Journal Archive > 2002 > February

Space odyssey

Throughout the cosmos, all histories are possible

Somewhere in the universe, the Red Sox are celebrating another World Series victory.

Wishful thinking? Not quite. That scenario is just one of millions that can be validated through the work of cosmologist Alexander Vilenkin.

Vilenkin, a professor of physics, investigates the origins of the universe. In a paper published last year in Physical Review, Vilenkin and a colleague theorized that in an infinite number of cosmic regions like ours throughout the universe, every possible history has been playing out an infinite number of times.

The constellation Hercules © EURELIOS

So, they postulated, somewhere in the universe, Al Gore was declared the winner of the 2000 presidential election. Elsewhere, Elvis still lives—or, more precisely, an infinite number of Elvises live.

At first grasp, to those who haven't devoted their lives to examining the underpinnings of the universe, it seems more like science fiction than science—like the episode of "Star Trek" in which Kirk and Spock accidentally trade places with an evil Kirk and Spock from another universe.

But this isn't TV. Vilenkin's thinking is based on scientifically accepted ideas about the origins of the universe; it is an extension of the cosmological theory known as "inflation."

Two ingredients
"The idea is pretty simple," Vilenkin says. "There are a total number of possible histories, which are finite. It's a huge number—but it's finite."

These "histories," Vilenkin says, "are not just human events, but everything that happens down to the atomic level. There may be subtle differences, histories that are changed a tiny amount, but not enough, [according to quantum theory], to be told apart. That's the first ingredient."

Alexander Vilenkin © Mark Morelli

The second ingredient, Vilenkin says, lies in the idea of inflation—the concept that our part of the universe went through a period of very rapid, accelerated expansion. The theory of inflation was pioneered about 20 years ago by cosmologist Alan Guth of MIT as an explanation of what occurred in the universe at the epoch of the Big Bang. Inflation, cosmologists believe, may account for the known characteristics of the universe.

"Initially, the theory was speculative," Vilenkin says. "Now, we have some observations that inflation predicted…the model of inflation was observationally confirmed last year."

As the universe inflates, regions like ours with stars, galaxies and life develop, while inflation continues in the rest of the universe, Vilenkin says.

"Because inflation continues for eternity, it will keep producing regions like ours, an infinite number of such regions," he said.

"With a finite number of histories for a region like ours, there is an infinite number of regions in which those histories can play out," Vilenkin says. "Any history that is not strictly forbidden [by the laws of physics] will repeat an infinite number of times.

"Other than [what is forbidden], anything, no matter how improbable, will happen."

Same universe, different regions
Vilenkin is careful to point out the difference between various regions of the same universe, as allowed for with inflation, and the popular concept of "parallel universes"—like in the television episode with the dual Kirks and Spocks.

"This is not parallel universes," he says. "What I'm talking about is the same universe, but different regions. We could, in principle, travel to those regions [in the future.]"

The issue of time presents an interesting question. "Time is a little tricky," Vilenkin says. "Do the histories occur simultaneously, or are there those that happened a long time ago or that will happen in the future? That's a somewhat subtler question—but there is a way of looking at it, according to which histories occur at the same time."

A 'metaphysical diversion'
Vilenkin co-wrote the paper with his long-time collaborator, Jaume Garriga of the Independent University of Barcelona. The two met while Garriga was a post-doc at Tufts. The work was funded by a grant from the Templeton Foundation of Radnor, Pa.

The bulk of Vilenkin's work focuses on the early universe and its implications for the present universe. Currently, he is conducting research on the subject of "dark energy," a gravitationally repulsive force that, it is theorized, contributes to the total energy of the universe. Vilenkin views the paper on repeating histories as a "metaphysical diversion."

"Physicists usually want to make predictions and see if their theory is correct. This paper was not of that kind, although, in principle, we could travel to one of those other parts of the universe, although we won't be able to do that anytime soon," he says.

"To a large degree, eternal inflation is not accessible to observation," he says. Vilenkin and Garriga have no plans to continue exploring the concept of repeating histories—"it was just an isolated piece of work, a metaphysical exercise," Vilenkin says.

Nothing new under the sun
And, an exercise that was not altogether heartening for the professor. "I find it pretty depressing," says Vilenkin. For example, "notice all the terrible things you can think of. You can be sure that they have happened somewhere in some different region of the universe.

"I would like to think about our civilization as being in some ways unique," he says. "There may be other civilizations that are more clever. But I like to think we're doing something creative, that we have a unique history and so forth. This picture tells us this is not so.

"No matter how much we try, we cannot come up with something new."

Vilenkin compared the situation to the era of Copernicus. "Initially, people believed that the earth was the center of the universe. They thought they lived at the center of the universe. Then, it was affirmed that our place in the universe was more or less the same as the other planets," he says. "It's a hard blow for people, not being very special."

Not all scientists share this glum view. "I should say there are other people, physicists, who do not get depressed," Vilenkin says. "Maybe, this [theory] is not a reason to be depressed. On the contrary, maybe it's a reason not to take things too hard."

Or a reason for hope to spring eternal. For Red Sox fans, there's another year—and another part of the universe—to pin their hopes on.