A Snapshot in Time of a Photon

  1. I'm not sure if there's a satisfying answer to this question, but I'd at least like to incite some discussion.

    I haven't had a formal education about photons or quantum mechanics, so all I know is what I've read about outside the classroom, but a buddy and I have been talking about them, as we've reached electromagnetic waves in our EM class. I know that a photon travels through space the way a wave would, but also exhibits particle-like properties (I've read up on the double slit experiment).

    Imagine we have a traveling photon. If we could freeze time, or just take a snapshot of an instant in time, would that photon still exist? Do photons exist in individual instants? Or do they need the progression of instants (the flow of time) to exist?

    I suppose I could ask this question of absolutely anything, but the photon is what came up in conversation, I think because it seems to me currently like an intrinsic property of a photon is its motion.
  2. jcsd
  3. A photon has a well defined wavefunction at any instant of time. Furthermore, given the photon's wavefunction at any instant of time you can calculate its wavefunction at any other time.
  4. Drakkith

    Staff: Mentor

    Does anything exist during an "instant" of time? Is this question even answerable? I'm not sure it is.

    Motion is something that can only be said to occur when comparing one object to another. It is not an intrinsic property of anything as far as I know.
  5. Ah that's a good point. Thanks!
  6. What if the thing requires the presence of other things in the universe in order to exist? I'm not saying this is true of a photon, but couldn't there be something for which this is true? If that were the case, it seems like motion relative to other objects could be an intrinsic property of something, doesn't it?
  7. Drakkith

    Staff: Mentor

    This isn't an answerable question. You're asking about something that would require nothing else to exist in order to find out if its true, and in which case we couldn't know anyways since we wouldn't exist. This isn't how science works.

    It's not the case according to mainstream science.

    Be aware that you're pretty far off into speculation land. I'd advise re-reading the rules so your thread doesn't get locked for speculating.
  8. I'm not sure this is completely applicable, and I'm by no means an expert on quantum mechanics, but does a photon need other things to be present in order to exist in a classical sense (so, in a defined state)? If nothing existed for a photon (or maybe any given thing) to interact with, wouldn't it be in some kind of state of quantum superposition?
  9. sophiecentaur

    sophiecentaur 14,715
    Science Advisor
    Gold Member

    I think you would have to say that it doesn't exist 'in the classical sense'. It is not a classical object. It really isn't like anything else you have come across in mechanistic Science and you cannot impose your intuitive rules on it. Bummer - but there it is.
  10. It is always in a state of quantum superposition. Even if it is in an eigenstate of one basis it is in superposition in another basis. That has nothing to do with the presence or absence of other objects.
  11. sophiecentaur

    sophiecentaur 14,715
    Science Advisor
    Gold Member

    Is that true? I would have thought that the wave function must relate to the source that generated it (directivity etc). Also, until it has been detected, what can you say about the photon that's definite? So at both ends, 'something else' has to be involved.
  12. I am not sure what you are asking here.

    The concept of superposition is a consequence of the fact that wavefuctions are vectors which can be represented in a variety of basis sets. It applies for any wavefunction regardless of how it was created, how many particles it consists of, and how you might plan to measure it.
  13. That sounds like the intuition I was going off of as well...
  14. You are asking that a photon traveling with a speed will exist in zero time interval ?
    There are two conditions
    i.) Photon is a form of energy(it does not have mass). Means it has speed(without mass). In zero time interval, it has zero speed.
    Answer: Photon will not exist.

    ii.) I think Photon have mass because it is not traveling with infinite speed. Means in zero time interval, it has zero speed but have mass.
    Answer: Photon will exist.
  15. berkeman

    Staff: Mentor

    Thread closed for Moderation...
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