M Theory | Towards a theory of everything?

Modern physics relies on two fundamental frameworks: general relativity, which describes gravity through curved spacetime, and the standard model of particles, which unifies other interactions using quantum fields. Both theories use fields as their core concept but operate in incompatible mathematical languages.

In the 1970s, theoretical physicists explored supergravity as a promising extension of general relativity. This framework emerged from considering spacetime symmetries beyond the four conventional ones: translations, rotations, time evolution, and reference frame changes.

Supergravity theory predicts extended objects called branes (short for membranes)—generalizations of black holes with multiple dimensions. String theory reveals these as fundamental ingredients of reality alongside strings.

In the 1980s, physicists discovered superstring theory, a revolutionary model combining string concepts with supersymmetry. This framework emerged as the first consistent quantum theory of gravity.

Taking string theory’s restrictions into account, researchers discovered superstring theory allows exactly five possible consistent universes, each with distinct properties determining which types of strings and interactions exist.

Researchers studying supergravity discovered an unexpected property: the theory accepts a maximum of eleven dimensions—one more than string theory’s required ten dimensions. This mathematical constraint pointed toward deeper unification.

By the early 1990s, Edward Witten and other researchers gradually discovered a network of subtle mathematical connections called dualities relating all string theories and eleven-dimensional supergravity to each other.

Using string theory dualities discovered in the 1990s, physicists could calculate black hole entropy microscopically for the first time, providing a concrete success for string theory and M Theory.

Research around string theory dualities led to discovering the AdS/CFT correspondence, a profound relationship suggesting certain universes can be completely described as holograms of their surfaces.

In 1995, Edward Witten proposed M Theory as a single fundamental framework of which the five string theories and eleven-dimensional supergravity are merely approximations—partial descriptions like half-drawn maps of an unknown landscape.

Despite M Theory’s mathematical elegance, physicists face profound challenges experimentally validating quantum gravity theories, including M Theory, string theory, and loop quantum gravity.