Big Crunch

The Big Crunch is a hypothetical idea about what might happen to the ultimate fate of the universe. In this idea, the expansion of the universe would eventually slow down, stop, and then reverse. The universe would start to shrink back in on itself until everything comes together in one point.

Most evidence today shows that this idea is probably not correct. Observations show that the universe is actually expanding and this expansion is actually accelerating, not slowing down. This makes other ideas like the Big Chill or Big Rip more likely. However, some scientists have suggested that a "Big Crunch-style" event might still happen because of changes in dark energy.

This idea was first suggested in 1922 by a Russian scientist named Alexander Friedmann. He created equations that showed the universe could either keep expanding or eventually start contracting, depending on how much matter it contains. If there was enough matter, the pull of gravity could stop the expansion and make the universe shrink back in on itself, similar to how a black hole works.

Overview

The Big Crunch is an old idea about what might happen to the universe far in the future. It suggested that if there was enough matter, gravity might pull the universe back together after the Big Bang. This would cause everything to collapse into a single point.

But studies in the late 1990s and early 2000s showed that the universe is expanding faster and faster, not slowing down. This discovery won a Nobel Prize in Physics in 2011. Because of this, most scientists now think the Big Crunch is unlikely, and other ideas like the Big Bounce might happen instead.

History

Richard Bentley, a churchman and scholar, once asked Isaac Newton if stars in a universe that does not go on forever might come together. This idea is called Bentley's paradox and is an early thought about the Big Crunch. Today we know that stars move and are not stuck in one place.

Albert Einstein at first thought the universe stayed the same size. He added something called the cosmological constant to keep the universe from shrinking. Later, work by Edwin Hubble showed the universe was growing, so Einstein changed his ideas.

Cyclic universes

A hypothesis called "Big Bounce" suggests that the universe might collapse and then start again with another Big Bang. This could mean the universe goes through endless phases of expanding and contracting.

Cyclic universes were an early idea by Albert Einstein in 1931. He thought there might have been a universe before the Big Bang that ended in a Big Crunch, leading to our Big Bang. Modern ideas, like the Ekpyrotic model by Paul Steinhardt, suggest the Big Bang happened when two special planes called branes collided. Another theory, conformal cyclic cosmology by Roger Penrose, proposes that the universe expands until everything turns to light, then starts over again. There is also loop quantum cosmology, which suggests a quantum effect prevents total collapse, leading to a Big Bounce instead of a Big Crunch.

Empirical scenarios from physical theories

Some theories say that if a special kind of energy, called quintessence, acts in a certain way, the universe might stop growing and start to shrink. This could happen in the next 100 million years. A study by Andrei-Ijjas-Steinhardt says this shrinking might last about a billion years before the universe starts growing again. These ideas are linked to theories about the universe going through cycles and ideas about quantum gravity.

But right now, what we see shows that the universe is still growing, so this shrinking might not really happen.

Effects

Imagine the universe slowly shrinking billions of years from now. As it gets smaller, galaxies would move closer together and merge. The space between stars would shrink until stars bump into each other. The heat would grow, causing stars to break apart. In the end, everything would be crushed into one very hot and dense point, similar to when the universe first began. Some thinkers wonder if this could start a new universe.

Main article: Big Bang

In culture

In the novel The Restaurant at the End of the Universe by Douglas Adams, there is a restaurant where people can watch the end of the Universe, called the "Gnab Gib". The idea of the Big Crunch has also appeared in other books and talks about space. In the Doctor Who television series, the opening credits show the universe expanding after a Big Bang, and the closing credits show it shrinking towards a Big Crunch.