String Theory

 

Physics is mysterious. Every time we learn something new in physics, it just opens a gateway of confusion about the particular thing we have learned. But perhaps this is the beauty of physics. The current popular model of the universe approximates that the whole of the universe comprises 5% normal matter (visible matter), 25% dark matter, and 70% dark energy. The reality we see in our daily lives is just a tiny fraction of the entire universe. What is the true nature of the universe? It’s such a hard question to answer. The most concerning theories in physics that have a precise answer to a lot of natural phenomena are the Theory of Relativity (at the macroscopic level) and Quantum Physics (at the microscopic level). String theory is believed theoretically to be held up as the approximate theory of everything, which could unite "relativity theory" and "quantum physics" together.

String theory is a model that physicists use to describe how forces are usually conceptualized on a gigantic level, like how gravity could affect tiny objects like electrons and protons. String theory is the idea in theoretical physics that reality consists of infinitesimal vibrating strings, smaller than atoms, electrons, or quarks. According to this theory, as the strings vibrate, twist, and fold, they produce effects in many tiny dimensions that humans interpret as everything from particle physics to large-scale phenomena like gravity. String theory came into existence during the 1960s under the domain of nuclear physics; the concept was not discussed much back then as it lacked a lot of scientific and theoretical evidence.

In the general theory of relativity, Einstein defined gravity as something that warps the whole space-time fabric. The effect of gravity is not significant at the particle level, but its effect can be experienced on the scales of planets, galaxies, etc., basically at a macroscopic level. In quantum physics, gravitons are considered elementary particles that carry the field of gravitational interaction. When physicists and mathematicians did some work on gravitons, they observed that when two gravitons interact with each other, the energy obtained is infinite, which is impossible, which questions the theory itself and the missing puzzle of mathematics. One possible solution, which physicists and mathematicians borrowed from string theory in the 1970s, is to get rid of the idea of problematic, point-like graviton particles. Strings, and only strings, can collide and rebound cleanly without implying physically impossible infinities. Working with one-directional strings solved the problem of getting infinities, reducing the complexities behind mathematics.

String theory simplifies the idea of complex particles to just one element: tiny vibrating particles called strings that bend, twist, and ultimately, based on their alignment, transform into different particles. A string of a particular length striking a particular note might gain the properties of a photon; another string folded and vibrating with a different frequency could play the role of an electron; and so on. With this recent development of technology, we still don’t have enough scientific resources to observe how string theory works in reality, but string theory is true in various mathematical aspects. It attempts to answer a lot of questions about black hole physics, early developmental cosmology, nuclear physics, etc. and has simulated a lot of developments in pure mathematics. The first theory of string theory only incorporated the idea of bosons; hence, it was also referred to as bosonic string theory. It later emerged as a superstring theory, which mostly discussed the supersymmetry between bosons and fermions. Five consistent versions of superstring theory were developed before it was conjectured in the 1990s that they were all different limiting cases of a single theory in 11 dimensions known as M-theory. During the development of string theory, a new concept called anti-de Sitter/conformal field theory correspondence (AdS/CFT) was developed that relates string theory to other physical theories related to black holes, quantum gravity, condensed matter physics, etc.

There are only four dimensions known to us so far: length, breadth, height, and time. String theory, however, requires several more dimensions for mathematical consistency. In bosonic string theory, spacetime is 26-dimensional, while in superstring theory it is 10-dimensional, and in M-theory it is 11-dimensional. Earlier, around the 1970’s a concept called supergravity came into existence. It basically combined gravity with super-symmetry. Many physicists believed that by exploring 11-dimensional supergravity, it would be possible to find a unified description of the four fundamental forces of nature. But soon, it was found out that this model didn’t exhibit the property of chirality so this theory of supergravity was abandoned. Unlike supergravity theory, string theory was able to accommodate the chirality of the standard model, and it provided a theory of gravity consistent with quantum effects. In 1987, Eric Bergshoeff, Ergin Sezgin, and Paul Townsend showed that eleven-dimensional supergravity includes two-dimensional branes. They looked like a sheet or a membrane wrapped in between those 11 dimensions. In the absence of an understanding of the true meaning and structure of M-theory, Witten has suggested that the title should stand for "magic", "mystery", or "membrane" according to taste, and the true meaning of the title should be decided when a more fundamental formulation of the theory is known. 

String theory has not only been a keen subject of physics but it has also solved several mathematics problems. While string theory has not yet been fully developed or experimentally verified, it has provided insights and potential solutions to several long-standing mathematical problems in physics such as black hole entropy, the hierarchy problem, dualities(S and T duality), conformational field theory, etc. It's important to note that while string theory has offered potential solutions to these mathematical problems, the theory itself is still a subject of active research and debate, and many aspects of it remain speculative. String theory, despite its potential and intriguing aspects, has faced several criticisms over the years as it lacks experimental pieces of evidence.