Zero - Charles Seife [75]
For most people, four dimensions are one too many. It is easy to see three of them: left-right, front-back, and up-down represent the three directions we can move in. The fourth arrived when Einstein showed that time was similar to these three dimensions; we are constantly moving through time like a car that’s speeding down a highway. The theory of relativity shows that just as we can change how quickly we rush down a highway, we can change the rate at which we move through time—the faster we go through space, the quicker we move through time. To understand Einstein’s universe, we have to accept the idea that time is the fourth dimension.
Four is reasonable—but 10? We can measure four dimensions, but what happened to the other six dimensions? According to string theory, they are rolled up like little balls, too tiny to see. When you pick up a piece of paper, it seems two-dimensional. It has length and breadth, but it doesn’t seem to have any depth at all. Nevertheless, if you take a magnifying glass and gaze at the edge of the piece of paper, you begin to see that it has a wee bit of depth. You need a tool to help you see it, but that third dimension is there, too tiny to see under normal conditions. The same is true with those extra six dimensions. In everyday life they are way too tiny to see; they are too small to detect even with the most powerful equipment that we could possibly manufacture in the near future.
What do these six extra dimensions mean? Nothing, really. They don’t measure anything that we are accustomed to, like length, breadth, width, or time. They are simply mathematical constructs that make the mathematical operations in string theory work in the manner that they have to. Like imaginary numbers, we can’t see them or feel them or smell them, even though they are necessary for doing calculations. Though it is a strange concept physically, it is the predictive power of the equations that interests scientists, rather than their comprehensibility—and an extra six dimensions do not constitute an insurmountable problem, mathematically. Spotting them might. (Ten seems small nowadays. In the past few years physicists realized that the many competing varieties of string theory are actually, in a sense, the same thing. Scientists realize now that these theories are dual to each other just as Poncelet realized that lines and points were dual to each other. Scientists now believe that there is a monster theory that underlies all of these competing theories: the so-called M-theory, which lives in 11 dimensions, not 10.)
Strings (or their more general counterparts, branes, a term for multidimensional membranes) are so tiny that no instrument can hope to spot them—at least until our civilization becomes much more advanced. Particle physicists look at the subatomic realm with particle accelerators: they use magnetic fields or other means to get tiny particles moving very fast; when these particles collide with one another, they spit off fragments. Particle accelerators are the microscopes of the subatomic world, and the more energy you put into those particles—the more powerful the microscope—the smaller the objects you can see.
The Superconducting Super Collider, a multibillion dollar project that was contemplated until the early 1990s, was going to be the most powerful particle accelerator ever built. It was to have more than 10,000 magnets arranged in a loop 54 miles around, about the size of the beltway highway that circles Washington, D.C. This is still not nearly powerful enough to see strings or curled-up dimensions—viewing