: The Big Crunch is a reflection of the Big Bang. After the Big Bang, everything in the universe began to spread around, and that's when the universe began to expand. And with that begins the gravitational force. Gravity attracts everything. This will gradually reduce the tremendous speed of spreading around everything. But since gravity will remain , the speed will decrease to zero for a while then the speed will work in the opposite direction. In other words, instead of spreading everything, they will start getting closer again due to the attraction between themselves. The contraction will start. The closer you get , the more gravity will work. It will increase the speed of approaching. In this way, everything will come together again at one point. The phenomenon of meeting at this one point is called "Big Crunch". And that point is called "singularity".