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B Light, Photons, Waves, Particles. Wave, Particle Duality.

  1. Dec 11, 2017 #1

    ISamson

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    Me and my friend have recently (half a year ago) had a huge debate, between ourselves, about the wave-particle duality.
    We took sides in light being a particle or a wave. I was for particle he was for waves. At the end of a hot-filled week of arguing, the debate ended up with the acceptance of light being as both. We just couldn't decide between the Double Slit experiment and the particles known as photons. Double Slit proves the argument for waves, but what are photons then? (This was my main argument for particle light). If light is wave, then what did all the wise physicists "invent" photons for?

    However, recent advances with String Theory have led me to confusion, as everything, all particles, end up being waves, or to be more precise, vibrating strings. (What is meant by strings? A form of matter (a new particle) like "String"?) If it is like this, then all matter is waves. Right?
    Am I missing some basic information on the field? Am I not up to date with some recent, recent advances in the field?
    I value your opinion and help.
    Thank you.
     
    Last edited: Dec 11, 2017
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  3. Dec 11, 2017 #2

    mfb

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    String theory is a highly speculative approach. Forget it. It leads to more confusion than clarity.

    A proper treatment of light needs quantum electrodynamics (and a few years of study to learn that). It is neither wave nor particle. Sometimes light behaves similar to what we would expect from a wave, sometimes it behaves similar to what we would expect from particles. That doesn’t mean it would be either of them.
     
  4. Dec 11, 2017 #3

    Orodruin

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    It is also worth pointing out that what modern physicists describe as "particles" are not small balls or anything that is remotely close to small balls. It is a nomenclature that has remained and stuck with us. Again, a proper treatment requires years of study of quantum field theory at A level.
     
  5. Dec 11, 2017 #4

    ISamson

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    What do physicists describe them as then?

    Ok, good.

    If light is neither a particle or wave, then what is light?
    Is it possible to describe 'light' in a paragraph, or is it necessary to learn physics for years? Can 'light' be described simply?

    Thanks for the replies.
     
  6. Dec 11, 2017 #5

    Orodruin

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    Excitations of quantum fields.
     
  7. Dec 11, 2017 #6

    ISamson

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    Wikipedia says: "Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum."
    , but are we talking about the electromagnetic spectrum?
    Where can I find resources for reading about light from a quantum physics' point of view?
     
  8. Dec 11, 2017 #7

    Nugatory

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    Googling for "quantum electrodynamics" and "quantum optics" will find a ton of stuff, but I'm not sure how helpful it will be. (And be warned that the article on quantum optics is among wikipedia's weaker ones).

    Feynman's book "QED: The strange theory of light and matter" is a good layman-level explanation, and I highly recommend it.
     
  9. Dec 12, 2017 #8

    bhobba

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    This thread is marked as B level - its can't really be explained at that level - you need at least an I level, and even then an A level thread would be better - but you can to a large extent get a 'feel' for whats going on at the I level.

    In that vein, and in the hope the OP and others reading this thread, can glean something from reading it see the following:
    http://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf

    Thanks
    Bill
     
  10. Dec 12, 2017 #9
    "Fifty years of conscious brooding have brought me no closer to answering the question, 'What are photons?'" A. Einstein
     
  11. Dec 12, 2017 #10

    bhobba

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    That was Einstein.

    This is now.

    I would say we know exactly what going on as a mathematical model - beyond that - I will leave up to philosophers.

    Einstein of course had a particular view of reality, which is why he believed QM incomplete - not incorrect - he thought the form it was bought into by Dirac was correct (in fact he considered Dirac's book his bible on QM - or something like that - and always carried a copy) but not complete. The then very popular Copenhagen interpretation grated at the view of reality he had. Was he correct - who knows - he was certainly correct about it being incomplete as quantum gravity readily attests to - although its issue is not as usually portraid - but that is a whole new thread in itself. These days Copenhagen, while still popular, has a lot of competitors, including the interpretation Einstein came up with called the Ensemble which is the one I hold to. Do I hold to Einsteins view of reality - no - I look on reality as what our models describe. Very unsatisfactory and quite likely circular - but hey - nobody said this stuff was easy.

    Added Later:
    What was Einsteins exact view of reality - it actually isn't too far from mine, but does differ in crucial areas. Here is an interview he gave that I think sums it up rather well:
    https://www.scienceandnonduality.com/wp-content/uploads/2014/09/einstein_tagore.pdf

    Just as an aside - and the mods can remove it as they see fit - I think Tagore was basically sprouting mumbo jumbo - but hey - Einstein is way smarter than me and maybe saw more clearly than I what his point was.

    Thanks
    Bill
     
    Last edited: Dec 12, 2017
  12. Dec 13, 2017 #11
    Laplace felt the same way 200 years ago. If history is any indicator, then the current models will be fundamentally revised. Models provide a recipe for predicting, I'm not convinced they necessarily provide knowing, e.g. the correlations from measurements of entangled photons, or the double slit.
    In order to make it complete he proposed hidden variables, which now most find incorrect.
    Our models employ the real numbers. Are they part of your reality? In trying to make that case you will become one of those "philosophers".
    I couldn't agree more. I'm surprised Albert deemed it worthwhile to engage with him (actually maybe he didn't, I think he was sarcastic when he said he was more religious than Tagore).
     
  13. Dec 13, 2017 #12

    bhobba

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    I have no doubt about it - but as some kind of limit our current theories will likely survive.

    Regarding the other Einstein stuff that's best done in another thread I will start on Einsteins view of QM - its getting rather off-topic for this thread.

    The new thread should be there in a couple of minutes and I will link to it, and link back to this one:
    https://www.physicsforums.com/threads/einsteins-view-of-qm.934283/

    Thanks
    Bill
     
    Last edited: Dec 13, 2017
  14. Dec 13, 2017 #13

    bhobba

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    I have started a new thread but must mention here just in case some don't get it - I am sure Einstein thought he was sprouting 'nonsense' and playing along a bit - the key point Einstein was making is objective reality exists independently of us and science's job is to find out about it. That was his belief. That was the issue he had with his good friend Bohr, Copenhagen and the subjective wave-function completely describing the world. Although I never understood much of what Bohr wrote, especially Complementary, his ideas while subtle, were not, well I wont mince my words, mystical gibberish.

    Thanks
    Bill
     
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