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B Info needed on origin of light

  1. Aug 6, 2016 #1
    Can someone please point me to a documentary or webpage that has a good detailed explanation on the origin of light during the big bang? Everything I've seen so far simply states that light "just happened" sometime right after the quark epoch.

    Well, how did it happen? Or do we not know? And if we don't know, then how do we know that light came into being after the quark epoch?
     
  2. jcsd
  3. Aug 6, 2016 #2
    The "cosmic microwave background radiation" is the glow left over from that first light... this wikipedia page has a good breakdown with many links at the end.
    https://en.wikipedia.org/wiki/Cosmic_microwave_background
     
  4. Aug 6, 2016 #3
    Thanks, I will read it and surely be back with many questions.:biggrin:
     
  5. Aug 6, 2016 #4

    bapowell

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    We don't know where it all came from: by the time measurable physics picks up (fractions of a second after the Big Bang), light and matter were there.
     
  6. Aug 6, 2016 #5

    Drakkith

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    If you accept that the very early universe was very hot and very dense (which is what current theory says) then it must have included light. Electrically charged particles radiate EM radiation when accelerated, and given that these particles existed in a hot, dense plasma, where they undergo frequent accelerations via collisions, they necessarily radiate visible light and other forms of EM radiation.

    How the universe came to be filled with this plasma is unknown at this time.

    Light does not "just happen" any more than particles "just happen". EM radiation almost certainly existed during the quark epoch and before.
     
  7. Aug 6, 2016 #6
    Wait, are you telling me there are models in which the universe was not very hot? That would totally ruin my whole understanding of how the universe came to be. What are the names of these models, and is there any chance they're right, or are they officially outdated?

    I understood from the wikipedia article that photons decoupled from matter after the quark epoch, at the same time the first hydrogen atoms were formed. Are you saying light existed earlier than that?
     
  8. Aug 6, 2016 #7

    bapowell

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    Light was there from the beginning: as long as you have matter and antimatter, you must have light because of annihilation processes.
     
  9. Aug 7, 2016 #8
    I'm not getting something. According to everything I'm reading, recombination didn't occur until after the quark epoch. There were photons, but they were somehow captured in the plasma. I've not seen anything that says visible light existed before the formation of electrons and protons. I'm certainly willing to believe wikipedia is wrong, but if so, then could someone point me to the right information?
     
  10. Aug 7, 2016 #9

    Drakkith

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    If there are, I'm not aware of them. The accepted model is that the very early universe was very hot and very dense and nothing short of a radical change in our understanding of cosmology is going to change that.

    Yes I am.

    Recombination merely caused the universe to become transparent to visible light. Light already existed well before then. The very early universe is believed to have been a dense soup of radiation, matter, and antimatter, with the radiation being continually produced and absorbed by the latter two. While nearly all of this radiation was extremely high in energy, a small amount would have existed as visible light and as the universe cooled down over time that proportion would have increased.
     
  11. Aug 7, 2016 #10
    Okay, now I understand. So did the photons themselves exist before the quark epoch? If so, do they have an idea of when photons were created, or how?
     
  12. Aug 7, 2016 #11

    bapowell

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    Are you even reading my inputs to this thread? If you have matter and antimatter (which you have in the very beginning) then, yes, you have photons.
     
  13. Aug 7, 2016 #12
    Yes, I am. But you have to understand this is all very confusing for someone who's not a physicist. Me trying to understand this stuff is the equivalent of you trying to learn a new language. I have no basis for knowing that matter anti matter annihilation equals photons.
     
  14. Aug 7, 2016 #13

    Vanadium 50

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    Then why did you tag this thread with an I and not a B?
     
  15. Aug 7, 2016 #14
    I'm actually a little confused about that. Does the tag refer to the OP's level of understanding, or the level of difficulty of the topic?
     
  16. Aug 7, 2016 #15

    bapowell

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    Sorry, didn't mean to move too fast. Look up matter/anti-matter annihilation.
     
  17. Aug 7, 2016 #16

    PeterDonis

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    It refers to the level at which you want answers. If you ask for answers at a level above your current understanding, you'll get answers that won't make a lot of sense to you. But they might serve as pointers to help you learn more.

    If you want this thread tagged as "B" instead of "I", I or one of the other moderators can do that. The "B" level answer to your question is pretty simple and has already been more or less given: photons were "created" along with all other Standard Model particles (quarks, leptons, gluons, etc.) at the end of inflation, when the hot, dense, rapidly expanding "Big Bang" state of the universe was formed.
     
  18. Aug 7, 2016 #17
    I think I understand now. So basically, all the elementary particles were already there as early as we can detect, and we're inferring (by equations I suppose?) that they were created by matter/antimatter collisions?

    And as the plasma cooled, the elementary particles formed the first atoms, which allowed recombination, and light became visible?
     
  19. Aug 7, 2016 #18

    Bandersnatch

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    Yes.
    It generally helps if you stop considering the BB as a creation story from some origin point until today, and instead realise that we're basically taking what we see today and it the past and extrapolating backwards in time beyond what we can see (i.e. contracting the universe similar to like its expanding), until the model tells us that the conditions were such that annihilation/creation in a soup of matter and radiation was commonplace, but if we try to take it back even further in time we just stop getting sensible predictions. So it's a well-established reasoning up to some time in the past, but asking where did it all come from in the first place is just not covered by the theory we've got. There's some ideas, like the inflation theory, that try to model energy in its various forms as 'freezing out' of some expansion-driving scalar field, but these remain on the more speculative side.
     
  20. Aug 7, 2016 #19
    So far as we know, did all the elementary particles emerge at the same time, or are there any hypotheses about which ones may have emerged first?
     
  21. Aug 7, 2016 #20

    Drakkith

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    They were continuously created and destroyed through interactions with matter and antimatter, both through matter-antimatter annihilations (and the inverse, the creation of matter-antimatter pairs from photons) and through acceleration of charged particles.

    I've changed the thread tag to a B.
     
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