Light = Particle or Wave? [Archive]

ZapperZ

Jul20-04, 09:01 AM

There appears to be a strong and continuing miconception about light/photons as far as this so-called "duality" is concerned. Let's get ONE thing straight here - Quantum mechanics does NOT have two separate descriptions of light for when it behaves as a "wave" and when it behaves as "particles". PERIOD! It has one, and only one, consistent description for light, and that's that.

Now, after reading that, would one still want to consider light as having a "wave-particle duality"?

From the way I see it, the continuing misconception here is due to the ambiguity of the quality used in the question. We apply our classical ideas of what "wave" is, and what a "particle" is. A particle, like a grain of sand, has a definite boundary in space, i.e. a grain of sand doesn't appear spread out that it's exact shape and boundary are vague. Thus, it has what we classically define as a particle. A wave, on the other hand, can spread out over space.

Now, a photon, as a particle, was NEVER defined this way! A photon description in QM is NOT defined as having an exact shape and boundary in space. It is defined as clumps of energy. So in energy coordinates, it has definite "points", but it has no definite "size" in real space! This isn't your classical particle.

Having said that, the most common explanation for the "wave-particle duality" is that light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect. Now, the fact that it is EASIER to describe an observation using one type of description while describing another observation using another type of description does NOT mean that they can't be described using ONE consistent discription. Most people often do not realize that one CAN describe interference effects (a typical wave phenomena) using photons![1] In fact, such technique CLEARLY explain diffraction patterns, and how the uncertainty principle is clearly at work. We don't normally subject students to such things because it is MORE involved than using the simple wave description. But we should not fool ourselves into thinking that the photon picture cannot be used to arrive at the idential phenomena that once thought can ONLY be described using the wave picture.

Again, one needs to learn QM and realize that there are no separate description for this wave-particle duality illusion. It is only a duality based on our pre-existing prejudice that something must either be a wave, or a particle. This "duality" thing only appears to be a major "issue" in pop-sci books and articles. It is a non-issue in QM texts.

Zz.

[1] T. Marcella, Eur. J. Phys., v.23, p.615 (2002).

Galileo

Jul20-04, 09:32 AM

Light is neither a wave nor a particle.
You cannot account for certain experiments when holding on to a corpuscular interpretation of light, and the same is true for a pure wave interpretation. Instead of that the new theory which explains these phenomona with fastastic agreement is quantum theory.

Furthermore, this is not a peculiarity of light. Also electrons, neutrons and so on are neither wave nor particle. So when we refer to particles, we don`t mean anything corpuscular or wavelike, but rather a physical entity which exhibits both properties (they cannot be seperated).
I guess this is where the term 'duality' comes from. I don`t like the term since it sounds like they act like waves on a summerday and like particles when it's raining. It's simply not so. There is a unified and logical way to describe the behaviour of particles, but we must abandon the thought of it being a wave or particle.

Les Sleeth

Jul20-04, 09:58 AM

Let's get ONE thing straight here - Quantum mechanics does NOT have two separate descriptions of light for when it behaves as a "wave" and when it behaves as "particles". PERIOD! It has one, and only one, consistent description for light, and that's that.

You seem a bit distressed to find out there are still people left who don't know everything about physics. I've thought that maybe PF should have a forum catagory called "Ask All the Stupid Questions You Want!" for those of us who want to understand, but don't yet and so are bound to have misconceptions.

My stupid question would be, is it possible a photon is oscillating between two conditions, one of which exhibits wave-like behavior, and the other which exhibits particle-like behavior?

ZapperZ

Jul20-04, 11:48 AM

You seem a bit distressed to find out there are still people left who don't know everything about physics. I've thought that maybe PF should have a forum catagory called "Ask All the Stupid Questions You Want!" for those of us who want to understand, but don't yet and so are bound to have misconceptions.

My stupid question would be, is it possible a photon is oscillating between two conditions, one of which exhibits wave-like behavior, and the other which exhibits particle-like behavior?

Distressed??!!

I'm not distressed. I had to use CAPS to make sure there is a clear emphasis on the main point of what I'm trying to get acrossed. This type of question appears repeatedly on here and elsewhere. I'm hoping that at the very least, people will pay attention to one or two sentences of what I wrote, so at least the effort I spent would not have been in vain. I have no delusion that this would stop the very same question from popping up again.

Secondly, why would a photon "oscillates" between two separate behavior when in QM, there is no separate behavior?

Zz.

JohnDubYa

Jul20-04, 11:52 AM

Particle. No experiment has ever been performed on a photon that demonstrated wave properties to my knowledge.

Les Sleeth

Jul20-04, 01:45 PM

This type of question appears repeatedly on here and elsewhere. I'm hoping that at the very least, people will pay attention to one or two sentences of what I wrote, so at least the effort I spent would not have been in vain. I have no delusion that this would stop the very same question from popping up again.

Logic and observation will explain why. Notice how many members we now have. In a couple of weeks, look again. More new members! A great many of them are students, ranging from grade school :bugeye: to graduate school. Some of us are laypersons simply interested in how the universe works. People come here excited to find an opportunity to learn, and hoping others who do know will be charitable. In an ideal world they/we might read past posts and find the answers to their questions. But that isn't nearly as much fun as having someone to personally interact with, especially if you want to ask follow-up questions. So I think part of the deal if you are going to help out at PF is patiently explaining things again and again.

In the past I've asked experts if they think it would be a good thing if everybody learned something about physics. If so, then it is obvious there are going to be different levels of understanding and interest, which means different levels of teaching and more patience :wink: (when it comes to patience, I'm not talking about enduring stubborn insistance on maintaining one's own theories, or coddling lazy minds unwilling to do a little research). I love the subject myself, but since it isn't my area of expertise, I don't have time to study it with the thoroughness required to be a physicist.

This isn't my forum, so I suppose if everyone thinks it should be sort of an exclusive club for current and future physicists, then that's that. If so, then maybe one day PF will offer a forum area called "Physics for Dummies." :tongue2:

Secondly, why would a photon "oscillates" between two separate behavior when in QM, there is no separate behavior?

Well, that's what I was asking you, the expert. You yourself said "light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect." I'll try to explain what I was thinking.

My question was asking if a photon's dynamics might include a photon oscillating between being a "clump" as you say, and opening up a bit to temporarily lose its clump integrity. That might establish phases which when observed one way reveal wave-like properties, and when observed another way reveal particle-like properties.

One reason I wonder about that is because of how background radiation has "stretched" along with the expansion of the universe since the big bang (at least, according to Marcus). Obviously radiation that is more expanded now was less expanded before, so right there is the possibility that radiation is oscillating between expansion and contraction in coherence with the historical and present universe.

ZapperZ

Jul20-04, 01:57 PM

Well, that's what I was asking you, the expert. You yourself said "light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect." I'll try to explain what I was thinking.

You read wrong. What I said was...

"Having said that, the most common explanation for the "wave-particle duality" is that light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect."

I said it was a "common explanation" that points to the existence of this so-called duality. But if you read the whole posting from where that came from, I insisted (repeatedly) that there is no such thing as a "duality". How can it when there is only ONE consistent description of light within QM? That was the whole point of my response. I do not know how else to make this any clearer. I have one description of light that can describe ALL the phenomena that it exhibits. So how can I answer your question anymore on the "duality" of light, when there isn't any!

Zz.

Thinkmarble

Jul20-04, 02:36 PM

Particle. No experiment has ever been performed on a photon that demonstrated wave properties to my knowledge.

