA on February 14, 2000, successfully entered the orbit of Eros and landed on it after a year of close-up survey on February 12, 2001, conducting very fruitful research of the asteroid.
However, we do not know all the near-Earth asteroids as well as we do Eros, and we have especially inadequate understanding of the smaller asteroids. For example, on March 18, 2004, the small celestial body 2004 FH flew over Earth’s surface at a distance of 43,000 kilometers, but scientists did not discover it until three days before the flight. If the thirty-meter-diameter celestial body had hit a medium-sized city, that city would have been demolished. Of course, such demolition is far from enough to destroy humanity.
Some of the closer near-Earth asteroids could bring great disaster if they collided with Earth. According to observation and analysis, the asteroid (29075) 1950DA will fly very low over Earth’s surface in 2880. If its orbit changes even a little, it may hit Earth. If this asteroid, which is 1.4 kilometer in diameter, collided with Earth, the disaster it would bring could affect Earth’s ecology on a global scale. Huge numbers of creatures (including humans) in a tens of thousands square kilometers range would be largely destroyed. Fortunately, there are more than eight hundred years left for us to re-evaluate the orbit of this asteroid and deal with its possible impact.
2. Comet Collision
Comets are composed of rock, frozen water, carbon dioxide, dust, and various impurities; they are celestial bodies of relatively small mass. If all the material in a larger comet were compressed together, its diameter would not exceed tens of kilometers.
The core of the comet is called the nucleus, and the outer cloudy layer encircling the core is called the coma. When the comet approaches the sun, strong solar winds and radiation pressure from the sun pushes the coma into a long tail. Comet tails range from tens of thousands of kilometers to hundreds of millions of kilometers in length. The comet tail usually has very sparse material; its density is only one quadrillionth of the earth’s surface atmosphere.
The path of a comet is very hard to predict, as their orbits can be elliptical, parabolic, or even hyperbolic. Moreover, the orbit of a comet is susceptible to influence from the planets it passes, and even the stars in the distance. As a result, some comets’ paths change constantly, other comets disappear into space, and new comets arrive inexplicably to the solar system.
Many comets exist in the solar system, but only 1,600 have been observed by scientists, and very few of their orbits have been grasped. The orbit cycle of comets also differs greatly. Short ones last a few years or more than one hundred days, while longer ones may reach thousands of years or even tens of thousands of years.
Comets themselves are very unstable. Every time they pass the sun, some of their material is blown away into space by solar winds, so a comet’s mass is always shrinking until only the nucleus is left. Some comets composed exclusively of ice and dust may eventually disappear completely.
Comets may also be disintegrated by the gravitational force of the sun or other planets. The famous Bella comet is one such example; its revolution cycle around the sun was 6.6 years. On January 13, 1846, the Bella comet suddenly split into two. When the two halves returned, they returned simultaneously as a pair of comets and disappeared after 1859. Large meteor showers occurred later where their orbit intersected with Earth’s orbit, indicating that the Bella comet had completely disintegrated.
When bigger comets collide with Earth, the threat the humanity is obvious. So far, the largest recorded comet collision happened on June 30,1908, when a violent explosion occurred atop Tunguska in Siberia, Russia. The huge fireball explosion could be seen and heard from more than one thousand kilometers away, and the shock waves from the explosion tore down and burned hundreds of square kilometers of forest. All the animals in the forest died, including a large group of reindeer that were grazing in the area. Fortunately, the area was uninhabited, so there were no human casualties. In later investigations, scientists found only burnt land and animal corpses with no trace of meteorites or craters. It is thus inferred that this was a comet com- posed completely of water. When the comet entered Earth’s atmosphere, the high temperatures produced by friction caused violent evaporation, which led to the huge explosion ten kilometers above ground.
Compared to large asteroids, the impact of comets has slightly less catastrophic influence on humanity; however, a large enough comet impacting Earth could still cause devastating losses to humanity—it would just not be enough to cause the total destruction of humanity.
Near-Earth comets are much smaller than near-Earth asteroids, and they generally have long tails that are easy to observe. At present, we have already observed about fifty near-Earth comets. This number is significantly less than that of near-Earth asteroids, seemingly indicating that the possibility of comets colliding with Earth is much smaller—that is not the case. The most prominent feature of comets is that they are extremely susceptible to disturbances from the sun and large planets. Comets at the very edge of the solar system may inexplicably travel to the inner side of the solar system sometimes. In short, the possibility of comets crashing into Earth is higher than that of asteroids colliding with Earth, and they are much harder to take precautions against; therefore, in recent years, scientist have paid more and more attention on comet research.
3. Comprehensive Analysis of Extraterrestrial Body Collision
The possibility of large extraterrestrial bodies colliding with Earth is very small, but a large enough asteroid hitting Earth could destroy humanity once and for all. That is why we cannot ignore the issue just because of its low probability. One chance encounter and humanity may never recover; more- over, such collisions can occur.
Exactly what kind of threat do extraterrestrial bodies pose to humanity? Many scientists have conducted in-depth research on this topic, but the views differ greatly. Different people have reached different conclusions. After considering a variety of different views, the following conclusions can be drawn:
a. The larger the celestial body, the less likely it will collide. As the large celestial objects of the solar system (including Earth) each orbit on their own trajectories over and over, the impact frequency will only decrease.
b. The following can be estimated concerning the impact frequency and perils of different sized celestial bodies:
i. A celestial body eighty meters in diameter may collide every one hundred years. Such a collision could destroy a large amount of life within an area of a few hundred square kilometers, and it would influence the ecological environment tens of thousands of square kilometers around it.
ii. A celestial body eight hundred meters in diameter may collide every two thousand years. Such a collision may result in the destruction of most life within tens of thousands of square kilometers and influence the ecological environment for millions of square kilometers.
iii. A celestial body three kilometers in diameter may collide every ten million years. This impact could destroy most life within one or two hundred thousand square kilometers, and the ecology of the entire world would be affected.
iv. A celestial body over ten kilometers in diameter may collide with Earth every seventy million years. This collision could cause the destruction of many species around the world and seriously damage global ecology; it would take many years for the earth to recover.
v. A celestial body over one hundred kilometers in diameter may collide once every hundred million years; it could destroy global ecology, humanity, and human civilization in one swoop.
c. The most terrifying and relatively realistic celestial collision would be a collision with the asteroid Eros. Eros is the largest near-Earth asteroid, and as a twenty-two-kilometer asteroid, it would cause massive casualties, devastate Earth’s ecology, and ravage human civilization upon impact. However, collision from Eros would not lead to human extinction. On top of that, Eros shows no sign of hitting Earth at the moment, and we employ very reliable tracking and observation of this asteroid as a cautionary measure.
In reality, we have now developed a considerable ability to guard against extraterrestrial body collisions. The development of space observation tech- nology has enabled us to develop a more detailed understanding of how celestial bodies operate and are distributed in the solar system. We are getting better at monitoring the larger celestial bodies that constitute a threat to the survival of mankind. As space technology continues to progress, we are increasingly capable of traveling in space. Humans have already landed on the moon, and consecutive Mars or other planet landings are fully achievable in this century. As for the explosion of nuclear warheads, they are not only capable of destroying large celestial bodies, but they can also change the trajectories of such bodies. Moreover, we not only have spacecrafts that can accurately send these nuclear warheads into the depth of space, but also intercontinental missiles that can send warheads into the space near Earth. With these conditions, it is becoming increasingly possible that humans will be able to intercept any celestial bodies that may collide with Earth.
Scientists have optimistically estimated that as long as we can predict possible celestial body collisions a few years ahead of time, we can change their trajectory and send them away from Earth. If we could predict such celestial body collisions a few decades in advance, we could use spacecrafts to send ordinary explosives into space, slightly changing the orbit of the celestial body and protecting Earth from impact. Therefore, as long as humans further improve their observation abilities, avoiding the impact of small celestial bodies is a very real possibility.
In fact, scientists possess a variety of suggestions for coping with celestial body impact. Some propose the use of lasers to slow down the asteroid and change its trajectory; some have suggested that a smaller asteroid can be propelled to collide with the asteroid coming towards Earth, changing its direction. Scientists have also proposed a number of options to prevent asteroid impact, like launching missiles or spacecrafts to crash into asteroids and change their trajectory; launching gravitational spacecrafts to approach and change the direction of asteroids through gravity; launching spacecrafts to land on asteroids and gradually change their orbit with electric motors; or fitting asteroids with solar sails to change their track.
