What is Theory of Relativity for Dummies

The Special Theory of Relativity literally revolutionized the world of physics and completely changed the generally accepted understanding of the world around us.

Many physicists are still engaged in heated discussions related to the Theory of Relativity. In this material I will try to explain as clearly as possible what this Theory of Relativity is.

Special and General Theory of Relativity

Back in 1905, the great physicist Albert Einstein published his work entitled Special Theory of Relativity (hereinafter referred to as SRT), in which an explanation of how to describe the movement between various inertial reference frames or, more simply, objects, which move relative to each other with a certain speed.

In his work, the scientist said that during the movement of two objects at a fixed speed, you need study their movement relative to each other, and not take one of the objects as an absolute system countdown.

Simply put, if conventional astronauts fly on one spacecraft, and you and your partner on another, then for in order to compare your observations, the only thing you need to know is the speed relative to each other friend.

Special theory of relativity

This is a unique subsection that studies an exclusively special case (that's why it is called that), in which the motion is uniform and rectilinear.

In the event that a material object is accelerated or moves in an arc, then ONE HUNDRED does not apply. In this case, it is already used General relativity (General theory of relativity), describing the movement of bodies in all other cases.

All of Einstein's Theory is based on the following main postulates:

1. The principle of relativity. According to him, all physical laws act even on objects that are inertial reference frames (move relative to each other at a fixed speed).
2. The principle of the speed of light. The speed of light is the same for absolutely all objects, and it does not matter at what speed material objects move relative to the light source.

Ether searches and experimental data

At the end of the 19th century, scientists of that time were actively searching for the so-called ether - the medium where, according to their ideas, light waves should have propagated. At the same time, an analogy with sound waves was considered, and they need a certain medium for propagation.

As a result of this, there was the conviction that the speed of light will change depending on the speed of the observer in relation to the ether.

Einstein, unlike his colleagues, decided to trust the results of the experiments and rejected the ether theory as untenable, and put forward his assumption based on the experimentally obtained data.

And he concluded that all physical laws, like the speed of light, are constant and in no way depend on the observer's own speed.

Homogeneity of space and time

So, according to SRT, there is an immutable connection between space and time. We all know perfectly well that our Universe has three spatial dimensions:

Down and up, left and right and back and forth. To this unchanging trio, the so-called time dimension is also added, and now these four dimensions are the basis of our space-time continuum.

So if you move at great speed, then specifically your observations regarding time and space will differ significantly from the observations of other observers who move with significantly less speed. It is difficult, now I will explain it with a simple example.

So, imagine two spacecraft. On one is you and you are holding a laser pointer. You turn it on and point it at a right angle at a mirror located on the ceiling, and watch how it (the laser beam), reflected vertically downward, falls on the floor.

Now imagine that it is your ship that is moving at a tremendous speed of half the speed of light. So, according to Einstein's special theory, this speed will be absolutely invisible to you.

But for observers on the second spacecraft, which is at rest, observing your experiment with a laser, they will see a completely different picture, namely:

An outside observer will see that the beam you emit will move diagonally towards the mirror (and not under a direct angle as in your case), then reflected from its surface, it will also go diagonally to the floor and fall on him.

In other words, the trajectory of the laser beam will be different for you and for an outside observer. This means that the time it takes for the beam to travel at different distances will also differ.

This phenomenon is referred to as time dilation, that is, time on your starship, moving at a great speed, will flow much slower than for outside observers.

This thought experiment shows that there is an inextricable connection between space and time. This connection can be clearly seen only when it comes to speeds close to the speed of light.

Combining mass and energy

In addition, the great scientist derived a formula according to which mass and energy have an inextricable connection:

So, according to the theory of the great physicist, when the speed of an object made of matter approaches the speed of light, then its mass increases. In other words, the higher the speed of an object, the greater its weight, which means that it becomes more and more difficult to disperse it.

So when a material object reaches the speed of light, then its mass will be equal to infinity.

Consequently, the heavier the body, the more energy is needed to accelerate it, and an infinite amount of energy is required to accelerate a body with infinite mass.

From this it follows that for material objects the speed of light is unattainable in principle.

Before this theory, no one saw an obvious connection between energy and mass, and it was Einstein who proved that the law of conservation of energy and the law of conservation of mass are parts of one general law mass-energy.

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