Then please explain interference effects under the assumption that photons are particles.
After you have done so explain the fact that photons have (AFAIK) a spin of 1*.

*this can actually not be explained by assuming that photons are particles or waves but rather only by assuming that they are in the new** category of quaobs (quantum objects).
There is one description (qunatum theory) which can explain all three things (photoelectric effect, interference, spin).
So saying that there are on thing ignores two third nature, saying that there is a duality leads to mushy brains and still ignores one third of nature.
**Can something be new when it is 60-70 years old ?

Les Sleeth

Jul20-04, 03:46 PM

I do not know how else to make this any clearer.

Well, you do seem to acknowledge behavioral differences (and I am not implying behavioral differences indicate duality), and then seem to contradict yourself in the following two statements:

". . . light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect."

". . . why would a photon "oscillates" between two separate behavior when in QM, there is no separate behavior?"

You read wrong. What I said was...

"Having said that, the most common explanation for the "wave-particle duality" is that light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect."

I said it was a "common explanation" that points to the existence of this so-called duality. But if you read the whole posting from where that came from, I insisted (repeatedly) that there is no such thing as a "duality". How can it when there is only ONE consistent description of light within QM? That was the whole point of my response. I do not know how else to make this any clearer. I have one description of light that can describe ALL the phenomena that it exhibits. So how can I answer your question anymore on the "duality" of light, when there isn't any!.

I don't believe I did read you wrong. I don't think there is any duality, and never have. I am not confused about your explanation in the slightest, I am NOT ( :smile: ) questioning your explanation, we are not disagreeing about duality.

From your point, I lept to wondering what is happening at the quantum level that might make it appear there is duality there. My point was to ask: what is causing the different observed behaviors (i.e., double slit/photoelectric), all falling under the single reality of QM?

I asked if it might be that a photon is continously phasing in and out of particleness; or, looked at from the opposite direction, might it be continuously phasing in and out of waveness. Since we know a photon (and all particles) are intense oscillators, why couldn't a photon be something singular which simply alternates between being more "clumped" and more spread out? Might that not account for the APPEARANCE ( :devil: ) of duality? And the reason we see the differences in the double slit experiment and the photoelectric effect is because each of those processes accentuates a particular phase.

ZapperZ

Jul20-04, 04:45 PM

Well, you do seem to acknowledge behavioral differences (and I am not implying behavioral differences indicate duality), and then seem to contradict yourself in the following two statements:

". . . light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect."

". . . why would a photon "oscillates" between two separate behavior when in QM, there is no separate behavior?"

You need to read that these are observations that classically are defined to be of two different nature . I then tried to emphasized that this is due to our prejudice from classical physics that these need to be of different nature. Nothing in QM indicates that these are of different beasts. When I can use one formulation to describe both sufficiently, then they are not "dual", they are "singular" in nature.

From your point, I lept to wondering what is happening at the quantum level that might make it [i]appear there is duality there. My point was to ask: what is causing the different observed behaviors (i.e., double slit/photoelectric), all falling under the single reality of QM?

I asked if it might be that a photon is continously phasing in and out of particleness; or, looked at from the opposite direction, might it be continuously phasing in and out of waveness. Since we know a photon (and all particles) are intense oscillators, why couldn't a photon be something singular which simply alternates between being more "clumped" and more spread out? Might that not account for the APPEARANCE ( :devil: ) of duality? And the reason we see the differences in the double slit experiment and the photoelectric effect is because each of those processes accentuates a particular phase.

"phasing in and out" of a photon (at least a real one as opposed to a virtual one) is not described in QM, at least it is not needed to explain the photoelectric effect, Compton scattering, diffraction, and two-slit interference. Besides, why do we need to impose this phasing in and out when QM already has a statisfactory description of this?

What is often overlooked is the most important but subtle aspect of something like the 2-slit experiment. That the interference effect is NOT really an intrinsic property of the object in question (i.e. not of the photon, electron, neutron, C60 molecule, etc), but rather due to the SUPERPOSTION OF PATH! If you scale your experiment according to the object in question so that it is of the order of the deBroglie wavelength, then the object is IRRELEVANT! The superpostion of all the possible paths thru the 2-slit is what is causing the interference! The object that is passing thru the 2-slit is incidental and irrelevant once the length scale has been taken into account. Again, this is clearly described in QM, and I have cited Marcella's paper that shows this in painful detail. It is even clearer if one uses the Feynman path integral approach.

Zz.

Les Sleeth

Jul20-04, 05:04 PM

"phasing in and out" of a photon (at least a real one as opposed to a virtual one) is not described in QM . . .

Actually I said phasing between being more spread out (wave-like) and being more "clumped" (particle-like).

ZapperZ

Jul20-04, 05:46 PM

Actually I said phasing between being more spread out (wave-like) and being more "clumped" (particle-like).

That too.

Zz.

reilly

Jul20-04, 10:52 PM

Not only is there duality in QM, but in classical physics as well: to wit, just think about the macroscopic treatment of alternating current. The idea of duality arose because of the apparent conflict between Thomson's particulate electron and the phenomena of electron diffraction - when such diffraction was found, it was a major mind blower. Electrons do sometimes behave as particles, sometimes as waves -- like in electron microscopes. The samething holds for light -- interference is wave-like, Compton scattering is particle like. Why deny our senses?

Certainly the background radiation observed as a relic of the Big Bang is nicely thought of as standard wave-like radiation. Bohr and his colleagues worried about this duality, and its implications for the conceptual apparatus of physics and philosophy -- tricky stuff. How coulkd this really weird stuff be?

Zz is correct in that there is a unifying perspective about all of this -- it stems from Quantum Field Theory, which easily allows both a field and a particle perspective. That is, QFT makes it possible to flip back and forth from photon states to field states all with in the same basic fornalism. But the math is highly sophisticated and formidable -- see, for example,Optical Coherence and Quantum Optics, by Mandel and Wolff, everything you wanted to know and didn't want to know about photons.

Think of duality as pragmatic -- sometimes you use your wave "glasses", sometimes your particle "glasses" to understand your measurements--you choose what works best for you. For the layman, focus on the physics, learn the history. Physics is the cumulative effort of many generations of physicists, what the old guys saw and thought is very important to understanding physics today.

Regards,
Reilly Atkinson

JohnDubYa

Jul20-04, 11:48 PM

Then please explain interference effects under the assumption that photons are particles.

Single photons do not exhibit interference effects.

After you have done so explain the fact that photons have (AFAIK) a spin of 1*.

Is there a law of nature that particles cannot have spin?

ZapperZ

Jul21-04, 06:41 AM

Single photons do not exhibit interference effects.

Actually John, unless I misread you, while you do need a lot of photons (or electrons or neutrons, etc) to be able to DETECT the interference effects, the interference pattern from, let's say, a typical 2-slit expt. is in fact the interference of a single photon with itself! In other words, 2-photon, 3-photon, etc interference aren't the same as single-photon interference.[1] That's why I mentioned earlier that what is significant here isn't the photon, electron, neutron, etc, but rather the superpostion of all the possible paths that ONE single object can take.

Zz.

L. Mendel, Rev. Mod. Phys., v.71, p.274 (1999).

Les Sleeth

Jul21-04, 10:24 AM

Zz is correct in that there is a unifying perspective about all of this -- it stems from Quantum Field Theory, which easily allows both a field and a particle perspective. That is, QFT makes it possible to flip back and forth from photon states to field states all with in the same basic fornalism. But the math is highly sophisticated and formidable -- see, for example,Optical Coherence and Quantum Optics, by Mandel and Wolff, everything you wanted to know and didn't want to know about photons.

