STRING THEORY

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What is the String Theory?

To put it simply, the theory states that the universe is built by vibrating strings that are smaller than even the smallest subatomic particles. It essentially aims to provide an explanation for the nature of the universe.

Also known as The Theory Of Quantum Gravity, the String Theory relates quantum physics and relativity. Quantum mechanics regulates astrophysical phenomena at the subatomic level whereas general relativity attempts to explain the interstellar workings of the universe. Therefore, the two theories tend to clash in their understandings. However, multiple scientists believe that the String Theory can help unite the two in order to solve certain disparities.

Since theorists believe that point-like particles cannot explain the workings of gravity, strings are introduced because if they collide, there will be no infinite energy problem.

These strings are One dimensional entities that are yet to be supported by mathematical solutions. Theory states that the strings can either be open or closed with their tiny dimension being the size of a Planck length (10^-32). At this size, the vibrational nature of the strings is what determines the characteristics of the particles.

DIFFERENT VERSIONS OF THE STRING THEORY

1. Bosonic String Theory
It was the first concrete version of the string theory and it only concerned bosons, which are a type of particle that transfers forces between fermions or matter. However, in order to negotiate the limits of the theory, Superstring theory was introduced.
2. Superstring Theory

It consists of multiple types:
- Type I has both closed and open strings
- Type IIA has closed strings
- Type IIB has closed strings
- Heterotic String Theory (SO(32)) has closed strings
- Heterotic String Theory (E8 x E8) has closed strings
These variations are due to different sets of strings.

3. M Theory

This theory, suggested by Edward Witten, states that all string theory versions are categories of one super theory which is based on 11 dimensions.

String theory needs to incorporate more space-time dimensions than the 3D and 4D models of space time that we have. Therefore, there are 26 dimensions in Bosonic String and 10 dimensions in Superstring Theory. While, the M theory has 11.

A crucial characteristic of string theory is called Supersymmetry. It is a mathematical property that requires every particle species to have a (partner known as superpartner). However, there are no superpartner particles that have yet been detected through experimental observation. Researchers defend this by elaborating that this is a result of their weight being heavier than those of their counterparts. Thus, they require a machine as powerful as the Large Hadron Collider at CERN to produce them.

LIMITATIONS

It must be noted that the string theory struggles to account for quantum physics and general relativity. It further introduces the concept of the multiverse where there may potentially be several universes, each tangled to create the supported particle physics. Additionally, string theory struggles to explain the existence of dark energy and dark matter while it lacks empirical evidence.