Particle or Wave: Questioning Human Mindset

[Nick1234]

Hi All,

I am not a physicist, so my question/comment may be stupid, but if I don't ask I will surely stay stupid, so I'll ask.

I understand that particles show both particle-like behaviour (when measured or "observed") and wave-like behaviour (when expanding, not observed). My question: does observation or measurement not simply mean "question it with our existing mindset"? To me, it seems obvious that if we question nature with our particle-mindset (or with what do we find out that it is a particle?) it is not surprising that we get a particle back as an answer.

In other words, may we have only waves and no wave-particle duality?

I've also tried to make this point on my recent blog post, where I question http://www.spreadinghappiness.org/2009/12/no-emptiness-stillness-or-eternity-questioning-physical-concepts-in-light-of-typical-human-thinking-mistakes/" .

A reply would be very much appreciated!

 

[sokrates]

There are certain experiments which are very difficult to explain by a wave picture.
Two common examples are:
http://en.wikipedia.org/wiki/Photoelectric_effect
http://en.wikipedia.org/wiki/Compton_scattering

Therefore, it is very hard to abandon the particle picture at all. The "quanta" would still be there, which has no wave-counterpart.

 

[Nick1234]

Hi Sokrates,

thank you for your answer. I know the photoelectric effect. In this experiment we "question" light by observing the effect it has on the electrons. My question starts at an earlier stage: why are we so sure that we "question" nature with the particles called electrons? How do we know they are particles?

 

[sokrates]

Hmm.. I am trying to fully understand your point.

But the reason is, I think, that we "falsify", "eliminate" other methods of questioning.
We are forced to believe in that conclusion, after a number of tests.

The name "particle" or "electron" are our inventions, but the phenomena and their properties are about the character of nature.

 

[DrChinese]

Hi Sokrates,

thank you for your answer. I know the photoelectric effect. In this experiment we "question" light by observing the effect it has on the electrons. My question starts at an earlier stage: why are we so sure that we "question" nature with the particles called electrons? How do we know they are particles?

This question is part physics, part philosophy. Yes, it is true to a certain extent that what you see is a function of how you look. But that does not mean that the wave picture is "correct" and the particle one is not.

As Sokrates says, there is behavior that the wave picture cannot explain. For example, you never see fraction of a wave, which you would expect. There are higher order photon effects that really require a particle perspective, see for example this:

"While the classical, wavelike behavior of light ~interference and diffraction! has been easily
observed in undergraduate laboratories for many years, explicit observation of the quantum nature of light - i.e., photons - is much more difficult. For example, while well-known phenomena such as the photoelectric effect and Compton scattering strongly suggest the existence of photons, they are not definitive proof of their existence. Here we present an experiment, suitable for an undergraduate laboratory, that unequivocally demonstrates the quantum nature of light. Spontaneously downconverted light is incident on a beamsplitter and the outputs are monitored with single-photon counting detectors. We observe a near absence of coincidence counts between the two detectors—a result inconsistent with a classical wave model of light, but consistent with a quantum description in which individual photons are incident on the beamsplitter. More explicitly, we measured the degree of second-order coherence between the outputs to be g(2)(0)=0.0177+/-0.0026, which violates the classical inequality g(2)(0)>1 by 377 standard deviations."

http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

 

[Neo_Anderson]

This question is part physics, part philosophy. Yes, it is true to a certain extent that what you see is a function of how you look. But that does not mean that the wave picture is "correct" and the particle one is not.

