The Science Behind Final Theory
The Theory of Everything
In the late 1960s and early 1970s physicists began to develop a new quantum theory proposing that all the fundamental particles are really minuscule strings, each less than a trillionth of a trillionth of a millimeter long. These putative strings could vibrate at a variety of frequencies, and each frequency would correspond to a different particle — a string vibrating in one mode would be an electron, a string vibrating in another mode would be a photon, and so on. In the mid-1970s researchers realized that a vibrating closed string (one in which the endpoints are joined to make a loop) would be equivalent to a graviton, the particle that is believed to convey the gravitational force. Thus, string theory became the first mathematical system to successfully combine gravity with quantum mechanics, an important step toward a Theory of Everything.
Unfortunately, string theory comes with a lot of baggage. It requires the existence of a whole new class of "supersymmetric" particles and at least six extra dimensions that have never been observed. (In one version of the theory, our universe is a four-dimensional "brane" moving through a larger, 10-dimensional "bulk." We don't perceive the extra dimensions because nearly all the particles in our universe are attached to the brane, stuck like flies to flypaper.) Worse, the equations of string theory are so ambiguous that they have not yet generated any predictions that can be tested by experiment. In fact, because the extra dimensions of string theory can be folded in so many different ways, the equations appear to describe a tremendously large number of possible universes rather than offer a unique explanation of the universe we live in.
Because of these failings, some scientists are investigating alternative quantum theories that can explain both gravity and particle physics. And a few maverick researchers have resurrected Einstein's idea of formulating a classical theory that underlies quantum mechanics, which would unify the fundamental forces and restore certainty to the universe in a single stroke. One of the clues suggesting the existence of this deeper theory is the holographic principle, which was originally devised to explain the properties of black holes and later generalized to apply to any region of spacetime. The principle can be stated as:
S ≤ A/4
In this formula, S stands for the amount of information contained in a region of space (information, in this context, means the positions and velocities of all the particles in the region) and A stands for the surface area of the region. Oddly, the maximum amount of information that can be crammed into the region is proportional to its surface area, not its volume. This principle appears to contradict the tenets of quantum theory, but it would fit naturally into a deeper, classical theory. Perhaps Einstein was closer to the truth than anyone realized.
One of the prominent advocates of a classical Theory of Everything is Nobel Prize-winning Dutch physicist Gerard 't Hooft. Another is British theorist Mark Hadley, who has resurrected another idea of Einstein's: that the fundamental particles are not objects traveling through spacetime, but rather tiny slipknots in the fabric of spacetime itself. Hadley has transformed the old concept of the geon — a "gravitational electromagnetic entity" — into the 4-geon, a particle model that includes "closed timelike curves" that loop back and forth in time. In essence, this spacetime knot is so twisted that it can be influenced by events in the future as well as the past. Although the concept is still sketchy, it may someday bridge the gap between quantum mechanics and a Theory of Everything.