PDA

View Full Version : How much do we know about mirrors, photons, and the mechanics of reflection?



CodeSlinger
2007-Oct-25, 04:36 PM
Over in the "Different Model of the Universe" ATM thread (http://www.bautforum.com/against-mainstream/66183-different-model-universe.html), Bob Angstrom stated:



Don’t worry if your model can’t explain how a mirror works because no model can. The conventional explanation about mirrors has something to do with photons bouncing off of a perfectly smooth metal surface so that the photons are reflected at the same angle of their arrival and the fidelity of the image is maintained. But at the atomic level, there is no smooth surface. A smooth metal surface is more like a floor covered with shiny ball bearings. A photon striking a single metal atom is likely to bounce off the atom in any random direction. However, if the atom is surrounded by other atoms all on the same 2D plane and within a wavelength’s distance, then the reflection is no longer random and light reflects from the surface in a predictable manner even if the light is reflected one photon at a time. Somehow a single photon (if there is such a thing) when it bounces off a single atom "knows" that it is surrounded by other atoms on the same 2D plane. The photon appears to be aware of its surroundings and this is where things begin to get weird.


And also:



I am no stranger to Feynman’s work which is why I say that we have no models to explain how a mirror reflects. Actually there are some really excellent models for reflection but none that have the imprimatur of any experts in the field such as Feynman which is why I say we have no good models although that is not my personal opinion. In lecture 2 Feynman explains how Newton’s corpuscular theory of light does not work. He goes on to explain how the wave theory of light also fails as does the photon theory. Photon theory is lacking because it offers no logical explanation for why a photon striking a pane of glass will either be reflected or penetrate. Any explanation is especially difficult when multiple panes of glass are involved because what happens at the surface of the first pane is determined by the position of the last pane at the bottom of the pile. Photons appear to have a magical awareness of their environment that no common sense theory can explain. Feynman continues by saying that in order to proceed we had to develop descriptive methods…"Sets of rules which are empty of models." These comments are to be found in the first 15 minutes of Feynman’s Lecture 2 if you want to check my statements for accuracy but nowhere does Feynman explain how reflection works. He only explains how we can determine the probabilities and direction of reflection.
Feynman’s discussion of photons reflecting from multiple panes of glass offers several examples of how photons act as though they have an awareness of their distant surroundings. I wouldn’t go so far as to say that light can "smell" its surroundings but Feynman does. 54 minutes into the lecture Feynman tells how a path of light can "smell" other possible paths in its neighborhood. Metaphorically speaking I’m sure.


Is it true that we have no good models to explain how a mirror reflects?

Is it true that photons have an awareness of their environment?

Cougar
2007-Oct-25, 04:58 PM
I would say no and no and ask for Bob's credentials. (Of course, my own credentials are nothing to write home about, but that shouldn't prohibit me from asking about someone else's.)

Noclevername
2007-Oct-25, 05:01 PM
The reflecting mirror model is how I first learned about photons. When I was five or six, IIRC.

Laguna
2007-Oct-25, 05:33 PM
A mirror reflection photons is school stuff...

korjik
2007-Oct-25, 05:42 PM
If I remember correctly, light dosent reflect as a particle but as a wave. The wave equations handle reflection perfectly fine.

As for reflecting single photons, things are going to get much more hairy pretty quick. You are talking about a QM treatment of a photon interacting with a many body solid. I would imagine that getting a realistic treatment into a solvable form is still pretty much impossible.

The fact that we cant get the model dosent mean it cant happen tho.

Noclevername
2007-Oct-25, 05:52 PM
For a single photon reflection, you treat it as a particle. It's First Law stuff, like a tennis ball bouncing off a flat wall. An equal and opposite reaction.

CodeSlinger
2007-Oct-25, 05:55 PM
To those who have responded "I learned this in school!", please reach back in your memory and explain the model that you were taught. I've read multiple explanations (ex. reflected light being photons absorbed and re-emitted by electrons), and am not sure which ones are just approximations intended as an introduction and which ones accurately represent our best understanding of reflection. korjik, can you go into more detail about how mirrors reflect light as waves?

CodeSlinger
2007-Oct-25, 05:57 PM
If we treat a single photon as a particle, what is it bouncing off of (electrons, atoms, ?), and what makes the angle of reflection equal to the angle of incidence?

Noclevername
2007-Oct-25, 06:05 PM
"Bouncing" is probably not the right word, I'm not sure what would be. But it's not a physical "contact" at that level, but an interaction of energy. I wish I knew enough physics to describe what I'm trying to say.

Cougar
2007-Oct-25, 06:28 PM
A mirror reflection photons is school stuff...
Yes, but the old "angle of incidence..." explanation is the high school explanation, which, as usual for high school explanations, does not include all the details and intricacies of the university or graduate-level explanation, which uses the full force of quantum theory.

Bob Angstrom
2007-Oct-25, 07:33 PM
I would say no and no and ask for Bob's credentials. (Of course, my own credentials are nothing to write home about, but that shouldn't prohibit me from asking about someone else's.)Taking an example from the first part of Feynman's lecture, when a photon strikes the surface of a pane of glass it either reflects or it penetrates. The probability that it will reflect is about 4 percent. This isn't an explanation, its a probability but that will serve for now. So when a photon strikes the glass surface it tosses the dice and either reflects or penetrates depending on the outcome. No, says Feynman. Put another pane of glass below the first and the probability of reflection varies anywhere from zero to eight percent depending on the position of the second pane of glass. This is where the probability leaves the rational world of Newton and Einstein and enters the Twilight Zone and all our models fail. Let's look at this again. A photon strikes a surface of glass and reflects as one of the four percent that probability dictates should reflect. How does this photon "know" there is not another glass surface below to reduce its probability of reflection to zero percent? Newton had an explanation. All reflections are from the bottom surface and when a photon "corpuscle" of light penetrates the first layer this "presets" the condition of the photon to reflect from the bottom surface. Feynman explains that this is wrong because photons are identical and they can’t be preset and besides reflections can come from the first surface.
Wave theory also "happily" has an explanation. Waves of light reflecting from the bottom surface interfere with waves from the top surface and either cancel or amplify the reflection. Feynman explains that this explanation fails with single photons because we only observe one path for the photon. I might also add that a particle can’t be in two places at a time and do as Dirac says, "Interfere with itself."
At this point Feynman abandons all models and explanations and resorts to "descriptive methods" and rules of probability. I emphasize that descriptions and probabilities are not explanations because they fail to explain why light behaves as it does. I am sure Feynman understands the lack of explanation and he does explain, 54 minutes into the lecture, why we only observe a single path for a photon. A photon does not take just one path. It takes every possible path….this way, this way, this way, this way, etc. Some paths are more probable than others and the less probable paths in one direction cancel the less probable paths in the other direction. A photon following the most probable path continues on its way because it "smells" (Feynman’s word) the other less probable paths in its neighborhood and knows to continue. This is why we only observe one path for the photon.
For some reason Feynman’s explanation smells a bit contrived to me but not to worry. Courgar says there is a good model to explain how light works so the professor will now expound.

dhd40
2007-Oct-25, 07:33 PM
Over in the "Different Model of the Universe" ATM thread (http://www.bautforum.com/against-mainstream/66183-different-model-universe.html), Bob Angstrom stated:



Is it true that we have no good models to explain how a mirror reflects?

