HOW WILL THE UNIVERSE COME TO AN END?

The universe will exist for so long that we can’t even fathom such a large interval of time. But when time finally does run out, how will it all end?

Theoretical astrophysicists who try to answer absurd questions will sometimes run into absurd problems. That’s how Matt Caplan, a physicist at Illinois State University, felt when he’d started to investigate the mystery of how long the universe would exist for a study—and stumbled upon black dwarfs in the process. They are an important part of his thesis of the big end, but unfortunately they are only theoretical. The absurd problem: Our universe, with its 13.8 billion years, is too young to accommodate them. Black dwarfs only emerge when white dwarfs (stellar corpses the size of Earth with the mass of the Sun) have cooled down—and since that takes at least a trillion years, Caplan had to reckon his way around the problem. Could the mystery still be solved?

Basically, yes. Since researchers in the 1990s have shown that there is not enough mass in the universe for a “big crunch” (the idea that the expansion of the universe will one day be reversed and all matter will be compressed into a single tiny point), everything points to the notion that the universe will just keep expanding until it’s cold, dark, and totally empty. Caplan calculated that the formation of the stars will be completed first in 10100 (googol) years. At that point the lights will start going out little by little. “The universe will consist of burnedout stars [white dwarfs] and black holes,” says Caplan. However under the pressure of Hawking radiation, at some point even the big world eaters will dissolve. In the end, Caplan says, “The universe will be a sad, lonely, cold place.” And a slow one at that. Because this cooling will only “end” in 101,100 years. The last “inhabitants” of space at that point will be the black dwarfs. And they will bid the universe farewell in an immense convulsion of trillions of supernovae. In 1032,000 years the last black dwarfs will also explode. The universe will officially be “dead.”

Another hypothesis about the end of the universe was espoused by University of North Carolina theoretical cosmologist Katie Mack. The concept of “vacuum decay” (see box at right) puts forth the idea that the vacuum of space is actually not empty at all but rather consists of a sort of residual energy. At present the energy level is stable, however should that change, the vacuum would break up and all the natural laws of the universe would break down. It would be the end, and, “In principle, the end could happen at any time,” says Mack. But there’s no need to be afraid. “Void dissolution is the most humane way the universe can end because you won’t see it coming. You won’t feel it, there won’t be tragic consequences—everything will simply be done.” The end of the universe could certainly be worse…

“In principle, the end could happen at any time. And when it does, you won’t see it coming.” KATIE MACK, COSMOLOGIST