Think of duality as pragmatic -- sometimes you use your wave "glasses", sometimes your particle "glasses" to understand your measurements--you choose what works best for you. For the layman, focus on the physics, learn the history. Physics is the cumulative effort of many generations of physicists, what the old guys saw and thought is very important to understanding physics today.

Thanks Reilly, I was thinking of QFT (what little I understand about it) when I posed my question. Probably no one knows the answer to my question. It seems what we have are methods of observation, math which accounts for the behavior, but no precise explanation of exactly what is going at the quantum level on that gives the two sorts of observations.

I like the "glasses" analogy because that is related to what I am asking. I'm wondering if the two different glasses we use are like polar filters which allow only one side of a particle's two hypothetical phases (i.e., my hypothesis) to appear. Likewise, when you say "to flip back and forth from photon states to field states," it sounds like what I am envisioning.

ZapperZ

Jul21-04, 11:21 AM

Zz is correct in that there is a unifying perspective about all of this -- it stems from Quantum Field Theory, which easily allows both a field and a particle perspective. That is, QFT makes it possible to flip back and forth from photon states to field states all with in the same basic fornalism. But the math is highly sophisticated and formidable -- see, for example,Optical Coherence and Quantum Optics, by Mandel and Wolff, everything you wanted to know and didn't want to know about photons.

I think I know what you are getting at here. Unfortunately, as you can see from the previous post, it can easily be misinterpreted or misrepresented. The biggest obstacle in this issue is trying to convey the meaning of the mathematics. QFT (and QED) makes NO provision for classical fields. Therefore, classical fields (and thus, "waves") essentially do not exist and are meaningless in QFT.

Then what are we left with? I hate to say we have a "particle field", because that again can be misinterpreted (refer to my discussion what classical particle is and why this is NOT what a photon is). Can I get away with saying a "quantum field" without grossly misrepresenting the mathematics? Maybe. If we stick by that, then I would not want to leave the impression that photons can flip back and forth between two apparently different perpective.

Zz.

ZapperZ

Jul21-04, 12:27 PM

I realize the burden is on me to make myself clear, and I haven't yet (and believe me, I am completely ready to accept that my idea is 100% wrong as soon as I can tell someone is responding to what I am saying).

I do NOT mean a photon "can" flip back and forth between "perspectives." I emphasize your use of the word "can" because what I am suggesting is that a photon must flip back and forth because that is part of what defines what it is. I am saying, or asking: what if a photon is rapidly (really rapidly) shifting between opening out and tightening back up? In fact, shifting so fast that both phases exist simultaneously, and would appear to exist simultaneously if we could observe the phases at the same time. That leads to the second concept of observation, which is that the methods we employ expose either one side of the shift or the other, depending on the method we use. I've included two little diagrams to explain my meaning.

In Diagram 1 is a platform which swings from side to side. The top figure represents when the platform is at the far left extreme, and the bottom figure represents when the platform is at the right extreme.

Diagram 2 represents what should happen if we could get the platform to oscillate between the two extremes fast enough. At some critical speed, the platform would appear to exist simultaneously in both the left and right positions, differentiating into left and right "phases."

That analogy might demonstrate simultaneity and phase differentiation, but it isn't the best analogy for explaining what happens on the human observational end (because the two phases are so similar). But say I had a device that only registered things angled to the left of it, and another device which only measured things angled to the right of it. Whichever one I rely on one to observe, automatically prevents me from seeing the other phase, which is still there counterbalancing its sister phase whether we can observe it or not. So, it isn't a matter of a photon "can" flip, or a photon's flip in "perspective."

I'm sorry, but I was under the impresson that you were asking for what we already know about photons and how they are described within the theory that works. I did not realize you were trying to offer an EXPLANATION for why they work, which isn't contained in the theory. I thought such things are usually confined to the Theory Development section and I typically do not wish to entertain such querries.

Zz.

Les Sleeth

Jul21-04, 12:39 PM

I'm sorry, but I was under the impresson that you were asking for what we already know about photons and how they are described within the theory that works. I did not realize you were trying to offer an EXPLANATION for why they work, which isn't contained in the theory. I thought such things are usually confined to the Theory Development section and I typically do not wish to entertain such querries.

Actually I was trying to find out if anyone (physicists I mean) is thinking this way, or is investigating this possibility. I thought I'd read something about QFT in Scientific American which hinted at this (at least, that's what I took from the article). But I do realize that for some, EXPLANATIONS can be really freaky, nerve wracking and downright ruinous to one's day. :rolleyes

On second thought, maybe you are right. I'll delete that that question here and move it to theory development while I see if I can find the SA article.

rayjohn01

Jul21-04, 01:19 PM

I agree with Zapper that QM provides a single description , but I do not think that it provides a 'seeable' one , and I think an experiment often emphasizes one characteristic over another.
Think of a bird chirp , you can examine it in time and you can look at it in frequency but these views seem mutually exclusive in any one experiment.
In fact the ordinary classical 'fourier transform' can be used to estimate Planks constant 'h'.
I also agree that the assumption behind interference ( two slit or otherwise) is that of single photon self interference , but QM deals with that by disolving the object into a many paths 'quasi reality' which is a mathematical formalism and in my view rather difficult to truly visualize.
As for oscillations -- okay as a thought -- bit like neutrinos , but does not appear necessary in a workable theory at present.
Ray.

ZapperZ

Jul21-04, 01:59 PM

I agree with Zapper that QM provides a single description , but I do not think that it provides a 'seeable' one , and I think an experiment often emphasizes one characteristic over another.

But I think that in many (all?) cases, it is because we have it ingrained in our view that 'wave-like" and "particle-like" are mutually exclusive and cannot be explained using one formalism. If one were to be born in a quantum universe and then later on learn about classical mechanics, I would suspect that one would look at the dichotomy of "wave" and "particle" to be rather strange, arbitrary, and artificial. The fact that all the so-called wave-like and particle-like properties can be explained using a single, coherent photon description is the clearest and strongest point that I can think of in favor of this argument. Just because things appear to look that they came from different phenomena does not mean they are different. Classical celestial mechanics and the mechanics of bridge building may appear to be different, but we all know they are governed by the same set of descriptions. No one would say that these are two different phenomena.

Zz.

terrabyte

Jul21-04, 02:16 PM

ZapperZ

Jul21-04, 02:46 PM

last thing i read about photons was they they are "particles" in the basic sense, and they exhibit wave properties because if their unique property of being first state energy.

their diffraction is not actually bending of the light, but rather the light hitting something and transfering its energy to it, and in turn that something jumps back down from its excited state and re-emits the light in a direction seen as "bent"

frequency and wavelength of particle light can be defined as particles per second.

forgot where the heck i read this at though, but it seems sound

I did plan on stopping my involvement in this string, but I think I still need to make more things are straighten out.

In a string a few weeks back related to a question on the uncertainty principle, I brought up the issue that one of the clearest demonstration of this principle is in fact something we observe very easily - the diffraction effect of light. Classically, we attribute this to an intrinsic wave property, but really, if you look at it closely, it is actually an in-your-face demonstration of the uncertainty principle. Let me explain...

Let's say you have a single slit alligned along the x-axis, so that the width d of the slit is along the y-axis. A monochromatic light is propagating along the z-axis and hits the single slit. At a distance after the slit is a screen, potosensitve paper, etc, etc, to record when a photon hits that location.