Read Richard P. Feynman´s "QED - The Strange Theory of Light and Matter" and you will know the "HOW", unfortunately not the "WHY"


Is it true that photons have an awareness of their environment?

That depends very much on what you understand by "awareness". Are boulders aware of the mountain slope? Is water aware of the water hose walls?

dhd40
2007-Oct-25, 07:36 PM
Taking an example from the first part of Feynman's lecture, when a photon strikes the surface of a pane of glass it either reflects or it penetrates. The probability that it will reflect is about 4 percent. This isn't an explanation, its a probability but that will serve for now. So when a photon strikes the glass surface it tosses the dice and either reflects or penetrates depending on the outcome. No, says Feynman. Put another pane of glass below the first and the probability of reflection varies anywhere from zero to eight percent depending on the position of the second pane of glass. This is where the probability leaves the rational world of Newton and Einstein and enters the Twilight Zone and all our models fail. Let's look at this again. A photon strikes a surface of glass and reflects as one of the four percent that probability dictates should reflect. How does this photon "know" there is not another glass surface below to reduce its probability of reflection to zero percent? Newton had an explanation. All reflections are from the bottom surface and when a photon "corpuscle" of light penetrates the first layer this "presets" the condition of the photon to reflect from the bottom surface. Feynman explains that this is wrong because photons are identical and they can’t be preset and besides reflections can come from the first surface.
Wave theory also "happily" has an explanation. Waves of light reflecting from the bottom surface interfere with waves from the top surface and either cancel or amplify the reflection. Feynman explains that this explanation fails with single photons because we only observe one path for the photon. I might also add that a particle can’t be in two places at a time and do as Dirac says, "Interfere with itself."
At this point Feynman abandons all models and explanations and resorts to "descriptive methods" and rules of probability. I emphasize that descriptions and probabilities are not explanations because they fail to explain why light behaves as it does. I am sure Feynman understands the lack of explanation and he does explain, 54 minutes into the lecture, why we only observe a single path for a photon. A photon does not take just one path. It takes every possible path….this way, this way, this way, this way, etc. Some paths are more probable than others and the less probable paths in one direction cancel the less probable paths in the other direction. A photon following the most probable path continues on its way because it "smells" (Feynman’s word) the other less probable paths in its neighborhood and knows to continue. This is why we only observe one path for the photon.
For some reason Feynman’s explanation smells a bit contrived to me but not to worry. Courgar says there is a good model to explain how light works so the professor will now expound.

Your typing speed seems to gain some second over mine :)

Noclevername
2007-Oct-25, 07:37 PM
Is it true that photons have an awareness of their environment?

They interact with their environment. But then so does everything else that exists. I wouldn't call it awareness.

Bob Angstrom
2007-Oct-25, 07:39 PM
I would say no and no and ask for Bob's credentials. (Of course, my own credentials are nothing to write home about, but that shouldn't prohibit me from asking about someone else's.)
Sorry, Cougar but I forgot to explain my credentials. I was a crank until I encountered Angus Graham. Graham is an autodidatic cosmologist with a black belt in Occam's razor. Now I know what I am. I am an autodidatic cosmologist with a white belt in Occam's razor.

CodeSlinger
2007-Oct-25, 07:43 PM
dhd40, I'm confused. You refer me to Feynman's book for the HOW of reflection, but also agree with Angstrom, who appears to be saying that no one, not even Feynman, knows the HOW. Do you think we know how reflection works, or no?

papageno
2007-Oct-25, 07:43 PM
As for reflecting single photons, things are going to get much more hairy pretty quick. You are talking about a QM treatment of a photon interacting with a many body solid. I would imagine that getting a realistic treatment into a solvable form is still pretty much impossible.


In most cases, the wavelength of electromagnetic radiation is large compared to the average distance between the atoms in a solid. So one can get away with treating the radiation as an external classical field.

Bob Angstrom
2007-Oct-25, 08:13 PM
Read Richard P. Feynman´s "QED - The Strange Theory of Light and Matter" and you will know the "HOW", unfortunately not the "WHY"



That depends very much on what you understand by "awareness". Are boulders aware of the mountain slope? Is water aware of the water hose walls?
This is true. Feynman explains the "HOW" but not the "WHY".
Can we explain the "WHY"?
Yes, just ask Cougar. He knows.

Are photons "aware" of their environment?
No.
Why not?
Photons do not exist.
Will I explain why photons do not exist?
Yes, been there done that.
Will I explain it again for those who missed it?
Yes, probably but not in this forum.
Why not in this forum?
I’m not that crazy.

CodeSlinger
2007-Oct-25, 08:28 PM
Bob, I started this thread to find out what mainstream science knows about photons and reflection. I would appreciate it if you kept any ATM claims like "photons don't exist" elsewhere. Maybe the ATM forum, although it sounds like you had an unpleasant experience there.

EvilEye
2007-Oct-25, 09:08 PM
Would a reflected photon do like the tennis ball also in that its "spin" or wave form would reverse?

..becoming sort of an "anti-photon"?

Cougar
2007-Oct-25, 09:38 PM
Would a reflected photon do like the tennis ball also in that its "spin" or wave form would reverse?

..becoming sort of an "anti-photon"?
Well, "bounce" is probably not a good analogy or term to use. As I understand it, photons are either scattered or they are absorbed and re-emitted. When striking a carefully crafted mirror, apparently the probability is high that they are absorbed by the opaque backing on the glass and re-emitted with the opposite momentum (and "angle of reflection", according to high school physics). Of course, some percentage of incoming photons scatter or are re-emitted at some other angle. With billions of photons, we don't normally notice the ones that don't follow the high-school rule. Also note that if the wavelength of the photon is long enough, there's a good probability that it will go right through the mirror as if it wasn't even there.

Noclevername
2007-Oct-25, 09:55 PM
I've thought of another analogy; Cometary orbits, or rather, partial orbits. A photon comes in, whips around an atom, and is flung back out again, minus a little of its energy.

Cougar
2007-Oct-25, 10:16 PM
I've thought of another analogy; Cometary orbits, or rather, partial orbits. A photon comes in, whips around an atom, and is flung back out again, minus a little of its energy.
Some mirrors are tinted or colored. How do the "reflecting" photons acquire the mirror's color? I'd say absorption by the mirror's atoms and re-emission. I thought Feynman's classic little book Quantum Electrodynamics made all this pretty clear.

Cougar
2007-Oct-25, 10:19 PM
I was a crank until I encountered Angus Graham. Graham is an autodidatic cosmologist with a black belt in Occam's razor. Now I know what I am. I am an autodidatic cosmologist with a white belt in Occam's razor.
I'm all for self-teaching. But after reviewing some of Graham's writings (http://www.journaloftheoretics.com/Articles/4-6/commentary4-6.pdf), I'd say he's not that good a teacher.

Kaptain K
2007-Oct-26, 12:36 AM
The answer lies in the 2nd paragraph you quoted from Bob Angstrom;

...no common sense theory...
There is no "common sense" in quantum mechanics. Bob's argument seems to be "nobody can explain this so I can understand it, so it must be wrong". This attitude seems to be common in the ATM crowd.