According to reports, the United States is studying the use of the Yarkovsky effect to change the orbit of asteroids. This is accomplished by unmanned probes hovering over asteroids to spray their surface and change their sunlight reflectivity, thereby changing their absorption of sunlight and heat, which in turn changes their orbit.
SECTION THREE: THREATS FROM EARTH
From space, our Earth stands out as a beautiful blue planet that is completely unique. It is the only ecological planet and the only civilized planet within humans’ current field of space vision. Its beauty is unparalleled.
The earth is mainly composed of metals and rocks, and its surface is mainly ocean. Earth is more than 70 percent composed of ocean, while land occupies less than 30 percent of the earth’s surface. Earth is not perfectly spherical in shape; its equatorial radius is about 6,378 kilometers, twenty-one kilometers larger than its radius. Earth’s highest peak is Mount Everest, measuring 8844.43 meters in altitude, and its deepest ocean is the eleven-kilometer deep Mariana Trench. Overall, the total surface undulation of Earth is twenty kilometers.
The earth’s interior is made up of the core, mantle, and crust, while the exterior is composed of the hydrosphere, atmosphere, and magnetic field. The different parts of Earth’s interior and exterior form the whole of Earth.
Earth is the mother of humans; it gave birth to and continues to nurture humanity. But the Earth is not a gentle mother—earthquakes, volcanoes, floods, and storms have claimed the lives of and brought suffering to count-less people and made many others homeless. We have profound understanding of Earth’s importance to humanity, and we are uniquely attached to it. Without Earth, humans would not be able to survive, which is why we must consider how Earth may influence human survival.
One: Plate Motions, Earthquakes, and Volcanoes
As early as the nineteenth century, while laying cables on the ocean floor, people discovered that the central seabed of the Atlantic was shallower than its edges. After further study of the Atlantic, a central ridge was discovered rising from the depths of the ocean. Islands like the Azores and Ascension are all the exposed parts of that ridge. While conducting echo detection in the Pacific Ocean afterwards, scientists found a long, flat-top seamount along the eastern Pacific seabed as well.
In the 1950s, research of the ocean became more thorough, and scientists confirmed that a continuous sixty to seventy thousand-kilometer-long submarine mountain range existed in the world’s major oceans. Since this mountain range was located in the center areas of the Atlantic and Indian oceans, it was named the mid-ocean ridge. The aforementioned Atlantic central ridge and Pacific flat-top seamount are both parts of the mid-ocean ridge. The total length of the mid-ocean ridge is enough to circle Earth twice; none of Earth’s land mountains can compare with this unseen mountain buried deep under the sea.
Further study of the mid-ocean ridge showed that a deep rift existed on top of the ridge, one thousand to two thousand meters in depth. It splits the mid-ocean ridge in two, a phenomenon that is particularly evident in the mid-Atlantic ridge. Frequent earthquake and volcano activity can be found near the mid-ocean ridge. Through seismic wave analysis, it is possible to determine that the seismic wave velocity at the mantle of the mid-ocean ridge is smaller than it is at other mantles, showing that the mantle material underneath the mid-ocean ridge is hotter and lighter. The continuous expansion of this material caused the mid-ocean ridge to rise up.
Further understanding of the ocean also includes oceanic trench detection; the deepest sea trench is two thousand meters higher than the world’s highest peak. Among the world’s oceans, the Pacific coast has the most wide-spread distribution of trenches, as well as the most significant drops.
After summing up large amounts of geological surveys and research data, scientists proposed the theory of seafloor spreading. They believe the upwelling of Earth’s mantle to be the driving force of the ocean’s expansion. The top of the mid-ocean ridge is like an outlet for the rising magma, which tears apart the oceanic crust and pushes it to the side. Once the magma cools it fills the tear, causing the mid-ocean ridge to expand on both sides. The uplifting of the mid-ocean ridge is the result of thermal expansion from rising magma.
To be specific, it is rising magma from the mantle that expands the mid-Atlantic ridge and splits the Atlantic Ocean into the West Atlantic and America side, and the East Atlantic, Africa, and Europe side. Continuously rising magma constantly pushes the oceanic crust of both sides, moving the western Atlantic Ocean and America further westward, and the eastern Atlantic Ocean, Africa, and Europe further eastward. That is why the Atlantic is becoming wider and wider.
Where does the space from the mid-ocean ridge’s expansion come from? In other words, as the Atlantic is widening, which area is shrinking accordingly? The answer lies in the Pacific Ocean on the other side of the globe. While rising magma at the mid-Atlantic ridge expands the Atlantic, the same is happening at the mid-Pacific ridge, only bringing different results. Since there is no more room to accommodate the Pacific Ocean’s crust, the oceanic crust must choose a downward subduction at the junction of land and sea, right were the trenches are located. Here, the oceanic crust goes underground and is melted into magma by the high temperature of the mantle. Therefore, as the magma at the mid-Pacific ridge propels the oceanic crust to expand, the Pacific not only does not widen but also must undertake the expansion from the Atlantic Ocean, narrowing it continuously as a result. For these reasons, we will find few trenches along the Atlantic, while the Pacific Ocean is surrounded by trenches.
Seafloor spreading is a continuation and development of the continental drift theory, and plate tectonics was built on its basis. Scientists believe there to be several clear fissures on the earth’s lithosphere; they divide the earth’s crust into several units signaled by mid-ocean ridges, trenches, and faults, forming relatively independent plates. These plates float on the mantle’s asthenosphere and are propelled into constant movement by Earth’s internal heat. By moving away from or against each other, plates form mountains, canyons, rivers, ridges, trenches, and island arcs.
Earthquakes and volcanoes are closely related to the tectonics and movements of plates. Historical earthquake and volcano distribution data shows that plate boundaries are consistent with the dispersal of earthquakes and volcanoes. For example, China’s Taiwan and Japan’s Ryukyu Islands are prone to earthquakes due to collisions between the Philippine plate and the Eurasian plate, and the Luzon volcano arc is located east of the north Luzon trough formed by these collisions. Earthquakes also occur frequently in the San Francisco area of the United States, which is due to the movements of the Pacific and American plates.
The disaster brought on by earthquakes and volcanoes is both persistent and large-scale. To use volcanic eruption as an example, on August 24, year 79, the Vesuvius volcano in Italy erupted suddenly, burying the bustling city of Pompeii in an instant. More than a thousand years later, people discovered this buried city by chance. The dying moments of the city’s residents had been clearly preserved, and it was clear how frightened and unprepared they were. In 1902, the Pelée volcano on the Caribbean Martinique island erupted. During the initial eruption on April 25, volcanic ash and steam shot into the sky, and the rumbling echoed into the distance. Residents of Saint-Pierre, ten kilometers away, watched this rare spectacle excitedly for days. However, on May 18, the volcano became suddenly violent and the eruption height rose to several hundred meters. Volcanic ash containing toxic gas bore down over Saint-Pierre. The beautiful harbor city lit up in flames, killing all 28,000 people; only one prisoner and one shoe repairman survived. Afterwards, it was learned that the prisoner survived because he was kept in an enclosed semi-basement; none of the police guarding him were spared.
The earthquakes produced by plate activity are even more destructive, such as the famous Japanese Kanto earthquake that resulted in 143,000 deaths. The earthquake that claimed the most lives in the past century was the Chinese Tangshan earthquake that occurred in the Tangshan city of Hebei province. At 3:43 in the morning on July 28, 1976, a 7.8 magnitude earthquake shook the slumbering city and destroyed the industrial city of Tangshan in mere seconds; 242,000 people were killed and 164,000 were seriously injured.
The Wenchuan earthquake that took place in Sichuan, China, was another deadly disaster. On May 12, 2008, at 2:00 p.m., the collision of the Indian plate and the Asian plate resulted in an 8.0 magnitude earthquake in the mountains of Sichuan. The destruction and scope of this earthquake surpassed even the Tangshan earthquake. The capital, Beijing, thousands of kilometers away, as well as neighboring Thailand, Myanmar, and other countries, all felt a significant shock. Ninety thousand people died or went missing, and more than three hundred thousand were injured. Thirty barrier lakes were formed in the alpine canyons. If this earthquake had occurred at night or in a densely populated area, the casualties would have been even more unimaginable.
Earthquakes and volcanoes also lead to tsunamis and fires. The 1923 Tokyo earthquake struck during lunchtime; the shocks from the earthquake overturned stoves and ignited over two hundred fires. More than one hundred thousand people were burnt to death.