Now let's say that the slit is open wide (i.e. d is much greater than the wavelength of the light). What you end up with on the screen is essentially the very same image of the slit, i.e. very little diffraction at all.

OK, next, you make the slit very small (d is comparable to the wavelength of the light). Now it gets interesting. You lose the shape of the slit, and now you get the Fraunhoffer pattern. You have a smearing of intensities in which the width of the 0th order pattern is LARGER than the width of the slit itself. In fact, the smaller the slit width is, the wider the 0th order smear.

There's nothing surprising (I hope) in what I've just described. What a lot of people do not realize that this is a direct manifestation of the uncertainty principle.

Let's look at the first instance when d >> wavelength. And let's say I have very weak source in which on average one photon are impinging on the slit at any given instant. Since d is large, the uncertainy in the location of this photon when it hits slit is also large. In fact, Delta(y) is of the order of the width of the slit d. If I want to know it's corresponding momentum in the y direction (i.e. p_y), then I look at where it impacted on the screen, and then using baby kinematics and geometry, I can find p_y.To get the spread in p_y, I will have to collect this info for many photons passing through the slit. This will give me Delta(p_y).

Now what happens when d<<wavelength? As the slit is made thinner, I know with increasing accuracy where a y-position of the photon is that passes through the slit. Thus, the uncertainy in the position of each photon that passes through the slit is not worse than the width of the slit, i.e. Delta(y) ~ d, and this is getting smaller and smaller, meaning I know more about where along y the photon was when it when through the slit.

If I try to measure its momentum, something interesting happens. One photon may hit the screen right in the same y-location as the slit, but another one will hit it way off the slit. Another one hits on the other side of the y-location, etc... in other words, as I collect more and more of photon impact on the screen, the photons seems to have a larger spread of p_y after they pass the slit! This is what will eventually form the wide 0th order diffraction pattern! The smaller the slit (the better I know the location of the photon the moment it passes through the slit), the wider the distribution of the momentum along the very same direction. You cannot predict with as good of an accuracy as in the first case the momentum of the next photon that will pass through the slit.

This is a rather long (and maybe even confusing) demonstration of the uncertainty principle. However, if you have read this far, I hope that it accomplishes two things: (i) that you realize that the photon picture CAN in fact describes what we used to think to be only something that can be explained by waves, and (ii) that you now understand how uncertainty principle works and how "obvious" it is in some cases.

Now I need to rest my fingers...

Zz.

terrabyte

Jul21-04, 05:04 PM

does the same thing hold for laser light travelling through a slit?

terrabyte

Jul21-04, 05:11 PM

ZapperZ

Jul21-04, 05:29 PM

in the model i described, diffraction is wholly based upon photon-energy interaction with the material you make the slit out of.

with a large slit, more light goes through that doesn't contact the material, and generally drowns out the effects of the light that does hit the material edges. as the slit gets smaller, that light that doesn't contact the edges of the material gets smaller, and the difracted light (photons hitting the edges of the material) becomes more apparant.

as described, the photons hit the edges and get absorbed kicking the atoms up to a higher energy state. the atoms then drop back to their natural state and emit the light in a random direction. this randomness is the dispersion we witness from the ultra thin slit.

i'm thinking that this also ties somehow into your "uncertainty principle"

It doesn't. Think about it. If you have a uniform density of photons per unit cross-sectional area, it means that roughly the same number of photons are "interacting" with the edge of the slit, no matter how large or how thin you make the slit. The photons that are not in the layer in contact with the slit doesn't really care where the edge of the slit is. So if we buy your scenario, the diffraction pattern should occur no matter what the size is.

Furthermore, the model of a beam of object scattering off the edge of an opening has a very different distribution than a diffraction pattern. You end up with something that looks like a gaussian distribution centered at the middle of the slit. This is certainly NOT the fraunhoffer pattern that is seen in a diffraction.

I need to point out that what I described isn't MY theory, nor something I dreamt up. It is out of QM itself. Anyone is welcome to pick up a QM text and verify it him/herself. It certainly isn't "my" uncertainty principle.

Zz.

terrabyte

Jul21-04, 07:29 PM

ZapperZ

Jul21-04, 07:57 PM

i said the diffraction does occur regardless of the slit size, but with a larger size the volume of light that doesn't come in contact with the slit sides is greater and that light drowns out the pattern so it's hard to detect it.|

That doesn't make sense. The photons that do not come in contact with the slit edge will just go through unscatterned. The ones that do will (if your model is correct), be scattered via large angles away from the axis of the slit (i.e. at very large y values in my earlier axis orientation). So how could the one that are not scattered "drowns out" the one that are scattered way off the center of the slit? You do know that the 0th order diffraction pattern can be way wider than the size of the slit itself, don't you? So the one that get deflected, say, 20 degrees from normal... how does that get drowned out as you make the slit wider?

Zz.

terrabyte

Jul21-04, 09:53 PM

the ones hitting the left side of the slit scatter to the right and have to travel through the flow of the main stream. the ones on the right scatter to the left and similarly have to travel through the stream.

the ones that hit the left and scatter MORE to the left are very faint <very small number of TRUE edge particles that can shoot that angle without hitting another material atom.

what happens when the slit is made extremely narrow is that noise that drowns out the particles from left to right and right to left is reduced enough to where we can view the scattering effects easily.

i really do need to find the text i read... it had diagrams and stuff

terrabyte

Jul21-04, 10:32 PM

this page gets into it a little as far as photon-atom interactions

Link to crack pot site deleted

gonna have to hunt down more stuff later, must... sleep

I suggest careful reading of ZapperZ's posts, much more reliable then random web searchs.

Integral

ZapperZ

Jul22-04, 06:40 AM

this page gets into it a little as far as photon-atom interactions

Removed link
Integral
gonna have to hunt down more stuff later, must... sleep

Yikes! You should learn to read established physics journals and texts, and not someone's personal website. I hate to think that you based your physics knowledge on something like this! If you really want to screw up your understanding of physics, then go to Crank Dot Net. You'll find enough "ideas" to even contradict what you read on that site. So then you will be left with the delima of which quack to believe in.

Secondly, it appears that when I said that even if the scattering off the edge of slit model is correct, you would only get something resembling a gaussian distribution of intensities behind the slit, this seems to have not made any impression on you. Keep in mind what a "gaussian distribution" looks like, and what an actual diffraction pattern looks like. You'll notice why those two are not compatible.

Thirdly, and this is the most imporant error in your whole model, is that you seem to not know that the scattering probabilty between two photons are unbelievably small. In the visible range, it is almost non-existent. Instead, we have a SUPERPOSTION of light - they passed though each other "unharmed". Thus, your argument that a large slit will cause more of the "scattered" photons to get washed out doesn't hold water. And we haven't talked about the validity of photons "scattering" off an opaque material that make up a slit.

Zz.

jatin9_99

Jul22-04, 11:22 AM

ZapperZ

Jul22-04, 11:36 AM

light has both the nature of wave and particle, as according to de broglie he showed his work as folllowing

einstien said e=mc^2 so this is particle nature

and max planck said h=wc where w is wavelenght and c speed of light
=> c=h/w
and e=mc^2
=> e=m(h/w)^2
this proves that light have wave nature too

Ok, now see what I mean? It is as if all the things that have been discussed here on this string didn't exist!

