What is the Big Crunch?
The Big Crunch is a hypothetical cosmological event whereby the entire universe collapses under its own gravity, ending in a black hole singularity. The Big Crunch is a possible scenario for the ultimate fate of the universe, along with others like indefinite expansion (the Big Rip or Heat Death), and the Big Bounce, where the universe would collapse but then re-expand. Many cosmologists considered a Big Crunch to be a plausible far-future outcome for the universe until 1998, when the dark energy, a mysterious force causing expansion of the universe to accelerate, was discovered, making indefinite expansion more likely. The prevailing model for the origin of the cosmos is Big Bang theory, which asserts that the present universe formed in a gigantic explosion 13.73 billion years ago. After Big Bang theory became well established and supported by many lines of evidence, scientists began to say, “We have a good model for the beginning of the universe — what about its end?” General relati
If astronomers were ever to discover that there is enough matter in the universe to cause its current expansion to slow down and stop, we would be living in a universe destined to collapse in the far future. Towards the end of this collapse, galaxies will collide and shred apart, and later on, even individual stars would collide so that the universe would become a hot dense gas at temperatures over a billion degrees. Cosmologists call this the ‘Big Crunch’ to distinguish it from the Big Bang. It will only happen if there is enough mass in the universe for the gravity of all its parts to overcome the current expansion speeds of all the galaxies. It does not seem that this is very likely since astronomers can only find about 10 percent of the mass needed to cause the universe to collapse. At any rate, this would not happen for another 30 billion years or so.
