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Thread: Photon age

  1. #1 Photon age 
    Moderator Moderator AlexP's Avatar
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    How do astronomers determine the age of photons? I looked at an article tonight about some galaxies that were discovered and the light from them took 9-12 billion light-years to reach Earth (they're significant because they're almost as old as the universe itself).


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    Administrator KALSTER's Avatar
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    I don't think photons age. They probably messured the red shift and compaired that to the type of galaxy and the type of light it should emit to figure out the distance. This makes me wonder that if all particles have half lives, do photons too?


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  4. #3  
    Time Lord
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    They'd have to emit something (like maybe another photon with less energy?), because otherwise it would violate the conservation of energy.
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    Moderator Moderator AlexP's Avatar
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    Quote Originally Posted by KALSTER
    I don't think photons age. They probably messured the red shift and compaired that to the type of galaxy and the type of light it should emit to figure out the distance. This makes me wonder that if all particles have half lives, do photons too?
    Worded badly, sorry. They don't age because they don't experience time, travelling at c. So then considering half-life is expressed as an amount of time, I wouldn't think they have a half life. So I guess the question is, how do they know how long ago the particle was emitted from its source? And I guess you answered that. More answers are still certainly welcome though.
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  6. #5  
    The Doctor Quantime's Avatar
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    What about an anti-photon? With anti energy?
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    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by svwillmer
    What about an anti-photon? With anti energy?
    Photons are their own anti-particle.
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  8. #7  
    Time Lord
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    Wouldn't that give them the ability to cancel themselves out, or am I misunderstanding what anti-particles are?
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  9. #8  
    Moderator Moderator AlexP's Avatar
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    Quote Originally Posted by Janus
    Quote Originally Posted by svwillmer
    What about an anti-photon? With anti energy?
    Photons are their own anti-particle.
    Yes. Doesn't mean you can't say 'anti-photon.' A photon can be called an anti-photon if it has the opposite helicity of another photon... Really, it's relative. Helicity I don't think really makes a difference except in a photon collision/annhilation scenario. There was a thread on neutral elementary anti-particles awhile back... The thing about anti-energy is just...no.

    Quote Originally Posted by kojax
    Wouldn't that give them the ability to cancel themselves out, or am I misunderstanding what anti-particles are?
    If an anti-photon collided with a photon, they would annhilate to produce...well, in this case, I guess two other photons.
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  10. #9  
    The Doctor Quantime's Avatar
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    Quote Originally Posted by Chemboy
    ...I guess two other photons.
    Or one REALLY big one

    No I mean one with both energy.
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  11. #10  
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    Quote Originally Posted by KALSTER
    . This makes me wonder that if all particles have half lives, do photons too?
    Interesting...to my very limited knowledge, photons are one of the purest form of energy...so i don't think that it would....hmmm....
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