And before someone tells me not to pop a blood vessel or something over this, let me just say that I'm not "distressed". I'm just disappointed that I wasted all that effort for nothing. Even after spending more than 10 years on the 'net participating in discussion forums such as this, it still doesn't lessen the disappointment whenever something like this occurs.

Zz.

Dodo

Jul22-04, 03:29 PM

May I add a layman's question to the thread?

19th century postulated an 'ether', as the medium on which light waves would propagate. The current story they tell you at school is that EM waves "carry their own media", being composed of, I seem to recall, two orthogonally-polarized components, one being the "E" and the other the "M". If this goes back to Maxwell, I suppose it might not be quite the "current" story. Then, which is?

And... in which way can this be related to gravity? In a sense, the "media" of gravity is the space itself, which is distorted by the presence of masses. Can (or cannot) be the same for light? Imagine light as a ripple in space - in which way could this account for the "alternate" particle explanation for light?

I apologize in advance for the complete sci-fi tone of the question - in the hope that the act of explaining to a layman can in itself be a source of enlightened amusement.

russ_watters

Jul22-04, 03:46 PM

Dodo, quite a number of experiments have been done in an effort to find a medium on which light propagates. None have been successful and the laws of physics work just fine without one. It appears that there isn't one (the Electric and Magnetic fields are not the same as the classical ether).

terrabyte

Jul22-04, 07:37 PM

Integral

Jul23-04, 01:41 AM

lol why delete my link.

i just pulled the first one i found that explained photon-atom interactions. i did not "base" my entire physics knowledge on "crackpot's website"

you people are way too touchy.

not gonna even bother taking this any further. <wave>
Why delete your link? Because it did not contain valid physics. This thread has been answered quite throughly by someone who knows what they are talking about. The fact that you were unable to identify the link as nonsense says that you either did not have sufficient knowledge of Physics to tell, or are a crackpot pushing bad information. I do not know, and I do not care, which. I just do not want crackpot links in the middle of a good thread. Please be more careful in the future. If you do not know, ask questions, do not post random links from the web.

terrabyte

Jul23-04, 01:50 AM

Are you saying photon-atom interaction is wrong?

i could have swore that was common physics. Energy kicks electrons into higher but unstable orbits, atom randomly kicks back down to lower orbit and emits a photon in a uncertain direction.

the rest of the page was pure gibberish of course, but that's not why i linked it.

anyways, i said i was gone <wave again>

JohnDubYa

Jul23-04, 04:22 PM

light has both the nature of wave and particle, as according to de broglie he showed his work as folllowing

And what physical property does this "matter wave" represent? If you draw a picture of this wave, what physical properties do the horizontal and vertical axes correspond?

Dodo

Jul24-04, 09:03 AM

Found this in Google's cache - guess it points to what I was looking for. Thank you all!

http://216.239.59.104/search?q=cache:SWDu2I0gBTMJ:arxiv.org/abs/gr-qc/9701034

Tsunami

Apr15-05, 04:47 AM

I think I know what you are getting at here. Unfortunately, as you can see from the previous post, it can easily be misinterpreted or misrepresented. The biggest obstacle in this issue is trying to convey the meaning of the mathematics. QFT (and QED) makes NO provision for classical fields. Therefore, classical fields (and thus, "waves") essentially do not exist and are meaningless in QFT.

Then what are we left with? I hate to say we have a "particle field", because that again can be misinterpreted (refer to my discussion what classical particle is and why this is NOT what a photon is). Can I get away with saying a "quantum field" without grossly misrepresenting the mathematics? Maybe. If we stick by that, then I would not want to leave the impression that photons can flip back and forth between two apparently different perpective.

Zz.

(Know that this comment comes from a student who only has introductory knowledge of QM: )

Maybe a nice way to explain the wave/particle behaviour of light, is that light behaves more like a particle when its energy increases? For instance, it's pretty useful to talk about microwaves as if they were particles. However, X-rays almost always behave like particle streams.
One could say that it's less probable that light with low energy behaves as particles than that light with high energy behaves like particles.. I think.

dextercioby

Apr15-05, 03:13 PM

(Know that this comment comes from a student who only has introductory knowledge of QM: )

Maybe a nice way to explain the wave/particle behaviour of light, is that light behaves more like a particle when its energy increases? For instance, it's pretty useful to talk about microwaves as if they were particles. However, X-rays almost always behave like particle streams.
One could say that it's less probable that light with low energy behaves as particles than that light with high energy behaves like particles.. I think.

Nope,it's incorrect.Light is either all wave (macroscopical/classical description,or all particle (microscopical/quantum description).There's no overlapping...And quantum/photonic description can account for macroscopical phenomena as well,it's just that the photons need to form a statistical ensemble (plus coherence,...).

Daniel.

Tom Something

Apr15-05, 05:09 PM

could someone describe how diffraction can be explained by the photons rather than waves?

misogynisticfeminist

Apr15-05, 09:17 PM

Particle. No experiment has ever been performed on a photon that demonstrated wave properties to my knowledge.

no no no. What about thomas young's experiment?

Photons are interpreted in terms of its wavefunction, the photon field in which photons are the quanta.

ZapperZ

Apr16-05, 07:44 AM

could someone describe how diffraction can be explained by the photons rather than waves?

You may want to read this thread:

http://www.physicsforums.com/showthread.php?t=68917

In addition, my journal entry on the misconception of the Heisenberg Uncertainty Principle illustrates this using the diffraction from a single slit due to photons. So you may wish to read that also.

Zz.

Tsunami

Apr16-05, 08:23 AM

Nope,it's incorrect.Light is either all wave (macroscopical/classical description,or all particle (microscopical/quantum description).There's no overlapping...And quantum/photonic description can account for macroscopical phenomena as well,it's just that the photons need to form a statistical ensemble (plus coherence,...).

Daniel.

Bah... now you got me confused again...

so both the wave and particle description are part of the same universal description of light (dixit ZapperZ) yet at the same time light is either all wave, or all particle....???

Something tells me that the case is :

either
1) I'm not going to understand any of this until I see a more expansive course about QFT.
or
2) Virtually nobody completely understands this and this is why the interpretations of you and ZapperZ (at least seem to) logically contradict.

marlon

Apr16-05, 08:37 AM

so both the wave and particle description are part of the same universal description of light (dixit ZapperZ) yet at the same time light is either all wave, or all particle....???

Zapper is correct. The duality exists only because of our 'classical minds' ; we wanna think in terms of either particles or waves. There is no problem with that but we do need to keep the correct perspective on things here. First of all 'particles' in this case does not mean little objects with finite boundaries. It means little finite pieces of energy (this is the actual quantization , right ?)

Secondly, and this is what dextercioby meant, in QM we have experiments that are better explained with the wave-like notion (eg the double slit experiment) and we have those experiments that are better described with the particle-like notion (eg photo-electric effect). However in the end both descriptions are just ONE SINGLE way of describing the physical properties of light....that is all.

Another common misconception is the fact that the photo-electric effect proved the existence of photons. That is not true because this photo-electric effect can be described in terms of the wavelike-notion of the incident EM-radiation too. It is only the atoms of the target electrode that are treated with QM. However, the particle-like notion of light is suggested by this experiment. If you wanna read more, check out my journal and find the article on creating an entangeled photon-state in an undergrad lab

marlon

EDIT : well, here's the article : Create entangled photons yourself in an undergrad laboratory :
http://marcus.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

ZapperZ

Apr16-05, 08:46 AM

Bah... now you got me confused again...

so both the wave and particle description are part of the same universal description of light (dixit ZapperZ) yet at the same time light is either all wave, or all particle....???

