3.1.1 Open or closed universe

Figure 2 An illustration of the theorised possible fates of the universe

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This is an image called ‘Future fates of rhe dark-energy university’. The three possible fates are: Big Crunch – quintessence in which dark energy reverses; Indefinite expansion – cosmological constant; Big Rip – quintessence in which dark energy destabilises.

Figure 2 An illustration of the theorised possible fates of the universe

You’ve already heard that the Universe is expanding, but consider what will happen in the future. Is the expansion going to go on for ever?

Astronomers used to think that there might be a point at which the Universe stopped expanding and started to contract. They described this as a closed universe, suggesting that the Universe might reach a point where the expansion would slow down as objects reached a maximum separation. Then it would recoil, collapsing back on itself.

During the collapse, the Universe would become denser and hotter until it ended in an infinitely hot, infinitely dense, singularity. A closed universe would lead to a big crunch – the opposite of the Big Bang.

However, more recent observations from space telescopes have concluded that this scenario is very unlikely. In fact the expansion of the Universe is accelerating. Astronomers describe this as an open universe.

If the expansion continues forever the matter in the Universe will be spread more and more thinly. Eventually, galaxies will run out of the materials they need to make new stars. Stars that already exist will slowly extinguish. At that point, the Universe will become dark, cold and lifeless.