The Big Crunch

When we were kids (about 2 decades back), we were taught in school & college that the universe is expanding and the expansion is accelerating. Also we were taught how gravity works and it led to sometimes wonder that the massive size of stars and galaxies shall one day be able to slow down and finally stop the expansion of the universe under the influence of gravity of each other (stars & galaxies). 

And eventually when  this happens the universe shall start to collapse back under the influence of gravity towards a final single point where all the matter & energy of the universe shall meet once again just like it might be existing before the big bang. 

Also this eld to wonder if our universe was expanding and collapsed into singularity before the big bang too? is it like a cycle where the universe expands & collapse and again expands till eternity (may be). Who knows, but the concept above that the universe may collapse into singularity is known as "The Big Crunch" as I came to know much later when I got easy access to the internet. 

As taken from wikipedia below:

The Big Crunch is a hypothetical scenario for the ultimate fate of the universe, in which the expansion of the universe eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach zero, an event potentially followed by a reformation of the universe starting with another Big Bang.

* Nothing is permanent in this world. The theories that are fact today, may be proven wrong tomorrow. So, keep thinking, keep progressing.