Something tells me that the case is :

either
1) I'm not going to understand any of this until I see a more expansive course about QFT.
or
2) Virtually nobody completely understands this and this is why the interpretations of you and ZapperZ (at least seem to) logically contradict.

Without even going into QFT, let's make sure we make something very clear here:

All of the properties of light can be described by QM, and even so-called wavelike properties can be obtained using the photon description.

Now, contrary to popular beliefs, especially among students, physics instructors are not heartless masochists who will force the students to use the photon description when the classical wave picture is easier and more direct to be used. That is why the classical wave theory are still used when we describe diffraction and interference effects, especially in classical optics classes. It doesn't mean, however, a unified QM description doesn't exist for such things. It is just more involved and requires a bit more of a sophistication in knowledge to do it. The classical wave picture is simply a "short cut" to getting what we want to get.

Zz.

marlon

Apr16-05, 08:55 AM

Just to add what Zapper has said, QFT does not 'explain' the duality more or better as QM. You know, everytime somebody drops the term QFT, my heart goes...You know why ? Well, because lot's of people like the use the posh-sounding epitheton QFT but i always feel the urge to ask : do you know what it means. I mean, if i were a professor teaching QFT, my first chapter in my course would explain why we need the quantum-part, why we need the fields part and why we need the relativistic part. Every principle of QM is copied, to some extent, by QFT since QFT really is the unification of both QM and special relativity. Beware, i said SPECIAL relativity and not GENERAL relativity....

marlon

Thomas2

Apr16-05, 08:57 AM

You read wrong. What I said was...

"Having said that, the most common explanation for the "wave-particle duality" is that light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect."The photoelectric effect can well be explained in terms of the wave picture if the wave-atom interaction is properly being considered. In contrast, the particle theory of light is completely inconsistent and would in fact not enable photoionization at all because (due to its small mass) the photon could not transfer enough energy to the photoelectron.
A further proof for the incorrectness of the particle model for light is the experimental fact that photoelectrons are not primarily released in the direction of propagation of light (as one should expect it for particles) but perpendicular to this in the direction of the electric field vector .

See my webpage http://www.physicsmyths.org.uk/photons.htm for more details (I can't copy the page here because it contains a number of formulae).

marlon

Apr16-05, 09:00 AM

In contrast, the particle theory of light is completely inconsistent and would in fact not enable photoionization at all because (due to its small mass) the photon could not transfer enough energy to the photoelectron.

Well, i don't want to be impolite but do you really mean this ? Anyhow, you are totally wrong...I suggest you actually check the history of the photo-electric effect-explanation and just to be sure, also double check what is meant by the words : "particle theory of light"...Why do you even bring the 'small mass' of photons...That small mass is ZERO

marlon

Thomas2

Apr16-05, 09:08 AM

...Why do you even bring the 'small mass' of photons...That small mass is ZEROWell ,that would be even worse, because then it could not transfer any energy at all. But I think you mix up mass with 'rest mass' here. Only the latter is zero in the relativistic theory of the photon, but since the photon does not rest in any reference frame it has a finite mass (or at least it is supposed to have).

ZapperZ

Apr16-05, 09:09 AM

The photoelectric effect can well be explained in terms of the wave picture if the wave-atom interaction is properly being considered. In contrast, the particle theory of light is completely inconsistent and would in fact not enable photoionization at all because (due to its small mass) the photon could not transfer enough energy to the photoelectron.
See my webpage http://www.physicsmyths.org.uk/photons.htm for more details (I can't copy the page here because it contains a number of formulae).

I disagree. I worked in photoemission spectroscopy for my postdoc, and if you look at the work by Spicer, who almost single-handedly pioneered this technique, you will see why what you said is incorrect.

Furthermore, since when does a photon have a "small mass"? The photon mass is irrelevant in a photoemission process. In fact, if a photon HAS a mass, a bunch of things from photoemission spectroscopy would be wrong, and the band structure we used in the semiconductors in your modern electronics should not work. This is because photoemission spectroscopy is the FIRST such technique that could independently verify the theoretical calculations of band structure of solids. And they all use the photon picture!

And I have said this so many times, I am beginning to bore myself. Look up "multiphoton photoemission". Now explain how the amount of photoelectrons detected as a function of the photon intensity have discrete dependence that just HAPPENS to coincide with the discrete number of photons being absorbed to cause that particular transition. Don't tell me the energy level of the material is discrete since this is a transition from a continuous conduction band into a continuous vacuum band. While the photoelectric alone cannot rule out the wave picture, I haven't seen even a single attempt at reconcilling the multiphoton process with the wave picture.

Zz.

marlon

Apr16-05, 09:15 AM

dextercioby

Apr16-05, 09:36 AM

Nice debate here,is it still in General Physics ?? Oh,i know Thomas2...Huge misconceptions...The bad part is that he don't seem to be willing to learn anything...

Daniel.

ZapperZ

Apr16-05, 10:06 AM

Well ,that would be even worse, because then it could not transfer any energy at all. But I think you mix up mass with 'rest mass' here. Only the latter is zero in the relativistic theory of the photon, but since the photon does not rest in any reference frame it has a finite mass (or at least it is supposed to have).

Typically, when someone says something like this, it shows that this person never went through any formal study of SR and QM. They are always surprised that light can have energy and momentum, but NO MASS! Horrors! It shows they haven't seen the complete derivation of the relativistic effects. If that is the case, most of the time, we always have to keep taking several steps backwards each time we introduce an explanation. This can be quite exasperating (at least for me), so I'll let others with more patience on this take over.

Zz [with 2 extra cups of coffee this morning]

Zz.

marlon

Apr16-05, 10:11 AM

This can be quite exasperating (at least for me), so I'll let others with more patience on this take over.

:rofl: Thanks but no thanks
I believe the guy with the promotion should do the 'most difficult' tasks :tongue:

Zz [with 2 extra cups of coffee this morning]

Zz.
Same here...

marlon

Thomas2

Apr16-05, 11:12 AM

Furthermore, since when does a photon have a "small mass"? The photon mass is irrelevant in a photoemission process. In fact, if a photon HAS a mass, a bunch of things from photoemission spectroscopy would be wrongWell, this would prove then that light has to be considered as a wave (see also my reply to Marlon above)

And I have said this so many times, I am beginning to bore myself. Look up "multiphoton photoemission". Now explain how the amount of photoelectrons detected as a function of the photon intensity have discrete dependence that just HAPPENS to coincide with the discrete number of photons being absorbed to cause that particular transition. Don't tell me the energy level of the material is discrete since this is a transition from a continuous conduction band into a continuous vacuum band. While the photoelectric alone cannot rule out the wave picture, I haven't seen even a single attempt at reconcilling the multiphoton process with the wave picture.How should a multiphoton transition work in the particle picture if you can't even make an individual one work? On the other hand, it is no problem with the wave-atom interaction model if the first transition is to a state below the ionization threshold and the lifetime of the level is long enough so that the electron can absorb another wave frequency that ionizes it finally.

Also, as I mentioned above already, the experimental fact that photoelectrons are primarily emitted into the direction of the electric field vector (i.e. perpendicular to the direction of propagation of light) clearly invalidates the particle picture.

