String Theory
All Roads Lead to String Theory (Polchinski)
Prior to the First Superstring Revolution
Early History S-Matrix Theory
Regge Trajectory
Bosonic String Theory Worldsheet
Bosonic String Theory
String Perturbation Theory
Tachyon Condensation
Supersymmetric Revolution Supersymmetry
RNS Formalism
GS Formalism
Superstring Revolutions
First Superstring Revolution GSO Projection
Type II String Theory
Type IIB String Theory
Type IIA String Theory
Type I String Theory
Type H String Theory
Type HO String Theory
Type HE String Theory
Second Superstring Revolution T-Duality
Horava-Witten String Theory
Holographic Principle
N=4 Super-Yang-Mills Theory
BFSS Matrix Theory
Matrix String Theory
(2,0) Theory
Twistor String Theory
String Field Theory
Pure Spinor Formalism
After the Revolutions
Phenomenology String Theory Landscape
Minimal Supersymmetric Standard Model
String Phenomenology


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M-Theory is basically a strongly-coupled theory in 11 dimensions from which other String Theories can be derived from.

MotivationEdit this section

DualitiesEdit this section


Dualities between the 5 string theories

In the Second Superstring Revolution, it was realised that the ordinary 5 String Theoryies were connected by 2 dualities, namely T-Duality and S-Duality/. To be specific, these dualities can be portrayed on a map as you can see in the image here.

This means that some of these String Theoryies are in fact equivalent, so that there are really just 2 distinct String Theoryies, the Type IIA String Theory, and the Type HE String Theory.

At strong coupling (take the S-Dual), these become M-theory on a circle and the Horava-Witten String Theory, respectively. Various physicists, including Edward Witten, Ashok Sen, Nathan Seiberg, etc., postulated (see for example, [1], [2] [3]) that these two String Theories are actually a \new theory, which came to be known as M-Theory compactified on a circle, and a line segment, respectively. This is also when Michael Duff coined the term "The Theory Formerly known as Strings" [4].

BranesEdit this section

While this is certnaily not proclaimable to be a motivation for M-Theory, it is worth stating here that the fundamental objects of M-Theory are not Strings, but actually 2-Branes and 5-Branes. This was not such a great surprise, because D-Branes already existed in ordinary String Theories.

SupergravityEdit this section

Following the "Dualities" section, it is obvious that M-Theory needs to be an 11-Dimensional theory. Now, 11-Dimensional Supergravity is of course, an 11-Dimensional Theory. Various Supergravity Theoryies, including $ \mathcal{N} =2 $ Supergravity, for example, are low-energy limits of Superstring Theoryies. Thus, it was therefore perceived as possible, that 11-Dimensional $ \mathcal N=8 $Supergravity lies in the low-energy limit of M-Theory/ .

Non-Perturbative FormulationEdit this section

Main Article: BFSS Matrix Theory

The non-perturbative formulation of M-Theory is BFSS Matrix Theory [5].

ReferencesEdit this section

  1. Witten, Edward (1996). "Five-Branes and M-Theory on an orbifold". Nucl.Phys.B 463 (6): 382-397.
  2. Sen, Ashok (1996). "Unification of String Dualities". Nucl.Phys.Proc.Suppl. 58 (6): 5-19.
  3. Townsend, Paul (1996). "Brane Surgery". Nucl.Phys.Proc.Suppl. 58 (6): 163-175.
  4. Duff, Michael. "The Theory Formerly known as Strings".
  5. Susskind, Leonard; Banks, T., Fischler, W., Shenker, S.. M Theory as a Matrix model: A conjecture.
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