# Is the time relative to the size

## What does “everything is relative” mean?

The principle of relativity is as follows: certain properties and physical quantities can only be defined or measured relative to an observer's perspective. The principle of relativity is a cornerstone of physics. It goes back to Galileo Galilei. It was further developed by Albert Einstein for the theory of relativity.

Specifying a speed, for example, only makes sense if it is specified relative to something else. Normally the other is the earth's surface at rest. But if you consider that the earth rotates and the earth moves around the sun, and the sun moves in the galaxy Milky Way, one could really come to the sentence: "everything is relative". The phrase "everything is relative" does not mean that everything is "irrelevant".

A measured value is called absolute when it stands for itself:

It is now 17 degrees Celsius.

A measured value is called relative when it is compared with another:

Today it is 20% warmer than last year at the same time.

Galileo Galilei formulated the principle of relativity on the basis of the controversial question of whether a ball on board a moving ship was in motion or at rest. His analysis of the problem was that the answer to the question depends on the position of the observer:

An observer who is also on board the ship sees the sphere at rest, while an observer on the bank sees the sphere move together with the ship.

The property of being in motion is therefore not a property of the sphere alone, but depends on the choice of the frame of reference.

According to Galileo, physical properties must be divided into relative, which therefore depend on the properties of the observer, and absolute, which can be determined or measured independently of the choice of the reference system.

In physical terms, the principle of relativity says that the same laws of nature apply in inertial systems that move uniformly relative to one another. When "strange effects" occur, it is often an indication that one is not in an inertial system.

An inertial system is a stationary or uniformly moving, unaccelerated system.

Everything seems to be normal in the dining car when things at the table behave as they always do. But if suddenly the coffee cup moves off the table, one can assume that one is no longer in an inertial system. The train brakes or accelerates - or drives too fast or slowly into a curve, that is also an accelerated movement.

The principle of relativity was extended to the theory of relativity by Albert Einstein. Einstein demanded the principle of relativity not only for the laws of mechanics, but also for electrodynamics.

The result was that in favor of a general principle of relativity one had to forego the idea of ​​an absolute space and an absolute time.

For speeds that are small compared to the speed of light, Einstein's principle of relativity changes over to Galileo's principle of relativity.

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Photo by Hannes Richter on Unsplash.