Warped Passages - Lisa Randall [150]
Today, both the string theory and the particle physics communities have a more sober view of their level of understanding than they did in the 1980s. We are trying to address difficult questions, and they will take time to answer. But this is an exciting time, and despite (or perhaps because of) the many unsolved problems, there is good reason to be optimistic. Physicists now have a better grasp of many consequences of both particle physics and string theory, and open-minded physicists today stand to profit from the achievements of both schools. That is the middle ground that some physics colleagues and I prefer—and it has led to many of the exciting results that we will shortly encounter.
What to Remember
The graviton is the particle that communicates the gravitational force, much as the photon communicates the electromagnetic force.
According to string theory, the fundamental objects of the world are strings, not pointlike particles.
Later models of extra dimensions won’t explicitly use string theory; at distances greater than the minuscule Planck scale length (10-33 cm), particle physics suffices.
Nonetheless, string theory is important to particle physics, even at low energies, because of the new concepts and analytic tools it introduces.
15
Supporting Passages: Brane Development
Insane in the membrane
Insane in the brain.
Cypress Hill
Ike Rushmore XLII decided to dive down once again to the minuscule Planck scale. Happily, his souped-up Alicxvr worked perfectly and he smoothly arrived in a ten-dimensional universe filled with strings. Eager to explore his new environment, Ike cranked up the hyperdrive attachment he had just purchased from Gbay. He watched with fascination as strings collided and tangled in mesmerizing ways.
Although Ike worried that the Alicxvr might break down, he was curious to learn more about this novel world. So he increased the pressure on the hyperdrive lever. At first strings collided together even more frequently. But when he cranked up the lever still more, he entered a new, completely unrecognizable environment. Ike couldn’t even tell whether spacetime was intact. But he kept cranking up the hyperdrive, and, strangely enough, emerged unscathed.26
However, his surroundings were now quite different. Ike was no longer in the ten-dimensional universe he had started off in. He was instead in an eleven-dimensional universe filled with particles and branes. And, odd as it seemed, nothing in this new universe interacted very much. When Ike looked back at his controls, he discovered that the hyperdrive lever had mysteriously been reset to low. Confused and rather exasperated, Ike cranked up the lever once again, only to find himself back where he started. When Ike checked the controls, he discovered the hyperdrive lever was once again back at low.
Ike thought his Alicxvr was probably malfunctioning. But when he checked his up-to-date manual he discovered that his device was operating perfectly—high hyperdrive in ten-dimensional string theory was the same as low hyperdrive in an alternate eleven-dimensional world. And vice versa.
The manual didn’t say what should happen when the hyperdrive wasn’t very low or very high, so Ike entered the spacernet and put himself on the wait-list for an improved version that would solve the problem. But the Alicxvr designers promised only that the release date would be some time within the millennium.
In today’s physics world, you might say that “string theory” is a misnomer. In fact, the theorist Michael Duff facetiously refers to “string