The Big Crunch, just as the Big Freeze or the Big Rip, which I will talk about in next articles, is a theory that speculates about how the death of the universe could be. We could also say that it is the opposite theory of the Big Bang.
What does the theory consist of?
The theory of the Big Crunch proposes a closed universe, that to say, a universe which is not infinite, with a great quantity of matter. In this universe, the gravity caused by the own matter, could slow down the expansion process of the universe, stop it, and consequently invert it.
In this way, the universe would compress and condense, for which the matter in it would finish by concentrating in an only point (a singularity), similar to the one existent before the Big Bang.
In other words, gravity would prevent the expansion of the cosmos, for which the latter would start shrinking, to finally concentrate all the matter in a unique point of space-time.
The process of the Big Crunch
According to the theory of the Big Crunch, in about 20 billion years, all the existent matter in the universe would force the universe to slow down and stop its expansion. So, the galaxies that nowadays go away from us would start to go backwards and as time goes on they would start to collide the ones with the others.
The temperatures would drastically increase as stars and galaxies would get closer more and more. Finally, all of them would merge in an incredibly hot, unique point. The universe would have come back to the state in which it was found before the Big Bang.
According to some theories, in this moment there could occur a process called “Big Bounce”, that to say, another Big Bang could occur. If this was the case, this process could be repeated indefinitely.
The observation of the light from the stars and galaxies shows us that most of them are moving away from us. This demonstrates that the universe is expanding. In addition, as we have known for a few decades, this expansion is not only taking place, but it is happening at an accelerated pace.
This seems to contradict what the Big Crunch theory proposes, for which many scientists consider this theory obsolete.