For the past four billion years, life on Earth has been endless. But now on Earth there are only nearly 10 million species of creatures, this number is only 1% of the total number of species that have ever lived on Earth, the remaining 99% has disappeared in the long river of the Earth. Although our planet is a vibrant planet, it is very difficult for any living species to survive long on Earth. Over time, the Earth’s climate will continue to change and some ancient species have been unable to adapt to this change, leading to extinction. In addition, life on Earth could also be threatened by deadly threats from space. For example, a gamma-ray burst from a supernova could destroy Earth’s atmosphere and cause deadly cosmic radiation to reach our planet’s surface. Most life on Earth wouldn’t be able to withstand this. 450 million years ago a supernova caused the first mass extinction of the space threat on Earth. On the other hand, the impact of a giant asteroid falling to Earth will also cause drastic changes in climate, disrupt the food chain and cause mass death for life on Earth. The fifth mass extinction 65 million years ago was probably also caused by an asteroid collision. In addition to the threat from space, on Earth there may be superbugs that humans can’t fight off. Humanity also possesses nuclear weapons capable of destroying all life on Earth. Although humanity has enough intelligence to create such a powerful weapon, it is not known if humanity is intelligent enough to not use nuclear bombs on a large scale. And also for various reasons, Hawking believes that in order to continue to exist, humanity must expand its habitat into space in the future. Only by taking precautions and leaving Earth before disaster strikes and colonizing other planets can humans better cope with unknown disasters. So which planets should humans migrate to? Is there a “Second Earth” in the universe? Proxima b’s host star is Proxima Centauri – part of a trio of strange stars that scientists are still studying. The other two stars are binary – meaning they orbit the same center of gravity and are collectively known as Alpha Centauri. Although this “Second Earth” has similar properties to the Earth – where we live, Proxima b is still a mysterious and alien world. In the solar system, although life can exist on some satellites, but apart from Earth, there are no planets suitable for human existence. To achieve the goal of space colonization, we can only look beyond the extent of the familiar solar system. Current statistics show that almost every solar system has planets, and there are hundreds of billions of stars in the Milky Way, so there should be multiple targets to choose from. People need to choose rocky planets that are in the habitable zone, because only when the distance between the planet and the sun is neither too close nor too far can liquid water exist on its surface. Proxima b exists right in the middle of the habitable zone of stars, where water could theoretically exist in liquid form. Compared to our sun, Proxima Centauri’s habitable zone is very close to its host star. Scientists once believed that red dwarf stars like Proxima could not exist on habitable planets that were orbiting so close. But now, scientists think red dwarfs might be the best place to look for other habitable planets. And recently, astronomers discovered that Proxima Centauri, the closest star to our solar system, has a planet called Proxima Centauri b. This planet is a rocky planet the size of Earth and it is also in a habitable zone. Although Proxima b is the closest exoplanet to the solar system at a distance of only 4.2 light-years, humans are currently not capable of flying to this planet. Even with today’s fastest spacecraft, if we want to set foot there, it will take us tens of thousands of years to fly to Proxima b. However, humanity has never backed down from difficulties, we have been able to cross the ocean, as well as cross the distant interstellar space to reach the strange world, so it is very possible in the future , people will set foot here.

