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Is speed relative or absolute?
If you throw a ball 50 mph, that speed is only relative to the Earth. From another perspective, the Earth is rotating and shooting through space, so the ball is traveling much faster that 50 mph. From another perspective, our whole solar system is hurtling through the galaxy, and so on. So it seems like when you ask how fast something is moving, you always have to ask "with respect to what."
So I've never been able to understand how light can have a constant speed. How can my motion only be measured relative to other objects while light can be measured absolutely?
3 Answers
- Big DaddyLv 77 years agoFavorite Answer
As you say, speed is always measured relative to something else. Relativity was developed with the fact that light is always measured to move at the same speed by any observer as a given, and then to find the consequences of that.
This fact is also noticed when you look at Maxwell's equations. The propagation speed of light falls naturally out of the equation. Because there is no special frame of reference for those equations, it is valid in all frames.
Not really an explanation, but take a look at this video:
- oldprofLv 77 years ago
Its simple...that light thing. It's always the same no matter what it's relative to.
And why that is is also simple. It's because both time and space adjust to make it so.
Now here's the hard part. We've no clue why time and space adjust to make the speed of light the same no matter what reference frame it's relative to.
- 7 years ago
The speed of light is constant in vacuum with respect to a stationary observer. If you find the speed of the light with respect to something it will be different. Its just that the magnitude of speed of light is so great that even if it is compared to the speed of a supersonic jet, it will still be of the order of 2.999999999...x10^8. So the change is negligible and hence it is said that the speed of light is constant
