# A brief Concept of String theory and Superstring theory

We live in an astonishingly complex universe. Human beings are curious by nature, and again and again, we have asked ourselves — why are we here? Where we come from, and where the world comes from? **What is the world made of? **We are privileged to live in a time when we have come close to some of the answers. String theory is our most recent attempt to answer the last of these questions.

So what is the world made of? Ordinary matter is composed of atoms, which in turn are made up of only three basic components: electrons spinning around a nucleus composed of neutrons and protons. The electron is really a fundamental particle (it belongs to a family of particles called leptons); But neutrons and protons are made of smaller particles, called quarks. The quarks, as far as we know, are really elementary.

The sum of our current knowledge about the subatomic composition of the universe is known as the standard model of particle physics. This describes both the fundamental “bricks” of which the world is constituted and the forces through which these bricks interact. There are twelve basic “bricks”. Six of them are quarks — and they have curious names: up, down, charm, strange, bottom and top.(A proton, for example, consists of two quarks above and one below.) The other six are leptons — these include the electron and his two heaviest brothers, the muon and the three neutrinos as well tauón

There are four fundamental forces in the universe: gravity, electromagnetism, and weak and strong interactions. Each of these is produced by fundamental particles that act as carriers of force. The most familiar example is the photon , a particle of light, which is the mediator of electromagnetic forces. (This means that, for example, when a magnet attracts a nail, it is because both objects are exchanging photons.) The graviton is the particle associated with gravity. The strong interaction is produced by eight particles known as gluons. (I prefer to call “Pegamoides”!) The weak interaction finally is transmitted by three particles, bosons W +, W-, and Z.

The standard model describes the behavior of all these particles and forces with impeccable precision, but with a notable exception: gravity. For technical reasons, the force of gravity, the most familiar in our daily lives, has been very difficult to describe at the microscopic level. For many years this has been one of the most important problems in theoretical physics — formulating a quantum theory of gravity.

In recent decades, string theory has appeared as one of the most promising candidates for being a microscopic theory of gravity. And it is infinitely more ambitious: it pretends to be a complete, unified, and consistent description of the fundamental structure of our universe. (For this reason, he is occasionally given the arrogant title of ” theory of everything .”)

The essential idea behind string theory is as follows: all the various “fundamental” particles of the standard model are really just different manifestations of a basic object: a string. How can this be? Well, normally we would imagine that an electron, for example, is a “little point”, without any internal structure. A point can do nothing but move. But, if the string theory is correct, using a very powerful “microscope” we would realize that the electron is not really a point, but a small “loop”, a string. A rope can do something besides move — it can swing in different ways. If it oscillates in a certain way, then, from afar, unable to discern that it is really a string, we see an electron. But if it oscillates otherwise, then we see a photon, or a quark, or any other of the particles of the standard model. So that,If string theory is correct, the whole world is made of strings only!

Perhaps the foremost stunning issue regarding string theory is that such a simple idea works — it is possible to obtain (an extension of) the standard model (which has been experimentally verified with extraordinary precision) from a string theory . But it is important to clarify that, so far, there is no experimental evidence that string theory itself is the correct description of the world around us. This is principally because of the very fact that string theory remains within the development stage. We know some of its parts; but not yet its complete structure, and therefore we cannot yet make concrete predictions. In recent years there have been many extraordinarily important and encouraging advances, which have radically improved our understanding of the theory.

**Superstring theory**

The superstring theory is a theoretical diagram to explain all the particles and fundamental forces of nature in one theory that models the particles and physical fields as vibrations thin supersymmetric strings move in a space-time of more than 4 dimensions.

One of the motivations used by superstring theorists is that the scheme is one of the best candidate theories to formulate a quantum theory of gravity. The superstring theory may be a shorthand of the supersymmetric string theory as a result of, unlike bosonic string theory, this is the version of string theory that incorporates fermions and supersymmetry.

The superstring theory comprises five theories or alternative formulations of string theories, combined in which supersymmetry requirements have been introduced

The fundamental idea is that the reality is strings that vibrate in resonance at a frequency of the Planck length and where the graviton would be a spin spin 2 and null mass.

Recently it has been possible to prove that several of these formulations are equivalent and after all of them there could be a unified theory or theory of everything . The five existing theories are no more than individual cases limit of this unified theory, provisionally known as M – theory . This M theory attempts to explain all existing subatomic particles at the same time and unify the four fundamental forces of nature. It defines the universe formed by a multitude of vibrant strings, since it is a version of string theory that incorporates fermions and supersymmetry.