Thomas2

Apr16-05, 11:14 AM

Typically, when someone says something like this, it shows that this person never went through any formal study of SR and QM. They are always surprised that light can have energy and momentum, but NO MASS! Horrors! It shows they haven't seen the complete derivation of the relativistic effects. It seems it is you who should brush up on his Relativity. Through E=m*c^2 each photon with energy E can be assigned a relativistic mass m=E/c^2 .

Doc Al

Apr16-05, 11:29 AM

It seems it is you who should brush up on his Relativity. Through E=m*c^2 each photon with energy E can be assigned a relativistic mass m=E/c^2 .
Given your track record on this site regarding relativity, you are in no position to lecture anyone. Unless specifically stated otherwise, "mass" generally means the invariant or rest mass.

Thomas2

Apr16-05, 12:54 PM

Given your track record on this site regarding relativity, you are in no position to lecture anyone. Unless specifically stated otherwise, "mass" generally means the invariant or rest mass.On the contrary, ZapperZ is in no position to make the suggestion 'this person never went through any formal study of SR and QM'.

dextercioby

Apr16-05, 12:57 PM

If u did (go),why don't u prove it?

Daniel.

Doc Al

Apr16-05, 03:55 PM

On the contrary, ZapperZ is in no position to make the suggestion 'this person never went through any formal study of SR and QM'.
Formal study or not, anyone curious about your grasp of special relativity is encouraged to review the posts you've made in the relativity forum. They will remove any doubt as to your mastery of the subject.

ZapperZ

Apr16-05, 07:03 PM

How should a multiphoton transition work in the particle picture if you can't even make an individual one work? On the other hand, it is no problem with the wave-atom interaction model if the first transition is to a state below the ionization threshold and the lifetime of the level is long enough so that the electron can absorb another wave frequency that ionizes it finally.

Correction. It is YOU who can't make a single-photon photoelectric effect to work. The rest of us can.

Also, as I mentioned above already, the experimental fact that photoelectrons are primarily emitted into the direction of the electric field vector (i.e. perpendicular to the direction of propagation of light) clearly invalidates the particle picture.

Excuse me, but can you point out to me how you could tell that from a simple photoelectric effect experiment? The light source is UNPOLARIZED. Don't believe me? Try it.

I worked with polarized photoemission spectroscopy from a synchrotron. My AVATAR that you see with my profile is the data taken with a light source polarized along one of the high symmetry direction of crystal structure. There is ZERO problem in dealing with such a thing with the photon picture.

Again, refer to ALL of Bill Spicer's work in photoemission and show me where there is a "problem" in dealing with the photon picture. So far, all you have shown is your inability to understand what has been formulated. You should never criticize something based on ignorance.

Zz.

Thomas2

Apr17-05, 04:03 AM

If u did (go),why don't u prove it?I don't have to prove anything to somebody whose major contribution in this forum (or in this thread anyway) is to personally attack other people anonymously under the cover of his username. Put your words where your mouth is and try to argue scientifically against what I said on my webpage http://www.physicsmyths.org.uk/photons.htm .

Thomas2

Apr17-05, 04:06 AM

Formal study or not, anyone curious about your grasp of special relativity is encouraged to review the posts you've made in the relativity forum. They will remove any doubt as to your mastery of the subject.Maybe I have studied special relativity just better and deeper than you have and have in fact a better insight and grasp of it (remember, everything is relative). But the 'mass' issue raised above is anyway only a semantic problem here. The important point is that a consequent application of the energy- and momentum conservation laws should not enable photoionization at all with the particle picture, whereas on the other hand the wave model is in fact consistent with the short times required for photoionization if one considers the wave-atom interaction properly (as shown on my page http://www.physicsmyths.org.uk/photons.htm ).

Thomas2

Apr17-05, 04:10 AM

Correction. It is YOU who can't make a single-photon photoelectric effect to work. The rest of us can.Only if you close your eyes to what I said on my page http://www.physicsmyths.org.uk/photons.htm . But anyway, it is more important that the wave model can, contray to common opinion, indeed explain the photoeffect if a proper wave-atom interaction model is used.

Excuse me, but can you point out to me how you could tell that from a simple photoelectric effect experiment? The light source is UNPOLARIZED. Don't believe me? Try it.I am not quite sure what your point is here. If you use polarized light, the photoelectrons will be emitted along the corresponding electric field vector; if you use unpolarized light, they will be emitted in the plane that contains all field vectors. In no case will they be emitted in the forward direction (and the the latter is what you would expect with particle collisions).

ZapperZ

Apr17-05, 07:52 AM

Only if you close your eyes to what I said on my page http://www.physicsmyths.org.uk/photons.htm . But anyway, it is more important that the wave model can, contray to common opinion, indeed explain the photoeffect if a proper wave-atom interaction model is used.

But this is saying nothing new. The photoelectric effect is KNOWN to be a STRONG evidence for the photon picture, but it also cannot rule out completely the wave picture. But you, on the other hand, somehow thinks it rules out the photon picture because of your inability to understand what "photons" are and confusing it with the need to have mass (i.e. your lack of knowledge of Special Relativity). This is bogus.

I am not quite sure what your point is here. If you use polarized light, the photoelectrons will be emitted along the corresponding electric field vector; if you use unpolarized light, they will be emitted in the plane that contains all field vectors. In no case will they be emitted in the forward direction (and the the latter is what you would expect with particle collisions).

Emitted in the FORWARD direction? What the....?

I could shine a plane polarized light, having the polarization vector PARALLEL to the surface of the photocathode. Guess what? If I scan for photoelectrons, I get then in ALL DIRECTIONS! Not only that, this is in the BACKWARDS direction with respect to the direction of the incoming light. We see this ALL THE TIME when we do ANGLE-RESOLVED photoemission spectroscopy (ARPES).

Question: how many times have you done the simple photoelectric effect that we ask students to perform in undergraduate labs, and how many times have you done the more sophisticated photoemission spectroscopy of any kind?

Zz.

ZapperZ

Apr17-05, 07:59 AM

Maybe I have studied special relativity just better and deeper than you have and have in fact a better insight and grasp of it (remember, everything is relative). But the 'mass' issue raised above is anyway only a semantic problem here. The important point is that a consequent application of the energy- and momentum conservation laws should not enable photoionization at all with the particle picture, whereas on the other hand the wave model is in fact consistent with the short times required for photoionization if one considers the wave-atom interaction properly (as shown on my page http://www.physicsmyths.org.uk/photons.htm ).

Correction: a bastardizaton of the energy-momentum conservation laws will not allow for the photon picture to work. A CORRECT application of it will. You have made ZERO reference to spicer's work, and all the subsequent advancement in photoemission spectroscopy in the study of materials. If all of these were based on the WRONG principles, there's zero reason why they work so accurately in determining the electronics properties of materials (open any photoemission text). This fact seems to be glaringly omitted in your criticism.

And please stop using your webpage as a reference. It's all "relative", remember? Having a webpage requires ZERO knowledge of physics. Just look at Crank Dot Net. If you think having webpages is how physics is done, then you've revealed an additional level of ignorance.

Zz.

Thomas2

Apr17-05, 11:10 AM

But this is saying nothing new. The photoelectric effect is KNOWN to be a STRONG evidence for the photon picture, but it also cannot rule out completely the wave picture.The photoelectric effect is supposed to be evidence for the particle picture and against the wave picture (see for instance http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html#c4 (Wave Particle Duality)).

