How in theory of relativity the speed of light is cosidered costanst?

Question

How it is possible that for all observer the speed of light is constant irrespective of their own speed

Answer 1

How is it considered constant? It just is. It's one of the two axioms of special relativity, the other being relativity itself: that it is impossible to determine your own speed without outside reference.

The weirdness of special relativity: clocks slowing down, meter sticks shrinking, and disagreements about simultaneous events are all logical conclusions of these two axioms.

In other words, two observers moving relative to each other both still measure the speed of a light flash as c, because to measure speed one must measure distance and time, and each observer's metersticks and clocks are measuring things that are different from the other's in exactly the right way that everybody measures c as the speed of light.

Answer 2

That's an excellent question. The only way the speed of light can be constant for all observers, is if different observer experience TIME differently.

For example: Say that I am "standing still" and watching a spaceship speed past me at 99.9999999% of "c" (where "c" is the speed of light). The spaceship has its headlights turned on.

From my perspective, the light from the headlights is going at exactly "c", and is just barely creeping ahead of the spaceship at about 7 miles per hour. If I watch for 1 second, the light is only a few feet ahead of the ship

But from the spaceship's perspective, the light from the headlights is going at speed "c", 186,282 mph. If the spaceship captain watches for 1 second, the light is many thousands of miles ahead of the ship. How can this be?

The only resolution is to assume "one second" of MY time is not the same as "one second" of the ship captain's time. That is, the clock on the ship is ticking 22,000 times slower than my clock. Thus, when the ship's captain measures the speed of the light beam relative to his ship, it seems not to be going at 7 mph, but at full light speed.

If the ship caption waits for "one second," he'll see that the light has traveled 186,282 miles away from his ship. But by that time, more than 6 HOURS have elapsed from "my" point of view.

This "dilation of time" is such a startling prediction that it was hard for people to accept at first; but it has since been verified by experiment many times.

Answer 3

In a vacuum the speed of light is constant, even time does not exist at this speed, it does not matter if you are going toward it or moving away from it, the speed of light is always the same, nothing could be more constant than that.

Answer 4

the speed of light is really the only constant that exists, everything else is relative to it. It doesn't always seem the same for an observer because their speed can change, what they are looking at is the difference between their speed and the speed of light, not the actual speed of light.

Answer 5

Well, no one knows why it is, we really aren't that advanced yet. All we know is that it IS true. If you're traveling at half the speed of light, and turn on a flashlight, the light won't look to be going at half the speed of light, it'll look to be going the full speed of light. However, to a stationary object viewing you and your flashlight, it would look to be traveling at half the speed of light in relation to you. Since it seems to go against most of the physical properties were know, it is a very difficult concept to comprehend.

Answer 6

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