Can we really say for sure what the distant future will look like? I don't even know when it will rain next month, and it seems that what will happen billions of years from now can only be a fantasy.
However, not everything is as unpredictable as the weather, and it is possible to predict the distant future, especially in astrophysics and cosmology. We can be sure that there will be a total solar eclipse in the UK on September 23, 2090, because the Moon, Sun and Earth are all moving steadily along predictable orbits with minimal disturbance, and the laws of gravitation have been fully confirmed. Similarly, we can use known astrophysical knowledge to predict what might happen as the universe expands.
This prediction method, known as "physical eschatology," was proposed by astronomer Martin Rees to predict the development of the universe using models constructed by astrophysics. Eschatology in the field of Christian theology deals with ultimate questions such as the end of the world, and Reese draws on this. A related classic was a 1979 article by Freeman Dyson discussing the prospect of life in the open universe. The paper argues that possible disasters such as the death of the sun and the escape of stars from the Milky Way could pose a threat to life on Earth in the distant future.
So, if humanity can continue into such a distant future, what are the most serious challenges it will face? We don't know how or if we can overcome these challenges, so I can only guess here. But what is certain is that these threats to the survival of human civilization are coming our way.
Question 1: Can humans transcend mammalian fate?
A typical mammalian species exists for about 1 million years. For mankind, in addition to the infectious diseases that may be caused by nuclear war to biological engineering, there are other dangers that may destroy mankind that need to be faced and solved urgently. Today, the risk of extinction caused by human self-inflicted sins is much higher than the probability of natural extinction events.
There are many other challenges that we have to address existing human existential risks and sustainability issues.
The first thing humanity faces in the next tens of thousands of years is the end of this interglacial age (the period between the two ice ages). Humanity is currently in the midst of a short warm interglacial period in a long ice age, and the earth will become very cold at the end of the interglacial period. However, our ancestors lived through the ice age, and it may not be a problem to live in the cold, but our ancestors were nomads, lived by hunter-gatherers, and did not yet have a global civilization.
Humans may also experience great climate changes between different geological periods. In ancient times, the earth used to be very cold, but it was also very warm. In the Eocene geological era between 56 million and 34 million years ago, the temperature of the earth was 10 degrees Celsius higher than it is now, there were palm trees and crocodiles in the Arctic, and the equatorial region was too hot, and humans living in such an equator could not survive without taking protective measures. There was also the "Ice Earth" period, when the entire earth was basically covered in ice and snow.
In addition, human beings may also encounter supervolcano eruptions, asteroids hitting the earth, gamma-ray bursts from the universe, or ecological emergencies and other dangers that can destroy human civilization. We humans know that these catastrophes have caused mass extinctions on Earth about every 100 million years.
Eventually there may no longer be a species of Homo sapiens, and humans may evolve into a new species. Human beings have been evolving and mutating, and have been screened by natural selection, that is, medical conditions are good today, but traffic accidents can also make people die young, as if it is a natural elimination. Modern biotechnology also allows us to improve our own genes, and even technology that can integrate humans and humans. It is believed that in a few million years, future humans will be unrecognizable to us, unless we deliberately decide to preserve our existing genes, not to let them change in any way, and to persevere for the long geological years to come.
If "humans" (let's call them humans) still exist in 1 billion years, they will surely have a long-standing civilization, capable of coping with planetary cataclysms, able to plan the future of humanity in geological time, and the difference between humans at that time and humans today is similar to the difference between our current humans and the extinct trilobites 250 million years ago. It is ironic that if humans want to live longer than other mammals, they have to transform into other species.
Question 2: Will it survive beyond the end of Earth's biosphere
In another 1 billion years (or hundreds of millions of years), the increased brightness of sunlight will bring doom to life on Earth.
The increase in solar heat exacerbates the weathering of rocks, triggering a series of chemical reactions that remove large amounts of carbon dioxide from the air during the carbon cycle, eventually destroying plants that photosynthesize with carbon dioxide. In addition, the Earth will heat up like a runaway greenhouse, evaporating more and more water vapor from the ocean, making the planet even hotter.
One way to do this is to build super-large-scale projects to protect the Earth's biosphere for as long as possible. At that time, humans could also perform geoengineering to add suspended particles that reflect sunlight to the stratosphere, or build a solar shutter between the Earth and the sun, or even move the Earth away from the sun.
Another solution is to transfer life on Earth to space, if humanity has not yet begun to migrate into space. The universe appears to have habitable planets, and the matter in space is billions of times larger than the Earth's surface. Even if the human colonization project of space is very arduous, let's not forget that we humans still have 1 billion years to improve technology, increase wealth, and build.
At this juncture, if human civilization wants to continue, it must go to the solar system to establish a new home.
Question 3: Will humans live until the sun's function weakens?
In about 5 billion years, the hydrogen fusion reaction in the sun's core will accelerate, helium will gradually increase, and the brightness of the sun will grow rapidly. At this point the Sun ends its main sequence phase and expands into a large red giant. Although the surface temperature of the sun will decrease at this time, due to the large surface area, the light emitted will be far more than the current sun. At this time, the end of the earth will come, and it is likely to be swallowed by the ever-expanding sun. Even if it is not eaten by the sun, it will be fried by the unprecedented intensity of the sun into a large stone without even a drop of wind. The Sun then "very quickly" (this is in terms of cosmic time, but about 1 billion years) ejects most of its material outward, forming a nebula, at which point the Sun becomes a small white dwarf.
If intelligent life in the solar system wants to escape this disaster, it must migrate to other galaxies. Of course, humans who had reached superintelligence at that time could also try to adapt to the environment at this time, but the sun that became a white dwarf did not have much light and energy to emit, and humans had to leave the solar system.
Reaching other galaxies and establishing new homes requires extremely fast spacecraft, otherwise it would take a very long time.
For future humans already living on the self-sufficient space life base of the solar system, it is also natural to find or establish new life homes when the sun dies, colonizes alien systems, and finds or establishes new life homes. But this requires a constant supply of energy for a long time, and the flight speed to galaxies outside the solar system cannot be too slow. In addition, there must be enough material to sustain this migration that spans thousands of years.
The most likely way to fly to galaxies beyond the sun is to use small nanorobotic spacecraft. Large starships require huge amounts of energy to reach a certain speed, and it is better to use small spacecraft that can use reflective sails and powerful rays to propel fast travel. Nanorobotic spacecraft are not only small in size, but also can be used in large quantities. If one launch fails, then launch a thousand.
Nanospacecraft can also carry genetic genes to create life, and even carry humans. Once in other galaxies, these small spacecraft can land on suitable asteroids, turn on solar collectors, mine materials, and build more robots, solar collectors, and factories. Eventually, space habitats will be built so that humans can reproduce human civilization on the life base built by these robots.