Warped Passages - Lisa Randall [5]
An example of a quasicrystalline pattern is shown in Figure 2. It lacks the precise regularity you would see in a true crystal, which would look more like the kind of grid you would see on a piece of graph paper. The most elegant way of explaining the pattern of molecules in these strange materials is with a projection—a sort of three-dimensional shadow—of a higher-dimensional crystalline pattern, which reveals the symmetry of the pattern in a higher-dimensional space. What looked like a completely inexplicable pattern in three dimensions reflects an ordered structure in a higher-dimensional world. The nonstick frying pans that are coated with quasicrystals exploit the structural differences between the projections of higher-dimensional crystals in the pan’s coating and the more mundane structure of ordinary three-dimensional food. The different arrangements of atoms, which keeps them from binding to each other, is a tantalizing suggestion that extra dimensions exist and explain some observable physical phenomena.
Figure 2. This is a “Penrose tiling.” It is a projection of a five-dimensional crystalline structure onto two dimensions.
Overview
Just as extra dimensions help us understand the confusing arrangement of molecules in a quasicrystal, physicists today speculate that theories of extra dimensions also will illuminate connections in particle physics and cosmology—connections that are difficult to understand with only three dimensions.
For thirty years, physicists have relied on a theory called the Standard Model of particle physics, which tells us about the fundamental nature of matter and the forces through which elementary constituents interact. * Physicists have tested the Standard Model by creating particles that have not been present in our world since the earliest seconds of the universe, and they’ve found that the Standard Model describes many of their properties extremely well. Yet the Standard Model leaves some fundamental questions unanswered—questions so basic that their resolution promises new insight into the building blocks of our world and their interactions.
This book tells about how I and others searched for answers to Standard Model puzzles and found ourselves in extra-dimensional worlds. The new developments with extra dimensions will ultimately take center stage, but I’ll first introduce the supporting players—the revolutionary physics advances of the twentieth century. The recent ideas that I discuss later are grounded in these stupendous breakthroughs.
The review topics we’ll encounter will, broadly, divide into three categories: early-twentieth-century physics, particle physics, and string theory. We’ll investigate the key ideas of relativity and quantum mechanics, as well as the current state of particle physics and the problems that extra dimensions might address. We’ll also consider the concepts that underlie string theory, which many physicists think is the leading contender for a theory that incorporates both quantum mechanics and gravity. String theory, which postulates that the most basic units in nature are not particles but fundamental, oscilllating strings, has provided much of the impetus for studying extra dimensions, because it requires more than three dimensions of space. And I will also describe the role of branes, membrane-like objects within string theory, which are as essential to the theory as strings themselves. We’ll consider both the successes of these theories and the questions they leave open—the ones that motivate current research.
One of the chief mysteries is why gravity is so much weaker than