Theory of relativity

Einstein's theory of relativity changed physics

Einstein's theory of relativity explains physical paradoxes

Einstein's theory of relativity consists of two parts: the special theory of relativity from 1905 and the general theory of relativity from 1915.

Halfway through the 19th century, natural phenomena were discovered that were contrary to Newton's law of gravity, which until then formed the foundation of physics. Many scientists tried to explain the contradictions, but Einstein hit the nail on the head.

Einstein's theory of relativity turned out to offer solutions for some phenomena that did not fit in classical physics. Relativity theory united the three fundamental theories: the law of gravity (or the law of gravity), electrodynamics and thermodynamics.

The special theory of relativity

Before Einstein drew his conclusions, he had to make short work of a number of scientifically accepted assumptions.

He started it in the early 20th century, and the work culminated in 1905, when Einstein published a number of articles in a physics magazine. The article also included his famous formula E = mc2 introduced.

In short, that formula means that energy (E) and mass (m) can swap places. Energy can be retained in matter with a mass, and that energy can be released later.

Before the special theory of relativity, people knew that 'air' can be converted into mass, and vice versa. You saw that as a material rust, for example, and after that it is heavier than before. People also knew energy in the form of heat and fire. But there was no connection between the two.

Strange phenomena have already appeared. For example, the Curie couple had done experiments which showed that some types of ore could emit particles for hours or even months. How that was possible was only a mystery.

Einstein came up with a completely new explanation: light. Or rather, the speed of light (c).

Light speed confuses science

It is perhaps difficult to understand how the speed of light can influence the formation of mass and / or energy. So first, let's look at the properties of light.

Before Einstein published his articles, scientists thought that phenomena such as light and sound always move at a speed that can be greater or lesser depending on where you are.

If you drive 50 kilometers per hour in a car and have a light with you, the light would, according to that idea, go 50 kilometers faster than if it were transmitted from a fixed point.

But at the end of the 19th century, physicists Albert Michelson and Edward Morley did a number of tests that showed that light does not go faster or slower when you "chase it".

Light speed is in a class of its own

Einstein also thought that the speed of light was a constant. He based himself on the light theory of another scientist: Maxwell, the founder of electromagnetism. Maxwell believed that a beam of light is moving because a small amount of electricity is formed, which, with its forward movement, forms a magnetic field that generates new electricity. Jumping like a goat.

But Maxwell never fully understood how the light could go faster or slower.

Einstein introduced a whole new idea, namely that light always moves at the same speed, whether it is emitted from a moving lamp or not.

Because electricity is always propelled by the magnetism that arises, Einstein also suggested that it will be faster than all "pursuers." In other words, light waves depart at the highest speed in the universe.

Mass is solidified energy

And what does the speed of light have to do with mass and energy? Imagine a space shuttle that goes almost as fast as light. The pilot keeps adding energy to the engines, but that energy cannot be used to exceed the speed of light. On the other hand, that energy cannot disappear either - it is compressed into mass. The space shuttle is therefore heavier. E (energy) becomes m (mass).

The sun is an inverse example. Tons of hydrogen (mass) disappear every second and are converted into energy.

Every substance on earth is therefore 'solidified' energy. And if that energy could be released, a piece of paper could already be responsible for the entire energy supply of the country.

But it is not easy to release that energy. The fuels that we use to get energy (such as gasoline) only release a fraction of the energy that is trapped in the matter.

Time is relative

That light has a constant speed has consequences for our understanding of time. When two spaceships send a light flash to Earth, the light moves at the same speed from the two spacecraft.

But if one spaceship hangs still and the other moves in the same direction as the light, one light will arrive later than the other. It depends on which space ship you are in. In the spaceship that hangs still, time will go faster than on board the spaceship on the move.

However, we never get close to the speed of light; the speeds at which we move on earth are so infinitely low that we do not experience those variations over time.

