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Winter 2005
photo by Mark Morelli
The Universe As Inquiry:
Alexander Vilenkin

At some time or other, just about everyone has looked up at the night sky and marveled at the moon, planets, and stars, wondering how this strange universe came into being.

Scientists today posit that the “Big Bang,” the theoretical “birth” of the universe, happened some 15 to 20 billion years ago—our small Earth is a relative newcomer, appearing on the cosmic landscape about 4.5 billion years ago and located in a galaxy that is but one of billions. Although much has been learned about the cosmos through observation and theory, many important questions remain.

An impressive number of answers—or at least tantalizing possibilities—have been advanced by noted physics professor Alexander Vilenkin, the director of the Tufts Institute of Cosmology.

Since arriving at Tufts more than a quarter century ago, Vilenkin has helped shape the field of cosmology, informing our conception of the universe on the most fundamental levels. He has had critical insights about the origins of the universe: the “inflationary” process that enlarged the universe in an explosive burst, filling it with matter and energy; the existence of multiple regions within our universe; and the role of primordial remnants called “cosmic strings” that stretch across space. His ideas have established his international reputation and his colleagues are among the most respected cosmologists at work today. Andrei Linde of Stanford University, for one, is quick to praise Vilenkin as “a deep and original thinker who hasmade profound contributions to our notions about the creation of the universe.”

Vilenkin, 55, wears that praise lightly at Tufts, where he spins theoretical models from a modest, book-cluttered third-floor office in Robinson Hall. A faculty member in the Department of Physics and Astronomy and director of the Institute of Cosmology, he is as unassuming as he is soft-spoken. He takes a moment to reflect when asked why he has devoted his life to working out elegant and sometimes mind-boggling mathematical models that have helped us understand the structure and history of the universe.
“Cosmology is an interesting field to have a conversation about,” he says, “but what got me fascinated is that not only can we talk about it, we can learn something about it. There is no question now that there was a ‘Big Bang’—we see the afterglow of the Big Bang in radiation coming to us from the remotest parts of the universe. So our theories have been confirmed. Still, there are some puzzling questions I’d very much like to understand. It’s a pleasure to think about them, and there’s always the hope that I might come up with an idea that provides some answers. It’s a great time to be in this field.”

There is not enough space in this magazine to offer a complete Vilenkin “primer” on cosmology. Still, here are three “big” ideas that offer a glimpse into his theories and how they have led to new understanding about that mystery called the universe.

1. The Beginning
The idea of inflation emerged in 1981 — an idea to which Vilenkin has made vital contributions. In essence, inflation is a violent, yet incredibly brief period of exponential growth during the first fraction of a second of its existence. Inflation ignited the “bang” behind the Big Bang, setting the universe on its current expansionary course. By combining inflation with quantum cosmology, Vilenkin showed how to produce a universe much like the one we see today.

How, asked Vilenkin, could matter, energy, space, and time have arisen spontaneously from nothing? In quantum mechanics, the reigning theory of physics on a small scale, particles spring into existence out of nowhere for a brief moment, then vanish just as suddenly. If particles could do that, Vilenkin surmised, why not an entire universe? He worked through the equations and showed how a universe might emerge literally from nothing. “It seemed like a totally crazy idea,” he admits, “but this is what the calculations were suggesting.” Vilenkin’s breakthrough provided the first mathematical descriptions of the creation of the universe. “At that time, the question of how the universe came into being was not discussed at all,” recalls Vilenkin. “The idea was that physics discusses how you got from ‘state A’ to ‘state B’ but it doesn’t answer the question: ‘Why was ‘state A’ there to begin with?’ It was kind of a taboo question. When I gave a seminar at Harvard, one guy came up to me and said, ‘It’s amazing to give a talk like that and survive!’ What used to be philosophy was becoming physics. Now it is a very active subject.”

As a follow-up, he made the astonishing suggestion that almost all inflation models are “eternal,” meaning that once the process starts, it never ends. Inflation, he said, is like a chain reaction, stopping in one region of space only to start in another, ultimately spawning an infinite number of separate regions, isolated from each other by distance and time, yet still part of a single, unfathomably vast entity. Vilenkin’s insights not only changed our conception of the inflationary process, they transformed our picture of the universe on a large scale, pointing to a complex, never-ending structure that continues to create worlds entirely beyond our view.

2. Ever-curious Cosmic Strings
The universe went through phase transitions in its earliest moments, transitions similar to the freezing of water. As a result, defects of various forms were produced, including linear strands that extend clear across the cosmos, thus known as “cosmic strings.” In the pantheon of weird objects in the universe, these hypothetical entities stand beside black holes as two of the most bizarre phenomena. Either infinitely long or closed loops, they are incredibly dense and yet thinner than a subatomic particle.

Vilenkin began thinking about cosmic strings in 1980 and since then has established himself as “the world leader” in developing the concept, according to MIT physicist Alan Guth.

In 1982, Vilenkin proposed that cosmic strings may have provided the seeds for galaxy formation—drawing matter together through unusual gravitational effects that warp the geometry of space. Since the 1990s, however, astronomical observations have made this scenario increasingly implausible. The theory that strings provided the glue that enabled galaxies and galaxy clusters to congeal wasn’t intrinsically flawed, Vilenkin explains. “It just described the wrong universe.”

That doesn’t mean we should write off the whole notion of cosmic strings, says Princeton cosmologist James Peebles. “The physics is as persuasive today as ever. I expect we’ll be hearing more about cosmic strings and, when we do, we’ll be returning to Alex’s fundamental papers.”

Cosmic strings might still exist, Vilenkin agrees. “The early universe went through several transitions, and it would be surprising if there are no defects.” He’s now investigating the “observational signatures” left behind by such defects, which could provide “a unique window on the high-energy physics of the early universe.”

Lately, superstring theorists, who dominate theoretical physics today, have also become enamored of cosmic strings, which seem to be a common byproduct of their cosmological models. This interest has led to a spate of papers and a “cosmic string revival” that vindicates Vilenkin’s pioneering work, according to MIT physicist Max Tegmark. “Alex Vilenkin does not hop on the bandwagon. But after a while, the bandwagon follows him.”

3. Déjà Vu All Over Again
Vilenkin’s idea of eternal inflation, if correct, led him to another startling observation about the universe. Based on the inflation model, there are, he said, a limitless number of regions (the same size as our observable region) within the universe, though separated by insurmountable stretches of space. In other words, an infinite number of regions exist beyond the visible world.

Pondering the implications of these multiple regions in a recent paper, Vilenkin and former postdoctoral fellow Jaume Garriga (now at the University of Barcelona) arrived at a jarring conclusion: the number of “histories”—or things that could possibly happen within these realms—is finite. “That means, if you have an infinite number of regions and a finite number of histories, it’s clear that these histories must repeat,” he says. “If you have dice, and you throw the dice, you have only a finite number of possible outcomes. Now imagine an infinite number of people throwing those dice. I can predict an infinite number of people who will get the same result that I get here.”

Vilenkin sees this as an extension of the Copernican revolution, which placed the sun, rather than the Earth, at the center of the universe. “We now see that we’re not the center of the universe, and we’re not special either,” he says. “Our history is typical among possible histories.”

So somewhere, in another universe, for example, will long-suffering Red Sox fans have to wait 86 years for the “Curse of the Bambino” to be lifted?

Yes, says Vilenkin, and he’s not particularly happy about it—on a cosmic scale. “I don’t like this conclusion,” he says. “I did not like to admit that we’re not special – good or bad, but at least I had hoped we might be unique!”