This last question, at least, has an answer. We don’t see the extra dimensions because they are too tiny to observe with any current technology. On Nova, Brian Greene gave us an analogy: If an atom was as big as our solar system, a string would be the size of a large shrub. To detect something that small, you’d need a particle accelerator the size of a galaxy.
Strings aren’t the only things the theory predicts. The other revelation has been a class of objects called “branes,” short for membranes. Over dinner at the Santa Barbara conference, Joseph Polchinski, from UCSB’s hosting Kavli Institute for Theoretical Physics, offered some illumination. Where strings exist at the subatomic level, branes are the structures the theory generates on the cosmological scale. Strings are tiny, branes are huge. If strings are like spaghetti, branes would be vast sheets of lasagna. Our universe, according to the theory, is a brane, a cosmic-scale incarnation of the same fundamental stringy substance. “You can ask what branes are made of,” Polchinski said, “but they’re not made of anything. They’re just the stuff the theory describes.”
While strings suggest a subatomic space that has yet to be detected, branes conform to some of our usual spatial conceptions. The brane of our universe is said to have the accepted dimensions of space and time. Yet it is seen as just one potential part of a much larger five-dimensional realm known as “the bulk.” Within the bulk, Polchinski told me, there may well be other branes. Here “the universe” becomes not just our brane but the total set of branes within the bulk-space.
String theory does not stop there. In Hawking’s version, an individual brane can be continually reborn. Other versions allow the possibility of branes that spawn from prior branes or infinitely foaming seas of branes, like a vast cosmological head of beer. In Santa Barbara, Leonard Susskind, one of the pioneers of string theory, presented an alarmingly fecund vision in which there were hundreds of “dimensions” of potential universes, with new ones coming into being all the time. Spaces upon spaces upon spaces, a multiplication of possibilities that defy the very notion of limit.
Although some physicists have objected to the almost organic proliferation that string theory allows, Derrida, I think, would be pleased by this explosion of ideas, which supports in the totality of its weirdness the fundamental theme of his talk.
With his impeccable tailoring and leonine presence, the most controversial philosopher of our time would command attention even if he wasn’t supported by the buttress of fame. Derrida told us that the “commandment” to live together imposes upon us demands “beyond law and nature.” Law, he said, is never sufficient to dictate our actions, which operate in a wider realm of possibility than the statutes of any legal system. Derrida urged us to embrace this “excess,” to live and love in a broader field of potential. And that is what I like so much about the new string cosmologies. Despite physicists’ desire for oneness, in the end their equations also have multiplied the possibilities, giving us a vast domain of potential in which the “natural laws” here on Earth are just one set among many. It is as if nature itself resists efforts to press it into a single mode, joining Derrida on the path of radical multiplicity. Whether we can prove the existence of these alternate worlds seems of little consequence.
In string theory we have discovered a language which may well be more lyrical than empirical, but which, in that very quality, enables us to contemplate a wild excess of other options. Derrida and Hawking — the physicist and the philosopher — would, I believe, have embraced one another.
