The probability of human beings being able to live on Earth is a very low lucky event, not only because the right location of the earth gave birth to life, but also because the surrounding environmental conditions helped it avoid one possible devastating event after another. Modern science has tried to find another planet that could be inhabited by Earthlings, but the results of both calculations and observations are very slim. The atmosphere shields us from the darkness of the universe, but we may still have to look at and accept the cold physical processes of the universe's motion with a rational eye.
This article is from B06-07 of the Beijing News Book Review Weekly's November 26 feature "Colorful and Cold: A Brief History of Cosmic Exploration".
Sun – breathing for help
Compared with black holes, the sun is much closer to us, and once the sun has some crisis, it will hit us more severely. The ejection of material caused by the Sun's common coronal activity can have a serious impact on particles and magnetic fields on Earth. In 1859, a coronal projectile caused the complete failure of Earth's telegraph system. Fortunately, the Earth has its own magnetic field and atmosphere, and the coronal projectile material is not directly shot at the Earth but is deflected by magnetic field interference or directly absorbed by the atmosphere. Even so, a large amount of electricity will still pass through the earth, which may directly damage power plants and power generation facilities. In order to avoid the losses caused by coronal ejection as much as possible, in 2018, a solar satellite was launched near the sun to observe the magnetic field activity on the sun's surface. If a large-scale coronal ejection is observed that will wreak havoc on Earth, NASA will send an early warning signal that humans can shut down some of the vulnerable systems and facilities in advance, minimizing the damage.
The sun gives birth to us and controls our destiny at the same time. It looks like a sphere, but it is actually a ball of plasma, a state of matter outside the liquid, solid, and gaseous states that we usually come into contact with, and only at extremely high temperatures will the gas lose its electrons and combine with the ions. This is the law of all star births. From a microscopic physics perspective, the massive sun is a blob of gas molecules, but it has an astonishing mass—imagine a balloon that has been inflated and weighs at the same time as a shot put ball. In nuclear fusion hardening and gas compression, the Sun's mass has reached 99% of the entire solar system.
But the sun — and all the stars — will have a crisis: a shortage of gas.
The formation and retention of stars can be understood as a breath of nuclear fusion, which converts hydrogen into helium, which produces more heat. At present, the sun has been breathing in the universe for 4.5 billion years, is in the middle age, and continues to become hot and bright, about 3 billion years later, the respiratory system will have problems, the surrounding hydrogen is exhausted, at that time, the sun will change from a star to a red giant star (all stars burn to the stage of the later stage), the volume expands by about 200 times, and the surface temperature will drop. At this time, the sun will become a completely red ball like in the children's painting.
After that, because the hydrogen is consumed, the sun will enter the process of helium fusion. A series of pulses and the collapse of the core will crush the sun's outer shell from the inside, turning it into a nebula, and in the center of the nebula, a white dwarf formed from the residual core. It would begin to cool, dim, stop glowing, and eventually turn into a black dwarf—a wreck of carbon and dust. The universe's current age (13.7 billion years) is not enough to form a black dwarf in it (200 trillion years), but it is most likely the end of all stars.
Andromeda Galaxy. The Andromeda Galaxy (numbered M31) is not far from the Milky Way, and it is the largest galaxy in the galaxy and looks very similar to the Milky Way. Current observations show that the Andromeda galaxy is rapidly approaching The Earth at a speed of 300 to 400 kilometers per second. At this rate, after about 4.5 billion years (3 billion years), the Andromeda galaxy will collide head-on with our Milky Way. It sounds like a devastating event, but miraculously, the astronomical reality is not, and the encounter between galaxies and galaxies is a common phenomenon in the universe and does not cause the destruction of stars, but the black holes in two galaxies converge into one and then recombine into a new, larger galaxy. At that time, if human civilization still exists on Earth, it is possible to observe two galaxies hanging like ribbons over the night. Compared to the massive galaxy merger, the devastation that asteroids inflict on Earth is much more terrifying.
New Planet – Looking for a Second Home
Regardless of the living conditions of the earth, it is our home. But it will one day be destroyed (although we doubt that human civilization will last until that time), so will we find a second habitable planet in the universe?