But you, on the other hand, somehow thinks it rules out the photon picture because of your inability to understand what "photons" are and confusing it with the need to have mass (i.e. your lack of knowledge of Special Relativity). This is bogus.I do not somehow think, but have shown on my page http://www.physicsmyths.org.uk/photons.htm that the photoelectric effect is in fact evidence for the wave picture rather than the particle picture. If you think it is bogus, then you should give detailed reasons why.

Emitted in the FORWARD direction? What the....?
I could shine a plane polarized light, having the polarization vector PARALLEL to the surface of the photocathode. Guess what? If I scan for photoelectrons, I get then in ALL DIRECTIONS! Not only that, this is in the BACKWARDS direction with respect to the direction of the incoming light. We see this ALL THE TIME when we do ANGLE-RESOLVED photoemission spectroscopy (ARPES).Your photoemission work is hardly relevant in this context: is obvious that from a solid surface photoelectrons will be emitted in all directions since they suffer scattering in the material. You need individual atoms i.e. a gas as a target to show the original angular distribution of photoelectrons, and this shows that they are primarily ejected along the electric field vector (see for instance http://prola.aps.org/abstract/PR/v37/i10/p1233_1 ). You can find this also theoretically derived in some Quantum Mechanics textbooks that deal with photoionization (e.g. Blochinzev), but most textbooks actually don't mention this.

a bastardizaton of the energy-momentum conservation laws will not allow for the photon picture to work. A CORRECT application of it will. Exactly, that's why most people consider the photoeffect erroneously to be evidence of the particle picture.

You have made ZERO reference to spicer's work, and all the subsequent advancement in photoemission spectroscopy in the study of materialsSpicer's work is hardly relevant for having established the photoeffect as evidence for the particle nature of light, so I don't know why you keep on mentioning it . Try to argue with basic and generally known experiments.

And please stop using your webpage as a reference.........Having a webpage requires ZERO knowledge of physicsSo does posting in Physicsforums. But if you have done some logic in the past, then you should know that either of them is not synonymous with zero knowledge. It is suggesting that it is which shows a level of igorance or maybe even of bad intentions.

Tsunami

Apr17-05, 11:45 AM

Without even going into QFT, let's make sure we make something very clear here:

All of the properties of light can be described by QM, and even so-called wavelike properties can be obtained using the photon description.

Now, contrary to popular beliefs, especially among students, physics instructors are not heartless masochists who will force the students to use the photon description when the classical wave picture is easier and more direct to be used. That is why the classical wave theory are still used when we describe diffraction and interference effects, especially in classical optics classes. It doesn't mean, however, a unified QM description doesn't exist for such things. It is just more involved and requires a bit more of a sophistication in knowledge to do it. The classical wave picture is simply a "short cut" to getting what we want to get.

Zz.

Ok...

so, we have light as quanta of energy... little blocks of energy. In certain situations, these little blocks of energy make up something that behaves like waves... this is especially through for blocks of energy with low frequency, or low-energy quanta. Is this correct?

Then, with all what has been said before, my puny mind only sees these options:

1) Wave-like behaviour is only true for low energy photons, while particle-like behaviour can describe all phenomena - thus, the wave-like behaviour is something like an approximation of the particle-like behaviour.
2) Wave-like behaviour can be applied to all phenomena, and particle-like behaviour can be applied to all phenomena - thus, there is a dual description, but both descriptions are always completely reconcilable (this doesn't contradict what ZapperZ said only if the unified description allows for both descriptions in every situation... the descriptions would simply be different approaches).
3) Some third option because I'm too tired to think straight at this moment.

ZapperZ

Apr17-05, 12:49 PM

The photoelectric effect is supposed to be evidence for the particle picture and against the wave picture (see for instance http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html#c4 (Wave Particle Duality)).

I do not somehow think, but have shown on my page http://www.physicsmyths.org.uk/photons.htm that the photoelectric effect is in fact evidence for the wave picture rather than the particle picture. If you think it is bogus, then you should give detailed reasons why.

I did already! You seem to be confusing "energy" with evidence of "mass" in the photoelectric effect! I can play your game too. If you think you have any validity, send it in to a peer-reviewed journal. Now THAT would determine if what you think is right is bogus or not.

Your photoemission work is hardly relevant in this context: is obvious that from a solid surface photoelectrons will be emitted in all directions since they suffer scattering in the material. You need individual atoms i.e. a gas as a target to show the original angular distribution of photoelectrons, and this shows that they are primarily ejected along the electric field vector (see for instance http://prola.aps.org/abstract/PR/v37/i10/p1233_1 ). You can find this also theoretically derived in some Quantum Mechanics textbooks that deal with photoionization (e.g. Blochinzev), but most textbooks actually don't mention this.

And this is where you clearly show your ignorance.

The photoelectric effect as described in the Einstein model is the effect done from a SOLID surface, and in particular, a METALLIC solid surface. This is where such a model is applied to, and NOT from a gas! The excitation comes out of a continuous conduction BAND, and not from discrete energy states exhibit by gas atoms and molecules!

So in effect you are applying a description in which it wasn't MEANT to be applied to. This is consistent with what you were trying to do when you implied that light has a "small mass". This is what I call the bastardization of physics principles - you simply use something without clearly understand when and where it should apply. So OF COURSE you get nonsensical answers! But don't blame the physics or our understanding of it for your mistakes.

Spicer's work is hardly relevant for having established the photoeffect as evidence for the particle nature of light, so I don't know why you keep on mentioning it . Try to argue with basic and generally known experiments.

Then you haven't a clue what spicer has already accomplished.

So does posting in Physicsforums. But if you have done some logic in the past, then you should know that either of them is not synonymous with zero knowledge. It is suggesting that it is which shows a level of igorance or maybe even of bad intentions.

I have published several papers on the photoemission spectroscopy, including in the Physical Review journals, the same journal that you cited above. So what have YOU done to show that what you have concluded is valid?

Zz.

ZapperZ

Apr17-05, 12:58 PM

Ok...

so, we have light as quanta of energy... little blocks of energy. In certain situations, these little blocks of energy make up something that behaves like waves... this is especially through for blocks of energy with low frequency, or low-energy quanta. Is this correct?

Then, with all what has been said before, my puny mind only sees these options:

1) Wave-like behaviour is only true for low energy photons, while particle-like behaviour can describe all phenomena - thus, the wave-like behaviour is something like an approximation of the particle-like behaviour.
2) Wave-like behaviour can be applied to all phenomena, and particle-like behaviour can be applied to all phenomena - thus, there is a dual description, but both descriptions are always completely reconcilable (this doesn't contradict what ZapperZ said only if the unified description allows for both descriptions in every situation... the descriptions would simply be different approaches).
3) Some third option because I'm too tired to think straight at this moment.

The problem here is that it isn't just a matter of the "source" here, which in this case, is light. It is also a matter of our DETECTION method, and that has nothing to do with light itself.

Again, the double slit, for example, isn't really a "test" of the light - it really is how light is reacting to the setup and the fact that it is given the ability to go through two different path equally well. Thus, if you look at the Feynman description of it, it really is the superposition of path, not the "interference of single photons", that is the origin of the interference pattern. Once we realize this, then we will notice that this isn't restricted to just light, but ANY object in which our ability to exactly track which "slit" that particle goes through is unknown.

With this in mind, look at how we handle and detect EM radiation of different wavelenths. You will notice that the longer the wavelength, our detection of it differs and goes more into the classical regime. Our instruments are now larger, something that we can start to comprehend, and begin to incorporate a lot more decoherence. So this is a function of not only the light property itself, but how we handle such properties.

Zz.