Bob Angstrom
2007-Oct-26, 02:51 AM
Cougar,

There seem to be some misunderstandings here on my part. I thought by your statement of "No and no." that you were disagreeing with my previous statement that we do not have a common sense model for how a mirror works and that you were prepared to enlighten us with an explanation that did make sense. I see now that you were replying to something else and that you were saying "No." we do not have a good model for how a mirror works. Just for clarity, if you are saying we DO NOT have a common sense model for light, I agree. So it is "No," and "No," for both of us on that issue. My apologies for the confusion.

Bob Angstrom
2007-Oct-26, 03:07 AM
The answer lies in the 2nd paragraph you quoted from Bob Angstrom;

There is no "common sense" in quantum mechanics. Bob's argument seems to be "nobody can explain this so I can understand it, so it must be wrong". This attitude seems to be common in the ATM crowd.My argument is that we do not have a "common sense" model for light and not even I have one that makes sense.
When quantum mechanics makes sense, you know you’re stoned.

dhd40
2007-Oct-26, 01:05 PM
dhd40, I'm confused. You refer me to Feynman's book for the HOW of reflection, but also agree with Angstrom, who appears to be saying that no one, not even Feynman, knows the HOW. Do you think we know how reflection works, or no?

I must have been misunderstood. QED knows the HOW, but not the WHY. That´s what I wanted to say. So I disagree with Angstrom about the HOW.

papageno
2007-Oct-26, 01:24 PM
Here are a few papers, at random:

Quantum Theory of Metallic Reflection (http://prola.aps.org/abstract/PR/v47/i11/p860_1)

Infrared Reflection from Metals (http://prola.aps.org/abstract/PR/v160/i3/p577_1)

Specular Reflection of Conduction Electrons at a Metal Surface (http://prola.aps.org/abstract/PRB/v8/i6/p2527_1)

Electrodynamics of a Semiclassical Free-Electron Gas (http://prola.aps.org/abstract/RMP/v39/i2/p361_1)

Quantum Structure in the Dielectric Function of Metals and Anomalous Propagation Modes (http://prola.aps.org/abstract/PR/v169/i3/p530_1)

Surface Roughness and the Absorption of Electromagnetic Waves in Simple Metals (http://prola.aps.org/abstract/PR/v181/i3/p1053_1)

Study of the Interaction of Light with Rough Metal Surfaces. I. Experiment (http://prola.aps.org/abstract/PRB/v2/i2/p309_1)

Study of the Interaction of Light with Rough Metal Surfaces. II. Theory (http://prola.aps.org/abstract/PRB/v2/i2/p321_1)

Theory of Optical Excitation of Plasmons in Metals (http://prola.aps.org/abstract/PRB/v2/i4/p835_1)

Conductivity of a semi-infinite electron gas: Effective "optical" surface region (http://prola.aps.org/abstract/PRB/v20/i8/p3186_1)

CodeSlinger
2007-Oct-26, 02:48 PM
dhd40, thank you for the clarification.

Bob Angstrom, I'm with Kaptain K here. Not having a model that fits "common sense" is not the same thing as not having a model, full stop. We've seen time and again that common sense, derived from our everyday experience, simply does not hold when we delve into the very small or go up to the very large. QED appears to do a fine job of explaining reflection and other behaviors of light, it just doesn't fit our "common sense". If all you're arguing is that we don't have "common sense" answers, then please refrain from making comments like:



Don’t worry if your model can’t explain how a mirror works because no model can.




I am no stranger to Feynman’s work which is why I say that we have no models to explain how a mirror reflects.


... which are mis-leading to the point of being disingenuous.

frankuitaalst
2007-Oct-26, 03:04 PM
"Here are a few papers, at random:"
Someone has also a subscription key ?

Jerry
2007-Oct-26, 03:06 PM
It surprises me when it is argued that we do not have a good model for mirrored surfaces. There is both the classical model of Newton, and the wave mechanics of Maxwell. Both models provide the correct results to some level of approximation. More exacting solutions can be found when radiation transfer rules are also addressed (accounting for small losses of energy.)

Where the models break down, is in the boundary conditions. But this is inevitable: The equations become grossly nonlinear: How do you characterize thermal imbalance in a mirrored surface that is a function of image composition? The only reasonable approach is to used statistical modeling, especially if you are trying to preserve the attributes of photons.

Whenever a statistical solution is necessary, it can be argued either way: The underlying physics are understood but the uncertainty principle limits the predictive range; or the underlying physics may not be completely understood but the uncertainty principle masks detection of the violations.

A good example of this dichotomy is the quantum Hall effect: It was determined 'electrons' did not statistically behave according to the current model's predictions, so the model was changed to accomidate the behavior observed. The new model may or may not be correct, but it works until the next quantifiable exception occurs.

Ivan Viehoff
2007-Oct-26, 03:46 PM
Seems we could do with remembering the famous experiments of a slow beam of photons, or indeed electrons, being diffracted. Diffraction fringes are explained classically as wave interference, but are still observed even when when the beam is slowed so that only one particle at a time is emitted and detected - it builds up the diffraction pattern statistically over time. Then if that wasn't confusing enough, there is the case when there are two slits. As the source is slowed, the two-slit diffraction pattern still appears. Classically, each particle can only go through one slit; but the appearance of the two slit diffraction pattern indicates that each particle seems to "smell" the other slit.

Cougar
2007-Oct-26, 04:10 PM
There seem to be some misunderstandings here on my part. I thought by your statement of "No and no." that you were disagreeing with my previous statement that we do not have a common sense model for how a mirror works and that you were prepared to enlighten us with an explanation that did make sense.
No. :) Those were my responses to CodeSlinger's two questions:

Is it true that we have no good models to explain how a mirror reflects?
Is it true that photons have an awareness of their environment?


...if that wasn't confusing enough, there is the case when there are two slits. As the source is slowed, the two-slit diffraction pattern still appears.
Yes, that's quite non-intuitive. But isn't the mirror problem a different situation?

alainprice
2007-Oct-26, 04:26 PM
Doesn't a reflected photon have a phase difference from the incicent photon?

AFAIK, there is a 180 degree phase shift which matches nicely with reflected waves. Therefore, I would treat reflection as a purely wavelike phenomena.

Bob Angstrom
2007-Oct-26, 04:56 PM
I must have been misunderstood. QED knows the HOW, but not the WHY. That´s what I wanted to say. So I disagree with Angstrom about the HOW.
I said in Msg #18, "This is true. Feynman explains the "HOW" but not the "WHY"." Are you saying Feynman doesn't know the HOW either? This is probably not the case but if you were to take the time to explain what you THINK I said about the HOW, I probably wouldn't agree with it either.

papageno
2007-Oct-26, 07:26 PM
"Here are a few papers, at random:"
Someone has also a subscription key ?

Have a look at the abstracts.
If you cannot find free copies of the papers you are interested in, let me know.

dhd40
2007-Oct-26, 08:00 PM
I said in Msg #18, "This is true. Feynman explains the "HOW" but not the "WHY"." Are you saying Feynman doesn't know the HOW either? This is probably not the case but if you were to take the time to explain what you THINK I said about the HOW, I probably wouldn't agree with it either.

