Let's talk about the relativity of time, the shortening of size, in short, special relativity in this article.

Special relativity is based on 2 postulates:

·      The laws of physics are the same for any inertial reference system

·      The speed of light is independent of the source. so it is absolute, not relative

The first postulate is the fundamental postulate of special relativity. It was also true for Newton's laws of motion, but Einstein developed this using Maxwell's laws of motion.  Maxwell determined that the speed of light has a certain value. In other words, the speed of light should be the same for both moving observers.

Take the ping-pong experiment on the train. The ball falls to almost the same point for the bouncer, while for the observer standing on the ground, the ball falls to the ground every forty meters.

Relativity of time. Image Credit: elektronikhobi

The same is true for light. When someone on the train turns on a flashlight, the distance the light reaches is different for the person on the train and the observer on the ground.

We know speed is distance divided by time. If these two observers have a dilemma about distance, it is because they disagree about the time the journey was made. In other words, the concept of absolute time disappears with relativity.

As for the second postulate:

Light is a type of energy made up of waves. People who started out with the idea that the environment is necessary for the transmission of energy and that an environment is necessary for the transmission of light came up with the concept of a captive clause in the 19th century.

In 1887, Albert Michel and Edward Morley conducted an experiment to prove the existence of the captive clause. They used the Michelson's interferometer for this experiment.

Michelson's interferometer

If the captive clause is present, the speed of light must vary depending on the movement of the source.

The speed of light is about 300,000 m/s.  We need to use very large velocities to change this value in any significant way—Michelson and Morley's experiment based on the earth's rotation around the sun. The speed of the earth's movement around the sun is 30 m/s. Rays sent in the direction of the earth moving in the captive clause must meet the resistance of the captive clause.

The speed of this light in the presence of captive clause:

300,000m/s - 30m/s = 299,070m/s

Michelson and Morley did their experiments with this in mind. They expected to notice a difference between the light paths on the detector. However, they could not observe any difference between the light paths according to the resulting pattern.

We said that the speed of light does not change regardless of the light source. As an object speeds up, time slows down for that object. When it reaches the speed of light, time stops for it. As objects speed up, they have kinetic energy. Some of these kinetic energies are transformed into mass. And objects with mass can never reach the speed of light because for this to happen, it must reach an infinite mass. However, the energy it receives must be infinite. This is impossible since the object in relativity has borders.

The second issue of relativity is length shortening. The specific length of an object is the lengths measured when that object is at rest. The measured length of the object while moving is always shorter than the specified length. And length shortening is always in the direction of travel.

Length shortening formula

What is the E=mc²?

This equation explains the conversion of energy to mass. According to the equation, the mass of an object with increasing energy also increases.

After Einstein published his special relativity in 1905, he realized that this theory was limited in 1907.  Special relativity was valid for objects moving in one direction at a constant speed. This theory became invalid when acceleration was involved. Einstein published his theory of General relativity after Special relativity.

İn the result:

Special relativity mentions that since time is not absolute, time slows down and expands with movement, dimensions shorten with motion, and there is no need to have a captive clause while these occur.


Mlodinow, S. H.-L. (2005). A Briefer History of Time. S. H.-L. Mlodinow içinde, A Briefer History of Time (s. 27-35). Istanbul : doğan kitap.

ÖZKARAYEL, L. (2014, 1 Eylül). 19. YÜZYILIN YANLIŞI: ETHER VE MICHELSON - MORLEY DENEYİ . august 2020 tarihinde Açık Bilim: http://www.acikbilim.com/2014/09/dosyalar/19-yuzyilin-yanlislanan-fikri-eter-ve-michelson-morley-deneyi.html adresinden alındı