The gods must be crazy
Wrinkle in time. Standard string theory requires at least seven extra dimensions, but, unlike the ones we know, they are "compacted," or wrapped into tiny arcs less than a trillionth the size of a proton. In the past few years, however, theorists have concluded that some extra dimensions could be as infinite as our familiar up, forward, and sideways. Another wrinkle in string theory, called M theory, holds that higher dimensions can form membranes--branes for short. Our universe might occupy one brane, while others, perhaps just a short "distance" away, may be home to different physics.
Confused? Don't feel bad. Even experienced physicists have a hard time visualizing such things. With branes, says Harvard University's Lisa Randall, another panelist at the meeting, "the [apparent] weakness of gravity starts to make perfect sense. It's not weak. It only looks that way to us." She and a colleague, Raman Sundrum of Johns Hopkins University, propose that gravity loses its strength as it leaks out of our familiar universe into the "bulk"--that unseen realm of higher dimensions. Other theorists, like Savas Dimopoulos of Stanford University, suggest that gravity originates in a parallel "braneworld" and seems weak to us because only a portion of its strength leaks onto our brane. Dimopoulos also thinks that dark matter, a mystery ingredient of the universe known only from its gravitational pull, is the shadowy echo of a parallel braneworld, or even a sign of folds in our own braneworld that allow gravity to take shortcuts to distant neighborhoods.
M theory has many other variants and oddball jargon, including flat branes, weak branes, colliding branes, skinny branes and, Spiropulu jokes, "my big fat Greek brane." But best of all, large higher dimensions like branes should be much easier to detect than the ultratiny packets of the original string theory. Experimenters see a good chance that a new, more powerful version of Fermilab's Tevatron particle accelerator or the European Large Hadron Collider, due in a few years, may slam protons, electrons, and other particles together so hard that signals of big extra dimensions will finally turn up. Such hints could take the form of so-called supersymmetric particles, predicted by string theory; "gravitons" that carry the force of gravity; or even tiny black holes that would evaporate instantly but leave a telltale signal.
Nobody pretends yet to know the answer. String theorist James Cline of Canada's McGill University sees rapid progress toward a new kind of physics, whatever it is. "There may be large extra dimensions; there may not be," he says. "These are wonderful times. New things are coming out every day. I think the chances that any one of the ideas around today is true are slim. But when we do find the right answer, it will look, and smell, just right."
In other words, it will be beautiful.
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