- Part two -
The Unified Theory of the Universe, or The Theory of Everything, is a hypothetical unified physical and mathematical theory that describes all known fundamental interactions. The term was originally used ironically to refer to a variety of generalized theories. Over time, the term became entrenched in the popularisations of quantum physics to denote a theory that would combine all four fundamental interactions in nature: gravitational, electromagnetic, strong nuclear and weak nuclear interactions. Moreover, it must explain the existence of all elementary particles. The search for a Unified Theory is called one of the main goals of modern science.
The idea of a unified theory arose thanks to the knowledge accumulated by more than one generation of scientists. As knowledge was gained, mankind's understanding of the surrounding world and its laws expanded. Since the scientific picture of the world is a generalized, systemic formation, its radical change cannot be reduced to a separate, even if the largest, scientific discovery. The latter can, however, give rise to a kind of chain reaction capable of giving a whole series, a complex of scientific discoveries, which will ultimately lead to a change in the scientific picture of the world. In this process, the most important, of course, are discoveries in the fundamental sciences on which it relies. In addition, remembering that science is primarily a method, it is not difficult to assume that a change in the scientific picture of the world should also mean a radical restructuring of the methods of obtaining new knowledge,including changes in the very norms and ideals of science.
The development of the idea of the world did not occur immediately. Such clearly and unambiguously fixed radical changes in scientific pictures of the world, i.e. There are three scientific revolutions in the history of the development of science in general and natural science in particular. If they are personified by the names of the scientists who played the most prominent role in these events, then the three global scientific revolutions should be called Aristotelian, Newtonian and Einstein's.
In the VI - IV centuries. BC. the first revolution in the knowledge of the world was carried out, as a result of which science itself was born. The historical meaning of this revolution lies in distinguishing science from other forms of cognition and mastering the world, in the creation of certain norms and models for the construction of scientific knowledge. Of course, the problem of the origin of the Universe has occupied the minds of people for a very long time.
According to a number of early Judeo-Christian-Muslim myths, our universe emerged at a certain and not very distant point in time in the past. One of the foundations of such beliefs was the need to find the "root cause" of the universe. Any event in the Universe is explained by indicating its cause, that is, another event that happened earlier; such an explanation of the existence of the Universe itself is possible only if it had a beginning. Another reason was put forward by Blessed Augustine (the Orthodox Church considers Augustine to be blessed, and the Catholic Church - saint). in the book "City of God". He pointed out that civilization is progressing, and we remember who committed this or that deed and who invented what. Therefore, humanity, and therefore, probably, the Universe, is unlikely to exist for a very long time. Blessed Augustine considered acceptable the date of the creation of the Universe, corresponding to the book of Genesis: approximately 5000 BC. (Interestingly, this date is not that far from the end of the last ice age - 10,000 BC, which archaeologists consider the beginning of civilization).
Aristotle and most other Greek philosophers did not like the idea of the creation of the universe, since it was associated with divine intervention. Therefore, they believed that people and the world around them existed and will continue to exist forever. Ancient scientists considered the argument regarding the progress of civilization and decided that floods and other cataclysms periodically occurred in the world, which all the time returned mankind to the starting point of civilization.
Aristotle created formal logic, i.e. in fact, the doctrine of proof is the main tool for deriving and systematizing knowledge; developed a categorical and conceptual apparatus; approved a kind of canon for the organization of scientific research (history of the issue, problem statement, arguments "for" and "against", justification of the decision); objectively differentiated scientific knowledge itself, separating the sciences of nature from metaphysics (philosophy), mathematics, etc. The norms of the scientific nature of knowledge set by Aristotle, models of explanation, description and justification in science have enjoyed indisputable authority for more than a thousand years, and much (the laws of formal logic, for example) are still effective.
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The most important fragment of the ancient scientific picture of the world was the consistent geocentric doctrine of the world spheres. The geocentrism of that era was not at all a "natural" description of directly observable facts. It was a difficult and courageous step into the unknown: after all, for the unity and consistency of the structure of the cosmos, it was necessary to supplement the visible celestial hemisphere with an analogous invisible one, to admit the possibility of the existence of antipodes, i.e. inhabitants of the opposite side of the globe, etc.