The largest tsunami on record happened on December 26, 2004, when an 8.9 magnitude earthquake shook the seabed of the Indian Ocean near Sumatra, Indonesia. The ensuing tsunami ravaged Indonesia, Sri Lanka, India, Thailand, and more than a dozen other countries. Even the distant east coast of Africa was affected. Most of the areas affected by the tsunami were famous tourist destinations, and as it was tourist season, tourists from all over the world had gathered on the waterfront, unprepared for the devastating catastrophe. The number of deaths and disappearances caused by the tsunami eventually exceeded 225,000.
The 9.5 magnitude Chilean earthquake in 1960 was the largest earthquake ever recorded. It brought on a tsunami that produced waves over twenty-five meters high; 10.7-meter-high waves were recorded ten thousand kilometers away from the earthquake’s epicenter. The main tsunami spread across the Pacific to affect Japan, the Philippines, and other areas across the ocean.
No matter how much devastation earthquakes and volcanoes may bring, they only affect individuals and groups. The overall survival and happiness of humanity is not threatened.
We should actually adopt a more objective and scientific view of plate activity. There would be no mountains and rivers without plate activity, and thus no ecological cycle. Earth would lack vitality, and life would have difficulty developing and evolving in such an environment.
After studying the planets and satellites of the solar system, astronomers argued that Earth is the only planet that has plate movement within this star system. To take our satellite moon as an example, we can see that its surface is covered in craters formed three to four billion years ago. The earth exists in a similar environment to the moon, but the initial traces on Earth’s surface have mostly been updated and are no longer visible. It is Earth’s unique plate tectonics that grants this 4.6 billion-year-old planet energy, so it is an important factor in Earth’s development as a planet full of life and civilization.
In reality, plate activity benefits mankind even while it brings disaster. The formation of many important deposits is closely related to plate activity, and plate activity leads to the exchange of material and energy between the litho-sphere, asthenosphere, hydrosphere, and atmosphere, producing the variety of minerals that humans use every day.
Two: Climate Change and Glaciation
The normal climate change of Earth follows a pattern: winter is cold, spring and autumn are warm, and summer is hot. This is because different parts of Earth receive sunlight differently. Even along the equator, where temperature differences are smaller, there are rainy seasons and dry seasons. There are often years when the climate is abnormal, hot spells may last longer, or the cold season may be lengthened. These instances usually bring trouble; for example, global warming can cause floods, hurricanes, epidemics, or increased agricultural pests; and drops in temperature can affect agricultural production, freeze livestock to death, cause traffic jams, and injure people through avalanches and other disasters. However, these do not significantly affect the survival of humanity. Agricultural production will fluctuate from year to year, and problems like disease, floods, and avalanches do no endanger humanity as a whole. Alternating seasons are especially beneficial to humans; they enrich our lives, and winters provide relaxing respite after the long planting and harvesting seasons. This has been the way of our ancestors for centuries. At the same time, everything should abide by a limit. Once this limit is surpassed, good things may become disasters, and tens of thousands of years of heat or cold would be a completely different situation.
The surface of Earth not only has seasonal changes, but also goes through long spells of extreme heat or cold from time to time. Sometimes these long spells last tens of millions or even hundreds of millions of years. Seven million years ago, the earth experienced a period of extreme cold, and snow and ice covered most of the globe for tens of millions of years. Even the equator showed traces of glaciers. One hundred million year ago, the earth also experienced a period of extreme heat. For tens of millions of years, ice melted in the two poles; Antarctica and Greenland were as warm as spring, and even dinosaurs roamed there.
The earth constantly fluctuates between hot and cold, and scientists have discovered a pattern to this fluctuation. A long cold period usually occurs every 250 million years; this is called an ice age. The temperature is not static during this time; in fact, every ice age can be divided into several smaller glacial periods (or glaciations), and the warmer interval between consecutive glacial periods is called an interglacial period. Currently, we are in an interglacial stage of the Quaternary glaciation (also known as the Pleistocene glaciation, or the current ice age). In the two million years of the Quaternary glaciation, there have been several glacial and interglacial periods, but we do not feel the cold of the ice age since we are in an interglacial period.
The last glacial period started eighteen thousand years ago and ended ten thousand years ago. During that time, Greenland, Canada, Alaska, Siberia, Iceland, and most of northern Europe were covered in ice and snow. Large amounts of seawater were converted to snow and ice, resulting in a 150-meter drop in sea level. The Bering Strait disappeared and joined North America with Siberia; in Asia, the seabed of China’s Yellow Sea and Bohai were exposed; the Korean Strait and the Tsushima Strait disappeared; Japan became connected with Eurasia; and Indonesia joined with Asia. In Western Europe, seawater withdrew from the English Channel, and the British Isles became part of the European continent. Australia connected with the Asian continent through a land bridge.
Scientists have done much research on the earth’s alternating glacial periods, and there are many differing views concerning its cause. For example, some people think that the uplifting of the Himalayas from the sea caused carbon dioxide in the air to combine with rock rising from the ocean, lowering the carbon dioxide content in the atmosphere and causing a drop in global temperature. Others believe there to be a dense interstellar cloud along the sun’s orbit around the Galactic Center that partially covers the sun and changes Earth’s surface temperature (though it is not visible from Earth to the naked eye). This theory is supported by the fact that ice ages share the same 250 million years cycle as the sun’s rotation around the Galactic Center. None of the current views can fully explain the fundamental cause of ice ages convincingly. It is most likely that ice ages are the result of a combination of factors, including some that we may not yet recognize.
The larger climate change cycles of Earth affect global ecology and human life, but they do not affect the overall survival of humanity. Global climate change happens gradually, not suddenly. In a glacial period, ice first covers the two poles and then extends from higher latitudes to lower latitudes. The higher latitudes of both the north and south hemisphere are not suitable for human habitation or farming; however, as ice and snow coverage expands, the sea will retreat and land will be exposed to create areas suitable for human habitation and agricultural production. Oxygen dissolves easier in colder seawater, making it more conducive to the growth of marine life, which is why the polar regions are swimming with fish and shrimp. Whales, seals, walruses, and penguins all survive in the polar regions due to a rich marine life food source.
As the global temperature continues to climb and melt the polar ice sheets, and sea levels rise and erode coastal lowlands, there seems to be less space for human habitation and farming. That is not the case. As temperatures increase and snow melts, the Antarctic continent and Greenland will become suitable for living and planting, and the originally harsh environments in northern Siberia, northern Canada, and northern Scandinavia will become pleasant pastures and farmlands. The increase in land also includes the land that had previously been pushed thousands of meters under water by ice sheets. Once the snow melts, they will rise continuously until they reach the surface. The rise in temperature will also be beneficial to plant life and animal reproduction. Climate change is able to maintain a balance on Earth; the ecological environment and humans’ habitation space will not change too drastically as global temperatures rise and fall.
Even if we take the situation to the extreme and reimagine the ice age of seven hundred million years ago when glaciers spread to the equator, the overall survival of humanity would not be in danger. The development of science and technology today is enough to produce fresh fruit and vegetables in greenhouses during the dead of winter, providing us with enough confidence to overcome glaciations.
In the two million years since the Quaternary glaciation, humans have evolved from ordinary people to Homo sapiens. Animals evolved thicker skin and longer hair to combat cold weather, but humans developed less and less body hair because we learned how to use animal skins as clothing and how to gain warmth from fire. Our brave ancestors did not flee to the warmth of the equator in the face of cold weather; instead, they moved boldly to Asia and Europe and survived in the more severe conditions there.
The cold of the glacial period caused ice to cover the higher latitude areas, and sea level to drop more than one hundred meters, causing the Bering Strait to vanish and forming the land bridge between Asia and Australia. Humans entered Australia via the land bridge and migrated to the Americas through the Bering Strait, spreading human footprints over the entire world.
Many creatures were unable to withstand the cold of the Quaternary glaciation and went extinct one by one, but humans continued to evolve and strengthen in the struggle against nature. Those primitive conditions did not destroy the ancestors of man; thus, we have no reason to fear that modern humans, who have higher degrees of wisdom and advanced science and technology, will succumb to the cold.
Simple life-forms existed on Earth 4.28 billion years ago, complex life evolved in the ocean 530 million years ago, and a variety of creatures came onto land 400 million years ago. During this period, the earth went through numerous glaciations and many species died out, yet life has continued to this day without interruption. Earth today has more wisdom and civilization than ever before, which shows us that glaciations are nothing to fear.