Well, there seem to be some contradictions in your statements.

From CodeSlinger´s No.1 post:
Originally Posted by Bob Angstrom
Don’t worry if your model can’t explain how a mirror works because no model can

Sorry, if I misunderstand something.

Bob Angstrom
2007-Oct-27, 07:19 AM
Well, there seem to be some contradictions in your statements.


Sorry, if I misunderstand something.I said Feynman explains the HOW but not the WHY and this sounds contradictory but Feynman explained the probability and rules used to describe how light works but he didn’t explain why light works the way it does.

I also said, "Don’t worry if your model can’t explain how a mirror works because no model can." This was in reply to another question from the ATM thread that you probably missed. There was also an earlier video where Feynman explained why all of our models eventually fail to explain the nature of light so we must forget theories and models and work with rules and probability instead.

CodeSlinger
2007-Oct-27, 01:18 PM
Bob Angstrom,

Please clarify what your claim is. I thought this...


My argument is that we do not have a "common sense" model for light and not even I have one that makes sense.
When quantum mechanics makes sense, you know you’re stoned.

...meant you're only arguing that we don't have a model that fits common sense. But in this recent post...



I said Feynman explains the HOW but not the WHY and this sounds contradictory but Feynman explained the probability and rules used to describe how light works but he didn’t explain why light works the way it does.

I also said, "Don’t worry if your model can’t explain how a mirror works because no model can." This was in reply to another question from the ATM thread that you probably missed. There was also an earlier video where Feynman explained why all of our models eventually fail to explain the nature of light so we must forget theories and models and work with rules and probability instead.


... you appear to be arguing once again that we have no model whatsoever of light behavior. So QM, QED explanations of light behavior don't count as models?

Nereid
2007-Oct-27, 03:07 PM
Perhaps a closer look at just what the question on the table is might help?

The scope of this forum is contemporary, mainstream astronomy, cosmology, astrophysics, space science, etc.

Within this context, the question on the table is something like "to what extent do, or can, contemporary physics theories account for the full range of observations of 'light' being reflected from surfaces such as mirrors?"

The answer to this question, given several times and in several forms already, is something like "Classical physics is all you need to account for a wide range of such observations; however, for many others you need QED." And, AFAIK, all "observations of 'light' being reflected from surfaces such as mirrors" can be accounted for, to within the experimental or observational errors, by these.

Of course, if the question is re-stated, more finely perhaps, or with a raft of associated definitions, then this (kind of) answer may be inadequate.

In particular, note that 'photon' is a theoretical construct, or an abstraction ... there are no photons in classical physics (for example), so using the term automatically constrains discussion to the framework of whatever theories incorporate 'photons'. Nothing new there, of course, that's part and parcel of all branches of modern science. However, it does open the door to something which is at least somewhat beyond the scope of this section of BAUT - philosophy.

CodeSlinger
2007-Oct-27, 04:51 PM
The following begins around 1:20:08 in part 2 of Richard Feynman's Douglas Robb Memorial Lectures (http://www.vega.org.uk/video/subseries/8):



One thing though, I must say, and that is this: We've been talking about light go through a vaccum and then I had a rule about it's reflected by a certain amount, when it goes a certain shrinkage when it comes off a surface, when it goes through a medium it gets slowed up, and so on.

These, it turns out, are not really the properties of light. They have to do with the properties of matter. You can't get reflection without having a piece of glass. It doesn't go slow unless it's in the glass. It, really, as it turns out, is not going slower. It's curious, and we're going to find out exactly what it does.

In order to explain it we have to know what the electrons in the glass are doing and how they interact with the light. And I'll summarize the most wonderful fact: it's that light never does anything, really, when you get down to it. Except to go, in a vacuum, from one place to the other. It's emitted by one atom, or particle, and absorbed by another. And it never goes and gets slowed down or gets reflected.

What reflection really is, is light goes down, it's absorbed by something which shakes it, and that emits a new light, which comes back. Reflected light is really not the same photon coming back as went in. A photon from the source went into the glass, and from the glass comes out a new photon.

This is an interesting thing that makes light, in the end, simpler and simpler and simpler. And what I was trying to get to in the last steps was to show you how ultimately simple it is when it's only in a vaccum. And the complications, the funny laws of reflection, and funny laws for going through glass, are really the result of the interaction of light and electrons.

And that's why this subject of discussing physics can't go on any further until I walk in to discuss matter, and the next lecture will be about matter, alright?

Thank you.


*bold mine

Sounds like a model of reflection and other light behavior to me. Bob Angstrom, I'm curious why you neglected to mention this portion of the lectures. More to the point, why you kept asserting that we (including Richard Feynman) have no such models when this was in the very lectures you have quoted and discussed at length.

CodeSlinger
2007-Oct-27, 04:59 PM
Nereid, thank you for your input. You're right, the question of how well physics can model/account for behavior of light such as reflection has indeed been answered. My thanks to all those who have helped me along the way.

I guess what I'm trying to do now (perhaps unnecessarily), having done more research into QED and what Feynman presented with regards to it, is to point out and correct false statements made by Bob Angstrom, in hopes that others will not be confused by him as I was.

CodeSlinger
2007-Oct-27, 05:13 PM
To answer my second question from the OP, the answer is no. In his lectures, Feynman does briefly mention photons smelling paths, but only as a throw-away metaphor. QED, which appears to be our best theory regarding light behavior, does not attribute to photons awareness of their surroundings.

Bob Angstrom
2007-Oct-27, 08:51 PM
Bob Angstrom,
... you appear to be arguing once again that we have no model whatsoever of light behavior. So QM, QED explanations of light behavior don't count as models?We have tens of models, perhaps hundreds, but we don’t have THE model that explains it all and we possibly never will. QM and QED have rules and probabilities devoid of all models unless you count Feynman’s "sum over histories" which is a ** model. I call it a ** model because that is what Feynman called it but it is the best ** he had to offer until something better comes along.

And photons are not really aware. Their awareness is an illusion.

CodeSlinger
2007-Oct-27, 09:26 PM
According to this Wiki page (http://en.wikipedia.org/wiki/Science), a scientific model is:

"... a description or depiction of something, specifically one which can be used to make predictions that can be tested by experiment or observation."

By that standard, "sum over histories" is not a model. The model QED and Feynman offers for the behavior of light, such as reflection, is that they are the result of photons interacting with electrons and other particles. Please read over the excerpt from Feynman's lecture I provided in post 47, specifically the bolded parts.

Please stop mis-representing what QED says.

Thank you for your retraction of the "photons have awareness" statement, but I find it depressing that you're still dancing about the "we have no models for light behavior" statement, now going from "we have no models" to "we have tens, perhaps hundreds of models".

G O R T
2007-Oct-27, 09:32 PM
To answer my second question from the OP, the answer is no. In his lectures, Feynman does briefly mention photons smelling paths, but only as a throw-away metaphor. QED, which appears to be our best theory regarding light behavior, does not attribute to photons awareness of their surroundings.

Indeed Feynman is far too often confusing with such metaphors.

Mentioned in post #1, any notion of a single photon "bouncing" off of a specific atoms valence cloud is amusing and most unhelpfull. With the uncertainty of which of the 1-2 billion atoms in the photons possible path will be the lucky one, they can only be considered as the interconnected group (surface) that they are. I am somewhat suprised that the subject is confined to specular reflection since the organized bending of light at a refractive interface is not random at the atomic level either.

