Thus, although it may be difficult to understand and a little intimidating to face, it is possible to simplify it into a series of main points that bring together its results and make them accessible to anyone who wants them. So we present to you **The five basic points** To finally understand the theory of relativity.

It puts a person on a train moving at 100 km/h. In parallel, another person on another train is moving in the same direction, but this person is moving at a speed of 90 km / h. Thus, for the observer of the second train, the first is moving at only 10 km/h, not the 100 km/h he would notice if his train suddenly stopped. That is, the speed at which you see the first train **Depends on whether your reference system** fixed or mobile. Well, with the light that’s not true.

Einstein asserts that no matter where you look from, whether you are moving or not, you will always appreciate the movement of light at the same speed: 300,000 km/s. Applying to your own game, we would have that person on the first train and the second would see the light moving at the same speed. Thus, the theory of relativity puts in **constant light**that is, a quantity that is always constant.

## Time is relative

Another major consequence of this theory is that time, unlike the speed of light,** Not at all** It will depend on the movement of observers. That is, two events appearing simultaneously from one person’s perspective may not be from another person’s. And the strangest thing about all of this is that **Both will be right**.

To understand it, Einstein takes back the mental example of trains. This time it involves the first person standing next to the tracks as the train passes. Then, just as the middle car in front of him, lightning strikes the first and last cars. Since he is at an intermediate distance from both events, their light reaches his eye at the same time and he can assert, without error, that the two rays have struck them. **At the same time**.

Now, for another person sitting in the same central car, inside the train, things would be very different, but also true. From his point of view, the rays will also travel the same distance, but due to the relative motion of the train, the light that comes from the lightning in the tail will reach the observer later. Therefore, this person, also without being mistaken, will say that lightning strikes **in different times**.

this idea **Very counterintuitive**, because it is paradoxical logic, but it is not. Another very useful example of this relativistic estimation of the passage of time is the double discrepancy, which is somewhat more complex, but intriguing.

## Time and space are not independent

Among other concepts, the theory of relativity stands out as important **Redefining the concepts of space and time**since they are not independent terms, but are combined into a single term known as **Free time**. It is something as if both concepts were inseparable companions: what happens to one will affect the other.

Einstein in one of his classes

Princeton University
This statement was, for Einstein, an obvious consequence of the relativity of time: if an event, such as a train lightning strike, occurs at a different time depending on the situation in which each person is, then both concepts must be together. in this way, **Neither of them can be treated independently** till the end

In the words of the physicist himself: “From now on, space and time are destined to fade separately into shadows and only the union of both can **part of reality**“.

## Mass equals energy

Do you know the famous equation **e = mk**^{2}? Well, it’s probably the most common consequence of the theory of relativity. In addition, it was a scientific milestone because, with this simple and elegant equation, Einstein was able to combine two amazing conclusions.

First, you claim that **Energy and mass are related** And that they can become, in practice, equivalent. As an illustration, a physicist asked you to imagine an object emitting two pulses of light in opposite directions. Since each impulse carries a certain amount of energy, the body’s energy decreases, as it gives it to those impulses. Well, Einstein determined through algebraic formulas that for this to be consistent, the object must also lose mass. This means that energy and mass are directly related.