String theory
String theory, (or super-string theory when coupled with Supersymmetry), is a class of models in theoretical physics which replace zero-dimensional points (particles) in four-dimensional spacetime with one-dimensional strings in an eleven-dimensional spacetime as the fundamental building block of the universe. The elusive goal is to develop a set of equations that unify all known natural forces (gravitational, electromagnetic, weak, and strong), according to some preconceived philosophical beliefs about how they ought to be unified. Leading proponents of string theory have been Edward Witten of the Institute for Advanced Study and Brian Greene, the renowned author of The Elegant Universe.
String theory (and its alter ego M-theory) is currently the most viable candidate for a unified theory of physics which describes all forces of nature, encompassing the physics of gravity as well as quantum field theory. Major research centers include, for example, MIT, with five faculty members and numerous postdocs and graduate students working in this area.[1]
Princeton University researchers have found new mathematical evidence that some of string theory's predictions mesh closely with those of a well-respected body of physics called "gauge theory," which has been demonstrated to underlie the interactions among quarks and gluons, the vanishingly small objects that combine to form protons, neutrons and other, more exotic subatomic particles. The discovery, say the physicists, could open up a host of uses for string theory in attacking practical physics problems.[2]
History
String theory originated in 1970 when particle theorists realized that the theories developed in 1968 to describe the particle spectrum also describe the quantum mechanics of oscillating strings. Supersymmetry was introduced in 1971. The watershed year was 1984, when string theory became accepted by the mainstream physics community as an actual candidate theory that could unite quantum mechanics, particle physics and gravity.
Falsifiability
There is much debate on whether string theory is truly scientific. Under the positivist philosophy, models must be falsifiable (i.e. it must be possible to define an experiment which could contradict the theory) for them to qualify as science, and then they must survive these tests. In more general terms, a model should be able to make predictions about the world we observe. String theory has yet to yield a particular definitive test, or to produce any models that resemble any known particles or forces.
The discovery of dark energy in 1998 was a particularly damaging blow to string theory. It was just the sort of thing that string theorists hoped to explain, and yet string theory cannot explain it. As of today, string theory has attracted strong intetrest among theorists but has not suggested any critical experiments.
Some string theorists, such as Leonard Susskind, say that string theory may not be testable but may still provide insights on multiple universes. His recent book is The Cosmic Landscape: String Theory and the Illusion of Intelligent Design.
Further reading
- Smolin, Lee. The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next (2007)part 2 online
External links
- The Elegant Universe (Nova TV Series discussing Strings)
- "String Theory, Black Holes, and the Fundamental Laws of Nature" (Harvard@Home 2007)
- "The Official String Theory Web Site" by Patricia Schwarz (PhD Physics, Cal Tech)
- interviews with leaders in the field: John Schwarz; Sir Michael Atiyah; Ed Witten; Jim Gates; Eva Silverstein; Juan Maldacena; and Brian Greene