Classical physics is of the opinion that any observers, regardless of location, will receive the same results in their measurements of time and extent. The principle of relativity says that observers can get different results, and such distortions are called "relativistic effects." When approaching the speed of light, Newtonian physics moves away.
Speed of light
The scientist A. Michelson, who measured the speed of light in 1881, realized that these results would not depend on the speed at which the radiation source moves. Together with E.V. Morley Michelson in 1887 conducted another experiment, after which it became clear to the whole world: no matter in which direction the measurement is taken, the speed of light is always and everywhere the same. The results of these studies were contrary to the ideas of physics of that time, because if light moves in a certain medium (ether), and the planet moves in the same medium, measurements in different directions can not be the same.
Later, the French mathematician, physicist and astronomer Jules Henri Poincare became one of the founders of the theory of relativity. He developed the Lorentz theory, according to which the existing ether is motionless, therefore the speed of light relative to it does not depend on the speed of the source. In moving reference systems, Lorentz transformations are performed, not Galilean ones (Galilean transformations, accepted until now in Newtonian mechanics). From now on, Galilean transformations have become a special case of Lorentz transformations when moving to another inertial reference frame at a low (compared to the speed of light) speed.
The abolition of ether
The relativistic effect of shortening the length, also called the Lorentz contraction, is that for the observer objects moving relative to him will have a shorter length.
A significant contribution to the theory of relativity was made by Albert Einstein. He completely abolished the term “ether,” which until then had been present in the arguments and calculations of all physicists, and he transferred all concepts about the properties of space and time into kinematics.
After the works of Einstein were published, Poincare not only stopped writing scientific papers on this topic, but did not mention the name of his colleague in any of his works, except for the only case of a reference to the theory of the photoelectric effect. Poincaré continued to discuss the properties of ether, categorically denying any Einstein’s publications, although he respected the greatest scientist and even gave him a brilliant characterization when the administration of the Higher Polytechnic School in Zurich wanted to invite Einstein to become a professor at an educational institution.
Theory of relativity
Even many of those who are completely at odds with physics and mathematics, at least in general terms, imagine what the theory of relativity is, because this is perhaps the most famous of scientific theories. Its postulates are ruined by the ordinary notions of time and space, and although all students study the theory of relativity, to understand it in its entirety is not enough just to know the formulas.
The effect of time dilation was tested in an experiment with a supersonic aircraft. The exact atomic clock on board, after returning, began to lag a fraction of a second. If there are two observers, one of which stands still, and the second moves at a certain speed relative to the first, the time for an observer who is motionless will go faster, and for a moving object the minute will last a little longer. However, if the moving observer decides to return and check the time, it turns out that his watch shows a little less than the first. That is, having traveled a much greater distance on the scale of space, he "lived" less time while moving.
Relativistic effects in life
Many people believe that relativistic effects can only be observed when the speed of light is reached or when approaching it, and this is true, but they can be observed not only by dispersing your spaceship. On the pages of the scientific journal Physical Review Letters you can read about the theoretical work of Swedish scientists. They wrote that relativistic effects are present even in just a battery for a car. The process is possible due to the fast movement of electrons of lead atoms (by the way, they are the reason for most of the voltage in the terminals). This also explains why, despite the similarities between lead and tin, tin-based batteries do not work.
Fancy metals
The speed of rotation of electrons in atoms is quite low, and therefore the theory of relativity just does not work, but there are some exceptions. If we move further and further along the periodic table, it becomes clear that in it quite a few elements are heavier than lead. A large mass of nuclei is balanced by increasing the speed of the electrons, and it can even approach the light.
If we consider this aspect from the side of the theory of relativity, it becomes clear that the electrons in this case should have a huge mass. This is the only way to preserve the angular momentum, but the orbital will be compressed along the radius, and this is indeed observed in atoms of heavy metals, but the orbitals of "slow" electrons do not change. This relativistic effect is observed in the atoms of some metals on s-orbitals having a regular, spherically symmetric shape. It is believed that as a result of the theory of relativity, mercury has a liquid state of aggregation at room temperature.
Space travel
Objects in space are at great distances from each other, and even when moving at the speed of light, it will take a very long time to overcome them. For example, it would take four years to reach Alpha Centauri, the closest star to us, a spacecraft with the speed of light, and it would take 160 thousand years to reach our neighboring galaxy, the Big Magellanic Cloud.
It’s still possible to fly to Alpha Centauri , because it will take only eight years, and for the inhabitants of the ship who feel the effect of time dilation, this period will be much shorter, however, upon returning from a trip to a neighboring galaxy, astronauts will find that three hundred and twenty have already passed thousand years, and human civilization may have long ceased to exist. Thus, relativistic effects allow people to move in time. This is considered one of the main problems of space exploration, because what is the point of conquering outer space if there is no opportunity to return?
Other actions
In addition to the famous time dilation, there is the relativistic Doppler effect, according to which if the wave source starts to move, then the waves propagating in the direction of this movement will be perceived by the observer as "compressed", and in the direction of removal the wavelength will be increased.
A similar phenomenon is characteristic of any waves; therefore, it can be observed on the example of sound in everyday life. The reduction of the sound wave is perceived by the human ear as an increase in tone. Therefore, when the signal of a train or car is heard from afar, it is lower, and if the train goes past the observer, making a sound, its height will be higher at the time of approach, but as soon as the objects align and the train starts to move away, the tone will sharply lower and will continue to continue on lower notes.
These relativistic effects are due to the classical analogue of the frequency change during the movement of the receiver and source, as well as the relativistic time dilation.
About magnetism
Among other things, modern physicists are increasingly discussing the magnetic field as a relativistic effect. According to this interpretation, a magnetic field is not an independent physical material entity; it is not even one of the forms of manifestations of an electromagnetic field. The magnetic field from the point of view of the theory of relativity is just a process that occurs in the space around point charges due to the transmission of an electric field.
Adherents of this theory believe that if C (the speed of light in vacuum) were infinite, then the propagation of interactions in speed would also be unlimited, and as a result, no manifestations of magnetism could occur.