For a while, Mars seemed like a good choice. It is not far from the earth, people have also found traces of water on it, but, first, the pressure of Mars is very low, if you immigrate to Mars, then everyone has the risk of suffering from decompression sickness, you must wear a special aviation uniform to live, second, the asteroid event just mentioned, some asteroids that may attack the earth will turn to Mars under the action of gravity, so in fact, the safety conditions of Mars are much inferior to the earth, and the last point, if you wait until the sun enters the stage of red giant stars, Then Mars, which is also a planet in the solar system, cannot survive. If we are to find a planet that can continue to live for a long time in the face of an unsavory crisis on Earth, we must look beyond the solar system.
Kepler-438b may be the closest habitable planet we have found to Earth, and on a habitability scale of 0 to 1, it received an assessment of 0.88. Be aware, though, that livability here is only relative. Kepler-438b is almost the same size as Earth, orbiting a red dwarf star in the constellation of Lyra, maintaining a light distance enough to ensure the presence of liquid water, and even the possibility of an atmosphere (which cannot be determined by observation for the time being), not far from us, only 12 light years. However, its surface temperature is 60°C, and every 100 days or so there is a flare release, releasing enough energy to destroy all life on the planet.
Kepler-438b.
Of the currently known planetary systems, the total number of discoveries is 2015, and none of them can have more than three Earth-like living conditions at the same time. Among exoplanets that cannot be directly observed, physical calculations and the dust traces carried by comets passing through these exoplanets can be calculated to meet the most basic point - can preserve liquid water - the existence of planets with little existence. Even if it exists, whether we can build a starship to reach the planet is a question. If you want to make a planet that barely meets several conditions, it is also an astronomical project, and humans need to build an atmosphere, build green plants, change the air environment, or for this reason, humans need to genetically modify their bodies to conform to the environment of the new planet, such as directly breathing hydrogen or changing bone density. Even if this technology can become an absolutely safe and stable general technology in the future, but the earth is not unique to humans, there are a large number of animals, plants and microorganisms, and even bacteria, they have formed a symbiotic relationship with humans, how can we transfer them to a new planet?
In short, even according to the concept of infinite possibilities in the universe, there must be a planet similar to Earth and life in a distant place, and we will not arrive; if we want to rebuild an Earth 2.0 version of the home where it is accessible, its amount of work is extremely large. From the existing horizon, the earth is a unique corner of the universe, and what we can do is to cherish as much as possible the time of its existence, to cherish all the wonderful phenomena that appear in it, nothingness is the essence of the universe, and life is a glimmer of light in nothingness, as the romantic physicist Carl Sagan said in "The Universe" -
"As you can see, space and time are intertwined. Planets and stars are also like humans, from birth to death. From the stellar point of view, humans, billions of creatures whose lives are fleeting, are crammed into an unusually cold, solid, and distant silicate iron sphere. ” "Looking at the universe, the future of each planet is determined by their current changes. And our little planet happens to be at an important fork in the road of history... Whatever choices we make in this day and age will profoundly affect generations of our children and grandchildren, as well as their destiny to reach the stars. ”
Asteroids – whether they can compete with them
The threat of the Sun is at least quite far away from us in time, while the threat of asteroids seems to have always existed. If the extinction of the dinosaurs was caused by the impact of an asteroid on the earth, then the time interval from the extinction of the dinosaurs to the modern human society derived from today is a blink of an eye for the earth.
The development of technology and civilization has made people forget these "blink of an eye" thing. Human society before the modern civilization was disturbed by various disasters and doomsday speeches, and had to face the plague, famine, the great flood of religious legends, and the final judgment. With the development of science, these things have gradually drifted away from society, people are busy in the evolutionary theory, physics, chemical discovery into optimistic eyes, when people step by step to discover the nature of the world, the so-called "end of the world" has become a fantasy. But in 1908, events on the banks of the Tunguska River awakened the apocalyptic consciousness of mankind. On June 30 of that year, an asteroid entered the Earth's atmosphere, then exploded in the air, and razed an area the size of the city of London in Siberia, and the explosion was detected by weather stations in St. Petersburg, Berlin, London and other places, but it was not until 20 years later that researchers traveled to the area to study the impact of the asteroid's attack on the earth.
