String Theory For Dummies
String theory, often called the “theory of everything,” is a relatively young science that includes such unusual concepts as superstrings, branes, and extra dimensions. Scientists are hopeful that string theory will unlock one of the biggest mysteries of the universe, namely how gravity and quantum physics fit together.

String theory features

String theory is a work in progress, so trying to pin down exactly what the science is, or what its fundamental elements are, can be kind of tricky. The key string theory features include:

• All objects in our universe are composed of vibrating filaments (strings) and membranes (branes) of energy.

• String theory attempts to reconcile general relativity (gravity) with quantum physics.

• A new connection (called supersymmetry) exists between two fundamentally different types of particles, bosons and fermions.

• Several extra dimensions to the universe must exist.

Superpartners in string theory

String theory’s concept of supersymmetry is a fancy way of saying that each particle has a related particle called a superpartner. Keeping track of the names of these superpartners can be tricky, so here are the rules in a nutshell.

• The superpartner of a fermion begins with an s, so the superpartner of an electron is the selectron and the superpartner of the quark is the squark.

• The superpartner of a boson ends in ino, so the superpartner of a photon is the photino and of the graviton is the gravitino.

Use the following table to see some examples of the superpartner names.

Some Superpartner Names
Standard Particle Superpartner
Higgs boson Higgsino
Neutrino Sneutrino
Lepton Slepton
Z boson Zino
W boson Wino
Gluon Gluino
Muon Smuon
Top quark Stop squark

Keeping track of string theory's many names

String theory has gone through many name changes over the years. The list below provides an at-a-glance look at some of the major names for different types of string theory.

Some versions have more specific variations, which are shown as subentries. (These different variants are related in complex ways and sometimes overlap, so this breakdown into subentries is based on the order in which the theories developed.) Now, if you hear these names, you’ll know they’re talking about string theory!

• Bosonic string theory

• Superstring theory (or Supersymmetric string theory)

• Type I, Type IIA, Type IIB, Heterotic string theories

• M-theory

• Brane world scenarios

• Randall-Sundrum models

• F-theory

Key events in string theory

Although string theory is a young science, it has had many notable achievements. What follows are some landmark events in the history of string theory.

1968: Gabriele Veneziano originally proposes the dual resonance model.

1970: String theory is created when physicists interpret Veneziano’s model as describing a universe of vibrating strings.

1971: Supersymmetry is incorporated, creating superstring theory.

1974: String theories are shown to require extra dimensions. An object similar to the graviton is found in superstring theories.

1984: The first superstring revolution begins when it’s shown that anomalies are absent in superstring theory.

1985: Heterotic string theory is developed. Calabi-Yau manifolds are shown to compactify the extra dimensions.

1995: Edward Witten proposes M-theory as unification of superstring theories, starting the second superstring revolution. Joe Polchinski shows branes are necessarily included in string theory.

1996: String theory is used to analyze black hole thermodynamics, matching earlier predictions from other methods.

1997: Juan Maldacena shows how it is possible to realize the holographic principle in string theory, which relates theories with gravity and theories without gravity living in one dimension less