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Photonic mass?

  1. Jul 30, 2006 #1
    Well we all know that photons have (or supposedly have) zero mass... But it is radiation...thus isn't it possible to freeze? such as like with the Bose-einstein condensate... so is it at ALL possible that a photon could ever have a mass, and if so...what could be its advantages
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  3. Jul 30, 2006 #2


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    How do you "freeze" radiation? And why is this necessary and a sign that it could have a mass?

  4. Jul 30, 2006 #3
    Scusami, but how do you relate radiation to the BE condensate ? What is the link here ?

  5. Jul 30, 2006 #4


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    Perhaps the OP is following some mental link like radiation-bosons-BE condensate.
  6. Jul 30, 2006 #5
    I wasn't saying they were related, It was an example as I heard that the BEC could be frozen on a physics website I recently visited, if I can find the link I'll gladly post...but to continue, "and a sign that it could have mass" I didn't say it could...perhaps I should have reprased it all..

    Is it AT all possible for a photonic particle, under any given physical condition to have a mass? and if so, would it be advantageous...I mean, photons are intensities of light.. And if light had mass it'd be solid...

    I'm not asking if it has been done because clearly it hasn't, but im saying *theoretically*. I've always been quite interested in physics and quantum physics since I was much much younger, but only recently started delving into it, with all the theories and experments that have been conducted, and though extremely fascinating, is quite difficult to comprehend without more knowledgeable advice on things. I just thought I'd inform you of my newcoming to QP as I didn't really want to be criticised out for my lack of viable knowledge.
    Last edited: Jul 30, 2006
  7. Jul 30, 2006 #6


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    Please do. I'd like to see what this is about.

    But even IF what you said is true, there's a flaw in the logic here. IF there are "frozen" BEC, there are also plenty of "non-frozen" BEC. Cooper pairs do not have to form at very low temperatures at all (100K is pretty "hot" as far as LHe is concerned). So the existence of BEC does not always results in something "frozen". Furthermore, by definition, BEC state implies long-range coherence, and this means the BEC particles essentially is everywhere all at once (as indicated by plane-wave states). That's why superfluids can flow with zero viscosity and supercurrent can conduct with zero resistance. So if anything, it is the opposite of "frozen".

    That last part boggles me a bit. Neutrino has mass. Have you ever seen a solid of neutrinos? Have you seen a solid made up of entirely of electrons?

    Having a "mass" has nothing to do with forming a solid. If you look into a solid state physics text, you'll see that the formation of a solid requires a stable inter-atomic and inter-molecular bonding. This means that the valence shell of the atom or molecule must make a stable overlap and be "compatible" with its neighbors, next nearest neighbors, next-next nearest neighbors, etc... This has nothing to do with having a mass.

    My guess here is that the OP read about "freezing" light in a BE condensate, which of course doesn't mean that you can freeze light, and doesn't mean that BE condensate can be frozen. I wish they didn't use that word to describe what was done.

    Last edited: Jul 30, 2006
  8. Jul 30, 2006 #7
    Thankyou for the clarification of the Frozen BEC.. It is often difficult to find reliable sources of information that are both accurate as well as efficient, when starting out and not really knowing what to look for. As for the light, I mean't mass as in if it <i>were</i> solid. Not whether having mass made it solid or not, but if it did have mass and it was solid. Even if it were not solid but had mass, could it be recorded in any other form of measurement excluding intensity and frequency. I'm sorry if I'm being irritating with my questions, of which to you I'm sure are exceptionally simple, but this is all very helpful for me
  9. Jul 30, 2006 #8


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    People have done various experiments which would be very sensitive to the mass of the photon if it had one. None of these experiments has actually found such a mass, but the uncertainties in the apparatus establish an upper limit on the mass (i.e. if photon had a smaller mass the experiment would not be able to detect it).

    A Google search on "photon mass upper limit" turned up a reference to an experiment from a few years ago that set an upper limit of [itex]10^{-54}[/itex] kg.


    I don't know if this is the current best limit.
  10. Jul 30, 2006 #9


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    I think the issue that's trying to be communicated here is the "freezing" of light in the BEC. It explains it breifly in my Modern Physics textbook, page 327-328, by Tippler and Llewllyn. It begins:

    "Using the quantum properties of atmoic energy states, tunable lasers, and a Bose-Einstein condensate (BEC) of sodium atoms, physicists have been able to slow a light pulse to a dead stop, then regenerate it some time later and send it on its way."