As Sokrates says, there is behavior that the wave picture cannot explain. For example, you never see fraction of a wave, which you would expect. There are higher order photon effects that really require a particle perspective, see for example this:

"While the classical, wavelike behavior of light ~interference and diffraction! has been easily
observed in undergraduate laboratories for many years, explicit observation of the quantum nature of light - i.e., photons - is much more difficult. For example, while well-known phenomena such as the photoelectric effect and Compton scattering strongly suggest the existence of photons, they are not definitive proof of their existence. Here we present an experiment, suitable for an undergraduate laboratory, that unequivocally demonstrates the quantum nature of light. Spontaneously downconverted light is incident on a beamsplitter and the outputs are monitored with single-photon counting detectors. We observe a near absence of coincidence counts between the two detectors—a result inconsistent with a classical wave model of light, but consistent with a quantum description in which individual photons are incident on the beamsplitter. More explicitly, we measured the degree of second-order coherence between the outputs to be g(2)(0)=0.0177+/-0.0026, which violates the classical inequality g(2)(0)>1 by 377 standard deviations."

http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

We can leave light out of the diffraction picture, as electrons and buckyballs can exhibit diffraction.
Other than diffraction, are there any other instances of light acting as a wave? Blackbody radiation, fine structure, Compton scattering, photoelectric effect, and inequality violation experiments all suggest particles.

 

[Lord Crc]

We can leave light out of the diffraction picture, as electrons and buckyballs can exhibit diffraction.
Other than diffraction, are there any other instances of light acting as a wave? Blackbody radiation, fine structure, Compton scattering, photoelectric effect, and inequality violation experiments all suggest particles.

I'm a non-physicist as well so this may be a silly question, however, how would you explain redshift from a particle point of view?

 

[sokrates]

We can leave light out of the diffraction picture, as electrons and buckyballs can exhibit diffraction.
Other than diffraction, are there any other instances of light acting as a wave? Blackbody radiation, fine structure, Compton scattering, photoelectric effect, and inequality violation experiments all suggest particles.

Other than diffraction, reflection, dispersion, refraction and interference or phase?...

The whole electromagnetic theory treats light acting as a wave, I think what's astounding is that light can behave as particle..

That's why from the times of Newton, people figured out the wave properties of light while it took an Einstein to figure out it can also behave as a particle.

 

[conway]

There are certain experiments which are very difficult to explain by a wave picture.
Two common examples are:
http://en.wikipedia.org/wiki/Photoelectric_effect
http://en.wikipedia.org/wiki/Compton_scattering

"Difficult" is a subjective word. These two particular experiments are only "difficult" to explain by a wave picture in the sense that certain math techniques like integration by parts are "difficult". People tend to forget that the particle explanations also have their difficulties. A small example would be to try and explain, since photons and electrons are supposed to be point particles with zero cross section, how do they collide at all?

 

[sokrates]

"Difficult" is a subjective word. These two particular experiments are only "difficult" to explain by a wave picture in the sense that certain math techniques like integration by parts are "difficult". People tend to forget that the particle explanations also have their difficulties. A small example would be to try and explain, since photons and electrons are supposed to be point particles with zero cross section, how do they collide at all?

Integration by parts is difficult?

No - unfortunately, there's no wave-like explanation for the irreducible quantum of electromagnetic radiation. See Dr. Chinese's post on the subject. A wave doesn't come in lumps.

People weren't baffled with wave-particle dualities, and mysteries of quantum mechanics because they couldn't handle a specific integral.

Electrons and photons are not supposed to be "point particles with zero cross section". Who says that? The quantum theory has a beautiful way of handling scattering which avoids philosophical questions like the radius of electron etc..

You can start by looking at Fermi's Golden Rule, etc...

 

[conway]

Integration by parts is difficult?

Well, yes. I thought I was pretty clear about this. It's "difficult" in the same sense that the wave explanation for, say, the Compton effect is "difficult".

No - unfortunately, there's no wave-like explanation for the irreducible quantum of electromagnetic radiation. See Dr. Chinese's post on the subject. A wave doesn't come in lumps.

Well, now you're upping the ante. I thought you originally said that the wave-like explanations were merely "difficult".

Electrons and photons are not supposed to be "point particles with zero cross section". Who says that?