The main problem of current physics is to be able to incorporate the force of gravity as explained by the theory of general relativity to the rest of the already unified physical forces. The superstring theory would be a method of unifying these theories. The theory is far from being finished and profiled, since there are many undefined variables, so there are several versions of it.

The underlying problem in theoretical physics is to harmonize the theory of general relativity, where gravitation and large-scale structures ( stars , galaxies , clusters ) are described, with quantum mechanics , where the other three fundamental forces that are described are described. They act at the atomic level.

The development of quantum field theory of an invariable force results in infinite (and useful) probabilities.Physicists have developed mathematical techniques of renormalization to eliminate those infinities of 3 of the four elementary forces – electromagnetism, sturdy nuclear and weak nuclear – however not of gravit. The development of the quantum theory of gravity must, therefore, come in a different way than those used for other forces.

The basic idea is that the fundamental constituents of reality are strings of a Planck length (close to 10-35 m) that vibrate at resonance frequencies . Every string, in theory, has a unique harmony, or resonance. Different harmonies determine different fundamental forces. The tension in the rope is of the order of Planck’s forces (1044 N). the graviton(name proposed for the particle that carries the gravitational force), for example, is predicted by the theory that it is a string with zero amplitude. Another key idea of the theory is that measurable differences between strings that recapitulate small dimensions in themselves and many that move in large dimensions cannot be detected. The singularities are avoided because the observable consequences of the ” great collapse ” never reach zero size. In fact the universe can start a small “big collapse” of processes, string theory says that the universe can never be smaller than the size of a string, at that point it could begin to expand.

Although the evident physical universe has 3 abstraction dimensions and a temporal dimension, nothing prohibits a theory from describing a universe with quite four dimensions, particularly if there’s a mechanism of “apparent unobservability” of the extra dimensions. That is the case of string theory and superstring theory that postulate compactified additional dimensions and that would only be observable in physical phenomena that involve very high energies. In the case of superstring theory, the consistency of the theory itself requires a space-time of 10,11 or 26 dimensions. The conflict between observation and theory is resolved by compactingthe dimensions that cannot be observed in the usual energy range. In fact, superstring theory is not the first physical theory that proposes extra spatial dimensions; At the beginning of the century, a geometric theory of the electromagnetic and gravitational field known as the Kaluza-Klein theory was proposed that postulated a 5-dimensional space-time .

The human mind has difficulty visualizing larger dimensions because it is only possible to move in 3 spatial dimensions. One way to deal with this limitation is not trying to visualize larger dimensions at all but simply thinking, when making equations that describe a phenomenon, that more equations should be made than usual. This opens up the questions that these ‘extra numbers’ can be investigated directly in any experiment (where results in 1,2,+1 dimensions would be shown to human scientists). Thus, in turn, the question arises as to whether these types of models that are investigated in this abstract modeling (and potentially impossible experimental devices) can be considered ‘scientific’. The six-dimensional shapes of Calabi-Yau they can have additional dimensions by superstring theory.

One theory that generalizes it is the brane theory , where the strings are replaced by elementary constituents of the “membrane” type, hence their name. The existence of 10 dimensions is mathematically necessary to avoid the presence of tachyons , particles faster than light, and “ghosts”, particles with a probability of null existence.

## Number of superstring theories

Theoretical physicists were disturbed by the existence of five different string theories. This happened under the so-called second superstring revolution in the 1990s where the 5 string theories were discovered, being different borderline cases of a single theory: the M theory

String Theory | ||
---|---|---|

Types | Spatial Dimensions | Details |

Bosonica | 26 | Only bosons, not fermions , means only forces, not matter, with open and closed strings; major defect: a particle with imaginary mass called tachyon |

I | 10 | Supersymmetry between force and matter, with open and closed strings, free of tachyons, symmetry group SO (32) |

IIA | 10 | Supersymmetry between force and matter, only with closed strings, free of tachyons, fermions without mass that rotate in both directions |

IIB | 10 | Supersymmetry between force and matter, only with closed strings, free of tachyons. mass-free fermions that rotate in only one direction |

HO | 10 | Supersymmetry between force and matter, only with closed strings, free of tachyons, heterotic , differ between ropes of right and left movement, symmetry group is SO (32) |

HE | 10 | Supersymmetry between force and matter, only with closed strings, free of tachyons, heterotic , differ between ropes of right and left movement, symmetry group E _{8} × E _{8} |

The five consistent superstring theories are:

The string theory Type I has a ten-dimensional supersymmetry in sense (16 supercharges). This theory is special in the sense that it is based on an open and closed orientation , while the rest are based on ropes with closed orientations.

