Merged Relativity+ / Farsight

Farsight said:
You are lost in maths. Displacement current is a feature of light. It's a time-varying electric field. And it does what it says on the can. It isn't called displacement current for nothing.
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Argument by etymology. New one!

Because that displacement current is alternating. That's why we have vacuum impedance, impedance being resistance to alternating current. The two waves "ride over one another", like two ocean waves ride over one another. There's a displacement up, then down. Then each continues on its way. So it looks like there was no interaction. But when you increase the energy the displacement is so drastic that each wave is displaced into itself. And ends up displacing itself into a closed path. Simples.
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Awesome.

Your proof that Maxwell's Equations imply photon-photon scattering is ... um ... a restatement of your unproven, unpublished crackpot theory of photons twisted into knots.

Dude, one of the reasons I disagree with your photon-knot theory is because they're so obviously not a solution to Maxwell's Equations. As I'm sure I've said repeatedly. You've never derived photon-knots from Maxwell's Equations; if you tried to do so you'd fail. I repeat: Maxwell's Equations are linear. They do not do what you have daydreamed they do.

Your walkthrough of "displacement current" is gibberish and corresponds to nothing ever seen in Maxwell's Equations, nor in E&M experiments, nor to anything in theoretical or experimental quantum electrodynamics. It's just pouring out of your head and yours alone.

I don't make mistakes. You just don't know much physics, that's all. I think it's because your physics degree was all maths. That's the usual thing. People spend three years doing maths, not physics.
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Actually, my undergraduate degree consisted entirely of drawing arrows on a ping-pong-ball with a marker. My master's thesis was on "staring at spirals" and my postdoc work consisted entirely of misquoting late-19th-century E&M lectures. I later joined the faculty at the Harvard Department of Numerology, where I've been combining physical constants, in various unit systems, into 1/137, ever since. It's a tough life but I'm good at what I do.

Huh? It's a photon-photon collider. We collide photons with photons. So then we know that photons interact with photons to create electrons and positrons. Duh!
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I'm sorry, I have been talking at you as though you'd seen a Feynman diagram at some point in your life. I guess I was wrong; it is impossible for someone who is even recognizes Feynman-diagram-language to write the sentence Farsight just wrote.

How low do we have to go? You don't know unit systems, you don't know what a vector is, you don't know what a linear equation is, now you don't know what a vertex is?
 
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Farsight said:
So do you see the problem yet? It doesn't offer any QUALITATIVE understanding.
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Crackpot index item #17. 10 points!

I disagree with you. Personally, I find QED and the Standard Model offers a terrific qualitative and intuitive understanding of particles, fields, and interactions. I have reasonably clear and grounded mental pictures, based in ordinary (and extremely familiar/intuitive/qualitatively-friendly) wave equations and Fourier transforms, of every quantity I write down in a QED calculation. I built that intuition while studying the math, so the math version and the mental-image-rich qualitative version coexist in everything I have to write down. "OK, there's the conserved fermion 4-current, and there's the other conserved fermion 4-current, and there's the Fourier transform of the interacting fields expressed in the free-particle basis".

It's so intuitive, in fact, that it almost feels as though you could guess the rules of QED (up to some factors-of-2 and Dirac matrices and whatnot) because it's obvious that this is how quantum particles should behave. In truth, this is not far from what Feynman did---read his Nobel lecture for a narrative account. He started with intuition---"this is how these fields ought to behave, and why, given what we know from experiment"---and then stepped in and checked those guesses rigorously.

You don't get that? You look at QED and it looks like gibberish? Of course it does. You barely know what QED is talking about. Of course you don't find a "qualitative understanding" in there, nor a quantitative one, nor anything useful at all. You never learned it. You never even learned the language in which to describe it.
 
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I want to comment on Farsight's apparent belief that "quantitative" stuff can be completely ignored in favor of "qualitative" discussion. This is wrong.

