7/3/2014 String Theory For Dummies Cheat Sheet - For Dummies

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Cheat SheetString Theory For DummiesFrom String Theory For Dummies by Andrew ZimmermanJones [with Daniel Robbins]

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 (usually unobservable) dimensions to the universe must exist.

There are also other possible string theory features, depending on what theories

prove to have merit in the future. Possibilities include:

A landscape of string theory solutions, allowing for possible parallel universes.

The holographic principle, which states how information in a space can relate

to information on the surface of that space.

The anthropic principle, which states that scientists can use the fact that

humanity exists as an explanation for certain physical properties of our

universe.

Our universe could be stuck on a brane, allowing for new interpretations of

string theory.

Other principles or features, waiting to be discovered.

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Superpartners in String Theory

String theorys 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 Theorys Many Names

String theory has gone through many name changes over the years. This list

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, youll know theyre talking

about string theory!

Bosonic string theory

Superstring theory (or Supersymmetric string theory)

Type I, Type IIA, Type IIB, Heterotic string theories (Type HE, Type HO)

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M-theory

Matrix theory

Brane world scenarios

Randall-Sundrum models (or RS1 and RS2)

F-theory

Key Events in String Theory History

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 Venezianos 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 its 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.