    It then goes on to explain how using a coupling beam to illuminate the BEC, whose atoms are in the ground state and all aligned, if you fire a probe beam into the BEC, it will shift the spins of the BEC, rapidly changing the refractive index of the BEC and slowing the light down inside it. Turning off the coupling beam will "freeze" the light inside the BEC, and turning the coupling beam back on will "unfreeze" the beam. Of course, I think the source of misunderstanding here is that the light isn't actually getting frozen - its information is stored in the shifted spins of the atoms, which unshift when the coupling beam is turned back on, regenerating the light pulse.

    So I think that's what this thread was meant to be about.
    Last edited: Jul 30, 2006
  11. Jul 30, 2006 #10
    :D thankyou for that read jtbell it helps a great deal. and Mute ty for clarifying what I mean't in my original post. But I heard they was only able to freeze the photon to 36mph. Either way, it is a very interesting read and thankyou :)
  12. Jul 30, 2006 #11
    Ok, enough of this! I think there is some serious misunderstanding which others tried to explain to the OP, so I will give it a stab:

    Photons travel at c. NOT AT 36mph no matter what one does.

    The common error seems to be with respect to thinking that if a photon enters a crystal or any substance, and that if it exits in a time far exceeding what it should in "free-space" that something has "slowed the speed of light"
    Not true!

    While traveling through a substance, a photon is absorbed, emitted, absorbed, emitted; again and again amongst the atoms during it's path through the crystal.
    What the DELAY is actually talking about has NOTHING to do with the speed of light of the photon itself, rather it is in reference to a delay in the absorption/emission cycle along it's path.


    You've played baseball, right?
    Think about this:

    You have 10 people in a straight line, spaced 100 ft apart each, and everyone is able to throw the baseball to the next person at 40mph.
    If one or more of the players "hold" the ball for an extended period of time before throwing it to the next player at 40mph, maybe collectively even taking an full hour before the ball reaches the last player, would this suggest that balls velocity is less than 40mph?
    Rather, what happened is that the balls velocity is the same, but the "catch and release" along the path has been slowed.
    Last edited: Jul 30, 2006
  13. Jul 31, 2006 #12
    Actually...I believe the scientists who did the experiment were referring to speed between point A and point B...
  14. Aug 1, 2006 #13
    All other arguments aside, think about this:

    If something moves at a velocity v, it follows the Lorentz transformations new value = (original value/(1-(v^2/c^2)^.5) such that time slows down, length in the direction of travel increases, and mass increases.

    As your velocity approaches the speed of light, c, the ratio of v^2/c^2 approaches the value of one, making the denominator, 1-(v^2/c^2), approach zero....which in turn makes the general expression approach infinity.

    Soo... The closer you get towards the speed of light (along with time slowing down to the point of stopping entirely and becoming infinitely long), you would become infinitely massive... Of course, the more massive you became the more energy would be required to make you go even a little faster, so you'd need an infinite amount of energy too and--


    If photons had any mass at all, they wouldn't be *able* to travel at the speed of light.

    I'm new, btw. Hi. :)
  15. Aug 1, 2006 #14
    Yes, my thoughts also. I think its just plain wrong :frown:

    When they can do that without the sodium, then ill agree they have "stopped light".

    Thats zero rest-mass, not to be confused with zero mass.

    If you stop light, you destroy energy, when you start it again you create it. This violates the thermodynamic laws that i know. Of course, if something stores that energy, then thats ok, but it isnt stopping light its storing it.
    Last edited: Aug 1, 2006
  16. Aug 1, 2006 #15


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    I've tried to imagine this since reading the article about 'stopping' light. Is there a physical way to describe how it stored? Or is it simply a notion of electron states (i.e. energy absorbing and releasing).

    One of the images I came up with in my mind is the light still bouncing around inside the lattice, not actually stopped, but contained.
  17. Aug 1, 2006 #16


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    But what is bouncing but absorbtion and reemission?
  18. Aug 1, 2006 #17
    That's an interesting question... I can't think of any situation in which photons could "bounce" within a set of opposing forces (gravity wouldn't really help and since photons are uncharged, electromagnetic forces are useless)...
  19. Aug 2, 2006 #18
    you can add scatterin processes to that. though if you look at inelastic scattering within the kramers-heisenberg formula those are also described by an absorption re-emission process.
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