Flash forward trillions of years, and the universe is expected to be a dark, cold, lonely place—but how will it end? A new paper predicts a last flurry of explosions before our known world goes totally black, ScienceAlert reports. "Galaxies will have dispersed, black holes will have evaporated, and the expansion of the universe will have pulled all remaining objects so far apart that none will ever see any of the others explode," author Matt Caplan, theoretical physicist at Illinois State University, says in a press release. "It won't even be physically possible for light to travel that far." Big stars will have detonated in dramatic supernovas, while smaller ones have quietly turned into dense husks known as white dwarfs. Those are expected to become dark, frozen objects called black dwarfs.
But the cold might not stop them from containing nuclear reactions. "Stars shine because of thermonuclear fusion—they're hot enough to smash small nuclei together to make larger nuclei, which releases energy," says Caplan. The remains of white dwarfs "are ash, they're burnt out, but fusion reactions can still happen because of quantum tunneling, only much slower. Fusion happens, even at zero temperature, it just takes a really long time." By long time, he means roughly 10 to the 1100th years, or saying "trillion" nearly a hundred times. Which means what to us? A Yale astrophysicist praises the work but tells Science that "any investigations of the far future are necessarily tongue in cheek." Caplan doesn't seem to mind, saying he became a physicist to "think about the big questions." (Read more astrophysics stories.)