View Single Post
Oct11-11, 01:23 AM
PF Gold
P: 1,376
Quote Quote by Bjarne View Post
Now we assume the meter stick always is comparable the exact same for both A and B.
Observer A and B will now in a certain period measure a photon traveling a certain distance (300,000 km).
Both observers agrees that this is what really happen.

Based on this observer A would say that the speed of light is exactly 300,000 km in one (of his) second.

But observer B would say OK I agree the distance the photon was travelling is 300,000 km ...
BUT I do not agree it took one second, - my clock shows it only took ˝ second, so here the speed of light is 600,00km/s
Do you prefer that solution?
Hmmm… So what we do next?
This is different from how Shapiro experiment was performed.
There is only one observer who is sending radar signals so that sometimes they are passing close to the Sun and sometimes far from the Sun. When you make a correction for time delay depending on signal's closest passing distance from the Sun you can consistently describe orbit of observed object (Venus).
In your case speed of light is always the same because proportion "m/s" does not change.

Quote Quote by Bjarne View Post
I have never heard about Shapiro time delay. If it really is certain and confirmed knowledge, and not something only at a test level, - yes we have a one more problem/challenge..
From Wikipedia about Shapiro delay:
"The time delay effect was first noticed in 1964, by Irwin I. Shapiro. Shapiro proposed an observational test of his prediction: bounce radar beams off the surface of Venus and Mercury, and measure the round trip travel time. When the Earth, Sun, and Venus are most favorably aligned, Shapiro showed that the expected time delay, due to the presence of the Sun, of a radar signal traveling from the Earth to Venus and back, would be about 200 microseconds,[1] well within the limitations of 1960s era technology.

The first tests, performed in 1966 and 1967 using the MIT Haystack radar antenna, were successful, matching the predicted amount of time delay.[2] The experiments have been repeated many times since then, with increasing accuracy."

Quote Quote by Bjarne View Post
Hmmm speculate, but not too loud, suggestion could be wrong, and we would look stupid.
What do you think the answer is (except that distances / the meter stick always are comparable the same lenght) ?
First of all speed of light globally is not the same everywhere.
Statement that "laws of physics are the same in all inertial reference frames" means that local experiments will give the same results. But global observations can be different.