Loop quantum gravity - what is it? It is this question that we will consider in this article. To begin with, we will define its characteristics and factual information, and then we will get acquainted with its opponent - string theory, which we will consider in a general form for understanding and interrelation with loop quantum gravity.
Introduction
One of the theories describing quantum gravity is a set of data on loop gravity at the quantum level of the organization of the Universe. These theories are based on the concept of discreteness of both time and space on the Planck scale. Allows the hypothesis of a pulsating Universe to be realized.
Lee Smolin, T. Jacobson, K. Rovelli, and A. Ashtekar are the founders of the theory of loop quantum gravity. The beginning of its formation falls on the 80s. XX century. In accordance with the statements of this theory, "resources" - time and space - are systems of discrete fragments. They are described as cells the size of quanta, which are held together in a special way. However, reaching large sizes, we observe a smoothing of space-time, and it seems to us continuous.
Loop gravity and particles of the universe
One of the most striking "features" of the theory of loop quantum gravity is its natural ability to solve some problems in physics. It allows you to explain many issues related to the Standard Model of particle physics.
In 2005, an article by S. Bilson-Thompson was published, who proposed in it a model with a transformed Rishon Harari, which took the form of an extended ribbon object. The latter is called ribbon. The estimated potential suggests that it could explain the reason for the independent organization of all subcomponents. After all, it is this phenomenon that causes the color charge. The previous preon model for itself considered point particles as the basic element. The color charge was postulated. This model makes it possible to describe electric charges as a topological entity, which can arise in the case of ribbon twisting.
The second article by these co-authors, published in 2006, is a work in which L. Smolin and F. Markopolu also contributed. Scientists have put forward the assumption that all theories of quantum loop gravity, included in the class of loop ones, state that in them space and time are states excited by quantization. These states can play the role of preons, which lead to the emergence of the well-known standard model. It, in turn, causesemergence of properties of the theory.
The four scientists also suggested that the theory of quantum loop gravity is capable of reproducing the Standard Model. It interconnects the four fundamental forces in an automatic way. In this form, under the concept of "brad" (intertwined fibrous space-time), the concept of preons is meant here. It is the brains that make it possible to recreate the correct model from the representatives of the “first generation” of particles, which is based on fermions (quarks and leptons) with mostly correct ways of recreating the charge and parity of the fermions themselves.
Bilson-Thompson suggested that fermions from the fundamental "series" of the 2nd and 3rd generations can be represented as the same brads, but with a more complex structure. Fermions of the 1st generation are represented here by the simplest brains. However, it is important to know here that specific ideas about the complexity of their device have not yet been put forward. It is believed that the charges of color and electric types, as well as the "status" of parity of particles in the first generation, are formed in exactly the same way as in others. After these particles were discovered, many experiments were made to create effects on them by quantum fluctuations. The final results of the experiments showed that these particles are stable and do not decay.
Strip structure
Since here we are considering information about theories without using calculations, we can say that this is loop quantum gravity "forteapots." And she cannot do without describing the tape structures.
Entities in which matter is represented by the same "stuff" as space-time are a general descriptive representation of the model that Bilson-Thompson presented to us. These entities are the tape structures of the given descriptive characteristic. This model shows us how fermions are produced and how bosons are formed. However, it does not answer the question of how the Higgs boson can be obtained using branding.
L. Freidel, J. Kovalsky-Glikman and A. Starodubtsev in 2006 in one article suggested that the Wilson lines of gravitational fields can describe elementary particles. This implies that the properties possessed by the particles are able to correspond to the qualitative parameters of the Wilson loops. The latter, in turn, are the basic object of loop quantum gravity. These studies and calculations are also considered as an additional basis for theoretical support describing the Bilson-Thompson models.
Using the formalism of the spin foam model, which is directly related to the theory studied and analyzed in this article (T. P. K. G.), as well as basing on the initial series of principles of this theory of quantum loop gravity, makes it possible to reproduce some pieces of the Standard Model that could not be obtained before. These were photon particles, also gluons and gravitons.
There isalso the gelon model, in which brads are not considered due to their absence as such. But the model itself does not give an exact possibility to deny their existence. Its advantage is that we can describe the Higgs boson as a kind of composite system. This is explained by the presence of more complex internal structures in particles with a large mass value. Given the twisting of the brads, we may assume that this structure may be related to the mass creation mechanism. For example, the form of the Bilson-Thompson model, which describes the photon as a particle with zero mass, corresponds to the non-twisted brad state.
Understanding the Bilson-Thompson Approach
In lectures on quantum loop gravity, when describing the best approach to understanding the Bilson-Thompson model, it is mentioned that this description of the preon model of elementary particles allows one to characterize electrons as functions of a wave nature. The point is that the total number of quantum states possessed by spin foams with coherent phases can also be described using wave function terms. Currently, active work is underway aimed at unifying the theory of elementary particles and T. P. K. G.