A photon need not be said to be aware of it's surroundings because there is always some probability that it actually is somewhere else in it's surroundings. :lol:

CodeSlinger
2007-Oct-27, 09:40 PM
Indeed Feynman is far too often confusing with such metaphors.

Feynman is certainly, um, lively with his metaphors :lol: Definitely confusing for the likes of myself. But it's also part of why listening to him is so much fun :)

Bob Angstrom
2007-Oct-28, 02:51 AM
The following begins around 1:20:08 in part 2 of Richard Feynman's Douglas Robb Memorial Lectures (http://www.vega.org.uk/video/subseries/8):



*bold mine

Sounds like a model of reflection and other light behavior to me. Bob Angstrom, I'm curious why you neglected to mention this portion of the lectures. More to the point, why you kept asserting that we (including Richard Feynman) have no such models when this was in the very lectures you have quoted and discussed at length.
I don’t care to get into a discussion of semantics about what is or is not a model. If you choose to call the your bolded parts of Feynman’s lecture a model, then it is a model. I call it a description. A descriptive model, how's that?

Why didn’t I mention that Feynman had a model for light and mislead you into thinking that he did not?
Let’s look at what Feynman said," What reflection really is, is light goes down, it's absorbed by something which shakes it, and that emits a new light, which comes back. Reflected light is really not the same photon coming back as went in. A photon from the source went into the glass, and from the glass comes out a new photon.
This is an interesting thing that makes light, in the end, simpler and simpler and simpler. And what I was trying to get to in the last steps was to show you how ultimately simple it is when it's only in a vacuum. And the complications, the funny laws of reflection, and funny laws for going through glass, are really the result of the interaction of light and electrons." So Feynman says it all boils down to light being a matter of light and electrons. And don’t take the rest, or any, of what I have to say seriously. Much of this is in the first part of Feynman’s lecture #2.Check it out for yourself.

We can run with the idea of light being a matter of photons and electrons and see where it goes. A photon strikes a glass surface and it can either be reflected or penetrate. There is about a four percent chance that it will be reflected and continue on its way and all this happens in a time extremely close to the speed of light. There is a slight delay at the glass surface presumably because the photon is adsorbed and then emitted as a different photon but it doesn’t really matter if there are one or two photons involved. The whole event is very, very close to the speed of light. If an electron adsorbs a photon, the photon can be adsorbed and held (the glass gets hot) or another photon can be emitted almost instantly. The second photon can go either up or down. If it goes up, the direction of travel depends upon the surface condition of the glass and whether it is rough or polished. If the surface is rough, the emission is largely random. If the surface is polished, the emission is no longer random but it is directed by the position of the atoms surrounding the electron and the photon leaves at the same angle it arrived. So the direction of the reflection is not "decided" at just the electron or the atomic level. It extends several atoms beyond the electron. If there is another pane of polished glass below the first, this changes the probability of reflection from 4 percent to roughly 0 to 8 percent depending on the precise positioning of the second layer. Move the second layer a fraction of a wavelength in one direction or the other and the probability changes. The second pane of glass can be a considerable distance away from the first and still have an effect. Now the electron at the surface needs to "know" the condition of its macro environment before it emits the photon. It needs to "know" if there is a second, third, or fourth pane of glass below and the precise position of the bottom layer. Is it smooth or scratched, clear or opaque.
Feynman’s "model" you cited works perfectly well within a narrow range of applications but I consider it to be a description rather than a true model. I have probably confused you again by now so look into Feynman for yourself and then you can explain to me how it really works.

I have tried to keep things just to one side of sanity so far but if you don’t mind crossing the line, here goes.
We have perfectly good models to explain how light works but when we get into the fundamentals we don’t have a model for any of our models and, in that sense, we don’t have a model. Just don’t ask me to explain that.
Before an electron at the surface of the glass can reflect a photon, it must "know" the quite precise position and orientation of many billions of electrons in its local and even not so local area. The time between adsorption and emission of a reflected photon is almost instant so the communication among electrons must be far faster than c. When the electron at the glass surface emits a photon, the photon has been, for the lack of a better word, "collectively aimed" by the many other electrons within its environment. If the original photon in our scenario came from the sun, an electron on the sun established a non-local connection with a receptive electron on Earth and then "aimed" for Earth.
There is no awareness among photons, even though they appear to be aware, for two reasons. The only particles exhibiting any form of awareness are electrons but electrons are only responding to information coming from their environment. There appears to be a constant exchange of information (whatever that might be) among electrons and it looks a lot like awareness. Also, if we consider light to be an exchange of energy quanta among electrons directed by probability waves, photons become redundant and we can dispense with them as a tool for explaining light. It all boils down to probability waves and electrons.

CodeSlinger
2007-Oct-28, 03:55 AM
If there is another pane of polished glass below the first, this changes the probability of reflection from 4 percent to roughly 0 to 8 percent depending on the precise positioning of the second layer.


No, if you watched the entire lecture, you would know that Feynman later corrected himself and wrote that with two panes of glass, the probability ranges from 0 to 16 percent, averaging at 8 percent. This is why I continue to be leery of your summarization of what QED and Feynman says. You keep posting as though you haven't even finished watching the lectures.



If the surface is polished, the emission is no longer random but it is directed by the position of the atoms surrounding the electron and the photon leaves at the same angle it arrived. So the direction of the reflection is not "decided" at just the electron or the atomic level. It extends several atoms beyond the electron.


Please cite your sources, I don't recall Feynman saying this.



Feynman’s "model" you cited works perfectly well within a narrow range of applications...


Please cite applications where the model breaks down.



Before an electron at the surface of the glass can reflect a photon, it must "know" the quite precise position and orientation of many billions of electrons in its local and even not so local area. The time between adsorption and emission of a reflected photon is almost instant so the communication among electrons must be far faster than c. When the electron at the glass surface emits a photon, the photon has been, for the lack of a better word, "collectively aimed" by the many other electrons within its environment. If the original photon in our scenario came from the sun, an electron on the sun established a non-local connection with a receptive electron on Earth and then "aimed" for Earth.


Please cite your sources for this as well.



Also, if we consider light to be an exchange of energy quanta among electrons directed by probability waves, photons become redundant and we can dispense with them as a tool for explaining light.


Quanta of energy is exactly what photons are! You haven't made photons redundant, you're just calling them by a different name. I thought you weren't interested in semantic games.

Nereid
2007-Oct-28, 03:56 PM
I don’t care to get into a discussion of semantics about what is or is not a model. If you choose to call the your bolded parts of Feynman’s lecture a model, then it is a model. I call it a description. A descriptive model, how's that?

Why didn’t I mention that Feynman had a model for light and mislead you into thinking that he did not?
Let’s look at what Feynman said," What reflection really is, is light goes down, it's absorbed by something which shakes it, and that emits a new light, which comes back. Reflected light is really not the same photon coming back as went in. A photon from the source went into the glass, and from the glass comes out a new photon.
This is an interesting thing that makes light, in the end, simpler and simpler and simpler. And what I was trying to get to in the last steps was to show you how ultimately simple it is when it's only in a vacuum. And the complications, the funny laws of reflection, and funny laws for going through glass, are really the result of the interaction of light and electrons." So Feynman says it all boils down to light being a matter of light and electrons. And don’t take the rest, or any, of what I have to say seriously. Much of this is in the first part of Feynman’s lecture #2.Check it out for yourself.

