String Theory: Putting the Universe in a String
By Tannishtha Bag and Sunam Biswas
As we go along with the scientifically accepted Big Bang theory stating that our universe originated from the singularity, the tendency to unify various theories and models explaining disparate phenomena which arose around the nineteenth and twentieth century seems very likely.
Presently, modern physics rests upon the theories of General Relativity (focuses on gravity for understanding the universe in regions of both large scale and high mass: stars, galaxies, clusters of galaxies) and Quantum Mechanics (concerning with the three non-gravitational forces, small scale, and low mass: sub-atomic particles, atoms, molecules).
Though thoroughly proven in their separate fields of relevance, none of the two justify phenomena at the Planck scale requiring a single unified force. Thus, a hypothetical framework, capable of fusing these incongruous theories and thus unveiling deeper realities of the universe — ’Theory of Everything’ was assumed to exist.
String Theory has been one of the contenders in this conquest of stringing the universe together in a single theoretical model.
Since the early 20th century, Nature’s fundamental constituents have been considered to be indivisible, dot-like particles — electrons, quarks, and neutrinos — bereft of internal machinery. String theory challenges this by proposing that at the heart of every particle is a tiny, vibrating string-like filament. It claims that the differences between one particle and another — their masses, electric charges, spin and nuclear properties — all arise from differences in how their internal strings vibrate and twist themselves in various complex ways.
Switching from dimensionless particles to unidimensional strings also adds extra dimensions to our currently approved 3-dimensional space model.
Delightfully, the mathematics revealed that one of these notes had properties precisely matching those of the ‘Graviton’, a hypothetical particle that, according to quantum physics, should carry the force of gravity from one location to another. Researchers have used results from anti-de Sitter/conformal field theory (AdS/CFT) correspondence in the formulation of string theory to answer many fundamental questions in quantum field theory, condensed matter physics, cosmology (specifically attempting to explain events just after the big bang) as well as quantum gravity (explains Black hole information paradox to some extent). It has also sparked the idea of the possibility of a multiverse (Each having a separate seemingly consistent vacuum model and cosmological constant)
While this theory seemed to lead the scientists closer to reality, several variables popped into the picture. Current comprehensions of String theory devices an enormous number of vacuum states (corresponding to the various shapes suggested for the extra dimensions of space), estimated to be around 10⁵⁰⁰, might be sufficiently diverse to accommodate almost any phenomenon that might be observed at low energies, and thus destroys the hope of using the theory to predict anything. None of the confirmed vacuum models in the string theory landscape is known to support a metastable, positive cosmological Constant on contrary to some popular dark energy models. In string theory, one must typically specify a fixed reference geometry for spacetime, and all other possible geometries described as perturbations of this fixed one. This contradicts the fundamental property of Einstein’s theory of relativity being Background independent.
Lack of technologies to function high energy experiments required for probing this infinitesimally small structure and several inconsistencies as compared to the presently approved theories have left String theory unresolved. An unresolved mystery that still holds some hopes to give new definitions to the universe or many other universes that might be existing out there.
References
https://en.wikipedia.org/wiki/Theory_of_everything
https://www.space.com/17594-string-theory.html
https://www.newscientist.com/article/dn16950-string-theory-a-beginners-guide/
https://www.smithsonianmag.com/science-nature/string-theory-about-unravel-18 0953637/
https://www.britannica.com/science/string-theory https://www.space.com/black-hole-information-paradox-mystery.html
https://phys.org/news/2020-07-anti-de-sitterconformal-field-theory-cosmology.html
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