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Author Topic: No wave-particle duality, just waves?  (Read 3796 times)

Offline McKay

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No wave-particle duality, just waves?
« on: 08/05/2014 13:59:42 »
Greetings. I was wondering about the nature of light.
What are the experiments for pro-particle nature of light? The photovoltaic experiment?
It kinda makes sense that it must be a particle to excite just a single atom, right? But what if the photon is still a wave, just a very narrow one? It could be narrow enough to excite just one atom, but still be a wave, couldnt it?

As the wave further travels, its width expands, but, as energy is conserved, it does so at the expense of its frequency - it gets lower.
And dont we see that in the universe already? The redshift of istant stars that we explain by the expanding universe, that isnt really understood at all..?


 

Offline alancalverd

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Re: No wave-particle duality, just waves?
« Reply #1 on: 08/05/2014 16:17:00 »
The "duality" word is misleading. Light is light, and it behaves as it does. We use two mathematical models to describe and predict the behaviour of electromagnetic radiation but it isn't one thing, the other, or both.

You can model the decreasing intensity of light with distance by either means, expansion of a wave or dispersal of particles, and you get the same answer. But the decreasing energy of each photon can best be modelled by wave Doppler equations for moving sources (as for Doppler radar and LIDAR) and relativistic effects on particles for cosmological red shift.

"Understood"? To the extent that a phenomenon can be predicted and correlated with other phenomena, yes.
 

Offline chiralSPO

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Re: No wave-particle duality, just waves?
« Reply #2 on: 08/05/2014 18:46:58 »
I recently read an interesting article (Am. J. Phys. 81, 211; doi: 10.1119/1.4780885) that maintains that there are actually no particles, only fields and waves. Particles are just easy to think about and model. (I suspect we may find that waves are also just a tool for modeling concepts that are currently beyond our understanding)
 

Offline JP

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Re: No wave-particle duality, just waves?
« Reply #3 on: 08/05/2014 19:52:27 »
Classical waves alone can't explain the photoelectric effect, which is why the "duality" is required.  (It requires light of above a certain frequency, not intensity to liberate an electron).

Classical particles alone can't explain interference effects observed in light.

That's why we say there is wave-particle duality: that light has elements of both classical particles and classical waves in its behavior.
 

Offline chiralSPO

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Re: No wave-particle duality, just waves?
« Reply #4 on: 09/05/2014 23:49:57 »
Classical waves cannot explain the photoelectric effect--True. But as I understand it, one can explain this with non-classical (quantized) waves, without invoking particles.
 

Offline dlorde

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Re: No wave-particle duality, just waves?
« Reply #5 on: 10/05/2014 00:05:31 »
Classical waves cannot explain the photoelectric effect--True. But as I understand it, one can explain this with non-classical (quantized) waves, without invoking particles.
Yeah, but wave-particle duality is the classical interpretation...
 

Offline chiralSPO

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Re: No wave-particle duality, just waves?
« Reply #6 on: 10/05/2014 00:42:48 »
"Yeah, but wave-particle duality is the classical interpretation..."

Fair enough...
 

Offline alancalverd

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Re: No wave-particle duality, just waves?
« Reply #7 on: 10/05/2014 01:34:58 »
The weasel word here is "interpretation". Clearly when a photon sets off from a distant galaxy it has no idea whether it is going to interact with a photocathode or another photon, so whatever it "is", it remains until that interaction is complete. Our problem is that we don't have a single equation or model that describes both interactions in a simple manner, but in any given circumstance the wave or particle model is adequately predictive.   
 

Offline McKay

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Re: No wave-particle duality, just waves?
« Reply #8 on: 17/05/2014 00:37:39 »
Classical waves alone can't explain the photoelectric effect, which is why the "duality" is required.  (It requires light of above a certain frequency, not intensity to liberate an electron).

Ah, but, actually, increasing the intensity of low frequency photons can, in fact, liberate electrons.
I saw an experiment done once in a institute where they used a very high intensity laser to excite fluorescent material with near infra-red radiation - explaining it with "squeezing two photons at an atom at once"..
 

Offline JP

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Re: No wave-particle duality, just waves?
« Reply #9 on: 17/05/2014 01:35:01 »
Classical waves alone can't explain the photoelectric effect, which is why the "duality" is required.  (It requires light of above a certain frequency, not intensity to liberate an electron).

Ah, but, actually, increasing the intensity of low frequency photons can, in fact, liberate electrons.
I saw an experiment done once in a institute where they used a very high intensity laser to excite fluorescent material with near infra-red radiation - explaining it with "squeezing two photons at an atom at once"..

Yes, two photon physics is possible, but I believe you need a LOT more energy than you'd predict with classical waves.
 

Offline lightarrow

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Re: No wave-particle duality, just waves?
« Reply #10 on: 17/05/2014 12:10:06 »
Greetings. I was wondering about the nature of light.
What are the experiments for pro-particle nature of light? The photovoltaic experiment?
I believe you intended "photoelectric effect" so I will consider this one, from here on.
I read a lot of discussions where many claimed a model for semi-classical interaction (light treated classically/detector treated quantistically) could explain photoelectric effect; among other things I remember, the electron is not liberated from atoms at the detector' surface but from inner atoms. So I don't think the photoelectric effect is a definitive prove for the corpuscolar behaviour of light. Maybe the Compton effect is better, from this point of view, but even better is the "Photon anti-bunching" or similar effects.
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It kinda makes sense that it must be a particle to excite just a single atom, right?
When we use the term "particle" we usually intend "corpuscle". But in quantum physics "particle" means "that particular physical system which is described by quantum mechanics and that in some circumstances can behave as a wave or as a corpuscle". More precisly, in quantum electrodynamics it means "quantum of a particular field", so a photon is "a quantum of electromagnetic field" and an electron is "a quantum of electrons field".

So, if you intended "corpuscle", then, in base of what I wrote up, I don't believe there is such a strong need of a corpuscle to excite a single atom.
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But what if the photon is still a wave, just a very narrow one? It could be narrow enough to excite just one atom, but still be a wave, couldnt it?
The problem is that every wave packet will disperse in a big region of space, giving it enough time, unless you invoke some sort of strange physical mechanism. So, a little wave packet emitted from a distant galaxy why would be detected in a single point of the detector? The same kind of problems come if you use a light source with very high spatial coherence, which "coherence lenght" is, for example, of some metres. Where are exactly the photons in that case?
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As the wave further travels, its width expands, but, as energy is conserved, it does so at the expense of its frequency - it gets lower.
No, the frequency cannot vary, in case is the intensity (the amplitude of the fields) which does it.
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And dont we see that in the universe already? The redshift of istant stars that we explain by the expanding universe, that isnt really understood at all..?
No, it's a totally different thing, you can't explain it in that way.

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lightarrow
« Last Edit: 17/05/2014 12:17:04 by lightarrow »
 

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Re: No wave-particle duality, just waves?
« Reply #10 on: 17/05/2014 12:10:06 »

 

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