Alright, friends. Here it is, my 100th and final astronomy fun fact! And what better topic to end on than the ultimate fate of the universe?
Scientists more or less agree that the universe started with the Big Bang, but they're not that sure about how -- or if -- it's going to end. As of now, there are three main hypotheses. (Notice that I say hypotheses and not theories, because scientific theories have been rigorously tested until they're all but proven true.)
1. The leading hypothesis is that the universe will end in the Big Freeze or Heat Death. This hypothesis says that the universe will continue to cool down until the temperature of the universe reaches absolute zero, the lowest possible temperature. This is a slow and boring death, all things considered.
2. The second possibility is that the universe will end with the Big Rip. In this scenario, the universe continues to expand at an ever increasing rate. Eventually, the mysterious force responsible for the universe's accelerating expansion will rip everything apart, including individual particles until nothing is left intact.
3. Finally, the universe could end in the Big Crunch. Here, the universe eventually slows down its expansion until it stops expanding altogether, and then turns back on itself, almost like a rubber band returning to its original state after being stretched to its limits.
But really, scientists won't know how the universe is going to end until we have a much better understanding of dark energy.
That's it for astronomy fun facts! I hope you learned some things :)