Three: Magnetic Field Disappearance
Space is full of cosmic rays that originate from high-energy particles and attack our planet incessantly at a speed close to that of light. If humans or other creatures were directly attacked by cosmic rays, the high-energy particles could penetrate cells—not only killing the cells but also changing or destroying genetic material.
We generally do not suffer the harm of cosmic rays because Earth’s surface has three layers of safeguards against them. The first safeguard is Earth’s surface atmosphere, which also happens to be the most powerful barrier. When cosmic rays travel to Earth at high speeds, they collide with the molecules and atoms in the atmosphere. After every collision, the cosmic ray’s energy decreases. Once the energy particles reach Earth, their energy level is so low they cause minimal damage to humans.
The earth’s magnetic field is another safeguard. When cosmic rays pass through the magnetic field they must use their energy to overcome the magnetism within the field. Some lower energy cosmic rays will be captured by Earth’s magnetic field without ever reaching Earth’s surface, while higher energy cosmic rays will also suffer great damage by the time they pass through. Earth’s magnetic field is the secondary barrier outside the atmospheric barrier.
The final layer of protection against cosmic rays is the interplanetary magnetic field from the sun. This field wraps around Earth’s magnetic field and serves a similar function in consuming the energy of cosmic rays. This magnetic field is vitally important in protecting life on Earth, yet long-term observance shows that the field is not always stable. It fluctuates in strength, swaps between north and south magnetic poles, and sometimes vanishes altogether, leaving Earth vulnerable. To consider the effects of geomagnetism disappearing, we must first understand the basic nature of geomagnetic fields.
In physics, we all know that electricity and magnetism can interact in a phenomenon called electromagnetism; that is, electricity can sense magnetism, and vice versa. Earth’s core is partially composed of molten iron and nickel; this liquid metal moves in a rotating motion within Earth’s core due to Earth’s rapid rotation. This is as if a giant electrical current were flowing underground, producing a strong magnetic field, which is Earth’s magnetic field.
The study of paleogeography found geomagnetic fields to be changing following this pattern: geomagnetic poles are located close to Earth’s poles. The intensity of the magnetic field will gradually weaken after passing the strongest point, disappearing briefly before gaining back its former strength. The magnetic poles will be reversed during this cycle. In the past seven hundred thousand years, Earth’s magnetic field has followed its current direction, but it was reversed in the 450,000 years before that. After studying the geomagnetic field’s movements over the past one hundred million years, it was discovered that the magnetic poles reverse every four hundred thousand to five hundred thousand years. The shortest reversal period was fifty thou-sand years.
A reasonable explanation for magnetic pole reversal has been proposed: it is caused by the flow direction change of molten iron and nickel in Earth’s core. The iron and nickel in Earth’s core does not always flow in one direction once the flow direction reverses Earth’s magnetic poles reverse accordingly. During the moment of critical pause when flow direction is changing, geo-magnetism will vanish briefly. Since the flow of molten iron and nickel at Earth’s core follows Earth’s rotation, the magnetic pile will not deviate far from the two poles, no matter its orientation.
What happens to Earth during the brief period of geomagnetism disappearance? One thing is for certain; under normal circumstances, cosmic rays and solar particles cannot cause lethal damage to humanity due to the protection from Earth’s atmosphere. In the four million years of human evolution, the Earth’s magnetic field has disappeared briefly numerous times without affecting mankind or other Earth creatures very much. Through research of atmospheric protection against cosmic rays and solar radiation, scientists have proven that geomagnetism disappearance will not have a decisive impact on the survival of humanity in normal circumstances. What about the unusual circumstances? In the next few billion years of human survival, unusual circumstances are likely to occur.
The most important sources of cosmic rays are supernova events in the Milky Way. Every supernova of considerable scale releases cosmic rays tens of thousands of trillions of times that of the sun. What would happen if a supernova event took place not far from us? Studies have shown that with the protection of the atmosphere, Earth’s magnetic field, and the sun’s magnetic field, high-intensity cosmic rays cannot compromise human survival as long as the supernova event is more than twenty-five light-years away. However, if Earth’s magnetic field disappeared at this critical moment, the situation would be much more severe. With the disappearance of geomagnetism, the earth would suffer attack from both solar particles and cosmic rays; the earth’s atmosphere and the sun’s magnetic field would not be enough to withstand such a double attack. Therefore, the safe distance would have to be pushed back to thirty light-years. Moreover, geomagnetism changes today indicate that a brief disappearance of Earth’s magnetic field will occur in the next ten thousand years.
In the next ten thousand years, the most likely supernova event close to Earth is Betelgeuse. Fortunately, Betelgeuse is 640 light-years away, meaning that Earth’s atmosphere and the sun’s magnetic field would offer sufficient protection, even if the outbreak coincided with geomagnetic field disappear-ance. In fact, there is no possible supernova within thirty light-years of us, and scientists have determined the probability of a supernova within that distance to be once every ten billion years. With such a small window of opportunity, it is extremely unlikely that such an event will occur simultaneously with geomagnetism disappearance.
Even if such an unlikely coincidence were to occur, we would not need to worry. Firstly, with Earth’s atmosphere and the sun’s magnetic field serving as two shields, cosmic rays produced by a supernova within close distance would be sufficiently weakened so as not to endanger the overall survival of mankind. Secondly, the strong cosmic rays generated by the supernova would not last long (a few weeks at most), and there would be warning signs in advance so that proper arrangements could be made to avoid injury. The walls and roofs of our houses can all offer protection from cosmic rays. As long as we properly fortify our dwellings and limit outside exposure, we can avoid being harmed by cosmic rays.
SECTION FOUR: THREATS FROM EXTRATERRESTRIAL LIFE
Extraterrestrial life refers to intelligent life from outside our planet; we usually call them aliens. People are quite keen on the subject of alien invasion. Many science fiction movies use this as a selling point and promote productions with this theme. However, actual alien invasion would be devastating to mankind, as humans would be a completely different species in the eyes of aliens. Aliens might treat humans without any sympathy or humanity, just as we have treated other animals in the past. They could carry out a massacre against us that would surpass Hitler’s massacre of the Jews. Of course, it is also possible that extraterrestrial life would be friendly and visit Earth in the spirit of tourism, friendship, or curiosity instead of invasion. In any case, it is much more important to safeguard against alien invasion and attack than to hope for friendliness.
So far we have not found any evidence of the existence of extraterrestrial life. Archaeological excavations and geological surveys of Earth have not turned up evidence of aliens visiting our planet in the past either. The idea of aliens is still a product of people’s subjective imaginations.
Even so, from the long-term perspective of human survival, we have sufficient reason to consider the threat of extraterrestrial life seriously.
Humans are the only intelligent life we currently know of. Apart from traces of life factors found in very few fallen asteroids, no other clues of extraterrestrial life have been discovered. We can only infer the possibility of alien existence through the study of Earth’s humans and deduce their possible location and threat to us accordingly.
One: Life on Earth
After close distance observation and in-depth scientific analysis of the solar system planets and their satellites, it can be confirmed that within the solar system, only Earth has the conditions to produce complex life. What gave Earth the power to produce life?
Celestial collisions were an inevitable process of Earth’s formation. Many asteroids, meteorites, and comets contain water molecules. When they collide with each other to form larger celestial bodies, these water molecules are transferred accordingly. Volcanoes and magma flow are formed through collisions, and their high temperature evaporates water molecules into carbon dioxide gas. Earth’s early atmosphere was mainly composed of carbon dioxide gas.
Carbon dioxide cannot nurture complex life; it produces a greenhouse effect instead. Shortly after the formation of the ocean, microbes formed in the water. The earliest microbes were born 4.28 billion years ago, only a few hundred million years after Earth formed. Large numbers of algae creatures appeared shortly after and absorbed carbon dioxide and released oxygen.
This process of carbon dioxide to oxygen conversion took more than three billion years because Earth had a high demand for oxygen. Oxidation reactions would occur when oxygen encountered most metals—iron oxide, copper oxide, and alumina are all conjugates of oxygen and elements. The oxygen released by algae had to meet the demands of these oxygen consumers first.
