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Wave-Particle Duality (QED)

  1. Jun 30, 2015 #1
    I have been reading Richard Feynmans Quantum Electrodyamics and quite early in the first chapter he asserts that Photons are particles. His reasoning that as you decrease the intensity of light incident on a photomultiplier the clicks which the multiplier make become less frequent but equally loud. He doesn't go into much more depth on this issue and assumes particles in there "corpuscular" interpretation. However I always imagined light as quanta. Packets of photons, so is it not the case that decreasing intensity just decreases the number of quanta?

    Feynman states there are properties which support his assertion and I was hoping Physics Forums could shed some light on them, excuse the pun
     
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  3. Jun 30, 2015 #2
    Wave particle duality is an outdated concept, in qft everything is fields. Once you quantize those fields, there are some states with definite momentum which can be interpereted as particles.
    People should really stop teaching wave particle duality.
     
  4. Jun 30, 2015 #3
    I'm just going into my honours year so wave-particle duality was a concert introduced! Any helpful resources?
     
  5. Jun 30, 2015 #4
    I am trying to understand the exact problem of particle wave duality. Perhaps somebody can correct me but it seems to me an electron is a negatively charged particle, i dont think most people would disagree. However, it has wave associations only when a voltage is applied to create a flow of electrons. Only then has it an electro magnetic field surrounding it in concentric circles, which rotate around an electric cable or beam of electrons in a direction as described by Maxwell's corkscrew rule. If the carrier frequency of electrons is modulated as in Radio, the radiating electric field causes the associated electromagnetic field, which is at right angles to the electric field, to reflect the electric field wave pattern. This electromagnetic field travels infinite distances the same as gravity and these waves react easily with other electromagnetic or magnetic influences.
    Recapping: an electron has no wave properties until a voltage is applied, but then it has.
     
  6. Jun 30, 2015 #5

    Nugatory

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    Google for "electron double slit".
     
  7. Jun 30, 2015 #6

    WannabeNewton

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    If I had a dollar for every time someone outside of PF preached this as dogmatically, I would have zero dollars.
     
  8. Jun 30, 2015 #7

    atyy

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    You will find the concept coherently formalized when you study quantum theory properly. The quantum particle is a fundamental concept in quantum mechanics. Unlike a classical particle, a quantum particle does not have simultaneously well-defined position and momentum. However, it is like a classical particle in that it can be counted using the integers. However, there is a wave equation that governs the probabilities of experiments performed on the particle(s).
     
  9. Jul 1, 2015 #8
    Yea I assumed anything quantum would obey the Uncertainty principle, it all seems rather vague at times. I suppose no one really knows
     
  10. Jul 1, 2015 #9
    I must admit I know nothing of quantum theory, but I do know how Televisions And Radios are designed and work. On tried and trusted physics formulas from people like: Faraday, Ohm, Watt, Maxwell, Lenz, and many more. I will however study more about quantum mechanic before I criticise it.
     
  11. Jul 1, 2015 #10

    phinds

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    No one really knows what? That quantum objects are just that and not classical particles or waves?
     
  12. Jul 1, 2015 #11
    Good luck King... If you are just being introduced to these ideas, and aren't going to be using them professionally, I have a piece of advice (as a non-physicist)... Learn the formulas, run the numbers and call it a day. OR, prepare to have your world view significantly altered for the rest of your life.
     
  13. Jul 1, 2015 #12

    atyy

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    There is no problem of "particle-wave duality". There is only a problem of "wave-particle duality". Kidding!

    There is no problem of either. "Wave-particle duality" is a loose term from early days when quantum phenomena were first being seen to describe that the phenomena resembled how classical particles and classical waves behaved. In those days, quantum theory was only known as incoherent pieces of the puzzle. Nowadays, we do have a quantum theory in which the pieces are coherently assembled. Some people don't like the term "wave-particle" duality because it comes from a time when people did not fully understand quantum theory. Others, like me, think the term is fine, since the early apparently disparate pieces have now been properly synthesized. Regardless, we all agree that we now have a quantum theory that makes complete sense.

    So there are no classical particles. There are only quantum particles, which differ from classical particles in that they do not have simultaneously well-defined positions and momenta. There are also no classical waves. Quantum particles are described by equations that have wave-like properties and particle-like properties, and yet are different from classical particles and classical waves.
     
    Last edited: Jul 1, 2015
  14. Jul 1, 2015 #13
    No one really know what electrons are, they have never been observed, along with a lot of constituent parts of matter (strings) it was a general comment which I regret ;)
     
  15. Jul 1, 2015 #14
    As far as quantum objects I suppose it's hard to say what they really are except from mathematical abstractions
     
  16. Jul 1, 2015 #15
    That is all fine, I'm aware I have only scratched the surface of the quantum world. However we do not have particle equations? We have wave equations? Or is this a matter of mere naming
     
  17. Jul 1, 2015 #16

    phinds

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    I don't know what a "particle equation" would be in this case. The wave equation gives the probability of finding the a particle if you measure for a particle.
     
  18. Jul 1, 2015 #17

    Strilanc

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    Come now, I count at least two dollars.
     
  19. Jul 1, 2015 #18
    But as far as the properties of said particle which we have a probability for?
     
  20. Jul 1, 2015 #19

    atyy

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    It is mostly a matter of naming. One could say we have wave equations for particles. It is best to learn the formalism properly, and just get used to the fact that different people use different naming conventions.
     
  21. Jul 2, 2015 #20
    Because if we call it a particle we collapse the wave function to a single point? So it cannot have a probability to be "everywhere" like quantum theory boasts
     
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