THE SLAYERS OF STRING THEORY
Like Albrecht, and like just about every other physicist, Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, started as a true believer in timeless law. In the 1980s he did some work on string theory. He also developed his own version of a multiverse in which every black hole spawns a new universe at its center. This introduced Darwinian natural selection to his idea of the cosmos: Whether or not a particular kind of universe proliferates depends on its fitness. The universes that are good at creating black holes thrive; it is no coincidence, he concluded, that we live in just such a universe.
As Smolin was developing this notion, he began to have misgivings about string theory, which has come to dominate the orthodoxy of theoretical physics. His 2006 book, The Trouble With Physics, was a withering attack on this orthodoxy. His big complaint about string theory is that it could lead almost anywhere. Rather than converging on a single set of laws—namely, the ones we can observe—it opens up a vast new array of untestable possibilities. This struck Smolin as a dangerous departure from experimentally falsifiable physics. If we really want to understand the basic laws of the universe, he argues, we must look for deeper explanations that do not dismiss the near-at-hand. And to do that, we might have to abandon our attachment to the idea of timeless laws.
Smolin takes particular issue with two tenets of present-day physics: the claim that time as we know it emerges from some deeper set of laws, like the quantum cosmological equations Albrecht works with, and the belief that our universe is just one of many.
The so-called multiverse theory of the universe arose, like string theory, as a way to explain away some uncomfortable mysteries in cosmology. The troubles began when scientists began to accept inflation, a theory developed by American physicist Alan Guth and his Soviet counterpart, Andrei Linde, in the early 1980s. Inflation holds that shortly after the Big Bang, a small shard of space-time underwent extremely rapid expansion, ultimately to become what we see around us: a universe of galaxies receding from one another. That theory opened up the possibility that other chunks of space-time went through their own inflation, creating a tremendous number of “pocket universes.”
Eventually this idea grew into what is now known as the multiverse theory, the notion that our observable universe is just one of perhaps an infinite number of cosmic domains, each with its own version of the laws of physics. In this view there is no need to explain why our universe has a particular set of physical laws, since somewhere out there exists a pocket universe for each possible set.
Smolin does not like some of the metaphysical overtones of today’s physics and cosmology, but he primarily rejects hidden dimensions in physics and multiverse approaches in cosmology for technical reasons. He sees problems, for example, in the details of quantum cosmology—the type of problems Albrecht has also encountered. These technical objections have given Smolin the uneasy feeling that there is something rotten at the core of physics.
That feeling began to take on more concrete form when he met Roberto Mangabeira Unger, a professor at Harvard Law School. Smolin had been invited to a conference (on art and critical theory) and was trying to decide whether to go when he saw Unger’s name on the guest list. Smolin had known of Unger’s work, and he was intrigued. A mutual friend put them in touch, and during several phone conversations about multiverses and the nature of time, they realized that they were soul mates in skepticism. A few years later, at Unger’s suggestion, Smolin organized a workshop at the Perimeter Institute called Evolving Laws and invited Unger to come and talk things over with the group. Now the two scholars are collaborating on a book, The Reality of Time and the Nature of Cosmological Laws.
As a nonscientist, Unger approaches the problem from the standpoint of philosophy. The problem with theories that include hidden dimensions and alternate universes, he says, is that they are not theories at all but allegories. There is no way to test them with any experiments or observations. String theory cannot be made to work in a world of only four dimensions. In response, string theorists posited the existence of seven extra dimensions that are hidden from us. Of course, no one has observed these extra dimensions of space, and worse, it is not clear that such an observation is possible. The equations of string theory predict that there are an unimaginable number of different possibilities for how those dimensions are configured—on the order of 10 to the 500th power. It would take more time than has so far elapsed since the Big Bang just to count them all.
The experimental basis for a multiverse theory is equally shaky. None of the other universes that crop up could ever be seen because the space between us and them would be expanding at faster-than-light speed.
Neither string theory nor the multiverse theory explain nature’s mysteries so much as explain them away, Unger concludes. “When we imagine our universe to be just one out of a multitude of possible worlds, we devalue this world, the one we see, the one we should be trying to explain,” he says. “The scientist should treasure the riddles he can’t solve, not explain them away at the outset.”
Unger and Smolin want to shift the emphasis in physics away from these possible worlds and back to the one real world—our world, which is saturated with time. They urge their colleagues to abandon the search for timeless truths like string theory.
More broadly, they argue that physics should refrain from spinning any theories that require the existence of things that could never be disproved, such as multiverses. And it should recognize that there is no ideal realm of perfect, timeless mathematical forms that embody the laws of physics. Time is inherent in the universe, and nothing exists outside of time. Smolin thinks that Albrecht’s clock ambiguity is a symptom of the larger problem with the current approach to physics.
Developing equations for a new kind of physics can come later, in Smolin and Unger’s view. For now they want to open a frank conversation about the rationale for looking at those equations in the first place. With only one time-saturated universe, physicists will have to revise the way they think about nature’s laws. If time is real, then everything in the universe is part of time and subject to it. The essence of time is change. What we call the laws of physics may also change with time. History will have to matter, even in this hardest of all sciences.