النسبية .. الفيزياء

Relativity .. Physics

Relativity

In 1905, Einstein presented his theory of relativity, which later became famous, and through it he explained the results of the experiments conducted by Michelson and Morley in 1887, through which they sought to know whether the speed of light was related to the direction of its movement relative to the rotation of the Earth. This is because they had compared the speeds of two light beams, one parallel to the rotation of the Earth and the second perpendicular to it, and it became clear to them that the two speeds were equal and that the speed of light was not therefore related to the speed of its source, that is, in other words, an absolute speed that is not subject to the speed of the person observing it. This was the most wonderful conclusion achieved.

It is worth noting that the rule adopted in linking speeds to each other is summarized by adding or subtracting them according to the following equation A B = A A + A B
Where A B represents the speed of A relative to the speed of B, and A A and A B represent the speeds of A and B separately. The choice between addition and subtraction depends on whether the two speeds are in the same direction or in different directions. However, if an astronaut tries to measure the speed of a light beam coming towards his vehicle that is moving at 90% of the speed of light, he finds that it is equal to the speed of light itself and not to the sum of his speed and the speed of light as required by the previous equation. The equation that Einstein presented to relate the speed of A to the speed of B is not the addition of A with B, but rather as follows: A B = (A + B) / (1 + A A B / H 2)

(Michelson-Morley test to prove the difference between the speeds of light in the two paths M-B, M-A)

(The traditional rule for calculating speeds does not apply to objects moving at speeds close to the speed of light)

An equation in which we replace the speed of B with the speed of light H, we find that A B = H. This equation is considered a general law in calculating speeds, and the results of Michelson and Morley's experiments were interpreted through it. However, it turns into a mere sum of speeds if the value of the latter is small relative to the speed of light itself. Even if it reached 200,000 km per hour, the difference in applying the two equations in calculating A B does not exceed one percent.

This equation formed the basis on which the theory of special relativity was built. It was called special because it only applies to moving objects whose speed remains constant, unlike the theory of general relativity, which also applies to accelerating objects.

This theory has many far-reaching consequences.

The first result is that if car B moves at a speed of AB relative to car A, its length, as seen by the pilot in the other car, will be as follows: L A B = L B root 1 - H2B / H2 where L B represents the length of car B at rest. This contraction in the length of the car is called the Lorenz-FitzGerald contraction, and can be neglected at slow speeds, and its value does not exceed 10-12 cm if the speed remains less than 800 km per hour. However, if the speed of the body reaches 90% of the speed of light, the contraction then becomes equal to half the original length. It should be noted that the pilot inside his ship will not notice any difference in its length because he is moving at the same speed as it. This difference in length is only noticed by observers who are moving relative to each other. The second result that emerged from the theory of special relativity is the increase of mass with velocity according to the equation m = m5/root 1 - v2/h2 where m5 represents the mass of the body in a state of stasis and k its mass if its velocity is v.

It is very clear that this increase can be neglected in the case of normal velocities. However, if the velocity reaches 99% of the speed of light, the mass becomes approximately seven times its original value.

The greatest effect of this increase in mass is the relationship between energy and mass that results directly from it. Einstein proved that the energy resulting from a mass m is equal to F = mh2, meaning that mass is, in the end, a form of energy. When it disappears, it is also transformed into energy.

(Astronomical proof of general relativity: The sun causes a distortion in the path of light, which results in an apparent shift in the position of the star)

(The elliptical orbit of the electron, which assumes a fixed mass to the left)

Another result of special relativity is that when two observers move at a constant speed relative to each other, each feels the other's clock slowing down.

This has little effect on the instantaneous concept of events. We do not perceive an event on the sun until eight minutes after it occurs, which is the time it takes light to travel from the sun to the earth. Similarly, we do not perceive an event on Jupiter until 43 minutes have passed. The event itself does not appear instantaneous to both observers, and Einstein believed that determining an event requires taking both time and distance into account on an equal footing. However, he advised that space should be studied using four dimensions, three for distance and one for time, thus forming a four-dimensional universe.

When Einstein published his general theory of relativity in 1916, he based all his information on the existence of a four-dimensional universe, and he found that Euclidean geometry is not suitable for studying such a universe, as a straight line usually follows the curvature of the earth, and this is sufficient for terrestrial measurements. In space, the straight line is determined by light rays that are subject to the laws of gravity, which make the universe a (curved) universe, the degree of its curvature being related to the masses it contains. The theory of the curvature of light was later confirmed by astronomical observations.