The string theory type II has two supersymmetries in direction 10 dimensions (32 supercharges). There are in fact two types of Type II ropes called type IIA and IIB. They differ mainly in the fact that theory IIA is non- chiral (conserving parity), while theory IIB is chiral (violating parity).

The heterotic string theory is predicated on a peculiar hybrid of a sort I particle and a bosonic string. There square measure a pair of forms of heterotic strings that take issue in their ten-dimensional gauge cluster : the heterotic string E eight × E eight and therefore the thus (32).(The heterotic name SO (32) is a bit inaccurate in the SO (32) of the Lie Group , the theories are a Spin (32)/ Z 2 ratio that is not equivalent to SO (32).)

The chiral gauge theories may be inconsistent in their anomalies. This occurs when a loop of the Feynman Diagram causes a break in the quantum mechanics of gauge symmetry. Nullifying anomalies is limited to possible string theories.

**Integrating general relativity with quantum mechanics**

The general relativity usually refers to situations involving large massive objects in distant regions of space-time where quantum mechanics is reserved for scenarios atomic scale (small regions of space-time). The two are very hard used together, and the most common case where their study is combined is black holes. Having “peaks of density” or maximum amounts of matter possible in space, and a very small area, the two must be used in synchrony to predict conditions in certain places; Even when used together, the equations crumble and provide impossible answers, such as imaginary distances and less than one dimension.

The biggest problem with its congruence is that, at dimensions smaller than those of Planck, general relativity predicts a certainty, a fluid surface, while quantum mechanics predicts a probability, a deformed surface; They are not compatible. Superstring theory solves this demand, commutation the classical plan of purpose particles with loops. These loops would have an average diameter of a Planck length, with extremely small variations, which completely ignores the predictions of quantum mechanics at dimensions smaller than those of Planck, and that for their study does not take into account those lengths.

**Falsificationism and superstring theory**

Many scientists have declared their concern that String Theory is not falsifiable and that it also lacks predictive power, and as such, and following the theses of the philosopher of science Karl Popper , String Theory would be equivalent to a pseudoscience .

As currently understood, it has a gigantic number of possible solutions.

The philosopher of science Mario Bunge recently stated:

Consistency, sophistication and sweetness area unit ne’er enough in research.

String theory is suspicious (of pseudoscience). It seems scientific because it addresses an open problem that is both important and difficult, to build a quantum theory of gravitation . But the theory postulates that physical space has six or seven dimensions, instead of three, simply to ensure mathematical consistency. Since these extra dimensions are unobservable, and since the theory has resisted experimental confirmation for more than three decades, it seems like science fiction, or at least, failed science.

The particle physics is inflated with sophisticated mathematical theories postulate foreign entities that do not interact appreciably, or nothing at all, with ordinary matter, and therefore, are safe to be undetectable. Since these theories are in discrepancy with the whole of Physics, and violate the requirement of falsificationism, they can be described as pseudoscientific, even if they have been swarming a quarter of a century and continue to be published in the most prestigious scientific journals.

The main criticism of the String Theory is that it is, fundamentally, impossible to falsify, due to its intrinsic nature: it has sufficient mathematical flexibility so that its parameters can be molded to fit with any type of observed reality . To illustrate the confusing situation that dominates this field of research, it is enough to cite the recent Bogdanov scandal , two brothers who managed to publish absurd and meaningless theories in prestigious scientific journals. The German physicist Max Niedermaier concluded that it was pseudoscience, written with a dense technical jargon, to avoid the system of peer review of theoretical physics. According to the physicist-mathematician John Baez, his work ” is a hodgepodge of seemingly plausible phrases that contain the correct technical words in the approximately correct order. But there is no logic or cohesion in what they write .” According to physicist Peter Woit in the prestigious magazine Nature :” The Bogdanoffs’ work is significantly more incoherent than anything else published. But the growing low level of coherence across the field allowed them to think they had done something sensible and publish it.