The remains of the Tunguska River are strange, it has only a circular center of explosion, and does not form a crater, and it is more accurate to speculate that the meteor has exploded in the atmosphere and did not directly hit the Earth. According to the explosion site, the asteroid is about 60 meters in diameter and weighs 100,000 tons. Its explosion over the banks of the Tunguska River released 10 million times the energy equivalent to the atomic bomb of Hiroshima, and if it were over the city, it would cause tens of millions of deaths, and if it had not exploded over the city but hit the surface, the consequences would have been even more unimaginable.
Another impact that modern humans have directly observed came from our distant neighbor, Jupiter. A comet hit Jupiter in 1994. Ironically, when the media interviewed the head of the European Astronomical Center a few months ago, asking the other party what the probability of an asteroid hitting a planet would be, the person in charge confidently said that the probability was only one in a million. A few months later, however, it happened on Jupiter. On July 16, Comet Shumek-Levy hit Jupiter at a speed of 60 kilometers per second, and five minutes later, the explosion spread to an area of 3,000 kilometers above Jupiter, finally forming an impact scar on Jupiter — the size of the scar is the same size as Earth.
This incident made people realize that probability does not work in the face of asteroid events. This is not to say that the person in charge of the speech at that time was talking nonsense, or that there was a problem with the logic of the cosmic physicists, and that there was nothing wrong with their conclusions as far as mathematical statistics were concerned. However, the base of asteroids in the universe is difficult to measure (the Smithsonian Astrophysical Observatory in Boston, USA estimates that the number of near-Earth objects may be 3 billion), and meteors and comet fragments themselves do not emit light, it is not easy to observe them in the dark universe, it is possible that when we observe them, they are already within easy reach of the Earth, like the Tunguska asteroid event, which occurs about every other century. They don't need to be huge, they only need a few tens of meters or so in diameter (maybe the size of half a parking lot), and they are enough to deal a devastating blow to humans after hitting the earth. For Earth itself, an asteroid impact is similar to a person being hit by a thrown paper ball, but for humans, it is equivalent to a nuclear explosion near every city.
We should be thankful for Earth's unique environment, which exists in such a dangerous shooting range in the universe, yet neighbors around us sometimes help block guns. The Moon may have played a part of the role in this. Jupiter mentioned above plays a greater role, because of its large size and strong gravitational field, many asteroids will be dragged to change their orbits, thus crashing into Jupiter, helping us avoid some possible asteroid events.
Astronomical researchers use the Turin Index to assess the risk of asteroids hitting the Earth, with an index scale ranging from 0 to 10. The current observed asteroid rating is 0 (no risk), the biggest risk is in 2004, asteroid 99942 (aka "Destroyer") was given an assessment of the Turin Index 4, after nearly 200 orbital observations, astronomers were shocked to find that it will hit the Earth in 2029, most likely to cause the destruction of human civilization. Fortunately, observations six months later show that after being disturbed by Mars' gravity, it has changed its orbit, and it will reach the closest location to Earth in April 2029 - 60,000 kilometers from the surface, and then change its orbit and fly to Mars. The probability of it hitting earth also dropped from 1 in 450 to four in a million.
Destroy the God Star.
If, one day, there is a real asteroid with a 100% chance of hitting Earth, and the current response for humans is to consider changing orbits and weapon attacks, we can create an explosion near the asteroid that will cause it to change orbit. Unless it encounters a particularly large planetary impact, humans still have the means to defend themselves. The most difficult point is how to observe them. These asteroids and dust fragments, which are only a few tens of meters in diameter, are nearly invisible in the universe. At the end of 2000, the probability of a celestial body hitting the Earth was one in five hundred, but observations could not determine whether the object was an asteroid or a space junk. There are many potential threats to the earth in the cosmic environment, and we can only keep an eye on the cosmic environment and try our best to catch any wind and grass in it.
Black holes – can it be used by humans?
In the current public perception of the universe, the black hole, without a doubt, has left us with the most terrible impression, it will swallow everything around us, even light can not escape.
