# Puzzled by light?

1. Dec 26, 2007

### Prasanna Suman

Puzzled by light???

Why has light same velocity when measured from any frame?

I know about Maxwell's theoritical deduction (but not clearly) and the Michelson-Morley experimental deduction.

When understanding light I tried to make it analogous with sound. It just further degraded the situation.

Can anyone help me?

2. Dec 27, 2007

### rbj

what, exactly, do you know about Maxwell's position on this?

well, that's a mistake. sound moves with the air. we know it when air is blowing past us and will not expect the speed of sound (relative to us standing in the breeze) to be the same in all directions.

now, think about this: would you know it if a vacuum was moving past your face? compared to a "stationary vacuum"? is there any physical meaning to the movement (or stationarity) of a vacuum?

3. Dec 27, 2007

### peter0302

Asking why the speed of light is always constant is kind of like asking why things always fall down or why the angles in a triangle always add up to 180 degrees. No answer really exists. :)

Einstein assumed the speed of light was constant and then derived special relativity, which provided experimentally verifiable predictions. Because many of the predictions turned out true, we assume the underlying postulates are all true. But, in fact, one of the predictions is that no influence can travel faster than light, and thanks to quantum entanglement the jury is still out on this one.

Then again, one can formulate other postulates and thereby _derive_ the fact that the speed of light is always constant. But then one could ask why those postulates are "true."

Until a more complete theory of spacetime can be formulated which encapsulates special & general relativity as well as all of quantum mechanics (including entanglement) no one will have a better answer to that question.