It creates an infinitely curved region of space-time, from which nothing can escape, not even light. Do black holes rotate? This is an interesting but not so simple question that I received in one of my recent lectures. To answer it completely and accurately, we need a clear understanding of the very verifiable properties of black holes as well as about the nature of rotation. To date, the concept of rotating black holes is not new. In fact, every object in the universe, once having a mass large enough to be spherical, will also have a rotation. Since mass exerts gravity, every object tends to compress itself – because its parts attract each other. For small masses, this gravitational compressive force – commonly known as centripetal gravity – is so small that it cannot exert any effect on the object, because it is simply an intermolecular force of cohesion. substance – especially solids – is much larger than it is. But with very large masses, on the other hand, the force of gravity is so great that matter will rearrange until it becomes spherical. That is, the state in which the force of gravity directed at the center of the object from all directions is equal to each other. That’s how every object as large as a planet or a star gets its spherical shape. At the same time, when there is such a large mass, another problem arises, and also related to gravity. Since no single star or planet is perfectly uniform, in fact the gravitational forces in their different regions are unequal. This difference is the main reason they oscillate, and hence the rotation. Thus, all large objects in the universe rotate because of their own gravity. What about black holes? The most common types of black holes known to scientists today are stellar-mass black holes. It is formed from the late-life contraction of the cores of massive stars. These stars are usually at least 8 to 10 times the mass of the Sun. Towards the end of their lives, their cores shrink very rapidly because the fusion reaction no longer produces enough energy to resist the contraction of that enormous mass. This sudden contraction causes an explosion that is considered one of the most violent events in the universe” supernova explosion. This explosion tore apart the stellar shell that was previously in the state of a red supergiant. The remaining core of the star shrinks and collapses to become a black hole. All stars rotate on their own axis (our Sun, for example, has a rotation period of more than 25 days). It is not difficult to speculate that something formed from a rotating stellar core would also have to rotate, because that momentum is simply still there. The same is probably true of supermassive black holes – black holes with masses ranging from hundreds of thousands to billions of times the Sun, located at the center of most galaxies ever observed. In fact, when the first image of a black hole was released in 2019, scientists were able to see the spirals of the accretion disk surrounding the black hole. It shows that the giant accretion disk is rotating, not fixed. Just like the fact that all the stars in each galaxy are constantly moving around the center of the galaxy (for example, our Sun takes about 230 million years to complete one full circle around the center of the Milky Way). Two things need to be clarified before concluding that the black hole rotates on its own The entire initial mass of the black hole – in theory – is packed into an extremely small singularity. It is so small that it can mathematically be considered sizeless. That singularity has a certain radius (Schwarzchild radius) known as the black hole’s event horizon, but it is just a region of pure space-time, not an object like it has a surface. like a star or a planet. As such, it is difficult to consider something with no dimensions, or a boundary without a surface, to be rotating, since there is simply no alternate motion of points to a particular surface. No radiation comes out from within the event horizon, which also means that all information inside a black hole is unknown. If matter were indeed crushed and completely collapsed into a single point, the space within the event horizon could itself be a place of absolute uniformity, i.e. no rotation would occur due to the difference. interesting. With these two points in mind, don’t forget that what we see spinning is itself just the accretion disk surrounding the black hole. Of course, one can also calculate the rotational speed of an accretion disk based on its mass when taking into account as well as when not taking into account the presence of a black hole at the center, from which to compare and predict. It looks like the black holes in those places are spinning very fast. Even so, given that we don’t know anything about what lies within the event horizon, or even something specific happening at its very edge, concluding that black holes are indeed rotate or not and how fast they rotate is still too early. Likewise, the charge of a black hole is also a purely theoretical concept and is calculated from solving Einstein’s equations. There is no way for us to verify if an electric charge really exists after being swept inside the black hole’s event horizon. In the future, to know more about this information, we will need to look forward to new generations of telescopes and new methods to image and track more black holes with much greater detail. compared to what there are today.

