s there one universe or many? That mind-dilating concept which has been challenging scientists in recent years is the subject of a book edited by Bernard Carr, resulting from three conferences held at Stanford and Cambridge Universities with the support of the Foundation.
Carr, professor of mathematics and astronomy at Queen Mary, University of London, compiled the work of 26 contributors, ranging from cosmologists and particle physicists to philosophers, under the title Universe or Multiverse? The views represented are similarly varied, encompassing all shades of opinion on multiverse theory, from the firmly committed to the deeply skeptical.
“What is clear,” says Carr, “is that what we call our universe—our visible universe—has to be only a small part of a much larger entity, because in the Big Bang picture you can only see to the distance light has travelled since the Big Bang, roughly 40 billion light years.” But the multiverse concept goes beyond this by positing other universes that are completely disconnected from ours. There are several theories that predict this: the cyclic model, the inflationary model, the brane model (in which universes are spread out in an extra dimension), the ‘many worlds’ model of quantum mechanics, and the string landscape model. There is also the notion that there could be different universes corresponding to all possible laws of physics.
All of this varied tapestry of speculation is considered in the book, whose contributors include Martin Rees, Stephen Hawking, and recent Templeton laureate John Barrow. The book was launched at the conclusion of the Templeton-sponsored strategy and planning workshop, “Toward a New Philosophy of Cosmology,” held at the Royal Society in London in May 2007.
This workshop was convened to consider “the state of the field” and was attended by many distinguished scientists, including Professor Lord Rees, who is president of the Royal Society, Master of Trinity College, Cambridge, and Astronomer Royal. The workshop considered such questions as: What are the laws of nature? Why do they exist? Does scientific explanation have intrinsic limits in cosmology? Why life? Why fine-tuning? Why the universe? Is there one universe or many?
Universe or Multiverse? is an attempt to address that last question in some detail. Carr rejects the frequently voiced criticism that this debate belongs to the realm of philosophy rather than science. “It’s certainly true that the multiverse is not part of science as we normally think of it, but that may just mean we need to change the nature of science. It’s true you can’t see these other universes, but there are lots of examples of things in physics that you can’t see. For example, nobody can see inside a black hole and yet everybody accepts that discussion of such regions is well within the domain of physics,” he says, before adding, “No one’s ever seen a quark.”
Is God incompatible with a multiverse? “Some people say ‘God or multiverse’ but that’s very naïve because if you’ve got a multiverse you could still have God. My personal view is that if God could create one universe, He could create as many as He wanted.” Carr points out that what gives an extra edge to the universe/multiverse controversy is the fact that, if there is only one universe, there is a problem explaining the fine-tuning of the physical constants required for life. A multiverse could remove the need for a “fine-tuner” (God?), which would be a relief to some physicists who are uneasy about the quasi-theological implications of fine-tuning.