I thought people generally said that. I would have thought it was something you yourself would say. About the "point particles" issue at least. As for the zero cross section, that was an extrapolation on my part based on what I would intuitively expect for the cross section of a geometrical point. Maybe there is a good explanation for how a point particle has a non-zero cross section, but it does seem to me like exactly the type of thing that would be "difficult" to explain. (In the sense, of course, that integration by parts is also "difficult".)

 

[sokrates]

Well, yes. I thought I was pretty clear about this. It's "difficult" in the same sense that the wave explanation for, say, the Compton effect is "difficult".

? - I don't know how a fundamental property of matter can be tied to a well-defined Mathematical method. What's the relation between integration by parts and wave-particle duality?

Well, now you're upping the ante. I thought you originally said that the wave-like explanations were merely "difficult".

Yes, I am still saying that. One can come up with an overly complicated wave-like model just to explain the particle properties of matter. Bohmian Interpretation attempts to do that, in my opinion. This is why I am using the word "difficult". One needs extra tools and machinery to "fit" the data with a wave picture.

Particle viewpoint on the other hand SIMPLY explains these experiments. So yes, wave-like explanations become difficult under certain conditions.

I thought people generally said that. I would have thought it was something you yourself would say. About the "point particles" issue at least. As for the zero cross section, that was an extrapolation on my part based on what I would intuitively expect for the cross section of a geometrical point. Maybe there is a good explanation for how a point particle has a non-zero cross section, but it does seem to me like exactly the type of thing that would be "difficult" to explain. (In the sense, of course, that integration by parts is also "difficult".)

I refrain from making comments about things that cannot be determined by experiment. In the future, if people can find a way to probe the geometry of an electron, if it even makes sense (experimentally) to talk about it, then we could talk about it.

You brought up the "zero-cross section" argument, so I don't think the particulate view has the burden to explain that. Nobody made a comment about the cross section of a particle.

 

[MaxwellsDemon]

I've answered a question on wave particle duality before, here's what I posted:

Bohr explained wave particle duality using the idea of complimentarity. Have you ever seen that picture where if you think about it in one way it looks like an old woman and if you think about it another way it looks like a young woman?

Here is the link if you haven't:

http://www.teachnet.com/graphics/powertools/puzzles/illusion1.gif

What Bohr suggested was that the wave picture and particle picture are like the old woman/young woman views. Neither view is really what the picture is of, but together they cover all the human ways of thinking about the picture. Objectively the lines that make up the picture exist independently of our ideas concerning their interpretation. Just as we can't "see" both the young woman and the old woman in the picture at the same time, we can't "see" entities as both waves and particles at the same time. They seem opposing and contradictory, but together they encompass all phenomena. The apparent contradiction is due to our human way of interpreting the phenomena. Bohr's point was that nature doesn't really care what we think of it. Opposites are compliments...its all very Zen. Definitely some Eastern philosophy creeping into science.

 

[cheesefondue]

does anyone know what would happen if one were to replace the screen in the double slit experiment with a photoelectric metal sheet. Would we observe both wave and particle nature in the same experiment?

 

[DrChinese]

does anyone know what would happen if one were to replace the screen in the double slit experiment with a photoelectric metal sheet. Would we observe both wave and particle nature in the same experiment?

Not really. As a general rule, complementarity means that you can see the wave, or the particle, but not both at the same time.

Of course, you can do experiments that APPEAR to give you both. But further analysis shows that is merely an illusion.

 

[sweet springs]

Hi.
I recognize my fingers typing this message not as waves but as a body composed of some materials. Am I all right?

 

[dmtr]

Here is an answer given by R. Feynman on the exact same question.



QED.

 

[dmtr]

Hi.
I recognize my fingers typing this message not as waves but as a body composed of some materials. Am I all right?

Here is another answer by the same guy on THAT question:

 

[Nick1234]

Hmm.. I am trying to fully understand your point.

