Events

By Richard Panek
The views expressed are his own.

For the first time in history our species has begun to answer some of the eternal questions about the universe: Where did it come from? Where is it going? We’re able to do so in part because of the discovery that is being recognized by this year’s Nobel Prize in Physics.

Before Galileo published the first discoveries he made with a primitive telescope, in 1610, cosmology—the study of the structure and evolution of the universe—was equal parts speculation and superstition. Even the subsequent, centuries-long discoveries of new planets, new moons, new stars, and new galaxies didn’t address the evolution of the universe. Not until Edwin Hubble’s 1929 discovery that, on a cosmic scale, galaxies appear to be receding from one another, carried along by the expansion of space itself, did the universe begin to acquire a narrative—a story that changes over time.

Even then theorists split into two camps: those who posited a universe that emerged in a “big bang,” and those who preferred a universe poised in a “steady state” through the continuous creation of matter. And there the theoretical divide, as theoretical divides must do in the absence of evidence, rested.

That evidence arrived in 1964, with the discovery of a remnant radiation that matched a prediction of the Big Bang theory. The answer to the question of where the universe had come from was beginning to find its answer—and cosmology was beginning its passage from metaphysics to physics, from speculation to science.

And what of the fate of the universe? Throughout the 1990s, two international teams of scientists raced each other to find out the answer. They reasoned that if the universe is expanding, and all the matter in the universe is attracting all the other matter in the universe through gravity, then the cumulative gravitational drag of all that matter on all that other matter would be slowing the expansion. The question was, How much? So much that the universe will eventually stretch as far as it can go, reverse direction, and collapse back on itself? Or so little that the universe will keep cruising, more and more slowly, until it reaches a virtual standstill?

By studying a form of exploding star called a Type Ia supernova at distances as much as half the way back to the beginning of the universe, however, these rival teams found that the expansion is behaving in a way they hadn’t anticipated. It’s speeding up.

The leaders of the two teams, Saul Perlmutter and Brian Schmidt, and the lead author of the Schmidt team’s discovery paper, Adam Riess, share this year’s Nobel Prize in Physics for that counterintuitive conclusion, which the two teams reached independently in 1998.

But knowing that something is accelerating the expansion of the universe doesn’t tell us what that “something” is. What component of the universe could possibly be capable of overpowering the effects of gravity on a cosmic scale? Until they can find out, scientists have given it a placeholder name, “dark energy.” That term in turn mimics “dark matter,” a discovery that entered mainstream astronomy in the 1970s.

Despite these shrugging monikers, dark matter and dark energy aren’t the speculative indulgences of cosmologists in ivory towers. The relic radiation from the Big Bang—technically, the cosmic microwave background—is in effect a baby picture of the universe. Everything the universe will evolve into is right there, in the contours and temperature variations of that radiation. Examine that radiation on a fine enough scale and you’ll see what the universe is made of, which is exactly what scientists have repeatedly done over the past decade, until they have refined the proportions with mind-bending precision: 72.8 percent dark energy and 22.7 percent dark matter, leaving only 4.5 percent the kind of stuff we’d always assumed was the universe in its entirety—stars, planets, galaxies, you, me.

The news that for thousands of years astronomy and physics have been missing most of the universe, however, doesn’t disappoint astronomers and physicists. As Perlmutter once told me, “I have the impression that most people don’t realize that what got physicists into physics usually is not the desire to understand what we already know but the desire to catch the universe in the act of doing really bizarre things.” And for a physicist, it doesn’t get much more bizarre than dark energy. To solve the mystery of what nearly the entire universe is made of will likely require a recalibration of Newton and Einstein, if not the long-awaited nuptials of general relativity and quantum mechanics. The problem of dark energy, a theorist once said to me, “is the most profound in all of science.”

The implications for philosophy, however, are no less profound. The discovery of dark energy gives us a strong clue as to what the fate of the universe will be—eternal expansion. But it also forces us to rethink what we mean by the word “universe”—a concept we last had to rethink on such a fundamental level back when Galileo walked into his garden in Padua and pointed a “tube of long seeing” at the night sky.

It’s 1610 all over again.