The geological era 530 million years ago was known as the Cambrian Era. During this time, a number of complex organisms seemed to appear simultaneously in the vast ocean; this phenomenon was known as the Cambrian explosion. We know that animals need oxygen to survive, so the Cambrian Era must have been an era when oxygen production exceeded oxygen consumption. The surplus of oxygen was a prerequisite for the Cambrian explosion. Organisms only existed in the ocean at this time, so the land was barren of life. One hundred million years passed—about four hundred million years ago—before life came to land. Plants and animals arrived on land at the same time.
While animals must absorb oxygen to survive, plants absorb carbon dioxide and produce oxygen; therefore, plants should have existed on land shortly after marine life came into existence. Why then did plants and animals arrive on land simultaneously after such a long interval? Scientific research shows that the ozone layer above Earth’s atmosphere formed four hundred million years ago, identical to the timeline of biological life arriving on land. Is this a coincidence?
The glory of the sun is often described as the number one element for life. Without the sun’s light and warmth, life could not be. The sun’s energy is nuclear energy, so its glory includes not only the warmth we need but also extremely strong lethal rays, like ultraviolet rays, X-rays, and gamma rays. If astronauts did not have protective devices, they would be killed by sunrays in space.
The atmosphere is a protective layer that absorbs harmful rays, but it is far from enough. About four hundred million years ago, the ozone layer formed due to a surplus of oxygen, and it proved to be particularly capable of absorbing harmful rays. Although the ozone layer is relatively small compared to the atmosphere, it was enough to protect life from harmful rays and allow them to emerge from the ocean’s protection and onto the land.
The moon is another great “shield.” As a satellite of Earth, it has blocked the attack of many foreign objects. At the same time, a series of other bigger planets like Jupiter, Saturn, Uranus, and Neptune revolve around the sun outside of Earth. They possess greater mass and stronger gravity than Earth. It is their gravity that pulls asteroids away from the inner circle of the solar system, shielding Earth from impact with extraterrestrial objects. Some scientists have asserted that Earth would never have conceived intelligent life without its protectors in the solar system. The birth of intelligent life takes a very long time, so if a large celestial collision occurred whenever the birthing process was close to completion, all past efforts would come to naught.
In recent years, humans have focused space exploration efforts on our neighbors, Mars and Venus. Our detectors have landed on these two planets and much close proximity observation has been carried out as well. Observations show that although Mars’ distance from the sun is only one third greater than that of Earth, its surface temperature is lower than -60⁰C. The diameter of Mars is only half of Earth’s diameter, and its mass is one- tenth of Earth’s, making it difficult to capture external air. Mars only has an extremely thin layer of air on its surface; its density is less than 1 percent of Earth’s atmosphere density and is mainly composed of carbon dioxide. Therefore, the environment on Mars is not conducive to the survival of life.
Venus has the most similar conditions to Earth. Its diameter is only slightly smaller than Earth, its weight is 80 percent that of Earth’s, and it is only a quarter distance closer to the sun. Unfortunately, if Earth were paradise, Venus would be hell. Its surface temperature can reach 500⁰C, there is no water, a thick layer of carbon dioxide atmosphere with pressure nine times higher than the Earth’s atmosphere blankets its surface, and traces of volcanic magma erosion linger all around. No life could possibly survive in such an environment; however, we have discovered traces of shallow oceans on the surface of Venus. These shallow waters disappeared about three billion years ago.
Why does Venus lack the ability to produce life when its planetary conditions are so similar to Earth’s? Moreover, why do these two similar planets have such differences in their natural environments? Many explanations have been suggested, and among them, two are highly recognized. The first view holds that the answer lies in Venus’ slightly closer proximity to the sun. When the sun’s temperature rose three billion years ago, it evaporated the water on Venus. This means that the one-quarter disparity between Venus and Earth’s distance to the sun completely changed the fate of the two planets.
The other view holds that the different fate of the two planets is not due to their distances to the sun but to Venus’ slow rotation. The metal magma at Earth’s center produced a magnetic field due to Earth’s rapid rotation, whereas the slow rotation of Venus could not produce such a force field. This foreshadowed the fate of the two planets. Scientists believe that the magnetic field plays a decisive role in planet evolution and the birth of life, because it prevents solar winds and cosmic rays from harming life. Venus experienced asteroid collision just like Earth in its early stages. It formed oceans and a carbon dioxide atmosphere as well; however, due to the absence of its own magnetic field, solar winds and cosmic rays eliminated algae and even bacteria from Venus. With no system to absorb carbon dioxide and produce oxygen, the carbon dioxide atmosphere thickened increasingly, strengthening the greenhouse effect and raising surface temperatures until all water was evaporated and the surface temperature reached its current 500⁰C high.
Mars does not have a magnetic field either, even though it spins faster than Earth. Its small mass does not allow for magma at its core, so Mars is also void of magnetic field protection. The air on Mars’ surface is also very thin and does not offer sufficient protection against solar particles and cosmic rays. If complex life-forms ever existed on Mars, they would have gone extinct some time ago.
When astronauts observed our planet from space, they found the earth to be a beautiful blue planet. It stands out like a small oasis in a vast desert. Over decades of research and exploration, scientists have marveled at the stringent conditions required to produce complex life. After summing up their results and carrying out a series of experiments, many returned to one simple starting point: Earth is just one occasional occurrence in space. On one occasional planet in one occasional star system in the vast universe, a series of occasional incidents occurred over a relatively short period of time to produce an environment suitable for life, thus producing a monumental miracle: the birth of mankind.
However, we are not satisfied with this explanation. One scientific conclusion is for certain: as long as there is sufficient time and conditions, material activity will produce life—even intelligent life like humans. Nonetheless, too much time and too precise conditions are required, so we cannot accurately predict whether miracles of life exist in other corners of the universe.
Two: Prerequisites for the Birth of Intelligent Life
1. Star Systems That May Produce Intelligent Life
The conditions required for the birth of intelligent life are extremely precise. First, there must be a stable and continuously burning star. At the same time, the planet in question must satisfy many requirements and encounter many chance opportunities over a very long period of time. Our current abilities are far from adequate to apply this series of conditions to all the planets outside the solar system; however, we can set out some of the prerequisites needed. It must be noted that these are merely the indispensable conditions required to produce life, not the conclusive conditions that will guarantee life. Intelligent life cannot exist without these conditions, but these conditions do not promise the birth of intelligent life, since there are still many factors we do not yet understand. Let us first analyze the stellar conditions required to conceive intelligent life.
The star that forms a basis for intelligent life must satisfy the following:
a. It must be a star in the stage of hydrogen fusion; only stars in this stage burn stably.
b. Life cannot be born in large star systems. The greater the mass of the star, the more intense its internal thermonuclear reaction is, and the shorter it stays in its main star sequence. For example, a star 1.2 times the mass of the sun only stays in its main star sequence for about three billion years; according to the birth time of humanity (i.e., five billion years), even stars slightly larger than the sun cannot suffice.
c. Smaller stars cannot produce intelligent life around them either. The smaller a star, the less light and heat it produces, the closer a planet must be to obtain necessary warmth and glory. However, when planets are too close to stars, the gravitational pull of the star will slow its rotation, causing one side of the planet to bask in light and warmth while the other side is swallowed by darkness and cold. Complex life cannot appear on planets like this.
In addition, once a star is small enough to be a red dwarf, its surface will be very unstable and produce large flares and lethal rays. This type of star system is not suitable for the survival of complex life; 70 percent of the Milky Way is composed of red dwarves.
d. A completely suitable star must have experienced billions of years of stable burning, since intelligent life itself takes billions of years to form.
e. Intelligent life can only exist on a solid planet that has carbon, nitrogen, oxygen, iron, silicon, and other heavy elements. Since heavy elements are produced by large stars, only second- or third-generation stars can produce life around them.
f. Many binary and triple stars exist in the universe, but these star systems cannot produce life. In a star system like this, the stars will interfere with the planets around them due to their gravitational pull, resulting in very unstable planets.
g. It cannot be too close to large stars. Large stars end their lives as supernovas; before intelligent life-forms are sufficiently evolved, they do not have the ability to prevent the thermal radiation and cosmic ray injury brought on by supernovas. It cannot be too close to medium-sized binary stars either, since they form supernovas as well.