We can run with the idea of light being a matter of photons and electrons and see where it goes. A photon strikes a glass surface and it can either be reflected or penetrate. There is about a four percent chance that it will be reflected and continue on its way and all this happens in a time extremely close to the speed of light. There is a slight delay at the glass surface presumably because the photon is adsorbed and then emitted as a different photon but it doesn’t really matter if there are one or two photons involved. The whole event is very, very close to the speed of light. If an electron adsorbs a photon, the photon can be adsorbed and held (the glass gets hot) or another photon can be emitted almost instantly. The second photon can go either up or down. If it goes up, the direction of travel depends upon the surface condition of the glass and whether it is rough or polished. If the surface is rough, the emission is largely random. If the surface is polished, the emission is no longer random but it is directed by the position of the atoms surrounding the electron and the photon leaves at the same angle it arrived. So the direction of the reflection is not "decided" at just the electron or the atomic level. It extends several atoms beyond the electron. If there is another pane of polished glass below the first, this changes the probability of reflection from 4 percent to roughly 0 to 8 percent depending on the precise positioning of the second layer. Move the second layer a fraction of a wavelength in one direction or the other and the probability changes. The second pane of glass can be a considerable distance away from the first and still have an effect. Now the electron at the surface needs to "know" the condition of its macro environment before it emits the photon. It needs to "know" if there is a second, third, or fourth pane of glass below and the precise position of the bottom layer. Is it smooth or scratched, clear or opaque.
Feynman’s "model" you cited works perfectly well within a narrow range of applications but I consider it to be a description rather than a true model. I have probably confused you again by now so look into Feynman for yourself and then you can explain to me how it really works.

I have tried to keep things just to one side of sanity so far but if you don’t mind crossing the line, here goes.
We have perfectly good models to explain how light works but when we get into the fundamentals we don’t have a model for any of our models and, in that sense, we don’t have a model. Just don’t ask me to explain that.
Before an electron at the surface of the glass can reflect a photon, it must "know" the quite precise position and orientation of many billions of electrons in its local and even not so local area. The time between adsorption and emission of a reflected photon is almost instant so the communication among electrons must be far faster than c. When the electron at the glass surface emits a photon, the photon has been, for the lack of a better word, "collectively aimed" by the many other electrons within its environment. If the original photon in our scenario came from the sun, an electron on the sun established a non-local connection with a receptive electron on Earth and then "aimed" for Earth.
There is no awareness among photons, even though they appear to be aware, for two reasons. The only particles exhibiting any form of awareness are electrons but electrons are only responding to information coming from their environment. There appears to be a constant exchange of information (whatever that might be) among electrons and it looks a lot like awareness. Also, if we consider light to be an exchange of energy quanta among electrons directed by probability waves, photons become redundant and we can dispense with them as a tool for explaining light. It all boils down to probability waves and electrons.
Hmm ... to some extent you seem to be saying that converting a consistent, QED-based, explanation of certain photon-electron interactions into ordinary words is fraught with difficulty.

However, what seems to be missing is (to me) the core aspect of the first question in the OP; namely, how well does (or can) QED account for all the relevant experimental and observational results?

Might this be an appropriate place to introduce another famous (if mis-attributed) Feynman quote, "Shut up and calculate"?

Bob Angstrom
2007-Oct-29, 01:41 PM
No, if you watched the entire lecture, you would know that Feynman later corrected himself and wrote that with two panes of glass, the probability ranges from 0 to 16 percent, averaging at 8 percent. This is why I continue to be leery of your summarization of what QED and Feynman says. You keep posting as though you haven't even finished watching the lectures.
You are right, Feynman later said the probability of reflection from the top surface varies from 0 to 16 percent with the addition of a second layer. The point remains that the exact amount of reflection from the top surface is determined by the precise position of the bottom surface so pick a number from 0 to 16… not my 0 to 8 percent. If you add more surfaces (panes of glass) the bottom surface still effects reflection at the top so an electron on the top must "know" the precise position of the bottom surface before it emits a photon. This makes light much more than a local effect.

Please cite your sources, I don't recall Feynman saying this. . One of my sources is Feynman’s book QED where he describes how the reflection from glass changes when you put a scratch in the glass. Reflection becomes random in the area of the scratch and, if you keep scratching the glass, reflections become even more random until the scratches are about one wavelength apart. Then the reflection suddenly becomes ordered and the surface is "polished". The critical distance over which this takes place is about one wavelength in all directions from the point of reflection.

Please cite applications where the model breaks down. .
The model works in the case of a "perfect" mirror. It fails as a model for other forms of reflection and it offers no understanding of why reflection works the way it does. But if want to know about angles of reflection, it is all you need or want.

Please cite your sources for this as well. .
That rambling thing at the end was my summary from several different sources but they all say pretty much the same thing. John Cramer’s Transactional Theory is one. http://www.npl.washington.edu/TI/

Quanta of energy is exactly what photons are! You haven't made photons redundant, you're just calling them by a different name. I thought you weren't interested in semantic games. There is a little more than antics with semantics involved when you compare energy quanta with photons in something like Cramer’s transactional theory. In Cramer’s theory, energy quanta don’t go flying through the air. The exchange is direct and non-local and they go from the source to sink without passing through anything. Not even the apparatus. If we consider Afshar’s double slit experiment using Cramer’s theory, a high energy electron in the laser establishes a two-way wave connection through the apparatus with a low energy electron in the detector. Once the connection has been established, the electron in the laser drops to a lower energy level as the electron in the detector jumps to a higher energy level. The detector gains a quantum of energy and goes "click". Photons in this view are imaginary little balls we toss around after the fact to explain what happened.

CodeSlinger
2007-Oct-29, 03:20 PM
If you add more surfaces (panes of glass) the bottom surface still effects reflection at the top so an electron on the top must "know" the precise position of the bottom surface before it emits a photon.

No, it doesn't. Feynman's explanation is that the bottom surface affects the total probability of reflection because that probability is based on the probability amplitude of all possible paths the photon can take, which includes paths involving the bottom surface. There is nothing whatsoever about electrons on the top having to "know" anything about the bottom surface.


The model works in the case of a "perfect" mirror. It fails as a model for other forms of reflection...

Ok, please cite where it is stated or shown that QED's mathematical or descriptive model fails for these other forms of reflection.


...and it offers no understanding of why reflection works the way it does.

QED describes reflection as the result of photons being absorbed and re-emitted by electrons in the reflecting surface, and also tells us how to determine how reflection will behave. I'm satisfied that QED does a fine job of offering an understanding of why reflection works the way it does. But if you still want to insist that it doesn't, well, ok.


That rambling thing at the end was my summary from several different sources but they all say pretty much the same thing. John Cramer’s Transactional Theory is one.

When you introduce statements from new theories (new in the sense of being new to the discussion), please clearly mark them as such. I see now that the statements in your summary indeed corresponds to Cramer's TIQM. But since you didn't mention this, it looked like those statements were part of QED, which they most certainly are not.


