I hope I was wrong about inflation. For decades, I’ve been bashing this theory of cosmic creation, lumping it together with strings, multiverses, and other highly speculative propositions sprung from the fecund minds of physicists.
Proposed more than 30 years ago, inflation holds that an instant after the Big Bang, gravity flipped inside out, briefly becoming a repulsive rather than attractive force. As a result, the cosmos underwent an almost unimaginably rapid growth spurt, which had a profound impact on its current structure, before slowing down to a more leisurely rate of expansion.
Many cosmologists fell in love with inflation, because it seemed to solve riddles posed by the conventional Big Bang theory. Why, for example, does the universe appear so uniform in all directions? The answer is that inflation smoothed out lumps in spacetime, just as blowing up a balloon smooths out its wrinkles.
From the start, inflation was always more a product of human imagination than empirical evidence. There has never been more than circumstantial evidence for its core mechanism—the reversal of gravity—and the theory came in many different forms. My favorite was the eternally self-reproducing chaotic inflationary model proposed by Andrei Linde, who along with Alan Guth and Paul Steinhardt is credited with inventing inflation. Linde’s theory implied that our entire observable cosmos is just a tiny bubble in an infinite “multiverse.”
Hence inflation, like string theory, has always suffered from what is sometimes called the “Alice’s Restaurant Problem.” Like the restaurant eulogized in the iconic Arlo Guthrie song, inflation comes in so many different versions that it can give you “anything you want.” In other words, it cannot be falsified, and so like psychoanalysis, Marxism and other overly flexible hypotheses it is not really a scientific theory.
Inflation enthusiasts have claimed vindication before—for example, in 1992, when a satellite produced a detailed map of the cosmic microwave background, the afterglow of the Big Bang; and in the late 1990s, when astrophysicists discovered that the expansion of the universe is accelerating. But neither of these supposed confirmations of inflation held up.
Just two years ago, inflation pioneer Paul Steinhardt wrote on the website Edge.org: “I think a priority for theorists today is to determine if inflation and string theory can be saved from devolving into a Theory of Anything and, if not, seek new ideas to replace them. Because an unfalsifiable Theory of Anything creates unfair competition for real scientific theories, leaders in the field can play an important role by speaking out—making it clear that Anything is not acceptable—to encourage talented young scientists to rise up and meet the challenge.”
Needless to say, I’m intrigued by the recent news that observations of gravitational waves provide “direct proof of the theory of inflation,” as Clara Moskowitz of Scientific American puts it. “The Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) experiment in the South Pole,” she continues, “found a pattern called primordial B-mode polarization in the light left over from just after the Big Bang, known as the cosmic microwave background (CMB). This pattern, basically a curling in the polarization, or orientation, of the light, can be created only by gravitational waves produced by inflation.”
“If corroborated,” Dennis Overbye writes in The New York Times, the BICEP2 study “will stand as a landmark in science comparable to the recent discovery of dark energy pushing the universe apart, or of the Big Bang itself. It would open vast realms of time and space and energy to science and speculation.”
I hope that turns out to be the case, because cosmology and physics desperately need a jolt of energy (which the anti-climactic discovery of the Higgs boson did not provide). But here is what I’d like to see: First, corroboration of the BICEP2 findings by other groups and observatories. Second, experiments from high-energy physics that provide corroborating evidence of the key mechanism of inflation. Third, an explanation of why the Alice’s Restaurant Problem isn’t still a problem. Fourth, why only inflation, and not other more conventional physical phenomena, can account for the gravity-wave findings.
When these conditions are met, I’ll become an inflation believer. But please don’t ask me to believe in the multiverse.
John Horgan directs the Center for Science Writings, which belongs to the College of Arts & Letters. This column is adapted from one originally published on his Scientific American blog, “Cross-check.”
Be First to Comment