|AstroNuclPhysics ® Nuclear Physics - Astrophysics - Cosmology - Philosophy||Gravity, black holes and physics|
UNITARY FIELD THEORY AND QUANTUM GRAVITY
B.1. The process of unification in physics
B.2. Einstein's visions of geometric unitary field theory
B.3. Wheeler's geometrodynamics. Gravity and topology.
B.4. Quantum geometrodynamics
B.5. Gravitational field quantization
B.6. Unification of fundamental interactions. Supergravity. Superstrings.
B.7. General principles and perspectives of unitary field theory
B.1. The process of unification in physics
especially physicists are deeply convinced of the comprehensibility of the world , especially nature. He
therefore strives to find a uniform explanation of the basic
building blocks of matter and the interactions between them. The
basis of scientific thinking is unification : in the vast diversity of
phenomena and events, to seek general
laws and a common
essence , to try to explain the diversity of phenomena on the
basis of as few basic laws as possible. It is based on the idea
that " nature is rich in forms,
but poor in laws
Thoughtful people have always longed for a theory that would describe and understand all the observed complexity and diversity of nature. The ultimate ideal is (if possible) to explain all the laws of nature using a single universal principle - to create a definitive final theory or a unified "theory of everything" ( TOE - Theory Of Everything ) ; to reveal a single law clarifying all the phenomena of the world.
Unitarization efforts are based on the belief in the material unity of the world , which is now the basis of all science. That there is some hidden universal structure in the Universe or the law on the basis of which the whole universe works. And it is physics that examines the most basic laws of nature, that has a unifying role among all the natural sciences. In the course of development, with the discovery of ever new phenomena and laws, physics seems more and more complicated, demanding and complex. However, this is only a partial external view. Within physics, in fact, there is also an integration process , the aim of which is to give a uniform description of physical phenomena.
Unitary "theory of everything": the end of physical research ?
Sometimes we encounter the opinion (especially in the scientific-popularization literature) that the successful construction of a unitary theory of the field, the "theory of everything", would mean the end of physics and even perhaps the whole of science - there would be nothing new to discover! This view is wrong for at least two reasons :
1. Quantum relations of uncertainty , if the new unitary theory did not overcome them in any way (which does not seem probable), fundamentally limit the possibilities of predicting phenomena.
2. We cannot solve the relevant equations accurately, except in the simplest and idealized cases. With the number of degrees of freedom (the number of bodies and particles) this becomes completely impossible, an attempt to make an accurate prediction necessarily dissolves into chaotic behavior (see §3.1, section " Determinism - chance - chaos? ").
So there is still a lot of intellectual work left, how to derive and understand the behavior of systems in complex and realistic situations from basic principles and laws. Due to its fundamentality, complexity and heuristic significance , this work does not compete with revealing the principles of unitary field theory.
stages of unitarization
The basic stages of unification in physics are shown in Fig.B.1. The first stage of unitarization actually took place in the very beginnings of physics as a science: it was a unification of " terrestrial " and " celestial " mechanics . Thanks to Galileo, Copernicus and Kepler, it became clear that the laws of nature observed here on Earth also apply elsewhere in the universe (the first more concrete confirmation of this was Galileo's observation of "mountains" on the surface of the Moon) . For real "father of unification" can be considered to I.Newtona that before about 300 year those formulated the law of universal gravitation and showed that the force of the Earth's gravity causing bodies to fall is identical to the force of keeping planets in orbit around the Sun, i.e., cosmic gravity.
The "classical" period of unitarization of physics can also include the unification of mechanics and thermals in the kinetic theory of heat, according to which the essence of thermal phenomena (formerly considered separate) is the kinetic energy of disordered and oscillating motion of molecules and atoms in matter.
A great example of unitarization in physics is the unification of electric and magnetic forces which previously seemed to be quite different forces of nature. In the first third of the 19th century, Faraday and Ampér discovered that magnetic forces (known until then only from permanent magnets) are created by the movement of electric charges. And changes in the magnetic field cause an electric field. This knowledge was further developed and generalized by J.C.Maxwell in his electromagnetic field theory (§1.5). The consequence of the unity of electricity and magnetism in Faraday-Maxwell electrodynamics is the existence of electromagnetic waves , which are emitted during the accelerated motion of electric charges.
The properties of these electromagnetic waves proved to be identical to the properties of light: there was also in addition, optical and electromagnetic phenomena were unified. Radio waves, heat radiation, light, X-rays and gamma rays, together with the classical and relativistic effects of electricity and magnetism, are therefore just different manifestations of electromagnetic interaction .
Fig.Bl Basic stages of unification of natural laws.
Weak and strong interactions and unification of individual types of interactions are not yet included in this scheme; the continuation of the scheme of unitarization in the field of unitary field theories is shown in Fig.B.8 in §B.6 " Unification of fundamental interactions. Supergravity. Superstrings. ".
The development of atomistics and quantum
in the first third of the 20th century showed that all the
diversity of chemical phenomena can be explained by
electromagnetic interactions and quantum laws in the electronic shells of atoms of individual elements; the same
applies to the physical properties of solids (crystal lattices - elasticity, strength, dislocation) , liquids and gases. Thus,
chemistry was in fact "absorbed" by physics, at least
as far as the foundations are concerned - see §1.1 "Atoms and Atomic
Nuclei", section " Interaction of Atoms " of the book " Nuclear Physics and Physics of Ionizing
The other two stages of unitarization are already related to relativity theory . In his special theory of relativity Einstein unified space and time into a single space-time continuum, in his general theory of relativity he unified space-time and gravity - he showed that Newtonian gravity and inertia are a together manifestation of geometric properties (curvature) of space-time, which has a dynamic character (Chapter 2 "General theory of relativity - physics of gravity") .
The last stage of unitarization takes place in the area of "elementary" particles . A huge amount of experimental knowledge about the properties and interactions of elementary particles, obtained in the 50s-80s, processed and unified in the spirit of a number of quantum-theoretical concepts, resulted in the so-called Standard Model of Elementary Particlesand their interactions (it is discussed in more detail in §1.5 " Elementary particles and accelerators ", passage " Standard model - unified understanding of elementary particles " of the book " Nuclear physics and physics of ionizing radiation ") . All matter in nature in its deepest interior consists of only 2 "families" of basic (elementary) particles - 6 leptons and 6 quarks , between which 4 fundamental forces (interactions) act: strong, electromagnetic, weak and gravitational . The first three of these interactions are described by exchanges of intermediate bosons with spin 1: strong interaction is mediated by gluons , electromagnetic interaction by photons, weak interaction by heavy intermediate bosons charged (W +, - ) and neutral (Z o ). Quantum theory for the gravitational interaction has not yet been completed, but can be described by intermediate gravitons (spin 2). The modern unitary theories that try to unify the various types of interactions between elementary particles, will be mentioned at the end of this chapter (§B.6 " Unification of fundamental interactions. Supergravity. Superstrings. ") . But before that, let's talk about geometric unitary theories that are most closely related to the subject of this book.
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