Warped Passages - Lisa Randall [40]
Both types of unanswered question—those that concern visible and purely theoretical phenomena—give us reasons to look beyond the Standard Model. Despite the Standard Model’s power and success, we’re confident that more fundamental structure awaits discovery and that the search for more fundamental principles will be rewarded. As the composer Steve Reich elegantly put it in the New York Times (when making an analogy to a piece he wrote), “First there were just atoms, then there were protons and neutrons, then there were quarks, and now we’re talking about string theory. It seems like every 20, 30, 40, 50 years a trapdoor opens and another level of reality opens up.”*
Experiments at current and future particle colliders are no longer looking for the ingredients of the Standard Model—those have all been found. The Standard Model nicely organizes these particles according to their interactions, and the full complement of Standard Model particles is now known. Instead, experimenters are looking for particles that should be even more interesting. Current theoretical models include the Standard Model ingredients, but add new elements to address some of the questions that the Standard Model leaves unresolved. We hope that current and future experiments will provide clues that will allow us to distinguish among them and find the true underlying nature of matter.
Although we have experimental and theoretical hints about the nature of a more fundamental theory, we are unlikely to know what is the correct description of nature until higher-energy experiments (that probe shorter distances) provide the answer. As we will see later on, theoretical clues tell us that experiments in the next decade will almost certainly discover something new. It probably won’t be definitive evidence of string theory, which will be very difficult to discover, but we’ll see that it could be something as exotic as new relations in spacetime, or new and as yet unseen extra dimensions—new phenomena that feature in string theory as well as other particle physics theories. And despite the broad scope of our collective imagination, these experiments also have the potential to reveal something that no one has yet thought of. My colleagues and I are very curious about what that will be.
Preview
We know about the structure of matter we just visited as a result of the critical physics developments of the last century. These stupendous advances are essential to any more comprehensive theory of the world we might come up with and were also major achievements in themselves.
Starting in the next chapter, we’ll review those developments. Theories grow out of the observations and deficiencies of progenitor theories, and you can better appreciate the role of more recent advances by becoming acquainted with these remarkable earlier developments. Figure 34 indicates some of the ways in which the theories we will discuss interconnect. We’ll see how each of these theories was built using the lessons from older ones and how newer theories filled in gaps that were detected only after the older theories were complete.
We’ll begin with the two revolutionary ideas of the early twentieth century: relativity and quantum mechanics, through which we learned about the shape of the universe and the objects it contains, and the composition and structure of the atom. We’ll then introduce the Standard Model of particle physics, which was developed in the 1960s and 1970s to predict the interactions of the elementary particles we just encountered. We’ll also consider the most important principles and concepts in particle physics: symmetry, symmetry breaking, and scale dependence of physical quantities, through which we’ve learned a great deal about how matter’s most elementary components create the structures we see.
Figure 34. The fields of physics we will encounter and how they are connected.
However, despite