Merged Relativity+ / Farsight

[thedopefishlives]

Exactly how will the photon-photon collider experiment prove that photons interact with each other? In what way will the results differ from the ones that ordinary QED predicts?

This is the question that I came here to ask. So, Farsight, say I hired some engineers and built a photon-photon collider. I attune the lasers to some wavelength (your choice) and let the beams fly. Exactly what should I expect my detectors to detect? If you cannot answer this question, then explain to me why I should listen to your theory as opposed to QED, which does answer this question?

ETA: I realize that you will disagree with my characterization of whatever it is you are presenting as "your theory", so instead of focusing on that, I would ask what "this theory" would predict (no matter to whom it ultimately belongs).

 

[lpetrich]

I don't have a problem talking about virtual particles.

Farsight, what you have a problem with, or else not have a problem with, is not a deciding factor. You are not a pope of physics.

I've referred to Matt Strassler's blog: where he says this:
"A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle".

Thump thump thump thump thump. Like a pile driver.

(similar quotes snipped for brevity)

This is what Daisie and Michael Radner, and also John Casti, have called research by exegesis or literary interpretation. It's how a theologian typically works.

I think there's a widely-shared misunderstanding of QED and the Standard model that will be corrected. Photons interact with photons. Photons couple with photons. Photons couple with themselves. And when they do, the thing you call the photon field becomes the thing you call the electron field.

Demonstrably false. That's making baby Richard Feynman cry.

Direct photon-photon interactions have been an unnecessary hypothesis, and there is no convincing evidence of such interactions. Indirect interactions are by way of virtual charged particles, and calculating with such interactions gets the right numbers.

You are lost in maths.

You won't get anywhere in physics with that attitude toward mathematics.

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.

Argument from etymology. As if there is no such thing as a misleading name.

I don't make mistakes.

LOL. Need I say more?

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.

This is a throwback to Aristotelian physics, which was all qualitative.

So do you see the problem yet? It doesn't offer any QUALITATIVE understanding.

Why does it have to?

I'm not some my-theory guy.

Irrelevant. If one advocates some theory, then one ought to accept responsibility for promoting it, and not try to evade criticism by whining "it's not my theory". Also, if it's not one's theory, then whose theory is it? For starters, links to search-engine results are NOT acceptable forms of reference.

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.

It's the latter, and it's a direct consequence of a perturbation expansion of QED. One treats free photons and charged particles as the unperturbed state and expands in powers of the photon-charged-particle interaction terms.

turning light into matter

Bzzzt. Link to search-engine results again.

One photons doesn't magically morph into an electron and positron which the other photon interacts with.

Why do you think it doesn't? Just because it seems totally absurd to you doesn't mean that it isn't true. Round-earthism has seemed absurd to some flat-earthers, for instance.

 

[Reality Check]

I've referred to Matt Strassler's blog: where he says this:

You do not have to keep quote mining the blog article to emphasize that lie about the blog contents, Farsight.
Virtual Particles: What are they?

The best way to approach this concept, I believe, is to forget you ever saw the word “particle” in the term. A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle. A particle is a nice, regular ripple in a field, one that can travel smoothly and effortlessly through space, like a clear tone of a bell moving through the air. A “virtual particle”, generally, is a disturbance in a field that will never be found on its own, but instead is something that is caused by the presence of other particles, often of other fields.

The fact remains that scientists use the term virtual particle to refer to "a disturbance in a field that is not a particle", has all of the properties of a particle but is "off-shell".

The inanity of relying on Matt Strassler's opinion as if it was religious text is that later he says that photons do spend time as virtual electrons and positrons:

Another example involves the photon itself. It is not merely a ripple in the electromagnetic field, but spends some of its time as an electron field disturbance, such that the combination remains a massless particle. The language here is to say that a photon can turn into a virtual electron and a virtual positron, and back again; but again, what this really means is that the electron field is disturbed by the photon. ...

But you, Farsight, say they do not !

 

[Reality Check]

And when they do, the thing you call the photon field becomes the thing you call the electron field.

The photon field is always the photon field.
The electron field is always the electron field.
And what does your latest prophet rolleyes say, Farsight.
Matt Strassler's blog

Another example involves the photon itself. It is not merely a ripple in the electromagnetic field, but spends some of its time as an electron field disturbance, such that the combination remains a massless particle.