There is a little more than antics with semantics involved when you compare energy quanta with photons in something like Cramer’s transactional theory.

After reading the link you provided on TIQM, I see what you mean. I retract my accusation of semantic shenanigans regarding photons and energy quanta. My apologies.

Bob Angstrom
2007-Oct-30, 09:59 AM
No, it doesn't. Feynman's explanation is that the bottom surface affects the total probability of reflection because that probability is based on the probability amplitude of all possible paths the photon can take, which includes paths involving the bottom surface. There is nothing whatsoever about electrons on the top having to "know" anything about the bottom surface.Yes this is in the lecture and it is a BIG part of the lecture or are you saying that I missed the part where Feynman says electrons at the top do not respond to the precise position of the lower surface? You have to watch the whole thing and not just the part about probabilities. Feynman explained early in the lecture that an electron at the top surface absorbs a photon and then releases a second photon and that constitutes reflection. Later in the lecture he was explaining how to calculate the percent of reflection from the surface. He failed to mention that the thing at the surface that does the reflecting is the electron he mentioned earlier but that should be obvious if you put the two together. Much later in the lecture he explained how the most probable light path "smells" the less probable light paths and continues while all the other light paths cancel out. Also, in the lecture he said that the average reflection from the top surface is 4 percent and he asked how the 4 percent of the photons that get reflected away know they should not have left the surface if the position of the bottom surface dictates a lower percentage. He explained that the bottom surface determines the percentage of light reflected from the top so the electrons at the top do not reflect photons until they know the very precise location of the bottom surface and that could be under several panes of glass and a considerable distance away. He even explained what happens at the top surface if the bottom surface is a pane of glass at the bottom of a muddy lake. The amount of light reflected from the top surface depends on bottom surface and that requires a "knowledge" of where the bottom is. If you put all of this together, Feynman does say that electrons at the top surface "know" (or smell to use Feynman’s word) the bottom surface. My words may not be exactly the same as Feynman’s but as Dave Barry says, "I AM NOT MAKING THIS UP."

I don’t have time to check the lecture but the numbers don’t make sense. Not that the exact numbers matter because the point here is that light is not just a local event. But, as I recall, Feynman said the reflection from the top surface was 0 to 8 percent for an average of 4 percent. You said Feynman later corrected the number to 0 to 16 percent so I was wrong. I think the 0 to 16 percent reflection was for a pane of glass with 0 to 8 percent reflection from the top and 0 to 8 percent from the bottom for a total reflection of 0 to 16 percent. This is from the part where he was multiplying percentages from the top and bottom. So I was right the first time. The reflection from the TOP surface is 0 to 8 percent.

Ok, please cite where it is stated or shown that QED's mathematical or descriptive model fails for these other forms of reflection.I don’t have QED on hand but I recall Feynman saying things like, "Don’t worry if you don’t understand this because nobody understands it." Much of the book is written against a background of uncertainty and nowhere does the math explain how the electron on the top layer of glass smells the bottom surface so it knows how to emit a photon.

QED describes reflection as the result of photons being absorbed and re-emitted by electrons in the reflecting surface, and also tells us how to determine how reflection will behave. I'm satisfied that QED does a fine job of offering an understanding of why reflection works the way it does. But if you still want to insist that it doesn't, well, ok.The math may work but for me the math is the least interesting part of QED. I am more interested in the rest of it. I would just like to know how an electron on top smells the bottom surface... and it does.

When you introduce statements from new theories (new in the sense of being new to the discussion), please clearly mark them as such. I see now that the statements in your summary indeed corresponds to Cramer's TIQM. But since you didn't mention this, it looked like those statements were part of QED, which they most certainly are not.Besides QED, I’ve read a few articles in the "Inquirer" about light so don’t expect all of my statements to be exact, numerically correct, verbatim quotes from Richard P. Feynman. I might draw upon other sources, misquote someone, or have a thought of my own. Just be warned.

Kaptain K
2007-Oct-30, 02:35 PM
The math may work but for me the math is the least interesting part of QED.
News flash!

QED is math! Everything else is window dressing (an attempt, obviously, in your case, unsuccessfully, to put the math in words the non-mathematician can understand). Forget the words and (in Feynman's words) shut up and calculate!

John Mendenhall
2007-Oct-30, 07:56 PM
Richard (Publius), how about weighing in on this thread, even though photons have zero rest mass?

It occurs to me that photons are reflected instantaneously. Can we make progress at the quantum level that way? What is going on when the wave hits the reflective surface? Is there self interference? How about at an angle?

CodeSlinger
2007-Oct-31, 06:09 AM
Watched Feynman's lecture once again tonight, and took careful notes of every place where statements from Bob's latest "summarization" were falsified. Afterwards, had a paper to edit. Bed time now, will post tomorrow.

CodeSlinger
2007-Oct-31, 04:21 PM
For those who are interested, here is the lecture by Feynman that Bob and I have been discussing.

Streaming RealMedia video (http://www.vega.org.uk/video/programme/46) (Full lecture series HERE (http://www.vega.org.uk/video/subseries/8))

In the remainder of the post, I will include timestamps wherever applicable so people can view the video and compare for themselves what Bob claims with what Feynman actually says.


Yes [top electrons "knowing" about the bottom surface] is in the lecture and it is a BIG part of the lecture or are you saying that I missed the part where Feynman says electrons at the top do not respond to the precise position of the lower surface?

WRONG. Throughout the discussions on reflection, Feynman does say that both the top and bottom surfaces affect total reflection. Which he explains as the result of multiple paths, some involving the top surface and others involving the bottom surface, interacting with each other. But he never says anything about electrons in the top knowing anything about the bottom. The closest he gets to that is when he talks about Newton's idea that something follows a photon from the top to bottom, to set up conditions correctly (4:10, 6:30). But this is in the context of discussing Newton's corpuscle/particle theory and its problems. Nowhere in the lecture is it stated or implied that QED attributes non-local awareness to electrons.


You have to watch the whole thing...

Oh, that's rich, coming from you.


Much later in the lecture he explained how the most probable light path "smells" the less probable light paths and continues while all the other light paths cancel out.

First, he says this while explaining why light tends to travel in a straight line, not in the context of reflection (54:40). Second, as I pointed out to you earlier in the thread, this is a throw-away metaphor. He says this exactly once, with literal hand-waving, and then never mentions it again in the 1 hour, 38 minute lecture. In fact, immediately after using this throw-away metaphor, he goes right back to explaining things with the model of path interaction. Your seizing on this metaphor and claiming that QED says photons or electrons have smelling-like awareness is blatant cherry-picking and taking a quote entirely out of context.


He explained that the bottom surface determines the percentage of light reflected from the top so the electrons at the top do not reflect photons until they know the very precise location of the bottom surface and that could be under several panes of glass and a considerable distance away...

The amount of light reflected from the top surface depends on bottom surface and that requires a "knowledge" of where the bottom is.

WRONG. What he says is that the bottom surface, together with the top surface, affects total reflection (4:01, 4:10), not that the bottom surface determines the reflection from the top surface. And nothing whatsoever about electrons in the top surface knowing about the bottom surface.