Ok, let me have one more go and then I shut up:

In the photoelectric effect, we see what happens to the electrons when light shines on the metal. We see the electrons emitting from the surface, and conclude quite reasonably that a wave-model could not explain the details of the phenomenon, but that a particle-model (and the mathematics that come along with it) can.

Now: how do we know that the emitted electrons are actually particles? If we take this for granted then yes, light seems to also be a particle. ("If you ask nature with the particle-mindset, you get a particle back as an answer" - it always shows wave-like behaviour if we don't look at it, i.e. if we don't ask nature with our existing mindset).

An integral part of quantum mechanics is to take the observer into the equation - have we done it in this experiment too?

 

[conway]

For the photo-electric and Compton effects, the wave-wave interactions explain things just as well as the particle model. Maybe better.

If you assume the electron is a particle, yes, then light also has to be a particle. But if you really treat the electron as a wave, then its interaction with classical light makes good sense. That was Schroedinger's motivation in developing the wave equation.

 

[Nick1234]

For the photo-electric and Compton effects, the wave-wave interactions explain things just as well as the particle model. Maybe better.

If you assume the electron is a particle, yes, then light also has to be a particle. But if you really treat the electron as a wave, then its interaction with classical light makes good sense. That was Schroedinger's motivation in developing the wave equation.

Ok, good. So where do we still need the particle model?

 

[sokrates]

For the photo-electric and Compton effects, the wave-wave interactions explain things just as well as the particle model. Maybe better.

Is this mainstream or is this your own view?

In my opinion, filling in beginners with Bohmian Interpretation (if that's what you have in mind) who have not even taken an Introductory Quantum Mechanics Class, is not the best way to go about informing them. Could you please show references as to how the wave-wave interactions and whatever you mean by that can explain "things just as well as the particle model"? What are the particle and wave-wave models anyway? As far as I know there's only one mathematical model, which is the Quantum Theory.

 

[sokrates]

Ok, good. So where do we still need the particle model?

We do need the particle model in many instances:

For instance, current flow in conventional resistors are carried out by electrons - but you do not even see a HINT of waves or wave functions in long, dirty, or hot conductors. Quantum effects show signatures only at very special circumstances such as clean samples, low temperatures, short distances, linear bias etc.. Most of the time you need a particulate view to understand current flow in devices. What's more, even the emergence of particle properties from wave functions is a topic of current research today. Physicists are still badly trying to understand and reconcile these two approaches. Although quantum theory is self-consistent and no duality assumptions are needed to be made in its formulation, conceptually wave-particle duality exist for us to interpret and understand things more easily.

In the photoelectric effect experiment, when people first did the experiment, they discovered the remarkable effect of "quantization of radiation". A wave, classically, can have a continuum of energy, so just by increasing it's intensity *the amplitude of the oscillation* - you should be able to increase its total energy and knock out electrons from a metal. But it turns out that no matter how much you increase the intensity of the light, if the frequency is not right, you cannot knock out a single electron from the metal. This experiment led to the inevitable conclusion: Light can also be thought as a collection of "photons" which carry an exact amount of energy which is determined by their frequency, which initially seemed at great tension with Maxwell's Equations and the classical electrodynamics.

But later on, all this was resolved because it turned out that Maxwell's equations could be thought of the Schrodinger equation for the photon!... The E-field in Maxwell's equations could be "thought of" the wave function of the photon. I think this is formally done in QED - where Feynman was an expert. Somebody posted a youtube link above, that shows Feynman talk about this particular issue.

The bottom-line is : We still DO need to use the particle and the wave picture of matter, be it photons, buckyball molecules, or electrons. The duality, in essence, is an illusion (see Dr.Chinese's posts also in this same thread) but it's a great conceptual crutch and helps us develop models, understand experiments, and interpret phenomena - without having to solve extremely complicated many-particle Schrodinger equations to arrive at both particle and wave nature of things.

