Fire or ice?

Gravity is the most important force in the universe: it anchors us to the Earth, the planets to the Sun, the stars to their galaxies. Gravity even will determine how the universe itself will end: in fire or in ice.

Early in the twentieth century, astronomers discovered that all the galaxies were rushing away from each other, like raisins in a rising loaf of bread. They concluded that in the distant past there had been a tremendous explosion, which formed the universe itself and sent all the material flying apart. They called this explosion "The Big Bang." Nobody knows what caused it.

If nothing halts this rushing apart of the galaxies, space will become emptier. The universe will continue to cool. It will end in "ice."

But maybe, just maybe, there's enough material in the universe so that its combined gravity will stop the expansion. Then, after pausing a moment, all the galaxies with their stars will rush together into a ³Big Crunch," an unimaginably hot blaze. The universe will end in "fire."

Is this mad rush away from us slowing down? We know that other galaxies are rushing away from us, and the more distant ones are going faster. But are they still going as fast as they once were? Are they still going fast enough to have gotten to where they are since the Big Bang?

We know exactly how fast they're moving from us, and this with the accuracy of a policeman giving out a ticket for speeding. In fact, the same principle -- the Doppler shift -- is used in both cases.

What we don't know is just how far away these galaxies are now. The measurement of distances in space is tricky at best, and we are looking at galaxies very, very far away.

Fire or ice? We donıt yet know the end.

But as the poet Robert Frost has said, "From what I've tasted of desire, I hold with those who favor fire. But if it had to perish twice...for destruction, ice is also great and would suffice"

(09/11/06)