Once Before Time - Martin Bojowald [42]
String theory now attempts to unify all forces and particles by reducing them to a single string-object. There are certainly many different ways to construct a musical instrument based on a vibrating string. Differences of tone color can be discerned even by inexpert ears. Similarly, different string theories, all having different excitations, can be constructed in physics. Masses or interactions of particles as predicted by differently constructed theories would be distinguishable with detectors of high-energy physics, such as the Large Hadron Collider (LHC) at CERN near Geneva, which was launched in 2008 (and relaunched in 2009). Often, differences can be so drastic that one would not even have to do an experiment to rule out the theory: The stability of atoms depends on the masses of protons and neutrons, sharply confining the set of theoretically possible values.
Music arises from the varying tones of different instruments. Theoretical physicists, more prosaically, are interested primarily in simplicity and efficiency in their descriptions of nature. A plethora of theories would be unwelcome; unity, as demonstrated by Maxwell’s exemplary electromagnetism, is preferred. String theory follows this ideal in an impressive way, not only in the potential power of its laws but also in their extremely elegant mathematical derivations. Here we do not have a whole orchestra of differently stretched strings, but only the soloist string theory itself. As it turned out after long years of research, all possible setups of fundamental strings are mathematically related. Various tone colors do not result in different physics; they are just different mathematical views of the same physics.
This statement is of unprecedented generality: All physical phenomena in gravity and particle physics could be described by a single theory without granting theorists any more freedom. Indeed, in the context of string theory one often uses the term “theory of everything” (TOE). Given sufficient control over the required mathematics, everything of interest could be computed in order to employ it subsequently for experimental tests of the theory. In principle, the theory can then be used to predict new phenomena, for instance at the time of the big bang.
In contrast to Maxwell’s theory, experimental tests (or just test possibilities) as well as technological applications are still to be developed for string theory. One of the reasons is the complexity of its underlying mathematics. On the one hand, this complexity is the basis for the theory’s uniqueness and its strong attraction for mathematicians and physicists alike; on the other hand, string theory appears as too grand a construct without (at least so far) being of much practical use. There are instead predictions of a rather worrisome nature concerning this theory’s usefulness. For starters, mathematical consistency requires that the theory use more than three spatial dimensions; most often it requires nine. Only three of them—height, depth, and width—are certainly visible, explainable by tiny extensions of the remaining six dimensions. As a water hose may appear as a one-dimensional line when seen from afar, a nine-dimensional space with six tiny dimensions would look like a three-dimensional one. Only at close range would one notice the extra dimensions. Since