How will the universe end? “Not with a bang but with a whimper,” wrote the American poet T.S. Eliot regarding the end of the world. But if you want a more definite response, you’ll find that physicists have spent countless hours turning this question over in their minds, and have neatly fit the most plausible hypotheses into a few categories.
“In textbooks and cosmology class, we learn there are three basic futures for the universe,” said Robert Caldwell, a cosmologist at Dartmouth University in Hanover, New Hampshire.
In one scenario, the cosmos could continue to expand forever, with all matter eventually disintegrating into energy in what’s known as a “heat death,” Caldwell said. Alternatively, gravity might cause the universe to re-collapse, creating a reverse Big Bang, called the Big Crunch (we’ll explain this later). Or, there is the possibility that dark energy will cause the universe’s expansion to accelerate faster and faster, evolving into a runaway process known as the Big Rip.
Before discussing the universe’s end, let’s go into its birth. Our current understanding is that time and space began during the Big Bang, when a subatomic, ultra-hot and super-dense point exploded outward. Once things cooled down enough, particles began to form larger structures like galaxies, stars and all life on Earth. We are currently living approximately 13 billion years after the universe’s start, but, given the different scenarios for its demise, it’s unclear how much longer the universe will persist.