Originally published 6 June 2000
We have been bombarded lately with doomsday predictions for the end of the world. Y2K came and went with hardly a blip. The so-called Earth-shattering planetary alignment of May passed without a ripple. And, of course, various fundamentalist cults still wait patiently for the long anticipated Rapture.
Meanwhile, the world goes on, the planets whirl in their ancient tracks, the galaxies spin.
Do scientists have their own theories about the end of time? You bet. But don’t bunker down yet. You have a few hundred billion years to get ready.
The universe began about 15 billion years ago in an expanding fireball of radiant energy. Space and time unfurled from a tiny seed of infinite energy, like a balloon inflating from nothing, cooling as it swelled. Energy became matter; matter became stars and galaxies, racing outward. Today, the galaxies continue to fly apart, impelled by their initial impetus, bearing clusters of galaxies to ever greater separations.
How will it end? There are two possibilities: Either the universe will expand forever, carrying the galaxies ever further apart, into cold and darkness, infinitely dispersed; or it will cease expanding and begin to contract, the galaxies drawing closer and closer, ending as it began in a blaze of radiant energy.
A whimper or a bang? A long glide into dark oblivion, or annihilation in a flash of blinding light? Two things are important to know: What is the rate at which the galaxies are flying apart? And how much matter is acting to slow them down?
During recent years, astronomers have made tantalizing progress toward finding answers. Several groups of researchers have been studying supernovas in distant galaxies. These extremely bright exploding stars can be observed billions of light-years away, and are used as indicators of the universe’s expansion rate. The data indicate that the universe is not slowing down enough to make the galaxies fall back upon themselves.
Other groups of astronomers have been comparing the actual distribution of galaxies to computer models for how the universe should evolve with different densities of matter. The best current fit between observation and calculation assumes that there is not enough matter to stop the expansion.
And finally, very recent observations of the so-called cosmic microwave background radiation — the light from the Big Bang stretched and cooled by the universe’s expansion — confirm that the universe will likely expand forever.
So, here’s the astronomer’s current doomsday scenario:
Five billion years from now the sun will begin to swell into a red giant. Its surface will balloon outward toward the Earth, cooling and reddening (even as the core collapses and heats up). Mercury and Venus will be consumed, and a bloated red star will fill Earth’s sky. Of course, all life on the Earth’s surface will have been extinguished; as soon as the sun starts to swell, the atmosphere and oceans will be boiled away and the surface sterilized. After some hundreds of millions of years as a red giant, the sun will collapse to a glowing ember — a white dwarf — that will slowly fade from sight.
Will the doomed planet Earth have thrown off spores into interstellar space? Will our descendants have discovered ways to travel among the stars? Will Earthlings have been incorporated into a greater and longer-lasting galactic civilization? Your guess is as good as any, but the story is not over yet.
A hundred billion years will pass and the universe will be stretched exceedingly thin by continued expansion. Local clusters of galaxies will amalgamate into supergalaxies, and supergalaxies will drift far apart. Within the supergalaxies, the last dregs of energy will be squeezed out of star-birthing nebulas. No new stars will be born. The sky will grow increasingly dark.
All ordinary matter will be compacted in dead stars — the cold cinders of white dwarfs, and those denser stellar remnants called neutron stars and black holes — or cold lumps of rock (perhaps even ghostly, lifeless space ships) adrift in the darkness. Life, which requires the extraction of energy from its environment to survive, will be increasingly hard pressed for resources. Planet by planet, the last flickers of animation and spirit will be snuffed out.
Somewhere, in a last pool of cosmic warmth, perhaps in a faraway galaxy, a final organism will expire. Life, which for billions of years had burned among the stars like a cool blue flame, will flicker out.
And that’s the (tentative) scientific story of the end of time.
Not nearly so dramatic as Y2K chaos, or a gravitational tug from aligned planets that causes California to fall into the sea. For the time being, and far into the future, just more of the same. When doomsday finally arrives, it will apparently be the unexciting equivalent of a long, dark cosmic sleep.
