Warped Passages - Lisa Randall [37]
Albion points out that “the distinction is becoming fuzzy again, catalyzed in large part by the study of extra dimensions. People are talking to each other.” The communities are no longer so rigidly defined, and there is more common ground. There has been a renewed convergence of purpose and ideas. Both scientifically and socially, there are now strong overlaps between model builders and string theorists.
One of the beautiful aspects of the extra-dimensional theories I will describe is that ideas from both camps converged to produce them. String theory’s extra dimensions might be a nuisance, but they might also prove to be an opportunity for finding new ways of addressing old problems. We can certainly ask where the extra dimensions are, and why we haven’t seen them. But we might also ask whether these unseen dimensions could have any import in our world. These dimensions might help explain underlying relationships that are relevant to observed phenomena. Model builders relish the challenge of connecting notions such as extra dimensions to observable quantities such as relations among particle masses. And, if we’re lucky, the insights based on extra-dimensional models might successfully address one of the biggest problems facing string theory: its experimental inaccessibility. Model builders have used theoretical elements derived from string theory to attack questions in particle physics. And those models, including the ones that have extra dimensions, will have testable consequences.
When we investigate extra-dimensional models later on, we will see that the model building approach in conjunction with string theory has generated major new insights into particle physics, the evolution of the universe, gravity, and string theory. With the string theorist’s knowledge of grammar and the model builder’s vocabulary, the two together have begun to write quite a reasonable phrase book.
The Heart of Matter
Ultimately, the ideas we will consider encompass the entire universe. However, these ideas are rooted in particle physics and in string theory—theories that aspire to describe the smallest components of matter. So before setting out on our journey to the extreme theoretical territory these theories address, we’ll now take a brief trip into matter down to its smallest parts. On this guided tour of the atom, take note of matter’s basic building blocks and the sizes of the objects that different physical theories deal with. They should provide a few landmarks that you can use to orient yourself later on and help you to recognize the components with which each area of physics concerns itself.
The basic premise in most of physics is that elementary particles constitute the building blocks of matter. Peel away the layers, and inside you will always ultimately find elementary particles. Particle physicists study a universe in which these objects are the smallest elements. String theory takes this assumption one step further and postulates that those particles are the oscillations of elementary strings. But even string theorists believe that matter is composed of particles—the unbreakable entities at its core.
It might be difficult to believe that everything is composed of particles; they certainly are not evident to the naked eye. But that is because of the coarse resolving power of our senses, which cannot directly detect anything anywhere nearly as tiny as an atom. Nonetheless, even though we can’t directly view them, elementary particles are the elementary building blocks of matter. Just as the images on your computer or TV are composed of tiny dots, even though they present images that appear to be continuous, matter is composed of atoms, which are in turn composed of elementary particles. Physical objects