# String theory

String theory is a theory of quantum and relativistic physics that aims to unify the forces of nature.

**theory**is a physical model that aims to unify the fundamental forces of nature . Simply put, this theory states that all kinds of interactions exist as a result of the oscillation of

**tiny one-**

**dimensional**

**strings .**

**String Theory for Dummies**

What we call string theory is nothing more than a large field of study in Physics that brings together the knowledge of **general relativity **with the foundations of **quantum ****mechanics** .

For area theorists, strings are the **smallest constituents of matter , with sizes compatible with the **Planck length (10 ^{-35} m). The way the strings oscillate is what shapes all the particles and forces that exist in the Universe.

Current **theory** about nature’s interactions is known as the **standard model** . The standard model is a theoretical construction product of the work of a large number of scientists over the last few centuries. However, among the forces existing in nature, the gravitational force cannot yet be explained in the same terms as the other forces. That’s why string theory came about: **to unify gravitational interaction with the quantum world** .

According to string theory, on very small scales, less than the size of the atomic nucleus , all matter can be described by **the vibrational modes** of small closed strings. Vibrational modes, also known as harmonics, arise when two or more waves meet at the same point, producing **standing waves** . Exactly the same way we produce musical notes when we play a guitar.

According to string theory, matter is made up of oscillating strings.

Briefly, we can say that **all particles** (quarks, electrons and even bosons) are **produced by different oscillations** of the strings. The reality, however, is that string theory is an **extremely complex mathematical theoretical object** , which emerged around 1960 and, since then, has undergone **changes and additions** in an attempt to satisfactorily explain the interactions of nature.

Unlike what human perception shows us, for Mathematics it is perfectly possible that there are **infinite dimensions perpendicular to each other** . It was for this reason that string theory became famous: its interpretations yielded results that suggested the existence of many dimensions beyond what we thought existed.

In 1919, the German physicist **Theodor Franz Eduard Kaluza** (1885-1945) suggested that our Universe could have more than **4 dimensions** (3 spatial dimensions and time). In addition, other geometric properties of space-time emerged, such as in 1926, when physicist **Oscar ****Klein** (1894-1977) proposed that the dimensions of the Universe could be **folded** over each other. Around 1970, physicists **Yoichiro ****Nambu** (1921-2015), **Holger ****Bech ****Nielsen** , and **Leonard ****Susskind** proposed that **vibrating strings** could be described by functionsmathematics already known to the physicists of the time, giving rise to string theory.

Initially, string theory had as main objective to explain aspects of the strong nuclear interaction, however, from 1974, the results of **John H. Schwartz** showed that such theory could be used to describe the gravitational force.

**String theory and dimensions**

The modern form of string theory emerged in 1984 by **Schwartz** and **Michael ****B. Green** . This new description, popularly called **superstring theory** , cosmic strings, or *superstrings* , brings string theory together with **supersymmetry** .

Supersymmetry is a principle of **quantum** physics that states that the particles that mediate forces, **bosons** , have **integer spin** , while **fermions** , the fundamental building blocks of matter, have **fractional spin** . According to the complex calculations of this theory, it would be necessary to have 9 spatial dimensions and a temporal dimension.

Currently, there are several studies based on superstring theory. In some of them, there are interpretations that demand the existence of **11 dimensions** , and some, a little more audacious, propose the existence of **27 dimensions** of space-time.

**String theory and multiverses**

While fascinating, the **idea of multiverses ****is unproven** . With the emergence of string theory and quantum mechanics, some questions led certain scientists to believe in the possibility of more **universes** , which, in some way, would be **related to the reality in which we live** .

In 1995, **Edward ****Witten** suggested that the various mathematical interpretations of string theory were actually the same thing, and thus gave rise to what we call **M-theory** , a unified theory. One of the assumptions that emerge from this theory is the possibility of “parallel” universes to ours. Altogether, there are different possibilities for what the multiverse would be:

- The Universe can be infinite, and therefore, taking into account the probabilities of an infinite Universe, it is possible that there are other planets exactly the same or similar to our Earth.
- The Universe is not finite, but it is so big that, in some regions, the physical parameters are different, despite obeying the same laws of Physics.
- According to the probabilities that govern quantum mechanics, there are precedents that support the existence of other universes coexisting with ours.
- The possibility of different universes, which are not connected to ours and which have physical laws that are completely different from the laws that govern our Universe.