THEORY OF RELATIVITY

THEORY OF RELATIVITY

The theory of special relativity, formulated by Albert Einstein in 1905, is one of the most important scientific advances in history. It altered our way of conceiving space, energy, time and even had philosophical repercussions, eliminating the possibility of an absolute space / time in the universe.

It is complemented by the theory of general relativity, published in 1915, which is somewhat more complex and which seeks to combine Newtonian dynamics with part of the consequences of the first special theory.

With the theory of special relativity, humanity understood that what until now had taken for granted that it was a constant, time, was actually a variable. Not only that, but space was also, and that both depended, in a new space-time conjunction, of speed.

Luis Álvarez-Gaumé, director of the theoretical physics group at CERN, explains in a telephone conversation:

The most important thing is to understand how time actually depends on movement, on speed. That's what changed everything.

Einstein was based on two hypotheses:

1.     The laws of physics are the same as long as the reference system is the same and inertial. That is, they both move at a constant speed. If a law is enforced in one system, it must also be enforced in the other.

2.     The speed of light is a universal constant, defined as c. That it was constant had been demonstrated some years before other two great scientists, Michelson and Morley.

But to get to the famous E = mc2 before we have to understand two very important concepts: on the one hand what exactly is relativity and on the other hand understand space-time and how to define what are known as lines of universe. Finally, although we will not deduce the mathematical steps necessary to reach the equation, we will see the consequences that it has and how it relates to the theory of general relativity. Let's go there.

¿What is relativity?

The situation that Einstein imagined has been used and explained to the fullest in schools and physics books. Imagine a train and two individuals, one of them is mounted in the same and another sees him pass at full speed from the edge of the road. The train moves at 200 kilometers per hour.

One moment, does it move? insurance? Yes and not at the same time. For the person sitting inside the train does not move, it is quiet. It only moves for the person at the edge of the road. It is something, indeed, relative.

Einstein later imagined that someone throws a ball at 20 kilometers per hour forward inside the train. For the person inside the ball moves at that speed but for the person who is down that ball moves, however, to 220 (200 + 20) kilometers per hour.

That is when it comes to remembering that the speed of light is constant, and it is when we begin to understand that something does not fit completely with the concept that time is also. Since the speed of light is always the same, when returning to the example of the train and the person inside if instead of throwing a ball lights a flashlight projecting a beam of light forward, the person below does not see that Propagate at the speed of light + 200 km / h, the propagates to the velvet light, no more, no matter how fast or how slow the train is, because it is simply a constant.

To understand the concept a bit better, let's look at the following example. It shows two photons of light bouncing infinitely between two mirrors and taking a time x to go from one to another.

 Space-time

In the words of Luis Álvarez Gaumé:

The revolution of the theory of relativity is that it creates a cone of light, both forward in time, and behind. Since what defines the limits of that cone is the speed of light and no particle can overcome it, nothing that happens can be outside the limits of the same.

That cone describes the observer moving through the hypersurface which is the present. "Up" are the events of the future, which is going to happen. Any possibility or fact has to occur within that cone. Below are the events that have happened to you.

Gaumé adds: "And be careful, it's not that things do not happen outside of that cone, they do happen, they just can not affect you. So that they could affect you have to overcome the speed of light. The cone is independent of the observer's movement speed. That's what forces time to depend on the state of the movement. "

The cone delimits events that may have an effect on others. The line of the universe is the union of the infinity of points corresponding to all that has happened in your life. Always inside the cone.

E = mc2

E = mc2 comes from a series of equations that, due to the more accessible character of this post, it does not make sense to explain here although for those who have average knowledge of physics and mathematics there is a fairly good explanation here. To get to the equation it is necessary to take into account two important laws:

Law of conservation of linear momentum: what basically means that when two objects collide at different velocity (and therefore different linear momentum) the result of the sum of both objects must have the same value before and after.

The famous law of conservation of energy: Energy is neither created nor destroyed, only transformed. It changes from one form of energy to another.

The really interesting thing about the equation is that it directly relates mass and energy. They are transformable. And even Einstein no one had noticed and thought they were independent things.

Explain it a little better: say a log burning in a fireplace. Once it has burned if we add the mass corresponding to all the ashes plus the gases that it has emitted, we would appreciate that the total mass has diminished, although it is minuscule. That mass is the one that has been transformed into energy, the heat of combustion.

In the case of firewood it is not very efficient, but in the case of nuclear power plants, for example, it is much larger and that is why we use it for the production of energy.

Although it is already flesh of another post, the way in which energy, mass and space-time are related is what is known as General Relativity Theory. And that's where gravity comes into play. However, the theory of relativity considers that gravitational effects are not created by any force, but find their cause in the curvature of space-time generated by the presence of matter. When gravity increases brutally, as in black holes, it is when these extreme curvatures occur that can be seen in films like Interstellar.