# String theory examples

The **string theory** is a proposal that tries to generate an explanation of the formation of the universe. Scientists who study this theory want it to be accepted as “the theory of everything.”

**What is string theory?**

To understand a little what this proposal is about, we must first know the fundamentals that shaped this criterion.

In the study of matter, it has been established that a body is made up of **atoms** and that atoms are made up of **electrons, protons and neutrons** . It has also been known that the latter are made up of leptons, in addition, there are other much smaller elements that **can be in the form of filaments, threads or ropes** .

The hypothesis we are talking about suggests that these tiny particles vibrate, **generating subatomic structures such** as the electron, the boson, etc. String theory is based on these vibrations.

This scientific study proposes that there are 11 dimensions within space-time. It is in these dimensions that the “strings” vibrate in many ways. Each of these ways corresponds to a type of fundamental particle: an electron, a photon, a quark, or any other.

**Characteristics**

String theory arises in contradiction to point-particle theory, which is also very difficult to prove. There are currently five superstring theories.

Scientists propose that the “strings” measure approximately 10 ^ -35 meters, which can be perceived as a “Planck length”, which is a scale of length where space no longer has a standard geometry.

The complexity of this theory, and in turn, the controversy surrounding it, is that in order to be validated by the entire scientific community, it must be accepted that there are more dimensions. This means that six more are added to the four known dimensions.

But why has no one “seen” these dimensions despite the fact that some mathematical data give rise to their existence? Some answer this question with the argument that they are compact dimensions to each other, which can even be a single structure.

**String theory examples**

Next, you will see an example of the five proposals of this theory that exist to date:

**Type I string theory** . It is composed of strings and D-branes, both open and closed, that vibrate in ten-dimensional space-time.

**Type IIA string theory** . It consists of strings and closed-only D-branes, along with gravitines.

**Type IIB string theory** . It is similar to Type IIA, but it is non-chiral, that is, it preserves parity.

**Heterotic string theory SO (32). **It is also known as Heterotic-O and is based on the symmetry group O (32).

**E8xE8 heterotic string theory. **Also called Heterotic-E, and is based on the exceptional Lie group E8.