What is String Theory?

String theory is a theoretical framework that tries to tackle the problems of how and why the universe is like what it is now. In string theory, point-like particles are replaced by one-dimensional entities called strings.

String theory explains how these infinitesimal strings travel and interact with each other. In normal classical distance scales (larger than the string scale), a string is very similar to a normal particle with its charge, mass and other characteristics. The characteristics of strings are directly controlled by their vibrational states.

One of the vibrational conditions of the strings matches the states of the graviton. It is a quantum particle that regulates gravitational force. In this regard, string theory is also called the theory of quantum gravity.

String Theory as Theory of Everything

The unification of quantum physics and relativity has been the biggest hurdle since the dawn of modern physics. Many famous physicists regarded the String theory as the Theory of Everything.

It is considered the ultimate framework that could merge general relativity and quantum physics. We cannot go beyond without a unified theory, because both mechanics control almost everything modern physics deals with.

Quantum mechanics regulates all phenomena at the subatomic level, and general relativity controls gigantic interstellar activities in the universe.

The weird part is both of them do not merge well together. Flag bearers of the string theory propose that string theory could solve the disparities between the two physical realms.

String Theory Origin

In general relativity, gravity is a force that bends and warps space-time around supermassive bodies.

Even though gravity is one of the four fundamental forces in nature, it is very weak compared to the other three forces (electromagnetism, weak force and strong force).

So it can’t be observed or identified on the scale of subatomic particles. However, gravity is very dominant in long-distance scenarios. It controls the structure of the macro universe (galaxies, planets, stars, moons).

As far as quantum mechanics is concerned, gravity doesn’t have much effect. The probable nature of the quantum realm also poses a significant challenge for the induction of gravity in the quantum realm.

Generally, gravity does not act as a particle as its own. Even if a hypothetical model is introduced to explain the particle nature of a gravity particle, it violates fundamental energy laws.

In the 1970s, theorists tried to discard the self-destructive idea of point-like gravity particles. Instead of point particles, strings were introduced.

Even if strings collide, there will be no infinite energy problem. Strings can smoothly smash and rebound without implying any physically nonsense infinities.

Bosonic string theory was one of the earliest versions of string theory. It only included fundamental particles called bosons. It was then evolved into superstring theory. It predominantly introduced a relation called supersymmetry between bosons and fermions. Later, physicists developed five concrete versions.

Strings in String Theory

String theory was developed from the idea of remodelling point particles to one-dimensional entities called strings. The interplay of strings can simply be stated by generalising the theory of perturbation from quantum field theory.

Since string theory has no full non-perturbative explanation, most hypothetical and theoretical questions are still out of their domain.

A string can be open or closed. An open string has two open ends, and a closed string forms a closed loop. Strings have a tiny dimension, approximately the order of planck length10^-32 meters. This is the scale at which quantum gravity is believed to become significant.

In classical or general relativity scales, strings are not very different from zero-dimensional point particles. The vibrational nature of strings determines the characteristics of the particle.