The Cosmos Revised

The universe has a habit of disproving “unassailable” facts

- Richard Panek

TO ASTRONOMERS IN THE 1990s, these three facts were self-evident: The universe is expanding; all the matter in the universe is gravitationally attracting all the other matter in the universe; therefore, the expansion of the universe is slowing.

Two scientific collaborations assigned themselves the task of determining the rate of that deceleration. Find that rate, they figured, and they would know nothing less than the fate of the universe. Is the expansion slowing just enough that it will eventually come to a halt? Or is it slowing so much that it will eventually stop, reverse itself and result in a kind of big bang boomerang?

The answer, which the two teams reached independently in 1998, was precisely the opposite of what they expected.

The expansion of the universe isn’t slowing down. It’s speeding up.

COSMOLOGY HAS OFTEN lent itself to unthinking assumptions that turned out to be exactly wrong. The ur-example is geocentrism. Over the couple of millennia before the invention of the telescope in the early 1600s, the occasional philosopher suggested Earth orbits the sun and not the other way around. But the vast majority of astronomers could simply look up and see for themselves. The sun orbits Earth. The evidence was, well, self-evident.

But then, most of the history of astronomy had relied on an unthinking assumption: The heavens would always be out of reach. Like the prisoners in Plato's parable, we would forever be at the mercy of our perceptual limitations, trying to make sense of the motions in a two-dimensional celestial realm that was the cosmic equivalent of a cave wall. The invention of the telescope in the first decade of the 17th century overturned both those assumptions: Earth orbits the sun; the heavens are at our fingertips.