A theorist takes his theory, winds up the mathematical machinery, and out pops a number. Let's say that you turn the QED cranks on the machinery related to the "electron magnetic moment". This involves doing a certain pile of combinatorics on a large set of Feynman diagrams, then turning that set into a series expansion. This expansion spits out the sum:

g = 2.00231930419922

Now, if the theory is genuinely wrong, that's just a random nonsense number. If the theory is wrong, the combinatorics were meaningless, the method for making a series out of them was gibberish, the idea of summing the series was just a joke, so of course if the theory is wrong the result bears the same relationship to reality as so many coinflips.

You then go out into Nature and measure g in an experiment. How likely is it, do you think, for the experiment to happen to spit out the (purportedly) totally random number

g = 2.00231930419922

The odds of that happening by luck (i.e., the odds of a wrong theory making the right prediction to 15 digits) is about one in a quadrillion. On the other hand, the odds of the right theory making the right prediction is, y'know, pretty good.

Do you see why this makes QED look like a good theory? It didn't get the right answer by random chance; it got the right answer because whatever physics nature is using must bear some very close relationship with the math the QED guys wrote down.

It's strange to want to categorically "ignore math" when the math seems to be such a strong weapon for discarding random false theories.

But that's exactly what Farsight is doing.

Also, Farsight has a theory he hasn't written down yet, which he hopes will someday produce a calculation which is not the QED combinatorics nor the QED power series nor the QED summation ... but he's betting that this totally different calculation will happen to spit out an electron magnetic moment of:

2.00231930419922

just like the QED calculation did. Wow, that's quite a long-odds bet; it's like winning two consecutive Powerball jackpots. Very strange thing to bet on.

Oh, and of course QED has correct predictions of the electron magnetic moment (15 digits), muon magnetic moment (11 digits), Lamb shift (6 digits), dozens of parameters related to e+e- scattering, etc. etc. etc. What an extraordinary coincidence for a totally random BS theory to spit out those numbers correctly, over and over and over, isn't it? How do you work it out that this agreement is totally meaningless and worth ignoring?

In what other fields of science is that the accepted practice---ignore experiment/theory agreement, place your bets on one guys who can draws arrows on ping-pong balls but can't do calculations?
 
Farsight said:
I think there's a widely-shared misunderstanding of QED and the Standard model that will be corrected. Photons interact with photons.
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Farsight, it is your repeated failure of reading comprehension that is the issue and needs correcting:
QED and Maxwell's equations state that photons cannot interact directly.
QED allows photons to interact indirectly which is observed.
 
Farsight said:
No. He said nobody understood why it works.
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You are still wrong (and essentially lying about what Feynman said), Farsight.
Reality Check said:
Feynman said "On the other hand, I think I can safely say that nobody understands quantum mechanics" and that it explains a lot (how electrons and photons behave) :jaw-dropp.
Introduction to the Quantum Mechanics lecture in The Messenger Lectures, 1964, MIT
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There is no "why it works" in the quotation.

What Feynman says is
* This is how nature behaves
* This is explained by QM
* Asking "But how can it be like that?" is not productive.

Feynman did not say "QED didn't say enough about the underlying reality" in that quote. I suspect that he would say that that what we observe is the actual reality, QM matches what we observe and thus QM is the underlying reality (until a better theory than QM comes along).
 
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Farsight: Do photons have direct interactions with each other

Farsight said:
But I do have a better understanding of QED than you.
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But the evidence is that you have no knowledge of QED, Farsight, other than misconceptions built on misreading Wikipedia articles :jaw-dropp!
You asserted on 25th May 2014, that
Farsight said:
Photons do have direct interactions with each other.
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But QED states that you are wrong:
Two photon physics: photons cannot couple directly to each other

But in case you have learned any classical or quantum electrodynamics in the last 3 days:
Farsight: Do photons have direct interactions with each other?
 
What I meant to add to the above post: theory/experiment agreement doesn't mean that you have the right theory. It means, almost certainly, that you have a theory which generates the same math as the right theory. It's like: the Bohr atom model was not the right model, but its answers depend mainly on its angular-momentum quantization, and on a wave equation with QM-like dimensional-analysis scaling factors. Those two features are present in the correct theory (Schrodinger's) which is why the almost-true theory and the actually-true theory give the same equations. Not just the same numbers, the same equations.

