The Future

Credit to:http://www.astronomy.ohio-state.edu/~depoy/courses/lecture.notes/theend.html

A key idea for determining the fate of the universe is something called Critical Density. The idea comes from gravity and the expansion of the universe, a high density means that the expansion of the universe will eventually slow and actually reverse and then there is low density which means that the universe will expand forever. Critical density is the point that separates what is considered low density and high density.

s <------- Density Parameter
If the density parameter is larger than one then it is considered high density, if it equals one then it is critical density, and if it is less than one then it is low density. Data suggests that the density parameter is less than one. High density is also referred to as a closed universe while critical density and low density is also called an open universe.

The Difference between a closed and open universe

In a closed universe, gravity will eventually re-collapse the universe back into a dense point just like how the universe started in the Big Bang model. And then the Big Bang would occur once more, this process is also know as a cyclic universe. In an open universe the universe will continue to expand forever and due to the conservation of energy and the 2nd law of thermodynamics the universe will eventually end up in a 'empty' and dark state. Stars no longer form since there is no more hydrogen or any material is so far spread out that stars forming is impossible. Black holes are one of the last things to exist but even then as they radiate their mass away they will also eventually disappear. It is also theoretically possible with some theories that matter itself could dissolve, 'protons decay into electrons, positrons, to neutrinos', this would occur before the evaporation of all black holes. And this all comes to an end in the Big Chill where the temperature of the universe reach 0k and is in a basic sense empty.

Currently we are in a stelliferous age, an age where stars are still being born. But once these stars stop being born and eventually all die off (100 trillion years) and then it will be the degenerate age which the universe just becomes dark and everything not tied to the local group will be further than one million mega parsecs.


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