He is talking about a single photon - no interaction with another photon possible!

Of course this could be your imaginary "Photons couple with themselves", i.e. photons act just as QED says they act - "couple" with themselves to split into virtual particles.

 

[Reality Check]

Missed this bit of ignorance:

I think it's because your physics degree was all maths. That's the usual thing. People spend three years doing maths, not physics.

Way to show that you know nothing about how physics is taught in universities, Farsight !
It might be possible (theoretically ) possible for someone to select BSc courses that only contained theoretical physics. For example they may have already selected a career in mathematical or computational physics. However any competent educator wild discourage this. Even someone heading for a career in theoretical physics needs some hands-on experience to relate the math to reality.

Each year that I spent gaining my degree involved experimental physics until my MSc which was all theory. I was a teaching assistant in the physics labs for one year.

ben m would have taken many experimental physics courses but more importantly he is a professional experimental physicist.

 

[Farsight]

Farsight, what you have a problem with, or else not have a problem with, is not a deciding factor. You are not a pope of physics.

No, not a pope, just the expert round here. I know far more physics than you and ben and zig put together. Your lack of physics knowledge is comical. Or should I say tragic.

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...So, Farsight, say I hired some engineers and built a photon-photon collider. I attune the lasers to some wavelength (your choice) and let the beams fly. Exactly what should I expect my detectors to detect...

Electrons and positrons. I'm not putting up "my theory", I'm saying the reality that underlies QED is not understood. Guys like lpetrich will tell you that photons don't interact with photons. In your photon-photon collider. Duh! And that you shouldn't listen to me. It's total nonsensical garbage from a bunch of naysayers defending an orthodoxy of ignorance that is nothing other than the science of stupid.

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...The inanity of relying on Matt Strassler's opinion as if it was religious text ...

Well, that's one way to dismiss the physics. And that's enough from you.

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Exactly how will the photon-photon collider experiment prove that photons interact with each other? In what way will the results differ from the ones that ordinary QED predicts?

1) You put photons in. They collide. With each other. Not with something else. 2) They won't. But people will appreciate that pair production occurs because photons interact with photons, not because pair production occurs. Spontaneously. Like worms from mud. Like magick. Woo!

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We've always been there, Farsight.

No you haven't. You're nowhere near. You're not even close.

Way to miss the point. The example was intended to illustrate the difference between a direct and an indirect interaction. It was not intended to show that photons are like balls.

It was rubbish. Care to "explain" an indirect interaction in a photon-photon collider?

Again, QED provides the correct quantitative answer for this experiment. Your "theory" provides no quantitative answer at all. Yet you want us to abandon QED in favor of your "theory". Why on earth would any sane person choose to do so?

Sigh. See above. I'm not putting up "my theory", I'm saying the reality that underlies QED is not understood. And I will also say this: no sane person would choose to claim that pair production occurs because a photon magically mystically morphs into an electron-positron pair. Now would they? But you would? It's comical, Ziggie. Or it would be if it wasn't so tragic.

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Objection! Assumes facts not yet in evidence.

You're right to object. Ask around about this. Ask if photons interact with photons. The answer you'll get from people like Ziggurat, who claim to be physics experts but aren't, will be no. If you challenge that he'll say you're insane. But photons do interact with photons. If they didn't, there wouldn't be any point in building a photon-photon collider. Now would there?

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I am the first to admit that my understanding of QED is far from good. However, with this response - thank you for it, by the way - I think I see the root cause of your confusion.

I am not confused at all. I have absolute crystal clarity.

Let's try this: using QED (and as much of the Standard Model as you need, that is not already in QED), can one make a prediction that electron-positron pairs will be produced in an experiment like the one described in the article you provided a link to? Is that prediction quantitative? Is it open to independent verification?

Yes, yes, yes.

If so, then you seem - to me - to be saying nothing other than that you don't like how this prediction is described, qualitatively.

You could say that. But it's more than that. I'm saying that QED is not understood. And that pair production is not understood. And the electron is not understood. Et cetera. Because "shut up and calculate" is not a substitute for understanding. Because we don't do physics to calculate. Instead we do it to understand the world. Something like that.

Have you, personally, on your own, checked the quantitative prediction? If so, is it correct (i.e. derived correctly, using QED)? If not, why not?

