Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Wave-particle duality/double slit experiment

  1. Apr 24, 2008 #1
    Is it true that particles behave like waves when there is no observer but behave like particles when there is an observer? If so, how does the observer impact the behavior of the particles? Do electromagnetic waves play a role? Any insight would be appreciated.
  2. jcsd
  3. Apr 24, 2008 #2


    User Avatar
    Homework Helper
    Gold Member

    I think there may be a semantics issue here. Point is, classically we expect certain types of behavior from things we label as waves (like periodicity, oscillations, interference) and a different type of behavior from things we label as particles (like definite rigid size, shape, etc).

    Now, in quantum mechanics, objects like electrons may show certain properties which we label as wave-like in some situations, and properties we label as particle-like in other situations, but there is a *single formalism* which we use to describe the electron. There really isn't any "duality" conundrum.

    It just turns out that, using this single formalism, objects like electrons are predicted to show wave-like behaviour in some cases, and particle-like behaviour in other cases.
  4. Apr 24, 2008 #3
    No. When there is no observer, particles behave like little green women. Prove me wrong...
  5. Apr 24, 2008 #4
    Shouldn't this be in the QM section.

    In here it's not likely to get a straight answer.

    And yes it is true, see the measurement problem, decoherence and particle wave duality, + the Feynman two slit experiment. Type that into Google, particularly the Feynman passage, and enjoy. :)
  6. Apr 24, 2008 #5
    Why was this thread put it GD?

    If everytime a 'beginner' asks a question that he should have researched first, and poster gives a 'funny' answer, instead of help---GD is going to be, or could be, filled by a 100 or more of these 'moved' threads a day.
    Last edited: Apr 24, 2008
  7. Apr 24, 2008 #6
    I researched the question but found no straight answer. In response to rewebster, I should have put this in quantum mechanics, but I thought I wasn't technical enough to understand the QM experts...I figured the GM would allow for a more 'funny' answer as you called it. The answer sidharth gave is exactly what I was looking for. Also, the very reason rewebster gave his post is the same reason why so many people remain beginners - - the problem of experts being annoyed by beginners and then beginners feeling like a beginner and giving up. If you don't like beginners then go to a forum with only experts.
  8. Apr 24, 2008 #7
    Furthermore, I don't think the question has been sufficiently answered by novices or experts. It seems to be a case of "Emperor's new clothes" for the experts and then swept under the rug. Remember and know that in a 100 years 90% of what the experts are saying now will be considered silly and perhaps even ignorant.
  9. Apr 24, 2008 #8
    I think a good point to note is that something can be a wave and a particle at the same time, it is either a wave or a particle but different experiments result in different results.
    Well it isn't up to us to prove you wrong, you have made a prediction of what exists when there is no observer, and now you need to back it up with some evidence in support of it. We can never prove you wrong, so there is no point in that! It is for you to prove it right! Is this somehow 'loosely' similar to Schrodinger's Cat? The whole idea of is it dead or not? My teacher said that he was using maximum and minimum points using calculus in work related to this? Is that just Quantum Mechanic, or does calculus relate to the cat in the box.

    Is it true that in single slit diffraction, the reason for the fringes is purely due to the fact that the maxima and minima are causing the fringes. Where as with twin slit, the two sources are interefeing with eachother? Some 'guy' told me that in single slit diffraction, the waves are interacting with eachother? That's a new one for me, can anyone explain this, that is if it is right!