The equations that QED spits out, using Feynman's methods, are the equations of the combinatorics of virtual particle path integrals. QED spits out exactly the same equations if you follow Schwinger's method, in which case the combinatorics-like terms come from chain rules and commutators generated by field operators. The resulting equation, evaluated in terms of experimental predictions, is verifiably correct.

How do you want your system to work, Farsight? Do you expect your ideas, when converted into a real predictive model, to spit out the same equations as QED? (What makes you think that? Where will the "combinatoric" terms come in? Or have you proven that the series is convergent? Quite a trick if true!) Or do you think your ideas, converted into math, will give a totally different equation that will spit out g = 2.00231930419922, with all digits in place, as the electron g-factor? (Also quite a remarkable trick. How do you know this is true? How many digits have you verified so far?)

(Or, more correctly: those are the questions I'd ask a physicist with a theory like yours. You, Farsight, are not a physicist, don't do math, don't compare theories to experiments, and don't care what QED says on principle.)
 
ben m said:
...Personally, I find QED and the Standard Model offers a terrific qualitative and intuitive understanding of particles, fields, and interactions...
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So, explain to the guys what happens in gamma-gamma pair production.

Take your time. In your own words.

This is going to be fun.

Click-click. Pull!
 
Farsight said:
Duh, no the elephant in the room is that it's a photon-photon collider and you're saying photons don't interact. I'm not deeply confused at all.
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Yes, you are deeply confused. The standard model says that there's no direct interaction, and so does Maxwell's equations. But the standard model also says that there is an indirect interaction, which is why the standard model does predict that a photon-photon collider will produce particles. But unlike your "model", it can actually tell me how many particles it will produce. You can't. Why would I pick a model which can't make any quantitative predictions over a model which can not only produce quantitative predictions, but accurate quantitative predictions? The answer is obvious: only a fool would choose the former over the latter.

Oh...
 
Ziggurat said:
Yes, you are deeply confused. The standard model says that there's no direct interaction, and so does Maxwell's equations. But the standard model also says that there is an indirect interaction, which is why the standard model does predict that a photon-photon collider will produce particles. But unlike your "model", it can actually tell me how many particles it will produce. You can't. Why would I pick a model which can't make any quantitative predictions over a model which can not only produce quantitative predictions, but accurate quantitative predictions? The answer is obvious: only a fool would choose the former over the latter.

Oh...
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Quantitative predictions? Why would anyone do that when one can write a book and pontificate by using pretty pictures, using sciency words, quoting Einstein and Maxwell and remaining ignorant of actual physics?
 
Farsight said:
SLAP! Wake up! It's a diagram. It isn't reality. The vertex isn't actually there. Capiche? There is no magical mysterious creation of an electron-positron pair from a single photon. There is no interaction between the other photon and an electron. Two photons interact. In a photon-photon collider. Have you got that yet?
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It's true that the diagram isn't an exact depiction of reality. It's a tool that facilitates the construction of the calculation for a specific circumstance. However, there is not just one diagram that goes into the calculation - there's a whole series. If the interaction is not indirect through the fields of other particles, why does the calculation give the right answer when you consider all those terms involving those other particles?
 
Farsight said:
...

All: here's the reportage:

"Matter will be created from light within a year, claim scientists
In a neat demonstration of E=mc2, physicists believe they can create electrons and positrons from colliding photons"

See where it says colliding photons? Photons interact with photons. Get used to it. Strewth!
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Why would anyone rely on QED or listen to the opinion of actual physicists when one has Ian Sample, science correspondent of The Guardian?
 
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Farsight said:
Sure. It's really simple. We've been talking about a photon-photon collider where photons interact. And yet here we have the usual-suspect feather-spitting ignorant naysayers defending the orthodoxy that says QED tells us that photons don't interact along with pair production occurs because pair production occurs. And here's you, you don't understand QED in the slightest, but you side with the patent nonsense. Duh!

All: here's the reportage:

"Matter will be created from light within a year, claim scientists
In a neat demonstration of E=mc2, physicists believe they can create electrons and positrons from colliding photons"

See where it says colliding photons? Photons interact with photons. Get used to it. Strewth!
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Hmm ... what does this 'reportage' say about QED, especially whether "QED tells us that photons don't interact" (your words)?

