Wave-particle duality/double slit experiment

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  • #1
francirp
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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.
 

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  • #2
siddharth
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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.
 
  • #3
humanino
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Is it true that particles behave like waves when there is no observer but behave like particles when there is an observer?
No. When there is no observer, particles behave like little green women. Prove me wrong...
 
  • #4
Schrodinger's Dog
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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. :)
 
  • #5
rewebster
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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.
 
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  • #6
francirp
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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.
 
  • #7
Normouse
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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.
 
  • #8
_Mayday_
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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.
No. When there is no observer, particles behave like little green women. Prove me wrong...

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!

_Mayday_
 
  • #9
_Mayday_
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...Remember and know that in a 100 years 90% of what the experts are saying now will be considered silly and perhaps even ignorant...

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.
 
  • #10
siddharth
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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.

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.
 
  • #11
_Mayday_
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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.

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"
 
  • #12
Normouse
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Certainty of laws

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.
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.
 
  • #13
esbo
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Personally I think everything is a wave and we only think it is a particle when we
manage to 'catch one'.
 
  • #14
Schrodinger's Dog
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Personally I think everything is a wave and we only think it is a particle when we
manage to 'catch one'.

Prove it. :wink:
 
  • #15
francirp
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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?
 
  • #16
FunkyDwarf
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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.
 
  • #17
Normouse
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Everything is important

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.
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.
 
  • #18
Normouse
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Sorry, "more complicated than---" . I reread it but missed error.
 
  • #19
Ken G
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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.
I would have just said, "a little like physics". Why fight the truth?
 
  • #20
FunkyDwarf
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Nature is rather continuous with no sudden jumps to "wierdness"
How do you know? Based on past experience? Thats just scratching the surface, what if thats the exception not the rule.
 
  • #21
Normouse
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How do you know? Based on past experience? Thats just scratching the surface, what if thats the exception not the rule.
If nature becomes as you are suggesting then "all bets are off" and we can forget the idea of science as we know it.
 
  • #22
FunkyDwarf
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If nature becomes as you are suggesting then "all bets are off" and we can forget the idea of science as we know it.

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 =)
 
  • #23
Normouse
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weirdness

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.
 
  • #24
ZapperZ
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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.

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.

Zz.
 
  • #25
Firefox123
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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.

"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....)?

There really isn't any "duality" conundrum.

Really?

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

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.

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?
 
  • #26
Normouse
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Refreshing

"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....)?



Really?

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?

Thank you for your clear headed, honest, not bound by the party line comments.
 
  • #27
Normouse
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More precisely

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.

Zz.

I didn't mean by "jump to weirdness" simply being non-linear but more strictly the idea of mathematical discontinuity. The old delta epsilon argument: there is no point in time that we can get arbitrarily close to and find all the material of a phase transition in one state and then find all the material in another state. That would be a "step function" which does not exist in phase transition just very rapid change at a certain energy. Each molecule changes states individually which I could consider continuous but non-linear. Instantaneous phase change would be discontinuous. I haven't researched your other example yet but I think you will again concede that the resistance does not change instantaneously. Maybe resistivity is a little different, please inform, but I think atom by atom the change takes place not all atoms of the material changing at once at a threshold energy level.
 
  • #28
FunkyDwarf
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Like i said i think its more of a moot point really because when you say 'jump to weirdness' or mathematical discontinuity you are applying your human intuition to a situation that might be counter intuitive and then getting annoyed when you get it wrong. Without knowing a complete laws of physics or 'backend code of the universe' if you like theres no way of knowing whats truely weird/incorrect. Obviously our current theories work pretty well and we can be assured that they will continue to provide correct data on the experiments they are related to. But for me science is like 20 questions. You can be thinking of an object and i can ask 19 questions to which the answer would be the same for both that object and something different, which i happen to be thinking of. If i stopped there id go away thinking about the wrong thing. If i asked the 20th question and got an answer which proved i wasnt thinking about the correct object then i have to rethink all the others two. In science the behaviour of stuff is the object and experiments are the questions. Theres nothing to say someone wont do an experiment tomorrow that completely turns everything on its head. Theres just no way you can say that for sure.

But now were getting nitpicky and off topic =)
 
  • #29
NYSportsguy
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Your are wrong and getting your concepts mixed up. The Particle-Wave duality is basically saying that light is made up of individual photons that act as waves when many photons are together. Sort of like a surfer on an ocean wave. The wave is the direction of motion and the surfer is considered the electron or photon.

Heisenberg's Uncertainty Principle basically says that you cannot ever measure both time and energy or location of an electron and it's momentum perfectly at the same time because the person doing the observation will "taint" or affect the true momentum (mass x velocity) and position of a photon or electron just by looking at it.

Quantum physics basically is somewhat disturbing because, unlike classical physics, scientists today cannot accurately predict where an electron will land or move next when it changes direction when after being hit by a photon. Scientists can only "guesstimate" using probability. Einstein had a problem with this because he refused to believe that God "liked to roll the dice" in cause and effect in science. However Niels Bohr, Max Born, Heisenberg and Wolfgang Pauli all said that Einstein was wrong and that atomic movements of particles is all random, and can never be predicted, only estimated - which to this day is the accepted fact.
 

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