Is our universe part of a larger multiverse?

Does the word “universe” best describe everything that exists – all of time, energy, and matter – or is it more appropriate to speak of a “multiverse”? With our current technology, we are unable to observe beyond our universe. But what if a “beyond” exists which has other universes besides our own? In recent years it has become recognized that many problems faced by astronomers and physicists might be solved if there were not just one universe, but multiple (and perhaps an infinite number of) other universes. The concept of a multiverse however, isn’t recent at all and has been discussed by scientists for centuries. We talked to Tom Siegfried, science journalist and author of The Number of the Heavens, a book which explores and examines how multiverse theory has evolved.

What is a common misunderstanding about multiverse theory?

The most common misunderstanding is that the multiverse is a theory that cannot be tested. In fact, the multiverse is not a theory itself, but a prediction of other theories that can be tested. One such theory is called inflation, which suggests that there was a rapid burst of expansion right after the birth of the universe. If this theory is correct, it is likely that there were many big bangs that would have produced sibling universes to our own. Inflation theory has passed many tests, although not yet enough to be definitively established.

What are some of the major schools of thought with regard to multiverse theory?

In addition to the idea of inflation producing many universes, superstring theory also suggests that there could be many possible universes with differing physical properties. (It’s possible that inflation is the mechanism for producing those different possible universes). Another idea is that there are extra dimensions of space beyond the three dimensions we can see, so that our universe might be like a soap bubble floating in those higher dimensions. If so, other such bubbles might also be floating in those dimensions. Since a soap bubble is like a membrane, these other universes are sometimes called brane worlds. Finally, quantum physics suggests the possibility that many possible different realities are created as observations or measurements are made. These different branches of reality are sometimes called a multiverse, but they are (if they exist) quite different from the cosmic bubbles like the one we live in. 

Why did you decide to write a book about multiverse theory?

I had long been interested in the issue of whether there are multiple universes and had written many times about the current debates. My interest in writing a popular science book was sparked when I read about the edict of the Bishop of Paris in the year 1277, condemning scholars who taught that there could be only one universe. (The Bishop said that they were denying the power of God to make as many universes as he wanted to.) The Bishop’s edict revived a debate that had begun in ancient Greece, when philosophers who believed in atoms argued for an infinity of universes, whereas Aristotle said there could be only one. After 1277, the debate persisted for centuries, and is still going on today, so I thought a book could tell the story of how arguments against the multiverse in the past had invariably turned out to be wrong.