If you put all of this together, Feynman does say that electrons at the top surface "know" (or smell to use Feynman’s word) the bottom surface.

WRONG, as shown above, and obvious to anyone who watches the lecture.


My words may not be exactly the same as Feynman’s but as Dave Barry says, "I AM NOT MAKING THIS UP."

Sadly, that appears to be exactly what you did.


But, as I recall, Feynman said the reflection from the top surface was 0 to 8 percent for an average of 4 percent. You said Feynman later corrected the number to 0 to 16 percent so I was wrong. I think the 0 to 16 percent reflection was for a pane of glass with 0 to 8 percent reflection from the top and 0 to 8 percent from the bottom for a total reflection of 0 to 16 percent. This is from the part where he was multiplying percentages from the top and bottom. So I was right the first time. The reflection from the TOP surface is 0 to 8 percent.

WRONG. Feynman says that we describe the total reflection from two surfaces as ranging from 0% to 16% because that is what we observe as the distance between the two surfaces changes. At some distances, we observe 0% reflection, while at others, we observe 16% reflection, with other percentages between 0 and 16 being observed at other distances (5:03). This is not true for a single surface, which simply has 4% reflection (3:07, 19:48). It is incorrect to say that the reflection from the top, or any single surface, is 0 to 8 percent.

Feynman's presentation of the QED explanation for how two 4% reflection surfaces produce a total reflection ranging from 0% to 16% starts at 19:48.


I don’t have QED on hand but I recall Feynman saying things like, "Don’t worry if you don’t understand this because nobody understands it." Much of the book is written against a background of uncertainty and nowhere does the math explain how the electron on the top layer of glass smells the bottom surface so it knows how to emit a photon.

Your claim was that QED fails for reflection for surfaces other than a perfect mirror (post 63). That's your support for that claim? Utter tripe! It's blatantly obvious that that quote in no way supports your claim. In fact, Feynman himself says that QED agrees perfectly with every phenemon ever observed with light (28:25).

The reason why the math does not explain how electrons smell is simple: despite your insistence, QED does not say electrons smell.


The math may work but for me the math is the least interesting part of QED. I am more interested in the rest of it. I would just like to know how an electron on top smells the bottom surface... and it does.

Nice back-pedaling, Bob. You've gone from "we have no models that can explain reflection!" to "oh right, QED has math that works, but it has no models!" to "well, ok, it has models, but it doesn't explain how electrons smell!". Once again, QED does not explain how electrons smell things because QED never claims that electrons smell things.

What I don't understand is why you have repeatedly written gross mis-representations of QED. It's so blatant that even someone like me can call you on your mistakes after watching the lecture a few times. You either do not understand QED yourself, or worse, you are intentionally mis-representing QED in order to advance your own ATM ideas.

You know what, I've reached the end of my patience. What's clear is that you are unable to portray QED accurately, and I just don't care what the reason for that is. Watch the lectures again, the links are up top. If you have the book, great, read it again. But do not presume to tell others what QED says.

mugaliens
2007-Nov-01, 07:16 AM
My argument is that we do not have a "common sense" model for light and not even I have one that makes sense.
When quantum mechanics makes sense, you know you’re stoned.

I find that statement somewhat off-target, Bob. If that's your experience, please simply say so, but to acuse others of not being able to understand... Well, how about letting them/us speak for ourselves?

Some of us do understand the Standard Model (http://en.wikipedia.org/wiki/Standard_Model).

No, we're not stoned, either. It took two years of college physics and a lot of time focusing on quantum field theory (http://en.wikipedia.org/wiki/Quantum_field_theory) and the various subsets for me to get to the point where I actually did understand it.

I certainly can't reproduce all the math, though because I do have a minor in math, I can at least follow most of it.

A purist might claim, "well, if you can't reproduce the math, you don't actually understand it."

Most people can't reproduce the equations which describe ocean waves, but they can still tell you that when you throw a rock into a pond, the ensuing waves diminish in energy according to the inverse-square law, that waves have an amplitude and frequency, etc.

So, they understand waves spreading out from a point source.

Ok - back to your regularly scheduled channel..

mugaliens
2007-Nov-01, 03:17 PM
The complementarity between particle-like and wave-like properties of quantum particles is well supported experimentally, as shown by the references I gave.

Afshar did nothing to change that.

Papageno, you seem to be pretty well-versed at finding references.

A long time ago, I remember reading about a dual-slit experiment where they passed photons through just one slit for a while, suspended the experiment for a while, then used the other slit for the second half.

The result was the same interference patter as if both slits had been used simultaneously.

The implication is that photons aren't directly interfering with one another. It's simply the wave-like nature of the photons, the interference pattern from passing a wave-like particle through one slit, the fact that the recording medium (photographic paper, back then) observed cumulative effects, so that it wasn't true interference, per say, but simply the cumulative nature of passing a wave-like particle through slits.

Any hits?

papageno
2007-Nov-01, 09:01 PM
A long time ago, I remember reading about a dual-slit experiment where they passed photons through just one slit for a while, suspended the experiment for a while, then used the other slit for the second half.

The result was the same interference patter as if both slits had been used simultaneously.


That is really, really vague.
Can you be a bit more specific? (That is, a range of years, or some names...)




The implication is that photons aren't directly interfering with one another. It's simply the wave-like nature of the photons, the interference pattern from passing a wave-like particle through one slit, the fact that the recording medium (photographic paper, back then) observed cumulative effects, so that it wasn't true interference, per say, but simply the cumulative nature of passing a wave-like particle through slits.


Are you sure that it was not the effect of diffraction by one slit (and then the other)?

Jim
2007-Nov-01, 09:31 PM
New thread (http://www.bautforum.com/against-mainstream/66555-afshar-experiment.html) created in ATM. Please pardon the confusion which will probably result.

John Mendenhall
2007-Nov-02, 09:31 PM
Papageno, you seem to be pretty well-versed at finding references.

A long time ago, I remember reading about a dual-slit experiment where they passed photons through just one slit for a while, suspended the experiment for a while, then used the other slit for the second half.



This sounds like an article I read (last 10 years, I think) where they were collecting the data in computer files. Like Mugs, I have no idea where it was published. As I recall, they got all kinds of weird effects just by manipulating the data files.

mugaliens
2007-Nov-03, 05:48 PM
That is really, really vague.
Can you be a bit more specific? (That is, a range of years, or some names...)

Areyou sure that it was not the effect of diffraction by one slit (and then the other)?

Two slits. One covered with tape for a while, during phase one. The other covered with tape during phase two, sometime later.

Same interference pattern produced as if they'd been conducted simultaneously.

I saw it in some film during the sixth or seventh grade, around 1975.

It's such a simple experiment, if there's no other information on it, it shouldn't be very difficult to reproduce.

papageno
2007-Nov-03, 08:40 PM
I saw it in some film during the sixth or seventh grade, around 1975.


Weird...
In the other thread I just posted a link to the classic single-electron interference movie made in 1974...

papageno
2007-Nov-03, 09:26 PM
It's such a simple experiment, if there's no other information on it, it shouldn't be very difficult to reproduce.


Considering how many references I found about Afshar's experiment, I don't think that such an experiment would have been ignored.

Are you sure your memory is serving you?