What will happen in 100 million years?
In our cognition, 100 million years is an unimaginably long time, but it does not change anything in the universe, for the sun, 100 million years will increase its brightness by 1%, and the temperature of the earth will rise as a result, but not to the extent that it cannot survive, for Mars, 100 million years is enough for its moons to crash into Mars under the influence of gravity, or to make Saturn's rings disappear completely.
But looking at the entire solar system, 100 million years is not enough to produce any significant changes, the sun has at least 5 billion years to live, and the life span of the planets is almost infinite without being disturbed by external factors.
The scientific community predicts that human civilization will become a first-class civilization in 500 years and a second-level civilization in tens of thousands of years, considering that the human ancestors came down from under the tree to today is only a few million years, so if human civilization can really exist for 100 million years, the degree of development of science and technology will be completely unimaginable to us, maybe the whole universe will be our backyard at that time, maybe we will have transferred to other universes by then.
For the Milky Way, the Andromeda Galaxy will collide with him in 3.75 billion years, because the distance between the two is 2.54 million light-years away, far enough for the expanding force of the universe to tear apart, and gravity will cause the two largest galaxies in the local group to move closer and merge into a new elliptical galaxy.
So in 100 million years, the constellation Andromeda will grow larger in the telescope's view, and it will get bigger and bigger, eventually covering the entire Milky Way and lighting up the Earth's night sky.
However, when we pull the time scale to the maximum, for example, 100 trillion years later, whether it is Andromeda or the Milky Way, in fact, it will not exist, because stars have a lifespan, for example, the sun is 10 billion years, and the longest-lived red dwarf star is only a few hundred billion years old, and all stars will be extinguished after 100 trillion years.
What's even more terrifying is that according to Hawking's black hole evaporation theory, black holes in the universe will continue to evaporate their mass due to the interference of quantum mechanics, and eventually disappear in the universe, so as long as the time is long enough, trillions of stars in the galaxy and Andromeda combined, as well as a large number of black holes, will eventually cease to exist.
This process is accompanied by an accelerated expansion of the universe, which will lead to an irreversible increase in entropy in the universe, and the final universe will be a state of heat death without stars, galaxies, and life, and the remaining matter will no longer be enough to form stars to illuminate the universe, based on the second law according to thermodynamics, in a closed system, where entropy or disorder increases over time, energy will dissipate in such a way.
If the parallel universe and the multiverse really do not exist, the universe will lose the opportunity for heat exchange, and we can say that the universe is on the road to heat death at the moment, but this road is too long, so that 100 million years is just a moment, and our human civilization is an instant within an instant.
In fact, because we are the only civilization on the earth, and at the same time we have not found an extraterrestrial civilization in the universe, scientists have no idea how far human civilization can go in the future, maybe we are lucky to become a space civilization, maybe we are unlucky that an asteroid will hit the earth tomorrow, not to mention the existence of various large filters.
So in the long run, what we can do is to try to fly out of the earth and even out of the solar system several years before the earth's resources, because only by fully branching out can the insurance of human civilization in the universe be improved.