But the time is relative, in contrast to the speed of light, which is constant.

Here you see a video that explains the phenomenon of relative time:

The twin paradox

The relative time is often illustrated with twins, half of whom go on a trip to a star at light years' distance, while the other half stay on Earth.

Transport is almost as fast as light, and as we now know, time will go slower for the traveling twin than for the twin standing still on earth.

Because time goes slower for the traveling twin than for the twin on Earth, the astronaut of the two will also age less quickly. When he comes home he is even a few years younger than his twin brother.

This is explained by the American astrophysicist Neil deGrasse Tyson in this video about relativity and the twin paradox:

The next step: the general theory of relativity

In the ten years after the publication of the special theory of relativity, Einstein was busy weaving the gravity into his theory. The result put an end to classical physics and the prevailing understanding of gravity.

According to Einstein, heavy objects can change the space geometry. Instead of considering gravity as a result of mass attracting mass - as Newton did - Einstein suggested that the space curves around objects of varying gravity.

A striking image of this is a bullet on a trampoline.

The cannonball makes a hole in the surface of the trampoline, and if you place a golf ball next to it, it rolls towards the cannonball. So mass does not attract mass, but objects simply follow the curvature of the space.

In this example, a golf ball will rotate at high speed around the cannonball, eventually bumping into it.

And that is exactly what happens to planets that orbit a heavy object, such as a black hole. First they will turn around it and finally be swallowed.

Light and time, which have no mass, will curve around the object and continue on the other side - unless the curvature is so great that the light starts to spin and cannot leave the black hole on the other side.

The greater the variation in gravity, the greater the curvature.

And there is Einstein's theory of relativity

Einstein's thoughts turn physics upside down. But why? At least Newton's explanation of gravity that interlocking bodies was very clear and simple.

Here on earth we all move at the same speed as the earth and the solar system rotate. That is why we feel that we are standing still. The variation that occurs when one is standing still and the other is driving is so small that we do not experience the difference in time personally.

Because we have about the same experience in terms of speed and time everywhere on Earth, Newton's gravitational theory is sufficient to understand the world.

But in the space, where the distances are greater and where the celestial bodies are heavy and move at great speed relative to each other, it is another matter.

Without relativity, GPS would be unusable

The general theory of relativity is of enormous importance for our conception of the concept of space and the universe. The big bang theory, for example, would never have arisen without the theory of relativity.

But the theory of relativity also plays a role in the more everyday phenomena.

Take GPS, for example, with which you can accurately determine your position on earth to a few meters. A GPS system receives information from satellites orbiting the Earth in a fixed orbit. If you are somewhere on earth, your GPS searches for the position of the satellites at exactly that moment.

Two things are important here. Firstly, satellites move faster compared to our resting position here on Earth. The time of a satellite is therefore 7 microseconds slower than on earth.

But the gravitational field also plays a role. The satellites are located at a distance of 20,000 kilometers from the earth. There, gravity is four times less than on the surface of the earth, which means that time is 45 microseconds faster. If you correct those two numbers, the time on a satellite is 38 microseconds faster.

That doesn't seem like much, but if you convert it into distance, then 38 microseconds time difference means an inaccuracy of almost 11 kilometers per day.

If you did not know the theory of relativity and were unable to correct the time differences, a GPS system would be unusable.

Relativity theory not yet definitively proven

Einstein's work was purely theoretical, and he wasted no time in proving his thoughts with experiments. But others picked up the thread. For example, an experiment was held in 1919 that showed that Einstein was right when he said that the light curves as a result of the space geometry.

Other parts of Einstein's theory were only proven around the year 2000, for example at the CERN research center in Switzerland.

Yet there are still elements in relativity that have not yet been definitively proven. But the more experiments that support the predictions of the theory, the stronger the theory becomes.

100 years after Albert Einstein published his theory of relativity, the theory (together with quantum physics) offers the best explanation for the way in which physics works in our universe.

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