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Does time stands still at c? And is room a point then?

  1. Feb 3, 2008 #1
    hello, does time stand still for objects which move with c, like photons? And is the room contracted so much that its a point for thus photons?
  2. jcsd
  3. Feb 3, 2008 #2


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    Hi Danov,
    no object will ever be seen to move at c from any point of view whatever. Look up 'special relativity'. Photons are not objects and don't have a point of view, so time as we experience it cannot be ascribed to photons.
  4. Feb 3, 2008 #3
    Why? Photons are waves and particles, Particle-Wave-Dualism. Or not?
    Photons have no mass but they have energy. And because Mass=Energy and vv that doesnt matters. We know that Myons, which move nearly c, contract the room very much and time is passing much slower for them. Thats why they reach earth-surface. So Photons dont have any time-passing and any room. And that is strange. Wouldnt that mean that photons from their point of view would be everywhere at any time? I mean from their point of view the room is contracted to nearly nothing and so they reach one specific point without the need to move plus the time stands still for the photon and it can be at several places at a any time or even at many places at the same time?

    Im sorry if I misunderstood something but I didnt studied physics yet.
  5. Feb 3, 2008 #4


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    This has been discussed about a zillion times before. While I could probably point you at some of the earlier threads, I've been a little busy recently :-(. I would suggest that if you really want a detailed answer, that you take a look at these earlier threads.

    The short answer given above is correct, however, even if you don't find it satisfying. Photons do not have a "point of view" in the standard sense. Assuming that they do leads to severe difficulties, much as assuming that division by zero is possible does.
  6. Feb 3, 2008 #5


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    Mass and energy are very different things, although they can be converted one to another. Photons do not have have mass and thus travel at c.

    If a photon did have a point of view it would be very strange. But I doubt if it has any usefulness as a concept.

    Well, the photons in a tight laser beam are not everywhere are they ? So some of what you say can be ruled out from common experience.

    You should read Richard Feynmans book on QED.
  7. Feb 3, 2008 #6
    But they do have relativistic mass and momentum...
  8. Feb 3, 2008 #7
    If you know about the invariant interval in relativity, ds, then you will know that ds is the proper time for the frame traveling along any path. But you will also know that a light-path is described by setting ds=0. So the proper time for the photon is not changing as it travels along the path. And this means that everything goes by the photon at the same time in its own frame. I guess that's your "point."

    Here's a teaser: If the photon passes everything at once, is it traveling at infinite speed?
  9. Feb 4, 2008 #8
    yes, but the important point to me is that something is able to travel at c

    ok, I chose a photon because its the only object i know which travels with c. Are there other objects that travel with c and therefore have no mass?

    And I just dont understand why a photon should not have a point of view. Im still in school 12th grade yet but does not everything have a point of view? Thats what relativity-theory says: Everything is relative.

    From OUR point of view they are not everywhere. But who knows how this looks like for a photon? Or what do you say? How much is room contracted for a photon? Lets say 1000 meters. And does time pass for a photon? If not: How much are 1000 seconds for a photon?
  10. Feb 4, 2008 #9
    It dont needs to travel at infinite speed because the room at c speed, I think, is contracted so much that a photon (or anything else that fast) can reach every place in practically no time. But maybe thats my problem: How much is a room contracted for objecs at c? Maybe its not as much as I think. And what is the maximal room contraction at extremely high gravitational fields. But wait! Isnt it infinitely high at extrem big gravitational fields like center of black hole?
  11. Feb 4, 2008 #10
    Look, the simple answer is the following:

    In length contraction, the limit of x' as v->c is 0. The limit of t' is infinity. So, let's assume you get infinitely close to c (without reaching it). The universe becomes as a point, and all clocks have essentially stood still. The answer to both of the OP's question is essentially yes, with the caveat that you can get infinitely close to c but cannot reach it.
  12. Feb 4, 2008 #11


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    Hi Danov,
    No, it doesn't. Relativity is about inertial frames which are alway linked to matter. A point of view must belong to something that can see.

    It is good that you explore these ideas and equations, but you must be aware that the Lorentz contraction no longer holds good when v=c.

    I wish you well with your studies.

  13. Feb 4, 2008 #12


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    A photon doesn't have a reference frame in relativity, so you can't really ask how much is a room contracted for objects at c. What you can do is ask what the length of the room is in the limit as an observer's speed relative to the room approaches c, and the limit in this case would be 0.
  14. Jul 26, 2011 #13
    Hi Danov.
    There is no actual answer that can be given to you about your question , this is because under the present set of "Rules" we work under (relativity etc) a photon has no point of view. And to most people the hypothetical point of view of a photon has no use, you might say that this is very unfair to the photon, which might indeed have a very extraordinary point of view. Now one day we could be in a position where we have the right set of "rules" that allow us to see this point of view but right now the only "observer" is you and me.
  15. Jul 26, 2011 #14


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    Hi, Infernos,

    Welcome to PF! This thread is three years old. We try to discourage people from posting in old threads like this. (It's referred to as "necroposting.")
  16. Jul 26, 2011 #15
    Hi bcrowell.
    Thanks for the heads-up on posting protocol, I posted only due to relevance this post still has when searching on this topic on google (very close to the top!)
  17. Jul 26, 2011 #16
    Hello Infernos,

    May be worth starting a thread of your own if you are looking for more specific information.

    The general quality of response on this site is usually good and there are some very valid and authoratative posters.
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