Nothing lives forever, not even our universe. Eventually it'll go kaput and be destroyed... but how? Smart people have wrapped their heads around the universe's destruction and have come upwith three different theories. The Big Rip, Heat Death (or the Big Freeze) and the Big Crunch and Big Bounce. They all sound like they're going to hurt.
Kurzgesagt put together a video explainer detailing the different theories. The Big Rip is basically when the universe expands so fast that gravity can't compensate and tears it apart. Space expands faster than the speed of light and no particle can interact with any other particle. It's going to be lonely as hell.
Another way for the universe to die is by heat death or The Big Freeze (it's probably the most likely result we have right now). Basically the gas clouds necessary to from stars will be exhausted and the universe will turn dark. It might open up room for another Big Bang but it just seems like a Big Sad.
The most uplifting way for the universe to be destroyed is through the big crunch and big bounce. That theory is based on the possibility that if there is less dark energy out there than we think, gravity will become the dominating force in the universe one day. That means the expansion of the universe will stop and reverse, with galaxies moving inward creating a universe that is smaller (and hotter). The smaller universe would eventually be sucked up by a black hole and then start expanding again. The idea is that this keeps happening forever. I'm good with that one. I guess.
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