# True Speed Of Light?

1. Nov 15, 2012

### mike777

Because time slows down at the speed of light does then light itself potentially travel at almost infinity per zero seconds?
(trying to leave aside relativity and gravity issues for a moment, so just theoretically?)

Is that then the real reason why nothing can go faster than light - ie. light is actually at infinite speeds only limited by the medium it travels in, our universe time/space in this case is limiting the speed in a less obvious but similar way that dense glass might change light speed and wavelength. It's not that light speed is the limit but that light itself is the only thing fast enough to fully reach whatever that limiting factor is?

I know it's a daft question as we are stuck in this universe and I realise it's getting back into an ether theory, but just hypothetically, as I then have some other questions?

2. Nov 15, 2012

### ghwellsjr

What is your definition of time that permits you to ask the question: "Because time slows down at the speed of light does then light itself potentially travel at almost infinity per zero seconds?"?

Einstein defined time as that which a clock measures. You cannot build a clock out of just light, you also need some matter. Matter cannot travel at the speed of light. Therefore, there is no definition of time that would apply at the speed of light. It's not that time slows down to the point of stopping at the speed of light, it's that the concept of time is meaningless at the speed of light.

Got it?

3. Nov 15, 2012

### DiracPool

A photon traveling at c expereinces no time. That is a definition. It has nothing to do with infinity or zero seconds. A photon passing through glass and slowed down expriences time because it is slowed down to less that c, but it is not the same photon, becuase it is a process of absorbtion and reeimssion through matter, so that point is moot.

4. Nov 15, 2012

### mike777

'The concept of time is meaningless' - therefore light would move instantaneously if it weren't being slowed by our type of universe?

5. Nov 15, 2012

### ghwellsjr

You know--you have a way of expecting answers from other people but when we ask you questions to try to help you, you just ignore them. I asked you a question--please answer it before going on to more questions:

6. Nov 15, 2012

### mike777

Ok, well I would define time as an event that takes place after another, for example a photon starting in one place of the universe and ending up at another, if no time is involved then it would exist in both and all places?

7. Nov 15, 2012

### ghwellsjr

Now I have to ask if by "event" you mean what is commonly understood by the term in the context of relativity? It is a set of coordinates according to a previously specified Frame of Reference. Accordingly, there is no problem with a photon starting at one location at one time and arriving at another location at a later time, traveling at the speed of light. Why do you say "no time is involved"?

8. Nov 15, 2012

### Whovian

What you may be missing is that, from a beam of light's point of view ...

Ignore that comment, there's no point in defining anything from a beam of light's point of view. However, from anyone else's point of view, it travels from point a to point b in time d(a,b)/c, where d(a,b) represents the distance between a and b.

9. Nov 15, 2012

### mike777

I've already got in trouble before by using the light's point of view!

Ok how about a place outside our frame of reference where the photon departs and arrives instantaneously because time is not a factor. Would that be the natural order of things were it not for our universe construction - ie. the nature of our universe restricts light speed?

10. Nov 15, 2012

### ghwellsjr

We're talking about Special Relativity where we restrict ourselves to flat spacetime--no influence or consideration of gravity. So in that context, there is no place outside any frame of reference. You're just making up stuff. You can dream up any answer you want but it's not allowed on this forum. It's called unfounded speculation. I also wouldn't say that "the nature of our universe restricts light speed". I would say that the speed of light, c, is part of the nature of our universe.

11. Nov 15, 2012

### DiracPool

Let's not get off topic here, I've had threads closed because of that. The OP's question is pretty straightforward. And the answer is, again, moot. Its like saying, well, if I were a linebacker trying to score a touchdown, could I do that instantaneously if there was no opposing team? The answer is...wait for it...yes, maybe in some string theory derived universe. But in the real world, we have a time limit, for whatever the restiction of the medium is, and that is the speed of light c.

So, yes, in real life there is an opposing team. And if you want to eschew that fact for speculative purposes, that is fine, but you're not going to get satisfactory answers.

12. Nov 15, 2012

### Staff: Mentor

There is no such place. An inertial reference frame in SR has infinite spatial extent.

You could certainly define such a reference frame, but it would not be inertial, by definition.

13. Nov 15, 2012

### mike777

Ok apologies, i am a novice so just trying to ask things that you guys may be able to enlighten me about, I can understand why hypothetical stuff leads to nowhere but it just helps me get my head around it all by thinking at extremes.
I was going to eventually get round to asking if that meant there were any merits in the ether theory as it would seem to solve a lot of questions revolving around missing dark matter etc.

14. Nov 15, 2012

### Staff: Mentor

Instead of thinking at extremes, you should start by learning the basic definitions and concepts. Once you have mastered the basics then you can look to more advanced concepts.

You are trying to play on the Olympic team without ever practicing or even learning the rules. You may think that is helping you get your head wrapped around things, but it isn't.

15. Nov 15, 2012

### mike777

You are so certain the rules are correct, seriously??
But apologies, I hadn't realised you are the olympic team who know everything and will solve all the mysteries, I will go and find a physics for dummies forum where hopefully they will be slightly friendlier than you lot!
(no offence, that's just from my frame of reference of course)

16. Nov 15, 2012

### Staff: Mentor

Yes. See the sticky about the experimental basis of SR. The evidence is overwhelming.

You misunderstood the analogy, sorry that it was not clear. Your "thinking at the extremes" is the Olympic team. That is what you shouldn't attempt until you at least know the rules and have practiced a bit.

17. Nov 15, 2012

### nitsuj

They are a friendly bunch here, just be easy on yourself princess

They won't let you speculate foolishly on physics. Foolish musings doesn't at all mean you're a fool. Leave your emotions out of these physics discussions, that too is non-sense.

mike777 very strictly, time slows down at the speed of light only comparatively.

Note this too, why are you not also asking "since length contracts approaching c, in the FoR of a photon is the photon instantly teleported to it's next event."

So if I think of those two questions, re-reading

Because time slows down at the speed of light does then light itself potentially travel at almost infinity per zero seconds?

The light travels zero length in zero seconds. The real deal is there are 3 spatial and 1 temporal dimensions in between those events.

Are we going to discuss the Block Universe concept now?

Last edited: Nov 15, 2012
18. Nov 15, 2012

### ghwellsjr

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.

19. Nov 15, 2012

### nitsuj

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. :uhh:

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.

Last edited: Nov 15, 2012
20. Nov 15, 2012

### ghwellsjr

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".

21. Nov 15, 2012

### nitsuj

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".

22. Nov 15, 2012

### ghwellsjr

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.

23. Nov 15, 2012

### nitsuj

oh I get it, it's a last word thing.

24. Nov 15, 2012

### DiracPool

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.

25. Nov 16, 2012

### harrylin

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."
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.