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True Speed Of Light?

by mike777
Tags: light, speed
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nitsuj
#19
Nov15-12, 12:57 PM
P: 1,097
Quote Quote by ghwellsjr View Post
Light does not travel zero length in zero seconds.

Look, in flatspace time, pick any two events. One of three things will be true:

1) You can measure the interval between those two events with an inertial ruler that is present at those two events. This measurement will be a pure distance, independent of any Reference Frame that we use to define the coordinates of the two events.

2) You can measure the interval between those two events with an inertial clock that is present at those two events. This measurement will be a pure time, independent of any Reference Frame that we use to define the coordinates of the two events.

3) You cannot measure the interval between those two events.

If the two events in question are the start and end points of a photon, then it is impossible to measure the interval because it is of the third type.

In Special Relativity, we follow Einstein's convention and assign a velocity to the photon of c. This means that all Reference Frames will agree that the velocity is c even though their different coordinate definitions will assign a different distance and a different time between the two events but none of them assigns zero distance or zero time between those two events.
Of course it doesn't travel zero length in zero seconds. That doesn't even make any sense, and it was supposed to come across as such.

I was raising the point of the other consideration; length contraction, pointing out, "hey if you feel light travels a length in zero amount of time..you must also say it traveled zero length.
ghwellsjr
#20
Nov15-12, 01:19 PM
PF Gold
P: 4,687
Quote Quote by nitsuj View Post
Of course it doesn't travel zero length in zero seconds. That doesn't even make any sense, and it was supposed to come across as such.

I was raising the point of the other consideration; length contraction, pointing out, "hey if you feel light travels a length in zero amount of time..you must also say it traveled zero length.
We don't want to entertain false notions. Even for a frame moving at very close to the speed of light (compared to another), the lenth and the time, although approaching zero, are still finite and divide to give c. If you tried to argue that a frame could be moving at c (compared to another), you would have to divide by zero to get gamma which is not allowed mathematically.

I think it is more important to stress that even if you accelerated to a speed that was very close to the speed of light, everything for you would be just as it was before you accelerated, and the measured speed of light would still be c, just as "far" away as it was before you accelerated. This is why Einstein said "the velocity of light in our theory plays the part, physically, of an infinitely great velocity".
nitsuj
#21
Nov15-12, 03:55 PM
P: 1,097
Quote Quote by ghwellsjr View Post
We don't want to entertain false notions.
Length contraction isn't a false notion, to maintain the logic I mentioned length contraction.

It's merely using the OPs scenario & a well known SR concept to help shed light on why the scenario doesn't make sense (or as you have called it, a false notion).

If the OP only considers time slows, they are missing two points, length contraction & more importantly but more difficult to grasp, it is ONLY COMPARATIVELY that time slows/ length contracts.


You mentioned the same thing with the Einstein quote regarding c being "an infinitely great velocity". In that case there is no comparative, all measurements are proper, so c is "an infinitely great velocity".
ghwellsjr
#22
Nov15-12, 04:28 PM
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P: 4,687
Length contraction all the way to zero is a false notion. It never happens nor can it ever happen...just like time slowing down all the way to stopping is a false notion.

Einstein didn't say that the speed of light is "an infinitely great velocity". It's not. It's finite. He said that it plays the part of an infinitely great velocity, meaning that it can never be reached.

The OP is proposing the idea that the speed of light is actually infinite but that the reason why it appears to be finite in our universe is that it slows down when going through a medium, in this case, ether. He's looking for support of that false notion.
nitsuj
#23
Nov15-12, 05:23 PM
P: 1,097
oh I get it, it's a last word thing.
DiracPool
#24
Nov15-12, 08:43 PM
P: 534
The OP is proposing the idea that the speed of light is actually infinite but that the reason why it appears to be finite in our universe is that it slows down when going through a medium, in this case, ether. He's looking for support of that false notion.
OMG people, it is meaningless to talk about anything faster than the speed of light? Don't you agree? What if we set c to 7.8 x 10^22? What difference would that make? Assuming, of course, that all the other physical constants were in alignemnt to make the universe work. It would just even out that way. Conjecturing on an infinite speed of light is simply special relativay-naivatee.
harrylin
#25
Nov16-12, 04:29 AM
P: 3,184
Quote Quote by nitsuj View Post
Length contraction isn't a false notion, to maintain the logic I mentioned length contraction.
Yes exactly, Einstein also clarified it in his first paper with "For v=c all moving objects—viewed from the “stationary” system—shrivel up into plane figures."
[..] You mentioned the same thing with the Einstein quote regarding c being "an infinitely great velocity". In that case there is no comparative, all measurements are proper, so c is "an infinitely great velocity".
I now think that that is not exactly what Einstein meant with that; it's more likely as ghwellsjr put it. But it doesn't matter, in view of the above citation.
I found your post #17 clear; let's see what the OP finds.
nitsuj
#26
Nov16-12, 09:44 AM
P: 1,097
Quote Quote by harrylin View Post

I now think that that is not exactly what Einstein meant with that; it's more likely as ghwellsjr put it.
Yea ghwellsjr put it more clearly, I was reiterating to show I understood in what sense c is an infinity great velocity, specifically plays the role of an infinitely great velocity.

Here is an a example of what I think ghwellsjr is doing.

ghwellsjr - "He said that it plays the part of an infinitely great velocity, meaning that it can never be reached."

a ghwellsjr style retort - "That is false, things travel at c all the time."


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