It is common knowledge that the Universe began with the Big Bang. However, it is not yet certain as to how it will eventually end. There are three possible scenarios for the death of the Universe:
- Heat Death
- Big Rip
- Big Crunch
The Universe is expanding at an accelerated rate – it is getting bigger faster than before. And whether this rate of expansion slows down or not determines the fate of the Universe.
Let us assume that this expansion keeps speeding up. This means that space is expanding faster than ever before. The increased rate of expansion is already pushing entire galaxies apart. In a few billion years, the expansion would be so fast that it would rip off entire stars from galaxies. Galaxies would wither away and die, isolating the stars. Then, the Solar System would be ripped apart, since the space between the Sun and the Earth too will keep expanding. Gravity would be the first force to give up, as due to increased distance, the force would not be strong enough to sustain planets, or even stars.
This accelerated expansion would rip to shred entire planets and stars, and even minute dust particles. Eventually, this expansion would also take place between individual atoms of a molecule. Soon, the expansion of space would be faster than light itself.
This would cause all matter to break down into quarks, leptons and gluons, which would never be able to interact in an ever-increasing fabric of space. The Universe would be full of particles and photons which would never interact with each other.
This expansion of empty space is given by Einstein’s Cosmological Constant, Λ. In quantum field theories, this energy of empty space is simply the vacuum energy of the fields penetrating all spacetime. It is this vacuum energy that acts like an anti-gravity, repelling all matter away from each other.
The biggest concern, however, is the inability of QFT to predict the strength of this effect. The value of this vacuum energy as given by field theories does not match experimental results at all. In a rare failure for QFT, the prediction is off by 10120, which indicates once again the wide gap in bridging gravity and quantum mechanics.
This Big Rip Scenario would leave the Universe just an ever increasing fabric of space and time, with all particles completely isolated and all photons redshifted to infinity.
The Big Crunch is a much more violent death, but something that promises the rebirth of the cosmos. More on that, soon.