These end-of-the-world scenarios are all pretty scary, but from a cosmological perspective they don't make much difference. We could blow ourselves up, or the earth could be shattered by collision with an asteroid, or we could escape all these fates and human civilization could survive far into the very distant future. But whatever happens in the cosmic near-term, according to two astrophysicists at the University of Michigan at Ann Arbor, the ultimate fate of the universe is sealed. And it's not very reassuring for life forms like us.

The forecast presented by Drs. Fred Adams and Greg Laughlin at a recent meeting of the American Astronomical Society predicts that the sun will die in 5 or 10 billion years, and that all the other stars will go out over the years that follow. The last stars should vanish in 100 trillion years, give or take a billion.

Fire or Ice: How will the Cosmos End?

And after that it only gets worse. In that poststellar twilight will remain dark masses like brown dwarfs and black holes, and the husks of dead stars: white dwarfs and neutron stars. But even they won't last. The decay of protons -- basic particles of all matter --will seal their fate. Physicists are still uncertain about the rate of such decay, but it's a good bet that 10 trillion trillion trillion years from now (that's 10 followed by 36 zeros), proton decomposition will have left nothing but a thin haze of particles -- electrons, positrons, neutrinos -- where once had been planets, stars, and galaxies. When the remaining black holes have radiated into nothingness (as a theory of Stephen Hawking's says they will, eventually), the cosmos will enter the dark era, where no known physical processes occur. What will happen then? Who knows -- but we will have ceased to exist long before.

There's still hope of a different outcome: Some astrophysicists think there may be enough mass in the universe to slow its expansion, eventually stalling it and even turning it back, so that all matter will collapse upon itself in a reverse of the Big Bang called the Big Crunch. But even if the human species survived until then, it's hard to see how we could outlive the ultimate collapse.

Against a background of such all-encompassing finitude, today's apocalyptic visions start to pale. But they remain the more frightening for their proximity: Destruction by asteroid could come tomorrow, but the cosmological Dark Era won't arrive for about 10,000 trillion trillion trillion trillion trillion trillion trillion trillion years.

The End of the Universe, In Four Acts

The Stelliferous Era

The one we're living in now, full of stars with planets and moons, asteroids and comets, galaxies and clusters. Most stars existing now will burn themselves out over the next 20 or 30 billion years. New stars will cease to form after about 100 trillion years, and the Stelliferous Era will end.

The Degenerate Era

In the wake of stellar burnout, the cosmos is a dimly lit shadow of today's--so dim that, to the human eye (if there were any to see), it would seem black. All that remains are the corpses of former stars and the dead hulks that never became stars: black holes, brown dwarfs, white dwarfs, neutron stars. As the ages roll on, protons decay. Atoms evaporate. After 100 trillion trillion trillion years or so, the universe is nearly unrecognizable--devoid of matter as we know it, and utterly dark.

The Black Hole Era

Defined by one familiar feature, black holes, which continue to devour nearby particles and grow larger. Slowly--very, very slowly--black holes radiate their energy away, until they disappear. At that point, some 100 trillion trillion trillion trillion trillion trillion trillion trillion years from now, there's nothing left but a diffuse sea of electrons, positrons, neutrinos, and radiation.

The Dark Era

Possibly the end of it all. Without significant physical processes generating movement or change, the cosmos may exist in that flat, lifeless, lightless state for eternity. Or something totally unforeseen could take place. That far in the future, even the astrophysicist's speculative tools break down. All we know is it won't be a place for Homo sapiens or their descendants if they resemble, however remotely, the life forms of today.

--Robert Killheffer