How to save mankind when the earth cannot live

  Let us imagine this picture: various disasters on the earth are becoming more and more frequent, volcanic eruptions, earthquakes, melting icebergs, rising sea levels gradually submerging the land… It is only a matter of time before the earth becomes an uninhabitable planet. Do not escape from the “end of death” earth and find alternative habitats.
  Now let us take an optimistic attitude to believe that, at least before the earth is uninhabitable, the technology we have invented and mastered is sufficient to lead the human species away from the earth. Then, even if humans disappear from the earth, the human species will not become extinct.
  Where are you going?
  Moving to another planet is a long-term dream of mankind. If we can immigrate to aliens, where should we go?
  A long time ago, some people thought that Mars and Venus might be good choices, but now we know that, except for the earth, other planets surrounding the sun may not be suitable for human survival. Obviously, we have to consider another star system. With our current level of science, it is still impossible to know the specific number of habitable planets among the more than 200 billion stars in the entire galaxy, or whether these habitable planets already have natives (aliens). Frank Drake, an American astronomer and founder of SETI, proposed the “Universal Civilization Equation” in 1961, which is the Drake equation. Drake’s equation mainly includes 7 factors, such as the level of stars born in the Milky Way, how many planets there are in the star, and whether the planets can adapt to the survival of life forms. He used the equation to calculate the probability of finding an alien. The results show that there may be about 10,000 detectable civilizations in the Milky Way, among which the nearest civilization may be about 1,000 light years away from us. The current evidence of research indicates that there may be many habitable planets in the Milky Way, and some estimates even reach tens of billions.
  In any case, this implies that if humans carry out colonization activities in other parts of the solar system, it will be difficult for the human species to be “eliminated”. Because even if it kills the human branch of one of the planets, humans on other planets still exist, and can learn from the tragic experience of their ancestors, develop and try new technologies, continue to explore, understand life elsewhere, and promote Human beings develop to a higher level.
  How to reach a habitable planet?
  Due to the distance between the Earth and other stars, assuming that humans begin to colonize the galaxy, the initial expansion rate should be slow. Because even if it is going to the trisolaris star system closest to the earth-Alpha Centauri, assuming it travels at 10% speed of light (about 30,000 kilometers per second), it will take about 40 years to reach it.
  Why was it selected as 10% the speed of light? First of all, we must consider the life span of human beings. At present, the average life span of human beings is 70 or 80 years old, and 10% light speed can at least allow human beings to reach the nearest star within a short life span. Second, relative to the speed limit-the speed of light, 10% of the speed of light is actually not fast, and it can also minimize the chance of collisions between the spacecraft and the interstellar gas and dust while traveling.
  So, how do we make the spacecraft get 10% light speed?
  Perhaps relying on a huge sail, or that to enter other star systems will be a “light sail” project (or solar sail). Since light also has energy, it can also produce light pressure when irradiated on an object. This principle is like the wind blowing on the sails of a boat, making the sails stressed. A light sail is like a solar panel that receives light. It is driven by a high-energy laser or microwave station near the sun. It uses photons in the beam to obtain power. After a long enough time, it will reach a considerable proportion of the speed of light.
  And recently, the physicist Stephen Hawking initiated the “Breakthrough Photo Star” project and proposed the development of a small light sail vehicle called “Star Tablet”. It is planned that it can reach the Alpha Centauri star at 20% of the speed of light after more than 20 years of navigation, and send back information about the star system to the earth. Although for now, this aircraft can only carry small items such as cameras and navigation systems, and its success or failure is difficult to predict, but it still points out a way for mankind to travel in space in the future.
  In addition to Lightsail, there are of course other possible interstellar propulsion methods, from antimatter fusion, interstellar ramjet thrusters to “hyperspace engines.” It is said that American scientists are secretly studying a “hyperspace engine”. Once the “hyperspace engine” is proved to be feasible, it will only take 3 hours to travel from the earth to Mars and 80 days from the earth to a planet 11 light-years away. Some scientists also predict that the time when a suitable spacecraft can be built and set off to the destination planet will be in the 26th century.
  After arriving at the destination, how to slow down and land smoothly is also a huge problem. The most reasonable way is to develop the so-called “magnet sail”. “Magnetic sail” usually refers to a magnetic field wrapped around a spacecraft with a polarity opposite to the solar wind (solar wind is a stream of charged particles with its own magnetic field), and fly out of the solar system through the repulsion between the magnetic fields. Here, what we want to use is not the solar wind, but in the final stage of reaching the destination, the diamagnetism of the particle stream emitted by the target star is used to slow the brakes.
  Space City rotating
  Given destined for other planets usually takes quite a long time, and some people do not want in Star Trek in their lives will be exhausted, so some people had the idea: to build a space habitat will not Will it be faster and more convenient?
  As early as the 1970s, after the Apollo successfully landed on the moon, Gerard O’Neill, a physicist and futurist at Princeton University in the United States, proposed the idea of ​​building an “orbiting space city”. What he envisioned was a huge cylindrical “spaceship” with a length of 32 kilometers and a diameter of 6 to 8 kilometers, capable of housing hundreds of thousands of people. It is fully enclosed, with the central axis as the axis of rotation, it rotates once per minute, and can generate the same magnitude of gravity as the surface of the earth. There is also a space dock on the top of the cylinder, where small spacecraft from the earth or other space cities can dock.
  If we want to build a city, we must first consider where the building materials come from. O’Neill believes that the required materials can be mined from nearby asteroids several hundred meters in diameter, and the solar system has millions of such asteroids.
  In O’Neill’s plan, the Space City is a cyclical ecosystem where people’s lives are completely self-sufficient. They can grow fruits and vegetables, raise livestock, set up factories, and recycle air, just like life on earth. If the earth is no longer habitable, humans do not need to travel to another star system to find a new home for human beings and live in this space city. Without the ravages of human beings, the earth may slowly return to its original state after hundreds of thousands of years, and then humans can return to the earth.
  NASA was very interested in this idea and funded several laboratories led by O’Neill to conduct in-depth research. But the space city plan is still a physical problem, waiting for scientists and engineers to slowly solve it.
  Backup humanity, save mankind
  Furthermore, it was suggested that the future of humanity can build a self-sufficient, like “world ships” Earth’s environment, can accommodate thousands of people. A huge “world ship” travels in space much slower than a light sail, perhaps only 0.5% of the speed of light (still 1500 kilometers per second). But the advantage is that there are many residents on the “ships of the world”, and they live on the ships for generations. Compared to transforming and settling on other planets or livable space cities, the residents of “world ships” can continue to be space explorers and move towards the next new galaxy without worrying about human life.
  It is estimated that the distance from one end of the Milky Way to the other is 100,000 light years. Once humans have created multiple “world ships” and set off on the “endless” interstellar migration journey, due to the isolation of interstellar space, their descendants may have more and more differences. Maybe by then, humans We no longer recognize each other’s relatives, even though each of them is an extension of human civilization.