 

[sweet springs]

Hi.
In Millikan's oil drop experiment, discrete value of electric charge is attributed to electron. It's the proof of particle nature of electron, isn't it?

 

[conway]

Is this mainstream or is this your own view?

In my opinion, filling in beginners with Bohmian Interpretation (if that's what you have in mind) who have not even taken an Introductory Quantum Mechanics Class, is not the best way to go about informing them. Could you please show references as to how the wave-wave interactions and whatever you mean by that can explain "things just as well as the particle model"? What are the particle and wave-wave models anyway? As far as I know there's only one mathematical model, which is the Quantum Theory.

"Mainstream" is a pretty subjective concept and I don't honestly know how to categorize my statements on that basis. If anyone is interested in exactly how you would explain either the photo-electric or the Compton effect by means of wave-wave interactions, I'd be willing to give it a try. Then you could decide for yourself whether it's "mainstream" or not. For the record, I'm not a Bohmian.

 

[sokrates]

"Mainstream" is a pretty subjective concept and I don't honestly know how to categorize my statements on that basis. If anyone is interested in exactly how you would explain either the photo-electric or the Compton effect by means of wave-wave interactions, I'd be willing to give it a try. Then you could decide for yourself whether it's "mainstream" or not. For the record, I'm not a Bohmian.

You use the word "subjective" for everything. Not everything is subjective..

I am interested in the formalistic or qualitative explanations of

*) Compton effect
*) Photoelectric effect
*) Electron-Electron interaction under high temperatures (no phase relationship)

from a wave-wave point of view, if that's not asking too much.

I am really wondering how you are going to build your argument.

 

[conway]

I am interested in the formalistic or qualitative explanations of

*) Compton effect
*) Photoelectric effect
*) Electron-Electron interaction under high temperatures (no phase relationship)

from a wave-wave point of view, if that's not asking too much.

Actually, that's asking a little much. I think I offered to do either one of (a) or (b).

 

[sokrates]

Actually, that's asking a little much. I think I offered to do either one of (a) or (b).

Oh I see. I thought you actually had something to offer.

 

[RogerDow]

Picking up on your Zen remark, I understand that the particle/wave problem essentially gives rise to quantum mechanics, via Schrodinger and others, and that in fact without quantum mechanics we can't explain lots of things. It is used in the design of flash memory etc. so it is pretty much here to stay, but the problem with quantum mechanics is that if the fundamental object is a point particle, the equations go haywire when trying to extend into the conventional world, and string theory was one very complicated way around that, by kind of splaying out the point particle? Anyway, my question is: I heard that someone had suggested another theory which replaces the point particle with absolutely nothing - the complete absense of space time - and that this more elegantly accommodated the problem. Do you know what the name of this idea/theory/person so that I can investigate it further? Instinctively I like the idea.

 

[WaveJumper]

Picking up on your Zen remark, I understand that the particle/wave problem essentially gives rise to quantum mechanics, via Schrodinger and others, and that in fact without quantum mechanics we can't explain lots of things. It is used in the design of flash memory etc. so it is pretty much here to stay, but the problem with quantum mechanics is that if the fundamental object is a point particle, the equations go haywire when trying to extend into the conventional world, and string theory was one very complicated way around that, by kind of splaying out the point particle? Anyway, my question is: I heard that someone had suggested another theory which replaces the point particle with absolutely nothing - the complete absense of space time - and that this more elegantly accommodated the problem. Do you know what the name of this idea/theory/person so that I can investigate it further? Instinctively I like the idea.

Sounds like you are talking about background-independent approaches to GUT.

http://www.2think.org/t000104284.shtml

The fundamental lesson of general relativity that there is no fixed spacetime background hasn't been explored fully and the implications could be profound. It would be an exaggeration to say that there has been a successful attempt to build a comprehensible conceptual model of what space-time really is, beyond that which has already been known for more than a century - that spacetime is relative to the observer's FOR.