Copy/paste: "The process is one of the most spectacular predictions of a theory called quantum electrodynamics (QED) that was developed in the run up to the second world war. "You might call it the most dramatic consequence of QED and it clearly shows that light and matter are interchangeable," Rose told the Guardian."

So, on the one hand, there's you, telling readers of this thread that "QED tells us that photons don't interact".

On the other hand, there's the very document you cite saying that the production of electron-positron pairs, in an experiment in which photons will interact with each other, is "one of the most spectacular predictions of a theory called quantum electrodynamics (QED)".

Earlier in this thread there are posts, by different JREF members, explaining some details of this prediction.

There have also been several posts, by you, claiming that QED does not, and cannot, predict production of electron-positron pairs (in the experiment described).

As I read these various posts, an explanation of "the process" has been given (not by you, of course), with the offer to explain it in more detail should anyone be interested (or at least provide references to material where such greater detail may be read). However, your claim is bald; there are no details, no references, not even a hint at what might be wrong about the QED-based explanation of how electron-positron pairs may be created in this experiment.

Why is that? Why do you seem so reluctant to write about the relevant details of QED? For example, why do you not refer to the details of how the prediction is derived?
 
All: Why have I got two notifications? If I find that some JREF "moderator" is giving free rein to abuse directed at me whilst unfairly penalising and/or censoring me for standing my ground, I will take it further.

Ziggurat said:
Yes, you are deeply confused. The standard model says that there's no direct interaction, and so does Maxwell's equations. But the standard model also says that there is an indirect interaction, which is why the standard model does predict that a photon-photon collider will produce particles. But unlike your "model", it can actually tell me how many particles it will produce. You can't. Why would I pick a model which can't make any quantitative predictions over a model which can not only produce quantitative predictions, but accurate quantitative predictions? The answer is obvious: only a fool would choose the former over the latter.
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So, please clear up my confusion. Do photons interact with photons? Or in gamma-gamma pair production, do photons interact with electrons? Because if it's the latter, I am confused about how you distinguish between science and magick.

Perpetual Student said:
Why would anyone rely on QED or listen to the opinion of actual physicists when one has Ian Sample, science correspondent of The Guardian?
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Because some of those so-called "actual physicists" are cuckoo-in-the-nest naysayers whose physics knowledge is scant. And because there's plenty of other reportage on this turning light into matter news. Wherein photons interact with photons. In a photon-photon collider. To create electrons and positrons. One photons doesn't magically morph into an electron and positron which the other photon interacts with. Duh! Got it yet?


edd said:
It's true that the diagram isn't an exact depiction of reality. It's a tool that facilitates the construction of the calculation for a specific circumstance. However, there is not just one diagram that goes into the calculation - there's a whole series.
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Fair enough edd.

edd said:
If the interaction is not indirect through the fields of other particles, why does the calculation give the right answer when you consider all those terms involving those other particles?
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Because the "fields of the other particles" aren't separate fields, but are aspects of what you'd call the photon field. It's akin to the way the electric field and the magnetic field are aspects of the electromagnetic field. You can see a hint of this in the Wikipedia two-photon physics article:

"Thus, two-photon physics experiments can be used as ways to study the photon structure..."

Sadly it goes on to say "...or what is 'inside' the photon" and even "the intrinsic quark content of the photon". Ouch, that's not good. You can see another poor effort in an historic version of the article:

"...but half wavelength is a positive charge and the next half wavelength is a negative charge."

This is however making some progress in that the leading portion of a photon can be likened to a partial positron, and the trailing portion can be likened to a partial electron. Which makes "study the photon structure" sound better. Which reminds me of this animation. I wouldn't say it's ideal, but I like to encourage this sort of thing.
 
Pardon the amateur intrusion by one with only metaphorical access to QED via popular science.

My question: Did not the validity of QED play out in the extremely simple example of glass manufacturers learning to use exact thickness to control reflective properties?

I read Feynman's popular book on the subject many years ago, and this is my recollection of (faulty?) conclusions I made at the time.
 
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