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Time dilation and light

  1. Mar 29, 2004 #1
    light or radiation from a faroff galaxy seems to us to have been travelling for, let's say, 5 billion years - but does relativistic time dilation affect it? are the light waves themselves much younger? maybe only a few thousand years?
  2. jcsd
  3. Mar 29, 2004 #2
    Strange...I never thought of light having a lifespan. I assumed it never aged.
  4. Mar 29, 2004 #3
    well the only reason it wouldnt age is because it has no mass...which is why i think time dilation must NOT affect it in any way...

    i could rephrase it - does time dilation only affect mass? is light absolutely mass-less?
  5. Mar 30, 2004 #4
    Photons in theory are ageless -
  6. Mar 30, 2004 #5
    yogi is right!
  7. Mar 31, 2004 #6


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    Staff: Mentor

    I think maybe the word I would use is "timeless." I think the key to quantum wierdness may be a result of this. Ie, how does light "know" which slit to go through in the two slit experiment if the slit is closed after the light passes throuh...?
  8. Mar 31, 2004 #7


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    Good point.Photon is somehow "aware" of the arrow of time and fundamental entropy law inspite of nonexisting time .This only shows that our spacetime concepts and our perception of it,are shaky and still need better clarification.
    Photon obviously has (*somewhere*) book -keeping info resource of boundary conditions experimental set of our universe.QM currently can't explain this,but reflection of that phenomenon is built into its' equations.
    Strong reason why Einstein considered QM to be incomplete theory.
  9. Mar 31, 2004 #8


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    The photon is not a little particle, rather uncertainty says it can't be separated out of its beam. So the entire path is the unit of behavior? So path "knows" conditions at both ends?

    (added) If you look at simulations of Feynmann's sum over paths in simple cases, it sure looks like this is happening. The anthropocentric "knows" is replaced by "consider all possible paths and add them together".
    Last edited: Mar 31, 2004
  10. Mar 31, 2004 #9


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    Not a "little" particle.That's for sure.Some interpretations of photon physics ,and that is what is bothering me (not just me) ,suggest that as long as it is in state of "travel" from the moment it is emmited to the moment it is absorbed ,it should be considered in a real physical sense located in its beam.But we can't know this without measurment!Even theoretical possibility of future tehnology to measure gravity field of propagating photon is still intaraction with its' path.And when photon interacts QM eqs formalism seems to indicate it can be split in many possible paths (pottential photons?). Than one path due to probability "wins" and original photon is reveiwed (becomes real) in one unit and proceeds travel (or it is absorbed so we lose information on it).Quite a headache to comprehand.
    Feyman made some clowning on it by saying "photon snifs all possible paths and chosses right path".But it doesn't help me much in understanding.
    I'm quite convinced that information can be transmited without "time" factor or perhaps even without energy expenditures,but the question remains how.
    Not with concept of uniformly traveling photon ,but perhaps with instant teleportation of photons' states.How this happens must be better physicaly explained than just through the math formalism of boundary conditions.
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