Among the books on loop quantum gravity, you can find a lot of information, for example, in the works of O. Feirin about the paradoxes of the quantum world. Among other works, it is worth paying attention to articles by Lee Smolin.
Problems
The article, in a modified version from Bilson-Thompson, admits thatthe particle mass spectrum is an unsolved problem that his model cannot describe. Also, she does not solve issues related to spins, Cabibbo mixing. It requires a link to a more fundamental theory. Later versions of the article resort to describing the dynamics of the brads using the Pachner transition.
In the world of physics there is a constant confrontation: string theory vs the theory of loop quantum gravity. These are two fundamental works on which many famous scientists around the world have worked and are working.
String theory
Speaking about the theory of quantum loop gravity and string theory, it is important to understand that these are two completely different ways of understanding the structure of matter and energy in the Universe.
String theory is the "path of evolution" of physical science, which tries to study the dynamics of mutual actions not between point particles, but quantum strings. The material of the theory combines the idea of the mechanics of the quantum world and the theory of relativity. This is likely to help man build a future theory of quantum gravity. It is precisely because of the shape of the object of study that this theory tries to describe the foundations of the universe in a different way.
Unlike the theory of quantum loop gravity, string theory and its foundations are based on hypothetical data, suggesting that any elementary particle and all its interactions of a fundamental nature are the result of vibrations of quantum strings. These "elements" of the Universe have ultramicroscopic dimensions and on scales of the order of the Planck length are 10-35 m.
The data of this theory are mathematically meaningful quite accurately, but it has not yet been able to find actual confirmation in the field of experiments. String theory is associated with multiverses, which are the interpretation of information in an infinite number of worlds with different types and forms of development of absolutely everything.
Basis
Loop quantum gravity or string theory? This is a rather important question, which is difficult, but needs to be comprehended. This is especially important for physicists. To better understand string theory, it's important to know a few things.
String theory could provide us with a description of the transition and all the features of each fundamental particle, but this is only possible if we could also extrapolate strings to the low-energy field of physics. In such a case, all these particles would take the form of restrictions on the excitation spectrum in a non-local one-dimensional lens, of which there are an infinite number. The characteristic dimension of the strings is an extremely small value (about 10-33 m). In view of this, a person is not able to observe them in the course of experiments. An analogue of this phenomenon is the string vibration of musical instruments. The spectral data that "forms" a string may only be possible for a certain frequency. As the frequency increases, so does the energy (accumulated from vibrations). If we apply the formula E=mc2 to this statement, then we can create a description of the matter that makes up the Universe. The theory postulates that the particle mass dimensions that manifest themselves asvibrating strings are observed in the real world.
String physics leaves open the question of space-time dimensions. The absence of additional spatial dimensions in the macroscopic world is explained in two ways:
- Compactification of dimensions, which are twisted to sizes in which they will correspond to the order of the Planck length;
- The localization of the entire number of particles that form a multidimensional Universe on a four-dimensional "sheet of the World", which is described as a multiverse.
Quantization
This article discusses the concept of the theory of loop quantum gravity for dummies. This topic is extremely difficult to comprehend at the mathematical level. Here we consider a general representation based on a descriptive approach. Moreover, in relation to two "opposing" theories.
To understand string theory better, it is also important to know about the existence of the primary and secondary quantization approach.
Second quantization is based on the concepts of a string field, namely the functional for the space of loops, which is similar to quantum field theory. The formalisms of the primary approach, through mathematical methods, create a description of the motion of test strings in their external fields. This does not negatively affect the interaction between the strings, and also includes the phenomenon of string decay and unification. The primary approach is the link between string theories and conventional field theory claims onworld surface.
Supersymmetry
The most important and obligatory, as well as realistic "element" of string theory is supersymmetry. The general set of particles and interactions between them, which are observed at relatively low energies, is able to reproduce the structural component of the Standard Model in almost all form. Many properties of the Standard Model acquire elegant explanations in terms of superstring theory, which is also an important argument for the theory. However, there are no principles yet that could explain this or that limitation of string theories. These postulates should make it possible to obtain a form of the world similar to the standard model.
Properties
The most important properties of string theory are:
- The principles that determine the structure of the Universe are gravity and the mechanics of the quantum world. They are components that cannot be separated when creating a general theory. String theory implements this assumption.
- Studies of many developed concepts of the twentieth century, which allow us to understand the fundamental structure of the world, with all their many principles of operation and explanation, are combined and stem from string theory.
- String theory does not have free parameters that must be adjusted to ensure agreement, as is required in the Standard Model, for example.
In closing
In simple terms, quantum loop gravity is one way of perceiving reality thattries to describe the fundamental structure of the world at the level of elementary particles. It allows you to solve many problems of physics that affect the organization of matter, and also belongs to one of the leading theories in the world. Its main opponent is string theory, which is quite logical, given the many true statements of the latter. Both theories find their confirmation in various areas of elementary particle research, and attempts to combine the "quantum world" and gravity continue to this day.
