Why M-theory is the main candidate for the Theory of Everything

The mother of all string theories has passed the test, which so far none of the theories of quantum gravity has been able to pass.

M-theory brings together all five non-contradictory versions of string theory (as well as a description of particles called supergravity ) into a single mathematical structure. In different physical conditions, it looks like each of these theories.

It's hard to be the “theory of everything.” TV has a difficult task - to shove gravity into the quantum laws of nature in such a way that on large scales gravity looks like the curvature of the space-time fabric that Albert Einstein described in his general theory of relativity. Somehow, the curvature of space-time arises as a common denominator of quantizing units of gravitational energy - particles known as gravitons . But naive attempts to calculate the interaction of gravitons lead to meaningless infinities, which suggests the need for a deeper understanding of gravity.

String theory, or, technically more correctly, m-theory, is often described as the leading candidate for TV in our Universe. But she has no empirical evidence, as there is no other alternative idea about how gravity can combine with all other fundamental forces. Why do m-theories give an advantage over others?

This theory, as is well known, claims that gravitons, like electrons, photons and everything else, are not point particles, but elusively tiny rezinochkami energy, or "strings", vibrating in different ways. Interest in string theory sharply increased in the mid-1980s, when physicists realized that it gave a mathematically consistent description of quantum gravity. But five well-known versions of the theory were “perturbative”, that is, they stopped working under certain conditions. Theorists could calculate what happens when two graviton strings collide at high energies, but turned out to be powerless before the fusion of gravitons so extreme that it creates a black hole.
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Then in 1995, physicist Edward Whitten discovered the mother of all string theories. He found various indications that string perturbation theories are combined into one coherent non-perturbation theory, which he called "M-theory". M-theory in different physical contexts looks like one of string theories, but it has no restrictions on conditions — and this is an important requirement for the theory of everything. Or at least that's what the Whitten calculations said. “Whitten could have given his arguments without writing down the equations of M-theory, which in itself is impressive, but leaves many unanswered questions,” explained David Simmons-Duffin, a theoretical physicist at the California Institute of Technology.

Another explosion of research happened two years later, when physicist Juan Maldacena discovered AdS / CFT compliance: the implementation of a holographic principle that combines gravity in a region of spacetime known as “anti-de Sitter space” (AdS), with a quantum particle description ( conformal field theory, CFT), moving along the boundary of this region. AdS / CFT gives a complete definition of the M-theory for a special case of the AdS space-time geometry, filled with negative energy, which causes it to bend differently than our Universe. For such fictional worlds, physicists can describe processes at all energies, including the formation and evaporation of black holes. The 16,000 papers that have been mentioned to Maldacen over the past 20 years are mainly trying to do this calculation in order to better understand AdS / CFT and quantum gravity.

This simple sequence of events led most experts to conclude that M-theory is the leading candidate for TV, even though its exact definition in the Universe, similar to ours, remains unknown. Whether the theory is correct is a separate question. The strings offered by her — like the extra convoluted dimensions in which these strings should vibrate — are 10 million billion times smaller than the resolution of such experiments as the Large Hadron Collider. And some macroscopic features of the theory that could have already been seen, like cosmic strings or supersymmetry, were not found.

Other TV versions have many different technical problems, and none of them have yet repeated the mathematical consistency of string theory, such as the calculation of, for example, a process such as the scattering of gravitons on top of each other. According to Simmons-Duffin, none of the rivals could complete the first step, or the first “quantum correction” of this calculation. One philosopher even claimed that the status of string theory, as the only known non-contradictory theory, is considered proof of its truth.

Among distant rivals, there are asymptotically safe gravity , the E8 theory [also known as the “ exceptionally simple theory of everything ”], non-commutative geometry, and causal fermion systems . Asymptotically safe gravity, for example, suggests that the force of gravity can change when moving to smaller scales so as to avoid infinite calculations. But so far no one has managed to get this trick to work.