In what form could life on earth end in the end? Photo: Astronomy Some scientists point out that the earliest life on Earth was born about 4 billion years ago. At that time, the Earth was continuously bombarded by space meteors, but life continued strongly. Earth’s history has seen many catastrophes, and each one is like the end of the world. Supernova explosions, asteroid collisions, large-scale volcanic eruptions, sudden climate changes … these events have claimed countless lives. During a number of mass extinction events, most of the species at that time had been wiped out. In the end, however, life still goes on. There will always be new species on Earth, and a new cycle will begin again. Although human life may be unimaginably fragile, turning the entire Earth into a barren land is not so easy. Here are some events that have the potential to wip out all life on Earth (very low probability and not happening in the near future). The impact of asteroids When an asteroid hits Earth, it releases incredible energy. 66 million years ago, an asteroid the size of a city crashed into the Gulf of Mexico and led to the extinction of the dinosaurs. At that time, all other creatures on Earth were almost wiped out. Although human ancestors were not born at that time, it may be the most important event in human history. Without the asteroid impact, dinosaurs could always be the lord of Earth, and other mammals could only exist in their shadow. According to geological records assessment, the frequency of Earth being collided by large asteroids is about 100 million years. However, smaller asteroid effects occur more often. There is even evidence that some people have died from the effects of asteroids over the past few thousand years. In 1888, in Sulaymaniyah, now in Iraq, a meteor strike killed one person and injured another. This is the earliest recorded asteroid accident. But what is the probability that Earth will be hit by a large asteroid? A 2017 study published in Nature has shown that to cause this asteroid must be large enough. Only the largest asteroids in the solar system (like Pallas and Vesta) can do this. Richard Binzel, a professor of planetary science at MIT, said even though an asteroid might one day come and destroy us, the likelihood is very low. Oxygen depletion Fossil of trilobite, one of the earliest arthropods on Earth. Photo: Shutterstock The chances of the latter being slightly higher than the previous. First, let’s go back to long history. Nearly 2.5 billion years ago, Earth went through a period known as the “Great Oxidation Event” – creating oxygen on a global scale. The increase in cyanobacteria causes a huge increase in the amount of oxygen in the atmosphere. Without this event, no oxygen-breathing animals would exist and the biological world would not have been diverse, from low-order monocytes to higher multicellular flora and fauna, including humans. However, about 450 million years ago, one of the most serious extinction events on the planet – the Ordovic -Silur mass extinction occurred. It could be due to the sudden drop in oxygen levels at that time, which lasted for millions of years. But why is this happening? During the Ordovic period, all the continents on Earth were connected to form the supercontinent Gondwana. At that time, most life on Earth existed in the ocean, but plants began to appear on land. At the end of the Ordovic period, the Earth’s climate suddenly changed, causing this supercontinent to be covered with glaciers. The sudden drop in global temperature alone is enough to cause the disappearance of many species. Then, when global oxygen levels plummeted, life on Earth experienced a second wave of extinction. Scientists can find evidence of this drastic change in sediment samples on the seabed. Some researchers believe that glaciers at that time caused a fundamental change in ocean stratification, and that the temperature and oxygen concentration of each layer of seawater differ. However, the exact cause of this significant reduction in oxygen is still being debated. Whatever the reason, more than 80% of the species on Earth disappeared during the Ordovic mass extinction. Such events happened in the past, will history repeat in the future? In fact, a recent study published in Nature Communications has shown that climate change reduces oxygen levels in the ocean, which can cause the extinction of some marine life. Gamma-ray bursts Gamma-ray bursts can originate in binary star systems. Photo: University of Warwick Gamma-ray bursts occur when a giant star dies, explodes like a supernova, and collapses into a black hole. It spits out stream of rays at the speed of light in the universe. Any planet in the path of this stream would lose its atmosphere immediately and be burned. When the gamma rays in the explosion hit the blue planet’s atmosphere, they will cause oxygen and free nitrogen atoms to collide, and some will recombine into N2O compounds, the destroyer. ozone layer. N2O is long-lived in the atmosphere, and they continue to destroy ozone until it falls to the ground through rainfall. If there was a gamma-ray explosion in the Milky Way, it could potentially cause the extinction of a large number of species on Earth. If the gamma-ray burst was aimed in the direction of the Earth, even if it lasted only 10 seconds, it would destroy at least half of the Earth’s ozone layer. Scientific research in recent decades has shown that even a small fraction of the ozone layer is destroyed enough to weaken Earth’s “natural protective layer” and cause serious problems. And if the ozone layer is depleted to a certain extent, the Earth’s food chain will be severely damaged, leading to the extinction of a large number of species. Death of the Sun. As the sun continues to age, more and more energy is released, which could eventually wipe out the oxygen in Earth’s atmosphere. Photo: Nasa A study published in the journal Nature Geoscience in March this year showed that regardless of whether or not a gamma-ray explosion occurs, in about a billion years, most life on Earth will die from lack of oxygen. A team of scientists working with NASA believes that this oxygen-rich atmosphere will not last forever. In a billion years, the activity of the Sun will cause the Earth’s oxygen levels to drop back to the levels they were before the “Great Oxidation Event”. The team describes the last moment before the Earth’s inability to support life as follows: “We find that the deoxygenation of the future is an inevitable consequence of increased heat radiation from the Sun. The exact timing of this process will be governed by the redox flow that changes between the geological mantle and the ocean-atmosphere system and the Earth’s crust. ” Conclusions are made after modeling and running simulation based on the algorithm hundreds of thousands of times. The start time and duration of this process will depend on a variety of factors, and can be as short as 10,000 years. But researchers point out that for Earth, in the end, this fate is inevitable. Fortunately, humanity still has 1 billion years left to find another way out.