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What is Light?

  1. Sep 21, 2008 #1
    I was thinking about light and baryonic matter.

    My understanding is that stars emit light by essentially converting their rest-mass energy into light energy according to the equation E = Mc2.

    I wonder though, does light travel into the depths of space forever? (meaning total baryonic matter would decrease with time) or is light soley an interaction between masses?
  2. jcsd
  3. Sep 21, 2008 #2


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    Total mass does decrease with time, although the number of baryons remains the same. For example He4 has slightly less mass than 4 x H1. However there are theories predicting proton decay, but this has never been experimentally verified.
  4. Sep 22, 2008 #3
    so the rate at which mass decays into radiation is greater than the rate at which decayed radiation is re-absorbed into matter.
  5. Sep 23, 2008 #4


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    I am not sure what you are trying to get at. Essentially almost all of the radiation in the universe (stars) results from fusion processes - the most important being 4 H1 to He4. These processes are extreemly unlikely to reverse.

    As a result the radiation spreads throughout the universe, including keeping life on earth. Some of it gets reabsorbed by matter in CHEMICAL reactions, not nuclear. Most of it just keeps going and heating things up.
  6. Sep 23, 2008 #5
    well think of light as photons and waves. Light will go on until it is absorbed by some form of matter.
  7. Oct 1, 2008 #6
    i think light is a photon particle which is emited out of the sun in a nuclear fussion of the hydrogen and helium atoms in the sun
    when these to highly charged atoms collide they release a higly charged proton this proton thravels in intense speed which emits light particles
    i honestly dont know how those particles glow
    plz answer :)
  8. Oct 1, 2008 #7


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    Photons emitted by the fusion process are not in the visible light energy range. They only very slowly work their way out to the photosphere. The number I recall is something like 10,000 yrs for a photon created in the center of the sun to find its way out to the suns surface. The visible light we receive is emitted by the photosphere which comprise only the very outer most layers of the sun.

    Photons do not "glow". Each one has an energy, which we perceive as color, that is determined by the source of the photon.

    To the best of my knowledge this is not a valid description.
  9. Oct 1, 2008 #8


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    I seem to remember something on the order of 100,000 yrs. Still, ridiculously long!
  10. Oct 1, 2008 #9


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    When a charged particle like an electron or proton accelerates or decelerates, it will give off electromagnetic radiation. This is what is done in radio broadcasting. If the electromagnetic radiation has wavelengths between 400 nm to 700 nm, it will be in the visible range, and we call it "light". But often "light" is used as a short hand for all electromagnetic radiation.

    Last edited: Oct 1, 2008
  11. Oct 1, 2008 #10
    He4 has 2protons /2neutons .4xH1=4p.how has he4 got less mass when mass-p<mass-n?
  12. Oct 2, 2008 #11


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    The difference in mass is the binding energy which holds the He4 nucleus together.
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