Throughout time, scientists have speculated about how could the death of the universe be. With our current knowledge of the universe, we have been able to develop diverse theories that explain how our universe will die. One of them is the named Big Freeze, which states that our universe will never stop expanding.
The future that awaits our universe mainly depends on the quantity of matter that forms it. If the density of matter is great enough, the gravity produced by itself would slow down, and consequently invert, the expansion process of the universe, as proposed by the theory of the Big Crunch. In the opposed case, in which the density of matter in the universe is not very elevated, the universe would undergo an infinite, and probably accelerated, expansion process. This is what we name the Big Freeze.
Based on current observations of the universe, the majority of scientists agree in the fact that it is very likely for the second option to take place.
An infinite expansion process
According to the theory of the Big Freeze, the universe continues to expand and it gradually arrives at a state of zero thermodynamics, with a temperature just over the absolute zero, in which it is incapable of support movement (and even less life). Now I will describe what it is that will take place until this moment arrives.
On a time scale of 1014 (100 trillion) years, the star formation process would have ended far away in the past, and the last stars would exhaust their fuel. In this scenario only dead and cold remainders of stars and planets, as well as dark holes, would remain. The temperatures at this point would be just above absolute zero.
What will happen next is very speculative, but, eventually, even the atoms that form the remaining matter would start to degrade and disintegrate, as protons and neutrons decay into electrons and positrons (the antiparticle of electrons), that over time would end up by colliding and annihilating each other.
Electrons and positrons would continue to annihilate each other, until in 10116 years hardly be any matter left in the universe. At this moment, the universe would only be formed by black holes, increasingly dispersed through the universe as the latter continues to expand. Eventually, even black holes would end up disappearing, releasing the named “Hawking radiation” that all black holes emit. In about 10200 years, the universe would only exist as empty space, with a temperature infinitesimally above absolute zero.
An alternative theory
However, with the recent discovery of dark energy, which forms most of the universe and causes an increasingly rapid expansion of the latter, scientists started to contemplate another option: the theory of the Big Rip. I will talk about this theory in the next article.