# String Theory

## What is String Theory?

String theory is a framework in particle Physics that replaces the subatomic particles with one-dimensional objects called strings. The traditional way of modeling the subatomic particles is by approaching them as zero-dimensional point particles. The string theory attempts to merge quantum mechanics with the general theory of relativity given by Albert Einstein.

It is an attempt to incorporate all of the natural forces- gravity, electromagnetism, strong force, and weak force in a single quantum mechanical framework. String theory is a broad area of research but lacks experimental observations.

### String Theory Explained

The theory aims to explain the most fundamental theoretical conundrum which is how gravity works for tiny objects like photons and electrons. It wishes to harmonize the theory of general relativity which describes gravitation and applies to large-scale objects such as stars, galaxies, etc., and quantum mechanics, which deals with the other three natural forces acting upon atomic particles.

When two gravitons smash together, they get an infinite amount of energy packed in a small space. To explain this, in the 1970s the physicist decided to get rid of the point-like gravity particles and replace them with one-dimensional strings. Only strings can collide and rebound cleanly without any physically impossible infinities. The string was the thing that tamed the infinities that comes up in the calculations.

The string theory meaning, one-dimensional tiny vibrating strings twist and turn in a complicated manner that looks like particles to us. A string of particular length, striking a particular note, gains the properties of a photon. Another string folded and vibrating at a different frequency plays the role of a quark. This theory not only described gravity for subatomic particles but also proved attractive due to its potential to explain fundamental constants like an electron’s mass. The next step, according to the physicist, was to describe the folding and movements of the strings, and eventually, everything else would follow.

The initial simplicity turned out to be unexpected complexity because string mathematics didn’t work in the familiar four dimensions. In addition to the four dimensions, three spaces and one time, strings needed an additional six dimensions which were visible only to the strings. By the mid-1980s, theoretical physicists came up with five conflicting string theories to explain string physics.

### Superstring Theory

Superstring theory is one of the five conflicting string theories presented. Supersymmetric string theory accounts for both fermions and bosons, incorporating supersymmetry to model gravity. The five theories have been unified and are regarded as the different limits of a single theory called M-theory.

This unification was brought about when in 1995, Edward Witten proposed a new set of techniques that redefined the approximation equations that were used so far. This led to a new finding that the string theory has seven extra spatial dimensions, not six. It also found out that the string-like structures were also made up of membrane-like structures which were called branes. The newer techniques also established that the string theories developed were essential all the same and were given a new name, the M-theory.

M-theory is likely inspired by the higher-dimensional objects called membranes. Since the theory currently has no solid mathematical equation, the M has no official meaning but remains a placeholder. The existence of a fundamental theory gave physicists the required understanding and confidence to develop fundamental equations and mathematical techniques for the five versions of the string theories.

One of the breakthroughs came when string theory accurately predicted the black hole entropy in the year 1996. It did not just give a rough estimation but a spot-on counting of the black hole’s makeup.

### Conclusion

The string theory simplified states that, one-dimensional objects called strings that unify all four fundamental forces in nature. Proving string theory has been possible theoretically only and the experimental observations are yet to be recorded. String theory for mathematicians can be regarded as a productive research program based upon the mathematical merit of the theory alone.

1. What are the Five Superstring Theories?

Ans- The five consistent superstring theories are as follows:

• Type I String Theory: This is the only theory based upon the unoriented open and close strings while all other theories are based upon the oriented closed strings. The type I string consists of only one supersymmetry in the ten-dimensional sense.

• Type II A String Theory: These theories have two supersymmetries in the ten-dimensional space based upon oriented close strings. It is non-chiral i.e. parity-observing.

• Type II B String Theory: Type IIB also has two supersymmetries in its ten-dimensional space based upon oriented close strings. This theory is chiral i.e. parity-violating.

• Heterotic String Groups: This theory arises out of a hybrid between type I and bosonic string. The two types of Heterotic string groups HO(E8 x E8) and HE( SO(32)) differ in their ten-dimensional gauge groups.

2. What Do You Mean By Supersymmetry?

Ans- Supersymmetry is one of the most essential features of string theory. Supersymmetry is defined as a mathematical property that requires every known particle species to have a partner particle species. This partner species is called a superpartner.

This property is often referred to as superstring theory for string theory. Superstring string theory, also called supersymmetry string theory, is an attempt to define all the particles and forces of nature in one theory by modeling them as a one-dimensional object called strings. As of now, a superpartner is yet to be discovered but according to scientists, this is due to their weights. If we succeed in finding a superpartner, it would provide evidence that the unification approach of string theory is on the right track.