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.