We have a famous theory about how the universe started,the big bang. So how would the universe end. Currently scientist have a few theories about how the universe would end. They are the big crunch, the big freeze and the big rip. This three theories are dependent on two important things that are in the universe dark matter and dark energy. Dark matter is this not well know thing that is found in space that draws matter together. Dark matter can be detected by measuring the difference in visible gravity( gravity caused by how stars and black holes) and the real gravity( gravity measured by the bend in light through gravitational lensing). This difference in estimated mass and real mass would be the mass of dark matter. Dark energy however is a force that pushes matter apart from each other. This force is also causing the expansion of the universe. Thus far away astronomical object are moving further away at an accelerating speed. This two forces are in constant battle to keep the universe in balance.
If the amount of dark energy is larger than the amount of dark energy, the universe would collapse on it’s self because all the matter in the universe are moving towards each other at such it becomes a singularity. This end would be called the big crunch.
If the amount of dark matter is about equal to the amount of dark energy , the universe would keep expanding until the entire universe becomes uniform in energy. This is because energy moves from a higher concentration to lower concentration .Thus the universe would become very cold and this end would be called the deep freeze.
If the amount of dark matter is lower than the amount of dark energy, the universe would keep expanding at a greater and greater pace until the universe explode like a balloon. This end would be called the big rip.
Our universe by scientist estimate consist of 27% dark matter and 68% dark energy . Thus by our estimate, our universe would experience a big rip end.