2. Planets That May Produce Intelligent Life
A suitable stellar environment satisfies only one condition in the birth of intelligent life. A suitable planet is also necessary, and it is much harder to come by. To use the solar system as an example, Earth is the only planet able to produce intelligent life. Even though Venus and Mars are very similar to Earth, they do not meet the necessary requirements. What conditions does a planet need to satisfy in order to produce intelligent life?
a. The planet must be large enough to “capture” atmosphere.
b. The planet’s atmosphere must be composed of carbon dioxide, oxygen, and also nitrogen. Hydrogen and helium exist in abundance within space, but planets with carbon dioxide and oxygen are rare.
c. The planet must be a metal-element based planet. In astronomy, all heavy elements apart from hydrogen and helium are considered metal elements; only metal planets are solid rock planets that can provide a foothold for life. Such planets are exceedingly rare in the universe.
d. The planet must be a suitable distance away from stars; this distance is called the habitable zone. If a planet is too far away it will not receive sufficient warmth; if it is too close it will be overheated.
e. The planet’s orbit around the star cannot have too large an eccentricity. If the eccentricity is too large and the orbit is flat oval in shape, the near point will be too close to the star and the far point will be too distant, resulting in extreme heat and cold.
f. The planet’s rotation axis cannot tilt too much. If the axis tilts too much, the planet will rotate on its side. Like Uranus, the planet will experience day for half a year and night for the other half. It will also experience half a year of summer and half a year of winter. During summer, light will bake the planet until temperatures reach hundreds of degrees, but in winter, there will be no light and temperatures will reach -200°C. This environment would not be conducive to life.
g. The planet must satisfy a variety of other requirements to produce complex life; some may be absolutely necessary while others may not. For example, it is generally believed that water is indispensable to survival of life, but there are differing views regarding this point. Life on Earth metabolizes on an oxygen-water system, and it is speculated that life on other planets may metabolize on a nitrogen-liquid ammonia system, or some other material system. A suitable magnetic field may be necessary, as it prevents cosmic rays and stellar radiation from harming life. The existence of a series of larger surrounding planets, like Jupiter, may also be necessary to block frequent impact from asteroids. And so on.
Three: The Location of Extraterrestrial Life
1. Possible Locations for Extraterrestrial Life
Let us take a look at the universe surrounding the solar system based on the above stellar and planetary requirements (though they are only necessary conditions and not sufficient conditions). We will use fifteen light-years as a boundary, since any distance beyond that would take hundreds of thousands of years of travel to on even the fastest non-manned spacecrafts.
There are thirty stellar system in this range, ten of which are binary stars and one triple star, so there is a total of forty-two stars. The only star that meets the stellar requirements is the Tau Ceti, 11.68 light-years away. Tau Ceti is a single G-star like the sun; it is yellow in color. The sun’s spectral type is G2, while Tau Ceti’s spectral type is G8, so it is slightly cooler than the sun (its temperature is 45 percent the sun’s temperature), and it stays in its main star sequence for about the same time, which is four billion to six billion years.
These conditions have made Tau Ceti an observation target for scientists. In recent years, astronomers have deduced that Tau Ceti may have five planets with masses two to seven times that of Earth. Among them, the fourth planet, called “planet e,” is in the habitable zone; its mass is 4.2 times the mass of Earth. At present, global scientists within the field all regard this speculation with great interest, as the existence of planet e and the possibility of it producing intelligent life all remain to be studied.
In conclusion, stars that can facilitate intelligent life are very rare, and it is even more rare for there to be suitable planets around them. Even if planet e did exist by Tau Ceti in a habitable zone, the probability of it meeting the other precise conditions for producing life are overwhelmingly negative. After all, the existence of a solid rock planet within the habitable zone of a suitable star is only one of the many basic conditions necessary to produce intelligent life.
Today, we can be certain that more planets exist outside of the solar system; only thousands have been discovered since 1995, and most of them are larger hydrogen and helium planets like Jupiter. We have not yet reached an in-depth level of observation and research regarding these planets; even the existence of planets around Tau Ceti are mere speculation.
Clearly, we cannot determine the location of extraterrestrial life according to planetary indicators; we can only rely on stellar indicators. Only one thing is for certain: planetary indicators will only be more stringent than stellar indicators.
2. The Search for Extraterrestrial Life
On March 2, 1972, the Pioneer 10 space probe was successfully launched into space by NASA. Its mission was to fly out of the solar system, after surveying Jupiter, in search of extraterrestrial life. On June 13, 1983, after crossing Neptune, it became the first man-made spacecraft to fly out of the solar system. An alternative definition of the solar systems stipulates that any area adhering to the solar system’s gravitational constraints belongs to the solar system. By this definition, Pioneer 10 still has to travel twenty thousand years before it leaves the solar system. Pioneer 10 carried a gold-anodized aluminum plaque marked with the cosmic positions of Earth and the solar system through multiple neutron stars, human figures of a male and female, and two circles indicating that the simplest material molecules were composed of two hydrogen atoms. This is a calling card of Earth’s humans that will last one billion years. It flies aboard Pioneer 10 towards Taurus; two million years later, it will reach the star Aldebaran.
A year later, Pioneer 11 followed its predecessor on April 6, 1973, journeying towards Aquila. It will take about four million years to reach this constellation. On August 20 and September 5 of 2007, NASA launched the two detectors, Traveler 2 and Traveler 1, towards Sirius and Ophiuchus. These two detectors both brought greetings from Earth.
Sending detectors out of the solar system is only one way we deliver information to extraterrestrial life; the more common way is to use radio waves to send messages. In July 2003, with the support of NASA and other authorities, more than ninety thousand “electronic greetings” from more than fifty- two countries around the world flew towards five stars similar to the sun. The former Soviet Union’s Yevpatoria Observatory was the first to send a greeting message to aliens as early as November 1962. They used ordinary telegram codes to issue the simple words—“Peace, Soviet Union, Lenin”—into the depths of space.
In November 1974, the world’s largest radio telescope was built in Puerto Rico; in celebration, the telescope sent a three-minute telegraphic greeting to the Messier 13 globular cluster. Later, the Yevpatoria Observatory sent greetings to extraterrestrial life two more times in 1999 and 2001. They also sent a music recording of an electric organ concert into space.
The United States’ Messaging Extraterrestrial Intelligence (METI) initiative plans to use radio or laser signals to send some “topic factors” to neigh- boring planets by the end of 2018. Then they plan to send signals to planets hundreds or thousands of light-years away; this will be the first time information will be sent clearly and continuously to extraterrestrial planets. The idea is to send continuous greetings towards one target planet for months or years in order to connect with aliens.
People have always had a strong interest in aliens. Not only are we keen to send information to aliens, but we also do everything possible to learn about them. Despite the many efforts to contact extraterrestrial life, so far no reliable evidence of extraterrestrial life has been received.
The UFO phenomenon has always been an unsolved mystery. We have had records of UFOs since ancient times. Many consider these UFOs to be evidence of aliens visiting Earth, but no real proof of alien encounters has been verified. There have been reports of alien sightings and even alien abductions. Logically speaking, such claims probably have very little truth to them. In 2009, the British government announced the closure of their official UFO investigation team due to it being “a huge waste of time and money.”
Four: Reconsidering Extraterrestrial Life
Though we have no concrete evidence of alien life and we understand that the conditions required to produce intelligent life are extremely stringent, we are certain that extraterrestrial life exists in the universe. Because the universe is extremely vast, even miracles of the smallest probability can happen.
According to modern astronomical observation and speculation, there are about two hundred billion stars in the Milky Way and three hundred billion galaxies in the universe, putting the number of stars in the universe at billions of trillions. Since the birth of the universe 13.8 billion years ago, stars have evolved through at least four or five generations (first generation star systems cannot produce life). Earth cannot be the only planet with intelligent life during all this time.
Even so, the possibility of alien life visiting Earth and threatening humanity is very small. Due to the exacting conditions required to produce intelligent life, it is unlikely that such life exists anywhere near us, and it would be even more unlikely that they could travel to us.
The power source for interstellar travel alone would be a big problem. The Apollo moon landing spacecraft was only forty tons, but its launch rocket was more than two thousand tons, most of which was propellant fuel. The moon is only 380,000 kilometers away; our nearest neighboring star is more than one hundred million times further than that.
The millions of years interstellar travel requires is another great consideration. A series of technical, physical, and psychological problems must be resolved for such a journey. Moreover, any intelligent person would lack sufficient motivation to carry out such a trip. Millions of generations of evolution and would pass by during this journey, and the end would not justify the means. If intelligent life really did exist, they would most likely choose to send probes or electronic messages towards Earth to satisfy their curiosity, just like us.
