Warped Passages - Lisa Randall [25]
Branes—membrane-like objects in higher-dimensional space—provide the necessary boundary conditions for worlds that “end.” As we will see in the following chapter, branes can make a world (or many worlds) of difference.
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Exclusive Passages: Branes, Braneworlds, and the Bulk
I’m gonna stick like glue,
Stick, because I’m stuck on you.
Elvis Presley
Unlike the studious Athena, Ike rarely read any books. He generally preferred playing with games, gadgets, and cars. But Ike hated driving in Boston, where the drivers were reckless, the roads were badly signposted, and the highways were invariably under construction. Ike always ended up stuck in traffic, which he found especially frustrating when he could see a nearly empty freeway overhead. Though the empty road would be tempting, Ike would have no way to quickly reach it since, unlike Athena’s owls, he couldn’t fly. For Ike trapped on slow roads in Boston, the third dimension was no use at all.
Until very recently, few self-respecting physicists considered extra dimensions worth thinking about. They were too speculative and too foreign: no one could say anything definitive about them. But in the last few years, extra dimensions have found their fortunes rising. No longer shunned as undesirable gatecrashers, they’ve evolved into highly sought-after, stimulating company. They owe their newfound respectability to branes and to the many genuinely new theoretical possibilities that these fascinating constructs have introduced.
Branes took the physics community by storm in 1995, when the physicist Joe Polchinski of the Kavli Institute for Theoretical Physics (KITP) in Santa Barbara established that they were essential to string theory. But even before then, physicists had proposed branelike objects. One such example was a p-brane (so called by p-layful p-hysicists), an object that extends infinitely far in only some dimensions, which physicists derived mathematically using Einstein’s theory of general relativity. Particle physics had also suggested mechanisms for confining particles on branelike surfaces. But string theory branes were the first known type of brane that could trap forces as well as particles, and we’ll soon see that is part of what makes them so interesting. Like Ike stuck on a two-dimensional road in three-dimensional space, particles and forces can be trapped on lower-dimensional surfaces called branes, even if the universe has many other dimensions to explore. If string theory accurately describes the world in which we live, physicists have no choice but to acknowledge the potential existence of such branes.
The world of branes is an exciting new landscape that has revolutionized our understanding of gravity, particle physics, and cosmology. Branes might really exist in the cosmos, and there is no good reason that we couldn’t be living on one. Branes might even play an important role in determining the physical properties of our universe and ultimately explain observable phenomena. If they do, branes and extra dimensions will be here to stay.
Branes as Slices
In Chapter 1 we looked at one way of thinking about the two-dimensional world of Flatland: as a two-dimensional slice of a three-dimensional space. In Abbott’s novel, the character A. Square took a journey beyond two-dimensional Flatland, into the third dimension, and recognized that Flatland was a mere slice of the bigger three-dimensional world.
Upon his return, A. Square suggested—logically enough—that the three-dimensional world he had seen might also be a mere slice: a three-dimensional slice of an even higher-dimensional space. By “slice,” of course, I don’t mean merely