Black holes form when massive stars collapse. Before becoming a black hole, the star maintained nearly constant gravity, but as it collapsed, the star began to shrink wildly, and the mass and gravity became infinite. In 1915, Einstein proposed general relativity, and later in Einstein's physical equations, it was found that the results of its calculations would become infinite in some cases, and this conclusion would destroy the known cosmic system. At that time, people were still struggling with the correctness of Einstein's formula and proposing some complementary ideas for the corresponding system of cosmic operation. (In addition, the white hole opposite the black hole, also speculated by the Russian physicist Igor Novikov from Einstein's equations in 1964, is highly likely to exist in theory, but there are no substantial observations yet.) ）
In 1970, humans first identified the existence of black holes. U.S. satellites have found near the constellation Cygnus that a planet 30 times larger than the Sun is being led by an invisible center. This is the first time that a black hole has shown its face to humanity. This seems to be a frightening picture of the future, will one day, there will be a black hole near the earth, the earth and the sun can not escape its clutches, a little bit by it to swallow up?
Japanese manga artist Junji Ito created such a planet in Hell Star, eating all other planets along the way, and finally extending his tentacles to earth. Junji Ito's manga works are undoubtedly a figurative expression of the future and the evil of human nature in extreme despair, but this ending may become a reality. Black holes are desperate and terrifying, but black holes are most likely the most core part of the universe itself, and it is speculated that the center of the Milky Way galaxy may be a huge black hole with a mass beyond human imagination, relying on constantly devouring stars to grow up.
"Hell Star", by Junji Ito, translator: Zheng Xiaolei, edition: Nova Press, October 2021.
According to the big bang and inflationary theory, the universe is constantly expanding, according to the theory after the big bang, the number and density of elementary particles in the universe have been fixed, if the universe is still expanding, then, the radius of the universe increases, the density of atoms becomes smaller, it is very likely that more and more black holes will appear in different parts of the universe, not to mention that stars will eventually become a black hole after a long time after the end of their lifespan. In 1982, The California Institute of Technology physicist Steven Fratzki deduced that the energy available from black holes would rapidly decrease, and modern physicists re-examined this idea and found a very bad result - the volume of a black hole may be beyond imagination, and if it continues to absorb energy, its volume will be larger than the universe we know.
But what people know about black holes is still being explored. In the established cognition, black holes and white holes are two phenomena that are theoretically diametrically opposed, white holes only release energy outward without absorbing any energy, while black holes swallow everything but do not release any survivors. But Stephen Hawking gave a speech in 2016 arguing that black holes aren't what people think they are, and that they're also emitting energy and even light outward. According to Hawking's research and calculations, "black holes appear to be emitting particles at a steady rate." The reason that ultimately convinced me that it was a real physical process was that the particles flying away were precisely geothermal. My calculations predict that a black hole will produce particles and emit radiation, just like other ordinary heat bodies, and the heat it possesses is proportional to the gravitational force on its surface, that is, inversely proportional to its mass size." Hawking's judgment not only subverted the cognition of ordinary people, but also made it difficult for a large number of physicists to accept for a while. Hawking even came up with a bolder idea of using miniature black holes — although unfortunately, even the sun-sized miniature black holes have not been discovered for the time being, hawking believes that the radiation of black holes can provide energy, and if one day a super-miniature black hole about the size of a mountain can be found, then the energy emitted by this black hole is enough to provide electricity to the entire earth.
Even if you can't find it in the universe, you can use gravity to artificially create a black hole in other dimensions beyond space-time (beyond the fourth and fifth dimensions). But because the black hole is too dense and will sink into the center of the earth, Hawking suggested that in the future, this miniature black hole that can generate electricity should be suspended in orbit around the earth.
It is not known whether one day, black holes will become a new source of energy for human development and utilization, and even if Hawking's idea can really be realized, it will certainly be a long and countless centuries later. Then, will this artificial black hole used to generate electricity break away from human control and turn back to the earth—the magic and horror of technology are perfectly unified in this idea? But I believe that in terms of human nature's demand for energy, desperate things will certainly be done by our future generations.
Author | Miyako
Edit | Li Yongbo Qingqingzi
Proofreading | Xue Jingning