Of course, someone might bring up the theory of time and speed from the general relativity theory. If Einstein’s formula was completely accurate, it further proves that interstellar travel is impossible, since it shows that time, speed, and weight are interrelated. When an object travels at a speed close to light speed, time will become very slow, while the object’s weight will increase. Once the object reaches the speed of light, its weight will reach infinity. In other words, before humans could reach the speed of light, we would be crushed by the weight of our own bones. There is also no force that could propel such a heavy spacecraft; this has been proven by high-energy particle accelerator experiments.
We also often see “wormhole” travel methods in sci-fi movies. Would that be possible?
The wormhole concept is an inference based on the theory of general relativity. It is also known as the Einstein-Rosen bridge. According to the wormhole concept, time and space can be warped to form a shortcut between distant points, or it could form a shortcut between now and the future or now and the past. Based on this concept, people have proposed ideas of time travel and time machines that can change time and distance at will.
Realistically speaking, the wormhole is still a very immature inference, and it brings up many questions that cannot be answered. For example, some have asked what would happen if a person traveled back in time to kill their mother before they were born, or if wormholes would allow astronauts to return to Earth before they even left. This is clearly illogical. Many aspects of the wormhole theory cannot be solved with current scientific cognition.
Even Hawking, who was always at the forefront of such academic discussion, admitted in his book, A Brief History of Time, that the possibility of time travel still awaits conclusion.
Over the past centuries, we have been committed to finding traces of extraterrestrial visitation on Earth, but no such evidence has been discovered. If Earth could produce simple life-forms 4.28 billion years ago, it would have had basic survival conditions back then. If aliens wanted to occupy, colonize, or vacation on Earth, they should have arrived a long time ago. Since no extraterrestrial life has visited Earth in the past billions of years, we have reason to believe they will not arrive in the billions of years to come. Of course, this is just one type of logical reasoning.
The universe formed 13.8 billion years ago. First-generation star systems cannot produce life, but second-generation star systems should have existed ten billion years ago. It takes about five billion years for intelligent life to form, which means the earliest intelligent life should have formed five billion years ago.
Five billion years is an immensely long time for an intelligent species, so it should have been sufficient time to develop all manners of technology. So why have aliens not visited Earth? I think there are only two possible reasons.
First, the natural laws of the universe make interstellar travel impossible to overcome, even for the most intelligent beings. Since intelligent life can only be produced under very specific circumstances, the instances of such life would be few and far between. Even the alien life closest to Earth would be distant enough to negate the possibility of visitation.
Second, whenever intelligent life is formed, nature will also endue it with inherent flaws. Such flaws will cause the intelligent species to self-destruct before they have time to figure out the logistics of interstellar travel. Also, these life-forms may stop the development of interstellar travel technology for some reason. This will be examined further in this book.
Although the possibility of alien invasion is extremely small, it should not be completely ignored. Two considerations will be proposed here as reference: first, the occurrence of any major event will have warning signs in advance, including alien invasion. We will have time to take precautions accordingly to defend our home planet; perhaps that is all we can do. Second, it is very foolish to devote much research and preparation against alien invasions today. If extraterrestrial life really did invade Earth, they would possess much more advanced technology compared to our hundred thousand years of human history. They would be at least billions of years more advanced than humans; we could not hope to catch up to that in a few thousands or millions of years. Moreover, Earth has possessed suitable living conditions for 4.28 billion years without any sign of aliens, so it would be unnecessary to devote efforts to prepare for something of such minimal possibility within such vast time constraints.
The committed observation of extraterrestrial life is not much of a problem, but the continuous attempts to communicate with and send information to aliens is irrational. According to previous analysis, the possibility of alien visitation is very small, so this conclusion means two things. On one hand, if we cannot connect with aliens, all our efforts will have been wasted. This is too high a price to pay just for the satisfaction of curiosity. On the other hand, if aliens really could receive our information and travel to Earth with unimaginably advanced technology, humanity could be facing overall extinction.
It has been said that it is immoral for us to only detect alien information and not share our information as well. This is a very naive view. We observe aliens out of curiosity and goodwill, but we cannot assume that aliens will share our attitudes. The laws of survival always favor that the strong, highly civilized creatures capable of visiting Earth may not regard us as “people” (we are not the same species, after all) and kill us at will. That could be the end of humanity. Today’s decision-makers and scientists should stop such potentially devastating behavior just for the satisfaction of curiosity or some other purpose.
SECTION FIVE: THREATS FROM EVOLUTIONARY LAWS
One: Inheritance, Mutation, and Evolution
Men produce sperm and women produce eggs. Both are cells. When a sperm cell combines with an egg cell it forms a fertilized egg. Fertilized eggs can split into two exact same cells, which can then split into four, then eight such cells, eventually forming a living person.
The formation of life is the result of cell division. This applies to humans and all other organisms. Why are people different from each other, and why are animals and plants each different in their own way? The secret lies within the biological cells.
There is a substance called DNA in cells; its basic unit is deoxynucleotides, and it stores the genetic code of life. Simply speaking, a cell is made of the central nucleus and the peripheral cytoplasm. There is a very important material called chromosomes inside the nucleus; it is the carrier of DNA, and it always exists in pairs: one half comes from the male parent, and the other from the female parent. This means that half of our traits are decided by the male parent, and the other half by the female parent. Humans have twenty three pairs of chromosomes.
DNA molecules are composed of two long chains in a double helix structure, which resembles a spiral ladder twisted together. The handrails of the ladder are made of phosphoric acid and deoxyribose, which is the backbone of DNA. The steps of the ladder are made of base pairs, and the genetic codes of life are engraved on them. The “genes” we usually refer to as the deciding factors of traits are fragments of DNA. According to results from the Human Genome Project, it is estimated that humans have twenty thousand to twenty-five thousand genes.
The two chains that form the DNA double helix structure are identical to each other but reverse in direction—that is, the two ends of the chain are reversed and wound together in a right-hand spiral. During cell division, the two long chains of the DNA molecules are split to form two separate strands, each of which is paired with other deoxynucleotides to form a new double helix structure. Each newly formed spiral is exactly the same as the original spiral, producing two identical DNA molecules. This is the self-replication function of DNA.
When we say that the DNA molecule self-replicates to form two double spirals exactly the same, we refer to an almost 100 percent accuracy. However, nothing is foolproof, and one accidental error will appear among numerous perfect copies. This is called a “mutation.”
On ranches, we sometimes find that cattle or sheep will produce an off spring completely different from its parents; this is an example of mutation. Distinctly different crop seedlings will also appear on farms, which is also mutation. The same phenomenon happens in humans as well. All creatures mutate; some mutations are inherited and some are not. Mutations are usually not beneficial, as they produce weaker individuals. Cancer is one such adverse mutation within the body; radiation syndrome is another example where high-energy rays penetrate into the cell’s nucleus and destroys the DNA structure, causing mutation.
In biological mutation, sometimes there will occur a mutation that produces a stronger individual. If this mutation can be inherited, it will form a stronger species. This is what we call evolution. Earth’s primitive life developed into the vibrant variety of creatures today through evolution; we humans are a product of evolution as well.
Reverse evolution also occurs in organisms when unfavorable mutation becomes a common phenomenon that can be inherited. This situation can also be called “degenerative evolution,” or “devolution.” Devolution will cause a species to be less adapted for survival and less suited to the environment, and they will usually go extinct after a period of struggle.
All species are evolving, and according to the theory of evolution, all creatures on Earth are descended from the same ancestor. Primitive life mutated differently in different environments, leading to the differentiation of animals, plants, and fungi. These life-forms continued to evolve; the strong survived, while the weak were eliminated in a process we call “natural selection” and “survival of the fittest.” It is also referred to as the law of natural selection; this is one of the most important laws in the theory of evolution.
Two: Reasons for Species Extinction
There are about 2,000,000 species of animals, 270,000 species of plants, and 35,000 species of microorganisms currently recorded, and scientists estimate the total number of biological species (recorded and unrecorded) in the world to be ten to thirty million. However, many more species have existed on Earth. We can almost be certain that the species on Earth today are less than 1 percent of the grand total, as over 99 percent have already gone extinct.
The extinction of Earth’s creatures in the past was mainly a result of natural forces. Life on Earth has existed for 4.28 billion years and gone through numerous extinctions, but life itself has never been interrupted. Since the Cambrian explosion, Earth’s creatures have experienced five major extinction events, the biggest of which was the Permian-Triassic extinction 250 million years ago. During this event, 90 percent of marine organisms and 75 percent of terrestrial life disappeared, yet many species were preserved. We know that since life began, Earth’s environment has never deteriorated so much that no creatures could survive; even during major extinction events, it was only certain creatures that could not adapt.
