# True Speed Of Light?

by mike777
Tags: light, speed
 P: 12 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?
 PF Patron P: 4,178 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?
P: 492
 Because time slows down at the speed of light does then light itself potentially travel at almost infinity per zero seconds
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.

P: 12

## True Speed Of Light?

'The concept of time is meaningless' - therefore light would move instantaneously if it weren't being slowed by our type of universe?
PF Patron
P: 4,178
 Quote by mike777 'The concept of time is meaningless' - therefore light would move instantaneously if it weren't being slowed by our type of universe?
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:
 Quote by 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?"?
 P: 12 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?
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P: 4,178
 Quote by 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?
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"?
 P: 634 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.
 P: 12 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?
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P: 4,178
 Quote by 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?
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.
P: 492
 'The concept of time is meaningless' - therefore light would move instantaneously if it weren't being slowed by our type of universe?
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.
Mentor
P: 15,619
 Quote by mike777 how about a place outside our frame of reference
There is no such place. An inertial reference frame in SR has infinite spatial extent.

 Quote by mike777 where the photon departs and arrives instantaneously
You could certainly define such a reference frame, but it would not be inertial, by definition.
 P: 12 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.
 Mentor P: 15,619 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.
 P: 12 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)
Mentor
P: 15,619
 Quote by mike777 You are so certain the rules are correct, seriously??
Yes. See the sticky about the experimental basis of SR. The evidence is overwhelming.

 Quote by mike777 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)
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.
 P: 1,071 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?
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P: 4,178
 Quote by nitsuj The light travels zero length in zero seconds. The real deal is there are 3 spatial and 1 temporal dimensions in between those events.
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.

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