I think many have heard that the universe is expanding. My readers have many questions related to this. In this article I have tried to answer the most typical ones.
When we look at distant objects, we can notice that they are moving away from us, and the further from us the object is, the faster it moves away. For example, objects located at a distance of 13.8 billion light years from us (
It would seem that there is a violation of the theory of relativity, which prohibits superluminal motion, but in reality this is not so. So distant galaxies move away from us not due to their own motion, but due to the fact that the space between us and them expands so quickly that for the distance increases faster than the speed of light.
Because space expands everywhere and everywhere evenly at all points. For example, if in the universe each meter of space increases by 1 centimeter in 1 second, then objects located at a distance of 1 kilometer from each other will move away from each other by 10 meters in 1 second. And at a distance of 100 kilometers — at 1000 meters. And at a distance of 1000 kilometers — by 10,000 meters, and so on — the greater the distance between objects, the more space between them appears per unit of time.
Why is the entire galaxy moving away from us? Does this mean that we are at the center of an expansion? At the center of the universe? No, it doesn’t. Since space is expanding everywhere and evenly, no matter which galaxy you choose as a point of view, everything from it will look as if it is in the center of the expansion, but in fact there is simply no center of expansion.
At a distance of about 46.5 billion light years lies the edge of the observable universe. We will never be able to see everything that is behind it. Simply because the photons emitted by objects located outside the observable universe will never reach us — the space between them and us will arise faster than the photons will have time to overcome it. This distance is also called
Now the next question arises — where is the universe expanding? The answer to it is utterly prosaic — nowhere. The point is that the universe is infinite and has no boundaries. Moreover, the universe has always been infinite, even at the time of the Big Bang. When a physicist or astronomer says that at the time of the big bang, the universe was compressed to a microscopic size, we are talking about the size of the observed universe, not the entire universe.
The expansion of the universe in this way is an internal process, not an external one. In the universe, the distances between objects increase, but the universe itself, as it was, remains infinite. The universe does not need any external space into which it would expand.
If we are expanding, why then will our galaxy collide with the Andromeda galaxy in a little over 4 billion years, and other galaxies collide — there is confirmation of this? It’s simple — the closer objects are to each other, the less space between them appears during expansion.
The distance between some nearby galaxies is small enough that, due to the forces of gravitational attraction, they approach each other faster than the space between them has time to expand.
In general, yes, but there are three possible endings: the big implosion, the big break, and the big freeze (heat death of the universe).
If the big collapse theory is correct, then at some point the forces of gravity of matter will stop the expansion of the universe and begin to compress it back into the singularity. Then a new big bang and a new expansion will follow — so the universe exists constantly expanding and contracting.
The second scenario — a big gap — is that the accelerated expansion of the universe will lead to the fact that the distance between elementary particles will increase so much that any kind of interactions between them will become impossible. This could happen in about 22 billion years.
The third scenario is that the forces of gravity will slow down the expansion of the universe, but will never stop it, which ultimately will lead to the fact that the distances between objects will increase, and the universe will «cool down» and sooner or later reach a state of thermostatic equilibrium.
Current observations indicate that the universe is likely to face a second scenario — a big rip. But this is not yet certain.