Relativity theory

Relativity theory – The physical concept of space and time, which was created by Albert Einstein, eliminated many contradictions in physics that arose at the beginning of the twentieth century. This concept has been helping us to study the processes in the universe for many years.
General characteristics
The adoption of the general principles of relativity explains the phenomenon of gravity as a manifestation of the geometric properties of space and time. According to the authors of this theory, substances, radiation and various physical fields are always present in the void of space. The arrangement of masses and energy are the defining geometric properties of the space-time in which matter is moving.
The reason for the need to develop a general approach to the theory of relativity was the discovery of a contradiction between the fundamental principle of special relativity (see here) and its basic principle – limiting the propagation speed of any signals to the speed of light, as well as the instantaneous action of gravitational forces implied in classical physics.
In addition, it was necessary to compare two quantities: the gravitational mass, which determines the measure of interaction of bodies in the law of universal gravitation, and the inertial mass, which determines the measure of acceleration of a body under the influence of force in Newton’s second law. There is a problem that arose simultaneously with Newton’s development of his theories, but he never found an answer to the question: how do these properties of a physical body, which manifest themselves in different situations, which are designated as masses, relate.
The fundamental principle of general relativity states that the gravitational field is an accelerated frame of reference. On the other hand, the values of the gravitational and inertial mass of the same body are equal. It follows from this that any observer inside a closed cabin has no experimental possibilities to verify the fact that it is moving at speed or is in a gravitational field.
According to the concept, all events in the universe take place in a four-dimensional coordinate system. Of these, three are spatial, and the fourth is time. Bodies with their masses create vibrations in four-dimensional space, which is Einstein’s. By doing this, they force each other to move along curved trajectories, which means their accelerated movement is analogous to gravity. This phenomenon is described using non-Euclidean, Riemannian geometry, which makes it difficult to visualize them.
With the help of general relativity, important conclusions can be drawn about how the universe works.
A light photon has mass, which is why it loses energy to overcome the gravitational field. At the same time, due to the decrease in the energies of photons, but not their velocity, light waves that deal with them according to the principle of dualism have longer lengths. A “gravitational redshift” appeared.
Due to the effects of gravity, time flows slower in it. However, this slowdown is greater the higher the field strength. The presence of this effect in our environment is minimal, but it is nevertheless present. So, a clock located one meter below the others in the Earth’s gravity field should lag behind the upper ones by 1 * 10-16 seconds every 10-16 seconds.
To date, the general theory of relativity has quite convincing evidence. These primarily include: measurements of deviations in the directions of propagation of starlight in the gravitational field of the Sun and the secular displacement of the perihelion of Mercury’s orbit – 43 angular seconds per hundred years; registration of “reddening” of photons of electromagnetic radiation in very intense gravitational fields of stars with high density; establishment of proportionality (because equivalence – equality – cannot be experimentally verified) of gravitational and inertial masses with an accuracy better than 10-12; a complete and rigorous description of the nature of black holes, the existence of which is no longer in doubt.
Level
With the help of special relativity, it is possible to understand that there is a relationship between time and space. This is manifested in shortening the length and duration of body movement, as well as in predicting the effect of increasing body weight with increasing speed. In its concept, there is no possibility of instant connection between any events that occur in different places in space, since the speed of propagation of the signal and the impact is equal to the speed of light in a vacuum.
Scientists believe that the basic idea underlying the special theory of relativity is that the rest mass of a light photon is zero, which means that it is impossible for an observer with superluminal speed to catch up with a photon and then move with it in the same direction at the speed of light. It contains all the main provisions of this theory.
If it is impossible for a material body to reach the speed of light, it is necessary to take into account the probability of an increase in its mass with increasing speed and the tendency to infinity as the speed of the body approaches the speed of light. The body grows in volume due to the energy that is spent on its acceleration, and moreover, the mass of the body is a measure of the energy that is contained in it.
A direct analogue of this dependence can be found in the famous Einstein relation: “the total energy of any body is equal to the product of its mass by the speed of light, which is raised to the second power.”
At the same time, an increase in body weight with an increase in speed is not felt in everyday life. An example is a spacecraft with a maximum speed of 11.2 kilometers per second (see Cosmic Velocity Two), which has a rest mass of 1.5 tons and has the ability to increase its mass due to the energy of rocket fuel by one milligram. With the help of the energy of the electric field of accelerators, which operate at a speed of 260000 km/ s, protons increase their mass. This fact has been experimentally confirmed during research on particle accelerators.
In order to fulfill the condition that an observer is unable to chase light and move at the speed of light, it is necessary to accept that the speed of light is the same regardless of whether the light comes from a source or it is stationary. It does not add up at the speed of light, as required by classical physics, in accordance with its laws. As a result, from the point of view of an observer outside a moving body, time in the coordinate system slows down, and the dimensions in the direction of movement decrease.
The size reduction and time dilation in daily life are very small. Let’s assume that the Earth has a diameter in the direction of its orbit at a speed of 29.765 km/s, which is 6 centimeters less than if it were moving in the opposite direction, from the point of view of an observer located at a distance from the Sun.
In fact, in order for a body with a rest mass to reach the maximum speed of light, three conditions must be met: an increase in its mass to infinity, a reduction in the size of the body in the direction of movement to zero, and a stop of time in the coordinate system that connects it with the environment.
All of this is true if we consider it from the point of view of an earthly observer who is watching the flight of a starship striving to reach the speed of light. Although, it would seem that the same thing can be applied to a member of the crew of a spaceship that is in orbit around the Earth and watching it. At first glance, the conditions in the coordinate systems that relate to the Earth and the spaceship are equal. This contradiction can be eliminated, taking into account the following circumstances. In order to achieve any velocity of one body relative to another body, it must be in a state of acceleration for some time. In this case, the coordinate systems that deal with these bodies turn out to be unequal, and the coordinate system that deals with a body that has acceleration is non-inertial. The effect of time dilation takes place in a non-inertial system, which is subject to acceleration, and the study of this phenomenon is carried out within the framework of the general (see here) the theory of relativity.
Due to the special theory of relativity, the photon cannot be used as the basis for creating a coordinate system. In this system, time is stopped, and the length in the direction of movement of the photon is zero.