Aristotle thought that the Earth is motionless, and the Sun, Moon, planets and stars revolve around it in circular orbits. He believed so, because in accordance with his mystical views, the Earth was considered the center of the Universe, and circular motion was the most perfect. Ptolemy developed Aristotle's idea into a complete cosmological model in the 2nd century. The Earth stands in the center, surrounded by eight spheres bearing the Moon, the Sun and five then known planets: Mercury, Venus, Mars, Jupiter and Saturn (Fig. 1.1). The planets themselves, Ptolemy believed, move in smaller circles attached to the corresponding spheres. This explained the very difficult path that, as we see, the planets take. On the very last sphere there are fixed stars, which, remaining in the same position relative to each other, move through the sky all together as a whole. What lies behind the last sphere was not explained, but in any case it was no longer a part of the universe that humanity observes.
Ptolemy's model made it possible to predict well the position of celestial bodies in the sky, but for an accurate prediction he had to accept that the trajectory of the Moon in some places approaches the Earth 2 times closer than in others! This means that in one position the Moon should appear 2 times larger than in another! Ptolemy was aware of this flaw, but nevertheless his theory was accepted, although not everywhere. The Christian Church accepted the Ptolemaic model of the universe as not inconsistent with the Bible, for this model was very good in that it left a lot of room for hell and heaven outside the sphere of fixed stars. However, in 1514 the Polish priest Nicolaus Copernicus proposed an even simpler model. (At first, fearing, perhaps, that the Church would declare him a heretic, Copernicus propagated his model anonymously). His idea wasthat the Sun is stationary in the center, and the Earth and other planets revolve around it in circular orbits. Almost a century passed before Copernicus' idea was taken seriously. Two astronomers - German Johannes Kepler and Italian Galileo Galilei - publicly supported Copernicus's theory, even though the orbits predicted by Copernicus did not quite coincide with the observed ones. Aristotle-Ptolemy's theory came to an end in 1609, when Galileo began observing the night sky with his newly invented telescope. By aiming a telescope at the planet Jupiter, Galileo discovered several small satellites, or moons, orbiting Jupiter. This meant that not all celestial bodies must necessarily revolve directly around the Earth, as Aristotle and Ptolemy believed. (Of course, one could still considerthat the Earth rests at the center of the universe, and the moons of Jupiter move along a very complex path around the Earth, so that it only seems as if they revolve around Jupiter. However, Copernicus's theory was much simpler.) At the same time, Johannes Kepler modified Copernicus's theory, based on the assumption that the planets move not in circles, but in ellipses (an ellipse is an elongated circle). Finally, now the predictions have coincided with the results of observations. Finally, now the predictions coincided with the observations. Finally, now the predictions have coincided with the results of observations.
As for Kepler, his elliptical orbits were an artificial hypothesis, and, moreover, "inelegant", since an ellipse is a much less perfect figure than a circle. Finding almost by accident that elliptical orbits were in good agreement with observations, Kepler was never able to reconcile this fact with his idea that the planets revolve around the Sun under the influence of magnetic forces. The explanation came only much later, in 1687, when Isaac Newton published his book "Mathematical Principles of Natural Philosophy". Newton in it not only put forward a theory of the motion of material bodies in time and space, but also developed complex mathematical methods necessary to analyze the motion of celestial bodies.
In addition, Newton postulated the law of universal gravitation, according to which every body in the Universe is attracted to any other body with the greater force, the greater the mass of these bodies and the smaller the distance between them. This is the very force that makes bodies fall to the ground. (The story that Newton was inspired by an apple that fell on his head is almost certainly unreliable. Newton himself said about this only that the idea of gravity came when he was sitting in a "contemplative mood", and "the reason was the fall of the apple") …
Further, Newton showed that, according to his law, the Moon under the action of gravitational forces moves in an elliptical orbit around the Earth, and the Earth and planets rotate in elliptical orbits around the Sun. (8) Newton's model is one body moving uniformly in absolute infinite space and rectilinearly until this body is acted upon by a force (the first law of mechanics) or two bodies acting on each other with equal and opposite forces (the third law of mechanics); the force itself is considered to be simply the cause of the acceleration of moving bodies (the second law of mechanics), that is, as if it exists by itself and from nowhere it comes from.
