Warped Passages - Lisa Randall [6]
Our proposal is based on warped geometry, a notion that arises in Einstein’s theory of general relativity. According to this theory, space and time are integrated into a single spacetime fabric that gets distorted, or warped, by matter and energy. Raman and I applied this theory in a new, extra-dimensional context. We found a configuration in which spacetime warps so severely that even if gravity is strong in one region of space, it is feeble everywhere else.
And we found something even more remarkable. Although physicists have assumed for eighty years that extra dimensions must be tiny in order to explain why we haven’t seen them, in 1999 Raman and I discovered that not only can warped space explain gravity’s feebleness, but also that an invisible extra dimension can stretch out to infinity, provided it is suitably distorted in a curved spacetime. An extra dimension can be infinite in size–but nonetheless be hidden. (Not all physicists immediately accepted our proposal. But my non-physicist friends were more quickly convinced I was on to something—not because they fully grasped the physics, but because when I attended a conference banquet after speaking about my work, Stephen Hawking saved me a seat.)
I will explain the physical principles underlying these and other theoretical developments and the new notions about space that make them conceivable. And later on, we’ll also encounter an even weirder possibility, which the physicist Andreas Karch and I discovered a year later: we could be living in a three-dimensional pocket of space, even though the rest of the universe behaves as if it is higher-dimensional. This result opens a host of new possibilities for the fabric of spacetime, which could consist of distinct regions, each appearing to contain a different number of dimensions. Not only are we not in the center of the universe, as Copernicus shocked the world by suggesting five hundred years ago, but we just might be living in an isolated neighborhood with three spatial dimensions that’s part of a higher-dimensional cosmos.
The newly-studied membrane-like objects called branes are important components of the rich higher-dimensional landscapes. If extra dimensions are a physicist’s playground, then braneworlds—hypothesized universes in which we live on a brane—are the tantalizing, multi-layered, multi-faceted jungle gyms. * This book will take you to braneworlds and universes with curled-up, warped, large, and infinite dimensions, some of which contain a single brane and others of which have multiple branes housing unseen worlds. All of these are within the realm of possibility.
The Excitement of the Unknown
The postulated braneworlds are a theoretical leap of faith, and the ideas they contain are speculative. However, as with the stock market, riskier ventures might fail but they could also reward you with greater returns.
Imagine the sight of the snow under a ski chairlift on the first sunny day after a storm, when untracked powder tempts you from below. You know that no matter what, once you hit the snow, it’s going to be a great day. Some runs will be steep and full of bumps, some will be easy cruisers, and some will be tricky routes through trees. But even if you take the occasional wrong turn, most of the day will be wonderfully rewarding.
For me, model building—which is what physicists call the search for theories that might underlie current observations—has this same irresistible appeal. Model building is adventure travel through concepts and ideas. Sometimes new ideas