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March 31, 2009

Infinite universes popping out of nothingness: Tufts cosmologist gives the 2009 Hofstadter physics lecture at Stanford

If you've seen one Big Bang, you definitely haven't seen them all, according to physicist Alexander Vilenkin, director of Tufts University's Institute of Cosmology. Vilenkin is the invited speaker for this year's Hofstadter Lecture, sponsored by the Stanford Physics Department. He will speak on April 6.

According to Vilenkin, the Big Bang that produced our universe is but one of an infinite number of universes that pop up from nowhere, mere bubbles in a larger universe of universes that is itself expanding at unimaginable speeds.

And that scenario, Vilenkin says, leads to an astonishing conclusion. With an infinite number of universes, all possible arrangements of space, matter and time will occur an infinite number of times.

"A striking consequence of the new picture of the world is that there should be an infinity of regions with histories absolutely identical to ours," Vilenkin has written. "That's right, scores of your duplicates are now reading copies of this article. They live on planets exactly like Earth, with all its mountains, cities, trees and butterflies. There should also be regions where histories are somewhat different from ours, with all possible variations." There should be countless regions, for example, where Al Gore became president of the United States.

The implication of these insights, the physicist said, can be depressing. Homo sapiens is not special in the universe; in fact, we're not even unique. That's a big step down from the days when humans considered themselves, literally, as the center of the universe.

Born in the former Soviet Union, Vilenkin received his undergraduate degree in 1971 from Kharkov State University. He was drafted into the army and then worked at various jobs, including night guard at a zoo, while doing physics research in his spare time. He immigrated to the United States in 1976 as a Jewish refugee.

He is an authority on what's known as the inflation theory of the early universe and the author of the popular book Many Worlds in One: The Search for Other Universes. It holds that universes pop forth from emptiness and then expand so fast that in a tiny fraction of a second a region the size of an atom is blown to dimensions much greater than the entire observable universe. In our local universe, this "inflation" ended about 14 billion years ago, and the energy that drove the expansion went to ignite a hot fireball of particles and radiation that we call the Big Bang. As the fireball expanded (at speeds much slower than inflation, yet fantastic by Earthly standards,) it cooled down, allowing stars to form. Gravity then pulled the stars together into the galaxies that still shine in our night sky.

Our galactic home, the Milky Way, will eventually meet its demise in one of two ways, Vilenkin said in an interview with the Stanford Report. Most likely is the collision of the Milky Way with the Andromeda galaxy, due to happen in a few billion years. But it is also possible that before then our own bubble universe will collide with another bubble.

If that collision occurs in our neighborhood, we'll never see it coming, Vilenkin said. It would be a very sudden, catastrophic ending. On the other hand, a bubble collision in the far reaches of our universe might do us no harm. We may even spot one of these bubble universes colliding with ours in the cosmic distance. But, as Vilenkin says, "It wouldn't look like much."

Such a collision would appear as a slight ripple in the otherwise extremely uniform cosmic radiation background. "It would look like a hot or cold spot in this background," he said. "There would be a little round spot where the density of radiation would be a little dimmer than elsewhere." Observers have already spotted an unexpected cold spot, he noted, "So, who knows—it could be the signature of a collision."

As cosmologists push on into the earliest micromoments of the Big Bang, the question inevitably arises, "What existed before the Big Bang?" The answer usually is "nothing," since there was neither space nor time before the beginning.

But Vilenkin has a more nuanced answer. If the laws of nature dictate how the universe could spontaneously pop out of nothingness, and if there is an elegant mathematical description of those laws, then perhaps the laws and the equations existed before the creation itself.

It's scientists' revision of an old question: "Where was God before God created the universe?"

Vilenkin's lecture, "Many Worlds in One," is scheduled for 8 p.m. Monday, April 6, at the Hewlett Teaching Center, 370 Serra Mall, Room 200. It is free and open the public. He also will speak at a more technical colloquium, "Measures of the Multiverse," at 4:15 p.m. Tuesday, April 7, in Room 201 of the teaching center.

The Hofstadter Lecture commemorates the late Nobel Prize-winning physicist Robert Hofstadter, who was a member of the Stanford faculty from 1950 until his death in 1990.



Dan Stober, Stanford News Service: (650) 721-6965,


Alexander Vilenkin, Tufts Institute of Cosmology:

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