Newton retained the consideration of mechanics as a universal physical theory. In the XIX century. this place was taken by a mechanistic picture of the world, including mechanics, thermodynamics and kinetic theory of matter, elastic theory of light and electromagnetism. The discovery of the electron stimulated a revision of ideas. At the end of the century, H. Lorenz built his electronic theory to cover all natural phenomena, but he did not achieve this. Problems associated with the discreteness of the charge and the continuity of the field, and problems in the theory of radiation ("ultraviolet catastrophe") led to the creation of a quantum-field picture of the world and quantum mechanics.
A classic example of the use of abstract concepts to explain nature was given in 1915 by Einstein, who published his truly epochal general theory of relativity. This work is one of the few that mark turning points in man's perception of the world around him. The beauty of Einstein's theory is due not only to the power and elegance of the equations of the gravitational field, but also to the overwhelming radicalism of his views. General relativity has confidently proclaimed that gravity is the geometry of curved space. The concept of acceleration in space was replaced by the concept of curvature of space. (2)
After the creation of SRT, it was expected that the universal coverage of the natural world could give an electromagnetic picture of the world, which combined the theory of relativity, Maxwell's theory and mechanics, but this illusion was soon dispelled.
Special theory of relativity (SRT) (special theory of relativity; relativistic mechanics) is a theory that describes motion, the laws of mechanics and space-time relations at speeds of motion close to the speed of light. Within the framework of the special theory of relativity, the classical mechanics of Newton is the approximation of low speeds. Generalization of SRT for gravitational fields is called general theory of relativity (GRT). SRT is based on two postulates:
1. In all inertial reference frames, the speed of light is unchanged (it is an invariant) and does not depend on the movement of the source, receiver or the frame itself. In the classical mechanics of Galileo - Newton, the speed of the relative approach of two bodies is always greater than the speeds of these bodies and depends both on the speed of one object and on the speed of another. Therefore, we find it difficult to believe that the speed of light does not depend on the speed of its source, but this is a scientific fact.
2. Real space and time form a single four-dimensional space-time continuum so that during the transition between reference frames the value of the space-time interval between events remains unchanged. In SRT, there are no simultaneous events in all reference frames. Here, two events, simultaneous in one frame of reference, look different in time from the point of view of another, moving or at rest, frame of reference.
The special theory of relativity retains all the basic definitions of classical physics - impulse, work, energy. However, something new also appears: first of all, the dependence of mass on the speed of movement. Therefore, one cannot use the classical expression for kinetic energy, because it was obtained under the assumption that the mass of the object remains unchanged.
Many theorists have tried to embrace gravity and electromagnetism with unified equations. Under the influence of Einstein, who introduced four-dimensional space-time, multidimensional field theories were built in an attempt to reduce phenomena to the geometric properties of space.
The unification was carried out on the basis of the established independence of the speed of light for different observers moving in empty space in the absence of external forces. Einstein depicted the object's world line on a plane (Fig. 2), where the spatial axis is directed horizontally and the temporal axis is directed vertically. Then the vertical line is the world line of the object, which is at rest in the given frame of reference, and the oblique line is the object moving at a constant speed. The curved world line corresponds to the accelerated motion of the object. Any point on this plane corresponds to a position in a given place at a given time and is called an event. In this case, gravity is no longer a force acting on a passive background of space and time, but is a distortion of space-time itself. After all, the gravitational field is “the curvature of space-time.
Fig. 2. Space-time diagram
Soon after its creation (1905), the special theory of relativity ceased to suit Einstein, and he began to work on its generalization. The same thing happened with general relativity. In 1925, Einstein began to work on the theory, which he was destined to study with short interruptions until the end of his days. The main problem that worried him - the nature of the field sources - already had a certain history by the time Einstein took up it. Why don't particles fall apart, for example? After all, an electron carries a negative charge, and negative charges repel each other, i.e. the electron would have to explode from the inside due to the repulsion of neighboring areas!
