# If time is relative, then why is the time parameter used in measuring the speed of light, which is constant and does not depend on the speed of the light source?

## Your Daily Equation | Live Q&A with Brian Greene

Last update: 5 answers

Previous questionI'm afraid to go on a quest with an actor. Is it really scary? How does he behave and how should I behave? (scary quest)?

Next questionWhat to do if you lost your iPhone?

## Answer 1

September, 2021I created a plan-no, not for 6 revolutions of the Earth around its axis, and not even 6 revolutions of the Sun or Galaxy, but ... The speed of light depends on the speed and direction of the light source, and depending on whether it is read it is a wave or a photon ...

## Answer 2

September, 2021What if we are measuring the wrong thing? If you reach the speed of light, then theoretically time will stop. Those. light has no speed. There is a speed of time through which light reaches us. The light itself is transmitted from object to object instantly according to the law of conservation of energy. And we only observe the passage of time, which we cannot understand, because are completely dependent on it and cannot influence it ...

This is of course my personal theory, but it seems to me much more likely than what the scientific world is stuffed with now - they build theories based on the theory that they came up with thanks to the theory of the theory of relativity, which is considered not entirely correct, but at the same time is a postulate for modern science.

## Answer 3

September, 2021The speed of light in a vacuum is constant, but space-time itself is not. This constancy (invariance) was not actually invented, but is a consequence of the principle of relativity.

You do not quite understand relativity correctly. I'll try to explain. I am far from gravitating objects (the curvature of my space-time can be neglected), and you are near gravitating object. We both measure the speed of light and, wow, it turns out the same. But if from my point of view I could take measurements in your area, I would get completely different values. The thing is that you are where space-time is curved (gravity).

Similarly, for a ray of light passing near a black hole (past the event horizon), it moves in a straight line and at a constant speed. From the outside it will look different - the beam has slowed down and changed its trajectory.

As strange as it may seem, relativism is constantly being confirmed. The simplest example is calculating the time in GPS satellites, because there in orbit the course of time is slightly different from that of the Earth.

Again, I remind you that this is an approximate and not entirely correct explanation, in fact, everything is a little more complicated: )

## Answer 4

September, 2021For the third time I will write this: the constancy of the speed of light is POSTULATE! From this postulate, it turns out that time is relative, as is length. In other words, there is an axiom about the constancy of the speed of light from which, as a theorem, the change in the length and flow of time is proved. The question confuses cause and effect.

## Answer 5

September, 2021Time is really relative (depends on the choice of reference system).

But the coordinate (length, distance) is also relative.

Linear velocity is the time derivative of the coordinate , but for rectilinear uniform motion, it can be expressed as follows:

c = (Change of coordinates) / (Change of time).

For the speed of light, the "relative change of lengths (coordinates)" is exactly is the same as the "relativity of the passage of time." They have the same "relativity" factor. It shrinks when dividing.

So it turns out that c is constant.