Through the study of species extinction, it can be concluded that extinction always results from one of these three factors:
1. Environmental Factors
Environmental factors are the changes in the natural environment that cause species’ extinction. The earth’s environment is affected by a variety of factors, like volcanoes, asteroid or comet collision, geomagnetism disappearance, and climate change—all of which change Earth’s environment significantly. Some organisms can readily adapt to changes in the environment, while others may evolve to suit the environment in a gradual process. These organisms survive. Any species that does not fit one of the above conditions will become extinct.
Environmental factors are the main factor in species extinction, especially large-scale extinction. Studies of the five major extinction events show that environmental factors were the main reason every time. It is easy to understand how environmental change leads to mass extinction. Most organisms are exposed to the natural environment and sensitive to environmental change; such changes will inevitably lead to adaption challenges. Dramatic changes in the environment are especially conducive to extinction.
2. Competition
Competition refers to the extinction caused by stronger species eliminating weaker species, or interdependent species reducing in conjunction. Competition also includes the extinction caused by intraspecific competition. Competition generally only leads to routine extinctions, not mass extinctions.
3. Devolution
Devolution refers to the adverse mutations a species might suffer when there are no environmental or other external factors that may affect the species. These adverse mutations are hereditary, leading to a devolution of the species as a whole.
Once the devolution of a species becomes an irreversible trend, it will become increasingly difficult for the species to survive. They will be continuously eliminated until the species goes extinct. Devolution usually leads to routine extinctions.
Three: Threats from Evolutionary Laws
Evolutionary laws act on all species, including humans. All species are subject to the ruthless laws of extinction, adapting, or going extinct accordingly. Does this mean that human beings might also become extinct from natural forces?
1. Threats to Humans from Environmental Factors
Most organisms are exposed to the elements and adapt to environmental changes in a very simple manner. If global temperatures drop, animals evolve thicker skin and longer fur; if global temperatures rise, animals evolve thinner skin and shorter fur. Those who cannot adapt this way face extinction.
Additionally, due to the food chain relationship between species, the extinction of one species will inevitably lead to the reduction or extinction of other species that prey on it. Since animals have no way to process their food apart from chewing, they cannot change inedible species into an edible food source. Though digestive systems can evolve, few species complete such evolution. Animals obtain food from nature; they cannot domesticate and breed food, so changes in nature will affect their food source significantly.
Humans are not in this situation because their intelligence has reached an absolute high ground, and humans have mastered far more advance technology. Humans interact with the natural environment in a completely different way.
Humans are no longer exposed in nature; we mastered the use of animal skins and fire tens of thousands of years ago. Today, things are even more optimistic; we can adjust to the outdoor temperature by changing clothes, and we can adjust to temperature indoors with heating and air conditioning. We can even design specialized clothing and work facilities for extreme temperatures.
In regard to the environment’s impact on human food sources, we have an unparalleled advantage over other animals. Millions of years ago, humans learned to crush shells with stones and eat the nuts. Later we learned to use fire to cook raw food. Ten thousand years ago, humans learned to domesticate poultry and plants, far surpassing other animals.
Today we have greenhouse vegetables and fruits to eat in winter; we can change the genes of crops to cultivate temperature-resistant, pest-resistant, disease-resistant crops; and we can breed all manners of livestock in all kinds of weather.
Humans are also an omnivorous species. Plants and animals—cooked or raw—are all suitable food sources for us. This makes it much easier for humans to solve the problem of food shortages when environmental changes occur.
Does this mean the environment does not have a decisive influence on mankind? Of course not. The previous sections of this chapter have outlined environmental impacts that may threaten humanity; however, an environmental threat that could lead to human extinction would be one that could completely collapse global ecology. It would be far beyond normal environ mental change. The nearest threat that would threaten human survival is the threat of the sun evolving into a red giant, but that is too far in the future to consider today.
2. Threats to Humans from Competition
Powerful dinosaurs once ruled the Earth. Let us use this to make a hypothesis: if dinosaurs and humans existed on Earth simultaneously today, which would dominate the other? I think the answer is clear—humans would dominate the huge dinosaurs, not the other way around.
An empty-handed man encountering a wolf in the wild will be torn to pieces, let alone if he comes across a dinosaur. However, humans as a group—especially highly intelligent humans who have mastered high-tech means—have unparalleled strength.
It is certain that no species on Earth could destroy the seven billion humans today through competition. From an evolutionary perspective, mankind would not allow any species to evolve enough to threaten human survival. Humans are completely capable of controlling plant and animal evolution on Earth—enough to ensure they never become threats to humanity. Microorganisms are the most difficult to control, as they are so small in size and vast in number, new viruses and bacteria can unexpectedly attack humans. Malignant infectious diseases are especially terrifying; however, the infectious disease control and treatment methods we possess today are enough to limit this threat within a certain range and prevent it from causing too much harm to humanity.
There are facts to support our capability. The Black Death of the Late Middle Ages killed half of Europe’s population, but Milan was saved from the catastrophe because the bishop of Milan ordered all patients, dead or alive, to be kept behind walls and buried. Later scientific development coined this effective method as isolation, and it is one of the most effective means to treat epidemics.
In 2003, a highly infectious and highly malignant infectious disease called SARS broke out in China. Due to the convenience of travel, this disease spread to more than thirty countries throughout the five continents in only two months. People were terrified of SARS; however, countries applied effective inspection and isolation methods and curbed its spread after only five or six months, even though there was no effective drug treatment. Ten thousand people were infected in the end, and the death toll was less than one thou sand. If this had happened one hundred years ago, the situation would have been much deadlier.
The antibiotics and drugs we now have are effective enough to treat most new diseases. Though our treatment of SARS was not especially effective, it was good enough to deal with the situation. We can be sure that although diseases brought on by microorganism evolution will cause some death and harm, the modern methods we have mastered can prevent them from destroying humanity.
3. Threats to Humans from Devolution
The devolution here refers to the devolution of human beings—that is, whether human beings will devolve due to irresistible genetic mutations resulting in extinction. For example, we might stop reproducing, or our intelligence may decrease until we become common animals, or some other type of devolution might occur.
According to the principle of evolution, the more an organ is used, the more it will evolve. Humans are the only creatures that use their brains to adapt to the environment; thus, humans’ brain capacity will only become more developed. In terms of creativity, human creativity has been steadily growing with no signs of stagnation or regression. As long as our intelligence does not devolve, humans are fully capable of dominating Earth and adapting to the environment continuously.
Even if humans did start devolving intellectually and physically in the future, the gene re-engineering technology we currently have would be enough to save ourselves after some development. Gene re-engineering refers to a technique that cuts, pastes, and repairs the genes on DNA using enzymes. This technology has already been widely used. Scientists can turn cotton red, yellow, or brown; they can produce seedless watermelon and seedless grapes; they can make frogs grow six eyes; and they can stop rats from growing tails. All this is the result of gene re-engineering.
If we wish to, humans can re-engineer their own genes in the near future. The Human Genome Project has conducted a comprehensive study and sequencing of the twenty thousand human DNA genes formed by three billion base pairs and has achieved considerable results. As biological science develops more in the near future, it is entirely possible that we will find out all about human genetic structures and genetic life codes. With a little more effort, humans will be able to freely re-engineer themselves.
We are pleased to see that current technology has succeeded in saving many endangered species. For example, British scientists have launched a plan to freeze and store the DNA of endangered species, and Chinese scientists have successfully cultivated the endangered yew tree and protected the endangered giant panda, Chinese alligator, crested ibis, and so on.
It is clear that any species mutation will not happen all at once. If we found signs of human devolution in the future, we would be fully capable of using bioengineering technology to prevent such adverse mutations, and we would have ample time to prepare for such an event. Therefore, devolution is not a factor that will lead to human extinction.
To sum up, if we use the sun’s evolution into a red giant in five billion years as a boundary, there are no factors in nature that will cause human extinction. In terms of natural chance, we have a long future ahead of us. This can also be proven through the survival of other species. Sixty-five million years ago, dinosaurs survived on Earth for 160 million years. Humans are stronger and smarter than dinosaurs and much more capable of adapting. It is only logical that humans will survive much longer than dinosaurs. Relative to the history of dinosaurs, we are yet in the infancy of our development. The idea that we have hundreds of millions of years ahead of us is just logical reasoning.