David H. Burns schrieb:
>> This is not so for light: No matter whether you're a stationary (hah!) 
>> outside observer or zipping along at near-lightspeed, you'll always 
>> see the light go at some 300,000 km/s relative to you.
> 
> We can't get out of the medium to observe light waves as we can with 
> water waves.

Well, then compare it with the perspective of a person actively 
swimming: Despite obviously being inside the medium, from his point of 
view water waves going in the same direction as he is appear to be 
slower than those going in the opposite direction.

You don't even have that with light, no matter how fast you "swim".

> I have heard the apparent decrease in the velocity of light is explained 
> by the interference of light
> re-emitted by the material so as to give the appearance of a decrease in 
> velocity. But the "true" velocity
> of the light remains that in free space. (I did not altogether 
> understand this and may have it wrong.)

Given that refraction normally occurs due to different /phase/ 
velocities of light in two materials, but at the same time there have 
been experiments reducing the /signal/ velocity of light almost to a 
standstill... no, I guess that's oversimplified.

> That may be what I was getting at, but also the fact that the 
> "relativistic" effects
> such as time dilation or increase in mass that I would observe in an object
> (say a space ship) moving with 99.99% the speed pf light relative to me 
> are *not*
> observed by its occupants and my observation is no more (or no less) 
> valid than theirs.

Which basically boils down again to saying that your /frame of 
reference/ (which includes sort of a local definition of length) is no 
more (or no less) valid than theirs.

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