Right Now, as far as scientists know, there are three potential ends to the universe, and the way it will end depends on the density of the universe itself. Depending on the density, there are three main theories on what will happen to the universe in the future. There is something called the critical density which will end up determining what will happen. If the universes density is less than the critical density, the universe is expected to end in a heat death. If this were the case, the big rip could also take place which is similar the heat death. If the universe density is more, something called the big crunch. The reason the universe may keep expanding even though there is gravity pulling everything inwards is because of dark energy, pushing everything farther and farther away from each other.

Heat death – For this theory to be true the universe has to keep expanding, and in this scenario the universe is finite without an infinite amount of energy. If these are both true all the energy in the universe keep spreading out until energy is so spread out the temperature in the universe approaches absolute zero, and nothing would happen after that point. Moreover, one type of energy is thermal energy, so if all the universes energy is spread out too far to create any heat, and all other energies are not abundant enough for anything to happen, the universe will basically freeze in time. In the next 1-100 trillion years, new stars will stop forming, since the gases needed to form a star will be used up. At this point in the heat death, most thing as we know them today will be gone, most of what is remaining being black holes and neutron stars. However, even these would eventually begin to cool and disappear, this will happen to black holes because of something called hawking radiation which they are predicted to release. Based on estimates, the complete stoppage of the universe would likely happen when the universe is 10¹⁰⁰ years old, when nothing will be left and never will be again.

Big Crunch – If the Universe were to end this way, that would mean eventually gravity would slow the expansion of the universe and eventually the universe would start to shrink. In this scenario, eventually star and galaxies would begin to hit one another, soon wiping out all potential life on this planet or others. The universe would become immensely hot as everything ever created gets brought back down into a single point. All the matter in the Universe being in a single point, sound familiar? If this were to happen, it could be completely possible that another big bang could happen, effectively resetting the universe back to its earliest stages. Even black holes would be squished into this single point and would basically be a recreation of what was before the big bang.

Big Rip – If this were to happen, the Universe would continue to expand just like the heat death, however this ending will happen with much more energy. Expansion would continue indefinitely until planets and stars are no longer able to hold themselves together, let alone other plants or solar systems close. The speed of the universe expansion would become so incredible it would overpower gravity and electromagnetic forces. Even individual atoms could potentially start to be torn apart, but first would come galaxies being stretch away from each other. After this solar systems would separate then planets would be ripped to pieces, and atoms at the very end. This would also depend on if dark energy gets stronger over time. If it did, in about 35-50 billion years, this event could happen and its not a long shot either.

Any of these events are a possibility in the future, and we have no way of concluding which of these three possibilities will end up happening, if any of them even do. There is also the possibility that the universe doesn’t end, it will keep expanding infinitely, but the universe is also infinite, so we are less likely to run out of energy that the heat death, especially if expansion starts to slow, but never stops, which is what would happen if the critical density is equal to the universe’s. There are still many things we don’t understand about the universe, and we will not have to worry about this ever, but its interesting for me to get an understanding of what may happen in our future.