Friday, March 24, 2023

# Theory of Relativity: Easy Explanation and Examples

From Galileo to Einstein, this article provides you brief historical introduction along with the invention and development of the theory of relativity main application which is derived from it.

## Galileo’s theory of relativity

17th century astronomer, mathematician and physicist Galileo Galilei He observed that for a passenger who was locked in the hold of a ship, it was impossible to know whether it was stationary or, conversely, moving in calm seas. According to Galileo, whether the ship is docked or moving in a straight line at a constant speed, an apple dropped by a sailor from the top of the mast returns right at its foot. In this way the Italian physicist Galileo founded his theory of relativity Which establishes the following premise: «The movement itself is like nothing». it translates to the impossibility of translation being straight and of uniform movement of a mobile body for an experience that is carried out only within it without reference to the outside world. Galileo’s theories would become part of the most brilliant predictions in the world of physics.

portrait of physicist Galileo Galilei

## Einstein’s theory of relativity

Galileo’s theory of relativity, as a rule applied to mechanics, was practically abandoned at the end of the 19th century, when physicists began to observe the movement of the Earth around the Sun by means of an optical experiment. I thought they saw that light cannot travel in a vacuum And for this reason they created a special medium that allowed this propagation. He called this medium “ether” (not to be confused with the ether of chemistry). So they expected that as the speed of sound travels through air, speed of light depends on the velocity of the source relative to the ether. This would allow, for example, to uncover the motion of the Earth with respect to the ether and thus, Invalidate Galilean relativity.

In the year 1887, Albert Michelson and Edward Morley managed to demonstrate, thanks to an experiment that later became famous, that speed of light in a vacuum, which is about 300,000 kilometers per second, Assumes the same as the motion of the Earth around the Sun. Hence, they fail to highlight the motion of the earth. Thus this result invalidated the aether theory and imposed the idea that light propagates without material support. speed of light in vacuum It then became an invariant, i.e. independent of the observer’s state of motion. Later, in an article published in 1905, Albert Einstein extended Galileo’s theory to all the laws of physics is known then. between them all, mechanics and electromagnetism, Which means that the speed of light is the same in all inertial reference frames.

File photo of Albert Einstein

## From special relativity (1905) to general relativity (1915)

In 1905, Albert Einstein succeeded in establishing the principle of special relativity, this type of setup notion of space-time and setting up a Relation between energy and mass. Special relativity also makes the speed of light (in a vacuum) an invariant quantity, which remains unchanged regardless of the position of the observer. Starting in 1907, Tried to describe gravity It is based on the simple idea that a person in free fall no longer feels his own weight. In 1912 he expanded on this idea by explaining light must have a curved path by gravity, Will be verified during the solar eclipse of 1919.Einstein would spend the next few years developing it The mathematical formalism that characterizes these concepts. On November 25, 1915 he was able to present Royal Prussian Academy Definite equations of the theory of general relativity. it is based on the principle of Similarities Between Gravity and Acceleration, And it would be highlighted in an article to be published on December 2 of the same year. These advances would be important for later string theories.

## relativity of time

To understand the consequences of Albert Einstein’s theories and postulates, we must think of a hypothetical train that travels in a simple and uniform motion at a speed close to the speed of light. Noticed by one of the passengers of the train two rays of light cast together in the center of the wagon, Hit opposite walls simultaneously. On the other hand, the station master does not see all this from the platform. Since the speed of light is the same for all observers, The light rays reach the opposite walls of the vehicle at different times Because one of the beam must reach the train. Thus the first result of Einstein’s relativity is that the simultaneous occurrence of two events Completely relative to the observer.

The path of light depends on the relativity of the observer

These results derive from an important conceptual inversion. Until then, time and place set the stage In which the events unfolded. He was considered a fundamental notion and motion was a notion that emanated from him. If time and space must adapt at an irreversible speed, They then become relative to the observer’s frame of reference and are therefore no longer independent, but form A new unified entity, space-time. This would greatly influence later theories about black holes.

## What are the applications of the theory of relativity?

variation The periods have been experimentally confirmed with great accuracy with the motion of the observer, Thanks to the disintegration of atmospheric muon or particle accelerators. Today, the theory of relativity of time is commonly used in fundamental physics, but it is also necessary to keep the theory of relativity in mind when Synchronize the clocks of satellite geolocation systems.

### In which year was Albert Einstein able to prove the theory of relativity?

Einstein proved the theory of relativity in 1912.

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