  10. Apr 24, 2008 #9
    The past doesn't provide any certainty for the future. I don't know how you came about that prediction. Think about it, what major discoveries have been made in the field of particle physics in the past 30 years? As far as I am aware the only BIG contribution is neutrino mass.
  11. Apr 24, 2008 #10


    User Avatar
    Homework Helper
    Gold Member

    No, refer to my post earlier. There it isn't a mechanism by which it switches from being a particle at some time to being a wave at another time. The problem is that you are trying to apply classical concepts to a quantum mechanical object. Fundamentally, there isn't any wave/particle duality. As I said, there is a single formalism which explains how the electron behaves.
  12. Apr 24, 2008 #11
    Sorry I may have put it poorly. I meant that something like a photon has wave and particle properties depending on the situation. This may still be incorrect though, but I have heard the photon being called a "Wave-icle"
  13. Apr 24, 2008 #12
    Certainty of laws

    The point being made is that we have to constantly review and reconsider our ideas that we think,presently, as being absolutely true. Our laws and ideas are in constant flux. The question of wave/particle duality still exists and it would seem normal that with a "fresh" brain examining things that question should indeed come up.
    By the way relegating that question to one of semantics is a bit high handed. Not attacking the user since he is just espousing the party line.
  14. Apr 25, 2008 #13
    Personally I think everything is a wave and we only think it is a particle when we
    manage to 'catch one'.
  15. Apr 26, 2008 #14
    Prove it. :wink:
  16. Apr 26, 2008 #15
    Oh, great...everything is a wave. That's not particularly easy to wrap your mind around. I mean, since a wave is just a disturbance from an equilibrium...everything would be a disturbance from an equilibrium?
  17. Apr 26, 2008 #16
    No everything is a particle, the wavefunction behaves like a wave. You can only classify things by what you measure them to do, when you measure something its in one place and one place only. What happens when you dont measure is irrelevent.
  18. Apr 26, 2008 #17
    Everything is important

    I agree with you basically and as I remember from a book I read about Einstein's life he agrees also. But that doesn't mean that what's happening when we don't measure isn't important in figuring out what is really happening. I think that is what we're after; what really is happening. Formalisms are nice and they work but sometimes not very helpful in imagining what is happenning. Because things are very small doesn't mean that no reality exists. Nature is rather continuous with no sudden jumps to "wierdness". Perhaps, and more likely, things are more complicated and we had hoped and we haven't quite figured out what is happening even though we know how to work with it, a little like gravity.
  19. Apr 26, 2008 #18
    Sorry, "more complicated than---" . I reread it but missed error.
  20. Apr 26, 2008 #19

    Ken G

    User Avatar
    Gold Member

    I would have just said, "a little like physics". Why fight the truth?
  21. Apr 27, 2008 #20
    How do you know? Based on past experience? Thats just scratching the surface, what if thats the exception not the rule.
  22. Apr 29, 2008 #21
    If nature becomes as you are suggesting then "all bets are off" and we can forget the idea of science as we know it.
  23. May 30, 2008 #22
    Well, weirdness is a relative term really. You learn how things should behave by observing the way they do behave, if you then encounter something thats different that implies the rules you were using were not complete or dont abstract well to both situations that doesnt mean you just throw up your hands and go play in the sunshine, you just need to rework things =)
  24. May 30, 2008 #23

    I agree with your assessment of how we see things,( judge whether it is weird or not), but the point was "jump" to weirdness. I would like to believe that nature tends to be more continuous rather than not. For example, how evolution worked,(is working), or how a ball travels in gravity.
  25. May 30, 2008 #24


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    That isn't a valid requirement. A phase transition is a well-known phenomenon. In thermodynamics, a first order phase transition is an abrupt change, where one or more state variable can be discontinuous. In another example, a superconducting phase transition is where the resistivity also changes abruptly.

    So your requirement that "nature tends to be more continuous rather than not" isn't necessarily valid. Maybe this is one more instance where nature isn't continuous.

  26. May 30, 2008 #25
    "Objects like electrons"? What does that mean? Exactly what kind of an "object" is an electron?

    Does the existence of a "single formalism" (or mathematical description) imply that we really understand what is going on here? Do we yet understand what exactly the "wavefunction" is (if it is anything physical at all....)?


    So we can completely explain quantum effects now on a qualitative basis? When did that occur?

    Yeah...but aren't these predictions kind of ad hoc equations?

    Can one derive the equations of matrix mechanics or Schroedinger's equation from first principles?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook