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Does a photon experience time?

  1. Jun 9, 2010 #1
    I have been looking around on the web, including this forum, regarding the question: "does a photon experience the passage of time?"

    reputable sites, including this one, and quotes from reputable people, seem to disagree.

    is the answer, "we don't know?"

    the implications of a photon not experiencing time are staggering to me. If a photon does experience time, i'm thinking the answer to that is also staggering.

    Could the answer be that both, they do experience time, and they do not?
     
  2. jcsd
  3. Jun 9, 2010 #2
    I think above all we need to know what you mean when you say "does x experience time?". For example, does an atom experience time?
     
  4. Jun 9, 2010 #3
    Do Photons experience time? Perhaps if we regard time as a corrosive force that wears out all it comes into contact with and then assess how long a photon exists, we might get some idea's. Or is it that photons actually play a role in the concept of "time"? are they one of the ingredients? Have the same photons existed since the start of time or were they before time?
    If a photon can exist without limitation in measurable time then the force of time is not exterting any influence on it? Or do photons exist beyond the reaches of the forces of time, if they do then it must be nice to be a photon ha ha. What can exert any influence on a photon or cease a photon to exist, are any of the effects produced by time as a corrosive force outlasting and wearing out most other things? If I fire a photon out towards the edge of the universe will it continue forever? Would time matter to it? Does it make a difference the density of photons? Your questions simply sparks other questions, some inside the box and some outside of the box? For example could photons exist in conjuntion with other materials and be an actual sensient being?
     
  5. Jun 9, 2010 #4
    Interesting question i don't have a physics degree,but surely if Photons do not experience time, they appear (at least to themselves) to be 1 dimensional lines from point of origin to there eventual absorption, or for there infinte journey outwards from the universe, So to them they are not particles but long 1 dimensional lines?

    I hope that makes sense?

    Jim
     
  6. Jun 9, 2010 #5
    I would say no everything in the universe is instantaneous to the photon , It was explained to me this way if I was looking at a clock ticking and then i started to move back at the speed of light the clock would appear to freeze because no new photons would reach me .
    Don’t ever believe anything I say ,
     
  7. Jun 9, 2010 #6
    But really, what do you guys mean when you say "it experiences time" or not? Are you imagining yourself to be a photon? Cause that's meaningless, I suppose. Are you giving the photon some kind of awareness? Or do you mean it in the purest sense as in: we say an object experiences time when there is a way to say that time has passed. If so, I don't think there's a way to say how long a photon has existed. I mean, I don't know, the question seems to be too open to give an answer to.
     
  8. Jun 9, 2010 #7

    rcgldr

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    A photon has a frequency, which is slowed down by the strength of gravity, just like sub-light speed clocks, so in that sense it has it has an aspect of it's state related to time, the cycling of it's frequency.
     
  9. Jun 9, 2010 #8

    DaveC426913

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    The answer is no.

    Dissenting opnions are based on ignorance.
     
    Last edited: Jun 9, 2010
  10. Jun 9, 2010 #9
    Is Mr. Vodka's answer of 'meaningless question' based on ignorance? Thats what I think too. But I suppose if I dont think that a photon can experience anything, it follows that it cannot experience time.
     
  11. Jun 9, 2010 #10

    DaveC426913

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    No, that is correct. It is meaningless to try to imagine what a photon experiences; the speed of light is an invalid reference frame.
     
  12. Jun 9, 2010 #11

    DaveC426913

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    This is a misunderstanding of GR and of photons.
     
  13. Jun 10, 2010 #12

    rcgldr

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    Well is gravitational red shift actually changing the frequency of a photon or is it just affecting an observer?
     
  14. Jun 10, 2010 #13

    diazona

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    I might say it affects how the observer sees the photon, but I'm not sure that statement does the concept justice. It's a tricky thing to articulate.

    The thing is, with or without gravity, a single photon will have different frequencies to different observers. So you can't really identify any particular inherent frequency of a photon, which is what you'd have to do to show that gravitational redshift changes the photon itself rather than the observer. (You can compare two different photons to establish that one has a higher frequency than the other, but you can't compare one photon with itself at another location with different gravitational properties.)
     
  15. Jun 10, 2010 #14

    rcgldr

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    True, since the photon has to be destroyed or captured in order to observe it. Still knowing that gravity affects time, if an observe observes a stream of photons with the same frequency, and that obsever moves into a stronger gravitational field, then if the photons weren't affected, the observer should see an apparent blue shift since the observers "clock" is running slower. Hoewver this isn't what happens.

    Regardless of the gravitational effect, frequency is a time related feature of a photon, and could be considered a photon's "clock". A meter is defined as a number of wavelengths of a certain frequency of light (I assume it's based on a "sea level" reference amount of gravity), and there's a relationship between time, frequency, the number of wavelenths, the speed of light, and the distance traveled (1 meter).
     
    Last edited: Jun 10, 2010
  16. Jun 10, 2010 #15

    DaveC426913

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    Frequency is only applicable if there's a time element. A comb has a number of teeth per inch but that does not mean the teeth are experienced temporally. It is the observer is moving relative to the comb that engenders frequency (event per unit time) upon the comb.

    This may seem like a spurious analogy but it's not; photons are not "moving through space in time"; photons are "fixed in spacetime".
     
  17. Jun 10, 2010 #16
    there is a super interesting paper on the feynman-stuckelberg interpretation of time symmetry at this local:

    http://arxiv.org/ftp/gr-qc/papers/9906/9906012.pdf


    I just found thgis - discusses the FS interpretation with respect to general relativity. gets kind of weird.

    My gut feeling is that the equations we have available to us are inadequate to determine what the photon 'sees' during its existence.

    keeping in mind that the equations of relativity deal with things which have mass. i haven't seen a substantial adaptation specific for massless objects in relativistic terms.
     
  18. Jun 10, 2010 #17
    The frequency of a photon is a measurable property, it is a property only applicable to the observer. Take for instance, the doppler effect. Since blue light has a higher frequency than red light, the spectral lines of an approaching astronomical light source exhibit a blue shift and those of a receding astronomical light source exhibit a redshift. This is a measure of our clock of the photon, not of the photon's clock.

    Relativity shows us that to different observers, we will measure different things. Any further interpretation is a postulate. If the comb is "fixed", then what element makes the observer in motion?
     
  19. Jun 10, 2010 #18

    DaveC426913

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    No, the equations we have tell us that trying to pretend a photon experiences anything results in an invalid reference frame. When we put numbers into the formula, we end up dividing by zero.
    We don't need to adapt them. They do work and they give us the answer that c is an invalid reference frame.

    The observer's passage through the timelike dimension.
     
  20. Jun 10, 2010 #19
    The observer's passage through time is not enough to induce the outcome of motion of surrounding objects. As I sit here, time passes on, and yet the book on my desk remains stationary. My original point is that we cannot specifiy an object as truly 'fixed' because an object is never 'truly' doing anything. We cannot say that photons are "fixed in spacetime", and that they are "not moving through space in time". A photon will have different frequencies to different observers because different observer's move at different rates of time, yes, but this does not imply the photon to be "fixed".
     
  21. Jun 10, 2010 #20

    rcgldr

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    The number of frequency cycles that occur during the "lifetime" of any photon, from emmision to absoprtion, will be fixed, and it is a feature of the photon that is independent of any observer. That's good enough to be considered the photon's "clock" for me.

    Regarding the equations for special relativity, those are meant for sub-light particles with mass that can never achieve light speed. Photons only exist at the speed of light, and they need a different set of rules.
     
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