Is our universe the only universe, or could it be one of many? Hard as it is to comprehend, cutting-edge theories are suggesting that ours may not be the only one. The entire history of our cosmos might be just one episode in a much grander "multiverse" consisting of many--perhaps infinitely more--universes.
On Thursday, Aug. 2, at the University of Hawai'i's Institute for Astronomy (IfA) in Pukalani, Dr. Alex Filippenko explained this revolutionary concept to a standing-room-only audience of scientists and space enthusiasts.
Dr. Filippenko, professor of astronomy at the University of California, Berkeley, has delivered over 700 public lectures on astronomy to a very wide range of audiences. He is one of a team of cosmologists who won the 2011 Nobel Prize in Physics, and is the recipient of the 2004 Carl Sagan Prize for Science Popularization.
Dr. Alex Filippenko, professor of astronomy at the University of California at Berkeley, is one of a team of cosmologists who won the 2011 Nobel Prize in Physics. He also received the 2004 Carl Sagan Prize for Science Popularization. Dr. Filippenko was voted best professor on the UC Berkeley campus a record nine times and was named National Professor of the Year in 2006.
Courtesy of Dr. Alex Filippenko
Currently, he plays a prominent role in science newscasts and television documentaries such as "Mysteries of Deep Space," Stephen Hawking's "Universe," "Runaway Universe," "Exploring Time," plus 40 episodes spanning six seasons of "The Universe" on the Discovery Channel.
Add his award-winning textbook, "The Cosmos: Astronomy in the New Millennium," now in its third edition, and his five richly illustrated video courses with The Teaching Company and you have a world-renowned expert in the field of cosmology.
"Multiverse is a new name for the universe," said Dr. Filippenko. It implies that the progression from atoms to objects, to planets, to solar systems, to galaxies and to the universe does not end there. "According to this idea, there isn't just one universe. Imagine an infinite number of them, all wrapped up within each other," he said.
Some universes may be indistinguishable from our own. In others, reality may be so radically different from ours as to be unrecognizable.
"The idea is most controversial at this time," said Dr. Filippenko, "but if it's right, our understanding of space, time and our place in the universe will never be the same."
The audience at IfA asked fundamental questions in a variety of ways. How did this notion of multiple universes arise? How can widely separated parts of the universe be related to each other?
"There is a form of energy that's essentially drawing the universe apart. So, space-time expands at an incredible rate," said Dr. Filippenko.
"When you see how this works in mathematics and physics, you realize it never really stops," he said. "The expansion continues, creating more and more things that you can consider to be potential universes."
There are scientifically valid reasons to think that other universes might exist. However, by its very nature, this interesting conclusion removes itself from the realm of science, at least temporarily. The reason is that we don't know of a way to contact other universes and perform experiments on them. In other words, the hypothesis generally seems to be untestable.
"One exception would be a different region in our universe that eventually becomes observable when photons reach us, perhaps far in the future," Dr. Filippenko said.
"There may be properties of our universe that depend on the existence of other universes. Thus, our descendants might eventually discover some method of testing for their presence," he said.
A related idea, promoted by a famous Russian-American theoretical physicist at Stanford University, Dr. Andrei Linde, is that quantum effects in an inflating universe spawn new, distinct, inflating regions within it.
"According to Dr. Linde, these inflating regions will subsequently produce regions that continue to inflate," said Dr. Filippenko. "The process never ends, so it is called 'eternal inflation.'"
Another world-renowned theoretical physicist, Dr. Benjamin Schumacher, professor of physics at Kenyon College in Ohio, and another lecturer in The Teaching Company's Great Courses, explained it this way.
"In some versions of so-called inflationary cosmology, the whole universe we see is just a small expanding bubble in an incomparably vaster sea full of other bubbles," he said. "Some of the details of the basic forces of physics might be different from one bubble to the next. Nevertheless, we would have a cosmos full of little cosmoses."
"However," said Dr. Schumacher, "quantum mechanics suggests another possibility. The so-called many-worlds view includes all possible universes in an infinitely branching quantum multiverse."
The problem with this view is that subtle ambiguities remain in the mathematics when you try to include the whole universe in the quantum framework.
"My own view of the many-universe idea is, use it and explore it, but don't necessarily believe it!" Dr. Schumacher said.
The subject remains hotly debated among many of the brightest minds in contemporary physics.
"It seems we are still left with the ultimate question," said Dr. Filippenko. "How and why did the universe occur?"
Perhaps there is no way, even in principle, for us living here inside our universe to answer this question on our own.
(The author thanks her brother-in-law, Dr. Ben Schumacher, for offering his professional opinions on the subject of this article.)