Loop quantum gravity - what is it? This is the question we will consider in this article. To begin with, we will determine its characteristics and factual information, and then we will familiarize ourselves with its opponent - string theory, which we will consider in a general way for understanding and interconnection 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 organization of the universe. These theories are based on the concept of discreteness, both time and space, on the Planck scale. Allows the hypothesis of a pulsating universe to be realized.
Lee Smolin, T. Jacobson, C. Rovelli, and A. Ashtekar are the founders of the theory of loop quantum gravity. The beginning of its formation falls on the 80s. Twentieth century. According to 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 fastened 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 of physics. It allows us to explain many issues related to the standard model of elementary particle physics.
In 2005, an article was published by S. Bilson-Thompson, who proposed in it a model with a transformed Harari rishon, which took the form of an extended tape object. The latter is called the 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 charge of color succumbed to the postulation. This model allows us to describe electric charges as a topological entity, which can occur in the case of twisting of ribbons.
The second article of these co-authors, published in 2006, is a work in which L. Smolin and F. Markopolu also participated. Scientists have put forward the assumption that all theories of quantum loop gravity included in the loop class claim: 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, determines the emergence of the properties of a theory.
Four scientists have also suggested that the theory of quantum loop gravity is capable of reproducing the Standard Model. It automatically interconnects the four fundamental forces. In this form, by the concept of "brad" (interwoven fibrous space-time), here is meant the concept of preons. It is the brads 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 predominantly correct ways to recreate the charge and parity of the fermions themselves.
Bilson-Thompson suggested that fermions from the fundamental “row” of the 2nd and 3rd generations could be represented in the form of the same brads, but with a more complex structure. Fermions of the 1st generation are represented here by the simplest brands. However, it is important to know 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 carried out to create effects of quantum fluctuations on them. The final results of the experiments showed that these particles are stable and do not disintegrate.
Tape structure
Since here we consider information on theories without using calculations, we can say that this is loop quantum gravity “for dummies”. And she can not do without a description of the tape structures.
Entities in which matter is represented by the same “substance” as space-time are a general descriptive representation of the model that Bilson-Thompson presented to us. These entities are the tape structures of this descriptive characteristic. This model shows us how fermions are produced and how bosons are formed. However, it does not answer the question of how to obtain the Higgs boson using branding.
In 2006, L. Freidel, J. Kowalski-Glikman, and A. Starodubtsev suggested in one article that elementary particles can be described by Wilson lines of gravitational fields. This implies that the properties possessed by the particles are able to correspond to the quality parameters of Wilson loops. The latter, in turn, are the basic object of loop quantum gravity. Still these studies and calculations are considered as an additional base 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 based on the initial number of principles of this theory of quantum loop gravity, makes it possible to reproduce some particles of the Standard Model, which could not get earlier. These were photonic particles, also gluons and gravitons.
There is also a gelon model in which brads are not considered due to their absence as such. But the model itself does not provide an accurate opportunity 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 particles with a higher mass value of more complex internal structures. Given the twisting of the brads, we have the right to assume that this structure may relate to the mechanism of mass creation. For example, the type of the Bilson-Thompson model, describing a photon as a particle with zero mass, corresponds to the state of the Brad in the not twisted 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 us to characterize electrons as functions of a wave nature. The fact is that the total number of quantum states that spin foams with coherent phases possess can also be described using the terms of the wave function. Active work is underway to unify the theory of elementary particles and T.P.K.G.
Among books on loop quantum gravity, you can find a lot of information, for example, in the works of O. Feirin on the paradoxes of the quantum world. Among other works, attention should be paid to Lee Smolin's articles.
Issue
An article in a modified version from Bilson-Thompson admits that the particle mass spectrum is an unresolved issue that his model cannot describe. Also, she does not solve issues related to backs, mixing Cabibbo. It requires attachment to a more fundamental theory. Later versions of the article resort to the description of the dynamics of the brads using the Pachner transition.
In the world of physics there is a constant confrontation: string theory vs theory of loop quantum gravity. These are two fundamental works on which many famous scientists of the whole 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 “evolutionary path” of physical science, which tries to study the dynamics of mutual actions, not between point particles, but with quantum strings. The theory material combines the idea of the mechanics of the quantum world and the theory of relativity. This will probably help a person build a future theory of quantum gravity. It is in view of the shape of the object of study that this theory tries in another way to describe the foundations of the Universe.
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 fundamental interactions are the result of quantum string vibrations. These "elements" of the Universe have ultramicroscopic dimensions and on a scale of the order of Planck's 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 evidence 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.
The basis
Loop quantum gravity or string theory? This is a fairly important issue that is difficult, but needs to be comprehended. This is especially important for physicists. To better understand string theory, it will be important to know something.
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 into the low-energy field of physics. In such a case, all of these particles would take the form of restrictions on the excitation spectrum in a nonlocal one-dimensional lens, of which there are an infinite number. The characteristic dimension of the strings is an extremely small value (of the order of 10 -33 m). In view of this, a person is not able to observe them during experiments. An analogue of this phenomenon is the string oscillation of musical instruments. The spectral data that "form" the string can only be possible for a certain frequency. As the frequency increases, so does energy (accumulated from vibrations). If we apply the formula E = mc 2 to this statement, we can create a description of the matter of which the Universe consists. The theory postulates that the particle mass sizes, which manifest themselves in the form of an oscillating string, are observed in the real world.
String physics leaves open the question of the dimensions of space-time. The absence of additional spatial dimensions in the macroscopic world is explained in two ways:
- The compactification of measurements that are twisted to sizes in which they will correspond to the order of the Planck length;
- The localization of the total number of particles that form the multidimensional Universe on the four-dimensional “sheet of the World”, which is described as a multiverse.
Quantization
This article discusses the concept of loop quantum gravity theory for dummies. This topic is extremely difficult to comprehend at the mathematical level. Here we consider a general idea based on a descriptive approach. Moreover, in relation to the two "opposing" theories.
To understand string theory better, it is also important to know about the existence of a primary and secondary quantization approach.
Second quantization is based on the concepts of a string field, namely, a functional for the loop space, which is similar to quantum field theory. Formalisms of the primary approach through mathematical techniques create a description of the movement of test strings in their external fields. This does not negatively affect the interaction between the strings, but also includes the phenomenon of decay and association of strings. The primary approach is the link between string theories and statements by the usual field theory on the world surface.
Supersymmetry
The most important and necessary, as well as realistic “element” of string theory is supersymmetry. The general set of particles and the interactions between them, which are observed at relatively low energies, can reproduce the structural component of the standard model in almost all forms. Many of the properties of the standard model acquire elegant explanations in the crayfish of superstring theory, which is also an important argument for the theory. However, there are no principles that could explain one or another limitation of string theories. These postulates should make it possible to obtain a world form similar to the standard model.
The properties
The most important properties of string theory are as follows:
- 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 the variety of their principles of work and explanations, unite and follow from string theory.
- String theory does not have free parameters that must be adjusted to ensure agreement, as, for example, is required in the standard model.
Finally
In simple terms, quantum loop gravity is one of the ways of perceiving reality that tries 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 refers 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 are confirmed in various fields of elementary particle research, and attempts to unite the “quantum world" and gravity continue to this day.