The universe has been expanding for 13.8 billion years, but scientists believe it will not last forever. Researchers have proposed several theories about its ultimate fate, with the Big Freeze, Big Crunch and Big Rip emerging as the most widely discussed possibilities. From a slow cosmic cooling to a dramatic collapse or even the tearing apart of space itself, these scenarios offer different visions of how the Earth, the Sun and eventually the entire universe could meet their end billions or even trillions of years from now.