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Are photons timeless?

  1. Jun 15, 2011 #1
    I'm not a physicist, I'm only taking my first subject on physics in Eng. here in Buenos aires, so I don't know much about it. But i find it so interesting that I spend some deep hours of thought ofently in it, and i just want to clarify this concern:

    According to relativity your local time respect with someone else's time will dilate in function of the gravity field and your speed respect to him (Is that right?). As you move faster time will flow slower (just a way of putting it because time doesnt flow, does it?). When you get close to the speed of light time will dilate asymptotically to infinite. So if you would move at te speed of light -wich is impossible because it would take an infinite amount of energy- your time relatively to the to the other observer will dilate infinetely.

    Photons travel at light speed. Therefore time doesn't flow for them. Does that mean that photons are timeless? Their existence is intrinsic to the time sacle of the Universe? Does a photon exist in itself without reggarding the events of the Universe? (I think i know they don't because if you can experiment with photons you are interacting with them of course, but i say it so you would point out what is the logic gap in this thought, if there is). What is it's nature of existence? What can you tell -anything- about a photon reggarding this aspect? Or - of course- What is wrong with my logic?

    Thank you!

    PS: Photons are massless aren't they? But they are quantums of energy wich is equivalent to some mass, so it still makes sense thinking about photons as something that can be subjected to the time dilation, doesn't it?


    Anymodal-
    Federico.
     
  2. jcsd
  3. Jun 15, 2011 #2

    Drakkith

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    Hit up the faq here and read about a frame of reference for a photon.
     
  4. Jun 15, 2011 #3

    DaveC426913

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    You're essentially correct. Photons do not experience time. It can have no frame of reference
     
  5. Jun 15, 2011 #4

    Pengwuino

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    They are massless and have energy, but that does not make it equivalent to having mass. They do have momentum, however.

    Photons do not experience time and that's just how they work. One thing you have to deal with is that not everything needs to experience every type of parameter you can imagine. For example, in thermodynamics you say that a large number of particles can have a temperature. The deal with thermodynamics and statistical mechanics, however, is the assumption of a large number of particles. If I were to isolate a single particle and ask "what is the temperature of this particle", the question would not make sense as a temperature is only applicable to a certain type of system. For the idea of relativity, time is a concept only applicable to massive systems.
     
  6. Jun 15, 2011 #5

    bcrowell

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    Hi, Federico,

    What you said in the main body of your post makes sense to me. The PS didn't make sense to me -- I don't see how mass is relevant.

    -Ben
     
  7. Jun 15, 2011 #6
    I think he is saying the energy of a photon is the same thing as mass, and since mass-carrying entities are subject to the other phenomena of shifted reference frames, time-dilation should be included.

    This misinterprets the mass-energy relationship, which not 'equivalence' in the complete formal sense. e=mc2 shows an 'exchange' relationship, as it were, but dollars are not the same thing as groceries.
     
  8. Jun 15, 2011 #7
    Thanks! you figuered what i meant (and expanded it and corrected it :P). What are phenomena of shifted reference frame other than time dilation?....


    Thanks every body for answering! i will reply you later
     
  9. Jun 15, 2011 #8
    Time dilation, energy increase (formerly loosely called 'mass' increase), and longitudinal length contraction, with respect to the frame of reference of a body with a different velocity, in Special Relativity.

    I'll let someone give you a more complete answer. My area is linguistics, not physics.
     
  10. Jun 16, 2011 #9
    I would disagree that photons are timeless in their experience. Photons have energy. And the Conservation of Energy has never been found to be violated in the universe. So photon energy is timeless in the sense that its energy is always conserved.

    However because Photons can be "Redshifted;" this means that as Photons travel through space they can experience an increase in their wavelength, a decrease in their frequency, and an increase in the time component associated with the frequency of the photon.

    See Wiki: http://en.wikipedia.org/wiki/Redshift" [Broken]

    Best
     
    Last edited by a moderator: May 5, 2017
  11. Jun 16, 2011 #10

    DaveC426913

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    None of the above means that the photon experiences time.
     
    Last edited by a moderator: May 5, 2017
  12. Jun 16, 2011 #11
    This is conflating the various uses of the terms 'timeless' and 'time'. One need only say that a fundamental property of light is frequency cycles/t. In that case we don't need red-shifting at all.
     
    Last edited by a moderator: May 5, 2017
  13. Jun 16, 2011 #12

    bcrowell

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    I don't think this argument quite works. First let's simplify it a little. The idea of using redshifts brings up all kinds of connotations of general relativity, but it's not necessary to get that fancy. It's clear on much more fundamental grounds that the properties of a photon can change over time, where time is measured in the frame of reference defined by some material observer. A photon that bounces perpendicularly off of a mirror flips its momentum vector, so its properties change over time, where time is measured in the frame of the mirror. If a particle couldn't change its properties over time at all, then that would be a completely noninteracting particle, and therefore we wouldn't be able to observe it.

    The problem with your argument is that it only shows the existence of some frame in which the photon changes its properties, but that isn't really the issue being discussed. The issue is whether there is a frame moving with the photon such that the photon's properties change over time. There isn't.
     
  14. Jun 16, 2011 #13
    DaveC426913 has it right. Although the photon exists in spacetime, it cannot experience the passage of time as material entities do. If it cannot be held in a state of rest, it cannot experience time.

    GrayGhost
     
    Last edited by a moderator: May 5, 2017
  15. Jun 16, 2011 #14

    atyy

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    What is time?
     
  16. Jun 16, 2011 #15

    Drakkith

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    It's a 4 letter word! Don't make me get the soap and wash your mouth out!
     
  17. Jun 16, 2011 #16

    DaveC426913

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    Start yer own thread.

    :wink:
     
  18. Jun 17, 2011 #17

    BruceW

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    When you do a Lorentz transform to a reference frame travelling at the speed of light, all time intervals and lengths become infinite.
    So this means looking at the universe from the photon's point of view doesn't tell us anything useful.
    If you think about it, from the photon's point of view, it would have no mass and no momentum, so it would cease to exist, so it makes no sense to look at the world through the photon's eyes. (Someone correct me if I'm wrong, but I think this is basically the right idea).
     
  19. Jun 17, 2011 #18

    BruceW

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    Sorry, I got a bit of that wrong.
    All lengths in the same direction as the photon would go to zero because of length contraction.
     
  20. Jun 17, 2011 #19

    bcrowell

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    It's what prevents me from giving a complete answer to that question right now :-)
     
  21. Jun 17, 2011 #20
    Baby don't hurt me...
     
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