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.
