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Question for all those who can answer

  1. Aug 14, 2012 #1
    How is it that light retains it's heat as it travels through the eternal cold bounds of space and reaches earth?

    How is it that this particle or wave can still touch my skin and heat my body and our planet if space is cold and one particle of light has a finite heat density?

    How is it that one photon doesn't lose its heat on its traverse toward earth if not all photons?


    [Moderator adding attribution for the following quote] http://answers.yahoo.com/question/index?qid=20100315201628AAPARV3
     
    Last edited by a moderator: Aug 14, 2012
  2. jcsd
  3. Aug 14, 2012 #2

    phinds

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    First, I would suggest, if you plan on continuing on this forum, that you use titles for your posts that have some meaning. "question for all those who can answer" is meaningless. Mention the subject that you want people to answer something about.

    Systems lose heat in outer space by radiating it away in the form of photons. What is it you think a photon would radiate away?

    The CMB has absolutely nothing to do with why/how photons retain their energy, so your proposed "short answer" is a total non sequiter.
     
  4. Aug 14, 2012 #3

    mfb

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    Heat is not a property of photons. Photons are not "hot" or "cool". They have a specific energy, if a photon hits you this energy can be converted to heat. The sun emits many photons, they fly through space without significant interaction (as space is a very good vacuum), and some of them hit you.
     
  5. Aug 14, 2012 #4
    If photons do not have specific temperature can they create a cold interaction with another type of matter?

    Or does this specific energy always create heat with matter?
     
  6. Aug 14, 2012 #5

    phinds

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    What exactly is a "cold interaction" ? Are you just making up a term here or am I missing something?
     
  7. Aug 14, 2012 #6
    I don't know what you mean by "cold interaction". The point is, a photon is a particle and it's emitted with a certain energy (this energy corresponds to a wavelength). It will keep this energy when it doesn't interact (gets absorbed) by stuff in it's way. UV-light (photons at the UV energy level) for example are absorbed by the earth's atmosphere. But a photon just travels along with unaltered enery if it doesn't interact. And in outer space there isn't much to interact with - so it can't lose much energy.
     
  8. Aug 14, 2012 #7
    If me absorbing the photon creates heat which would be a hot interaction of the particle could the opposite happen within some other form of matter that's what I was asking, if the particle has no temperature then I had to phrase it somehow, either cold interaction or hot interaction.

    It either creates heat or creates a reduction in temperature. If it has no temperature. That's all I was asking.
     
  9. Aug 14, 2012 #8
    Remember I know nothing about physics. Look at it like that.
     
  10. Aug 14, 2012 #9

    phinds

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    Just FYI, having "no temperature" is a meaningless concept for a macroscopic object (but not for a photon).

    The fact that a photon has no termperature is somewhat irrelevant. It has ENERGY. Have you ever sat out in the sun on a hot sunshinny day? What do you think it is that is hitting you, making your skin hot? Reread mfb's post.
     
  11. Aug 14, 2012 #10
    So basically the photon has this type of wavelength of energy which can be absorbed by matter thus creating heat?

    If there is nothing to absorb the energy it can never create heat and fly endlessly through the universe, kind of like a distant star shinning its energy upon us?
     
  12. Aug 14, 2012 #11
    Does the energy retained in the photon ever increase or is it constant within each photon?

    I know that there is no mass in a photon but is it possible for photons to collide?
     
  13. Aug 14, 2012 #12
    As long as it doesn't interact (like in outer space), its energy is constant. Only when it gets absorbed it can generate heat. By the way it's not "kind of like" the shining of a distant star. The shining of a distant star are photons (just like all other light).

    I don't know about photon-photon collisions but probably someone more knowledgeable than me can answer that question. :wink:
     
  14. Aug 14, 2012 #13
    Thanks guys for all your help, I appreciate it. Thanks for answering my questions. That photon to photon collision question is still up for grabs anyone.
     
  15. Aug 14, 2012 #14

    phinds

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    Photons don't "collide" with each other any more than radio waves do.
     
  16. Aug 14, 2012 #15
    If two photons occupy the same point in space, they can create another particle with the sum of their energy though right? I'd draw a Venn diagram if I knew how to do it here :)
     
  17. Aug 14, 2012 #16

    phinds

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    I have no idea what you are talking about. Photons can occupy the same space in the same way radio waves can occupy the same space. Nothing happens. They don't "occupy the same space" as though they were little tiny billiard balls.
     
  18. Aug 14, 2012 #17
    And a photon does have mass, just not rest mass. It's always moving and possesses an amount of energy dependent on frequency which can be equated (I think) into relativistic mass.

    Maybe a real physicist could confirm or deny that for me. (I think more clearly when confident, even when wrong) :)
     
  19. Aug 14, 2012 #18
    Yeah, never mind, I was thinking of pair production. Which actually happens spontaneously if the photon has enough energy?
     
  20. Aug 14, 2012 #19
    Relativistic mass isn't a useful concept, which is why it is no longer used. 'Relativistic mass' is just the energy divided by by the speed of light squared, so it makes more sense just to refer to it as the energy. Saying that photons have mass is very misleading.

    Only in certain situations. Specifically, when the photon is in the vicinity of a nucleus. Without a nearby nucleus to absorb momentum, the interaction wouldn't be able to conserve momentum, and wouldn't be possible.

    The photon must, as you say, have a certain energy for this to occur in the first place. Above that amount, the probability of the pair production occurring increases as the energy of that photon increases, assuming of course that a nucleus is in the vicinity to allow momentum to be conserved.
     
  21. Aug 15, 2012 #20

    mfb

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    Photons can be absorbed without (significant) heat involved - this is the concept of photovoltaics, for example.

    In theory, there are photon-photon interactions - but they are extremely rare.
     
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