In a sense, this problem has persisted to this day. A satisfactory theory has not yet been built that describes the forces that act inside the electron, but the difficulties can be circumvented by assuming that the electron has no internal structure - it is a point charge that does not have dimensions and, therefore, cannot be torn apart from the inside.
Nevertheless, it is generally accepted that the main provisions of modern cosmology - the science of the structure and evolution of the Universe - began to form after the creation in 1917 by A. Einstein of the first relativistic model based on the theory of gravity and claiming to describe the entire Universe. This model characterized the stationary state of the Universe and, as shown by astrophysical observations, turned out to be incorrect.
An important step in solving cosmological problems was made in 1922 by Professor of Petrograd University A. A. Friedman (1888-1925). As a result of solving cosmological equations, he came to the conclusion: the Universe cannot be in a stationary state - all galaxies are moving away in a forward direction from each other, and therefore they were all in the same place.
The next step was taken in 1924, when the American astronomer E. Hubble (1889-1953) measured the distance to the nearest galaxies (at that time called nebulae) at the Mount Wilson Observatory in California, and thereby discovered the world of galaxies. When astronomers began to study the spectra of stars in other galaxies, something even stranger was discovered: our own galaxy had the same characteristic sets of missing colors as stars, but they were all shifted by the same amount towards the red end of the spectrum. Visible light is vibrations or waves of the electromagnetic field. The frequency (number of waves per second) of light vibrations is extremely high - from four hundred to seven hundred million waves per second. The human eye perceives light of different frequencies as different colors, with the lowest frequencies corresponding to the red end of the spectrum,and the highest to purple. Imagine a light source located at a fixed distance from us (for example, a star), emitting light waves at a constant frequency. Obviously, the frequency of the incoming waves will be the same as the one with which they are emitted (even if the gravitational field of the galaxy is small and its influence is insignificant). Suppose now that the source begins to move in our direction. When the next wave is emitted, the source will be closer to us, and therefore the time it takes for the crest of this wave to reach us will be less than in the case of a fixed star. Consequently, the time between the crests of the two arriving waves will be less, and the number of waves we receive in one second (i.e., the frequency) will be greater than when the star was stationary. When the source is removed, the frequency of the incoming waves will be less. It means,that the spectra of receding stars will be red-shifted (redshift), and the spectra of approaching stars should experience a violet shift. This relationship between speed and frequency is called the Doppler effect, and this effect is common even in our daily lives. The Doppler effect is used by the police, who determine the speed of vehicles from afar by the frequency of radio signals reflected from them.
Having proved that other galaxies exist, Hubble devoted all subsequent years to compiling catalogs of distances to these galaxies and observing their spectra. At that time, most scientists believed that the movement of galaxies occurs at random and therefore the spectra shifted towards the red side should be observed as much as those shifted towards the violet. What a surprise it was when most of the galaxies showed a redshift of the spectra, that is, it turned out that almost all galaxies are moving away from us! Even more surprising was the discovery published by Hubble in 1929: Hubble discovered that even the magnitude of the redshift is not random, but is directly proportional to the distance from us to the galaxy. In other words, the further away a galaxy is, the faster it moves away! And this meant that the universe could not be static, as previously thought,that in fact it is continuously expanding and the distances between galaxies are growing all the time.
The expansion of the universe means that in the past its volume was less than it is now. If time is turned back in the model of the universe developed by Einstein and Friedman, events will go in reverse order, as in a movie played from the end. Then it turns out that about 13 billion years ago the radius of the Universe was very small, that is, the weight of the galaxy, the interstellar medium and radiation - in a word, everything that now makes up the Universe was concentrated in a negligible volume, close to zero. This primary superdense and super-hot state of the Universe has no analogues in our contemporary reality. It is assumed that at that time the density of the substance of the Universe was comparable to the density of the atomic nucleus and the entire Universe was a huge nuclear drop. For some reason, the nuclear droplet was in an unstable state and exploded. This assumption is at the heart of the big bang concept.
- Part two -