No. Because it's not the issue. The issue is how gamma-gamma pair production actually works and what the electron is, et cetera.

Accepting - provisionally - that the prediction is correct, and that it will be experimentally verified, how would you describe the relevant parts of QED, qualitatively?

It would take me too long to give you that, but I'd be referring to TQFT and electromagnetic geometry, and saying the electron field is a particular "configuration" of the photon field, that they are two aspects of the selfsame thing, and that virtual photons and virtual electrons are but "chunks" of field rather than actual particles.

 

[thedopefishlives]

Electrons and positrons. I'm not putting up "my theory", I'm saying the reality that underlies QED is not understood. Guys like lpetrich will tell you that photons don't interact with photons. In your photon-photon collider. Duh! And that you shouldn't listen to me. It's total nonsensical garbage from a bunch of naysayers defending an orthodoxy of ignorance that is nothing other than the science of stupid.

Swing and a miss. You have given me no reason to believe you (if you don't want me to call it "your theory", fine, but you are the one espousing it) over against QED, because QED also predicts "electrons and positrons" and, in addition, tells me how many I can expect. The prediction made by QED is superior to the one made by this theory, and since the experimental evidence matches the predictions made by both theories (including the more detailed ones from QED), I choose the theory with the superior predictive power. Thanks for playing.

 

[Farsight]

Nope! As usual, you're wrong wrong wrong. I was on the committee, years ago, supervising an undergrad thesis on this topic (knotted light)... It's just a propagating laser beam with a funny-looking intensity/polarization profile. No interactions. None...

Get off your high horse with your straw-man argument. I referred to some bona-fide physics articles. And look at what you said to Hlafordlaes:

Photon-photon elastic scattering *would* cause scattering in a "room full of light", but when the photon energy is low, then the cross section is ultra-ultra-low... The cross section increases when you're dealing with higher-energy photons; I think it depends on (photon energy / electron mass)^4. When you get to photons above the electron mass, a new final state becomes accessible: gamma+gamma --> electron+positron.

As for you, weren't you linking a few posts ago to the proposal to observe light-light interaction for the first time using ultrapowerful lasers? Doesn't it ring the slightest alarm bells to claim, a few posts later, that light-light scattering was observed in 2010? Not only do you think they discovered it in 2010, you must think the discovery was so uncontroversial that they didn't mention it in the press release so you have to read between the lines.

Oh spare me the feather-spitting squawk of puffed-up outrage. No. Because I've already referred to the SLAC experiments in 1997. Go read what I said. And don't think for one minute that a photon-photon interaction somehow turns on like some magic switch once you exceed some particular energy.

It's also possible that, Farsight being new to this, there's a horrible difference of terminology at work.

Only I'm not new to this. And I am a stickler for terminology.

Farsight, ordinary wave interference is not what a physicist would call "a particle interacting with itself"; interference of two waves, as in diffraction, or a double-slit experiment, or whatever, is not evidence of an interaction.

No problem. We're all familiar with the way waves can cancel or reinforce one another. And how they can ride over one another and keep going.

It's just a linear wave equation. The word "interaction" is used when something else is going on, something that can't be described by a superposition of plane wave solutions. It just occurred to me that this might be one of your confusions, and I don't want to get dragged into a 10-page argument about whether the double-slit experiment is "evidence" that photons "interact". It's not, it's evidence that photons obey a wave equation.

No, I'm not confused. In photon-photon interactions the waves don't just ride over one another and keep going. In simple terms: they displace one another, curling each other up such that each is forever moving through itself displacing its own path into a chiral closed path. Only then we don't call them photons any more.

OK, Farsight, here are the electromagnetic field tensor components for a pair of photon beams (one of amplitude A, frequency w, one of amplitude B, frequency n... Go ahead, do the math...

Groan. You're totally barking up the wrong tree. You have no concept of electromagnetism whatsoever. How many times do I have to tell you it's one field? Start again. A photon has an energy E=hf where h is Planck's constant of action and f is frequency. One way to state the dimensionality of action is momentum x distance. OK? Now take a look at some pictures of the electromagnetic spectrum. Look at the waveform. Look at the amplitude of that waveform. Well lummee, it's the same for all photons. But we can only make 511keV electrons. Let's see now, why might that be? Come on, give an answer instead of getting lost in maths when you don't even understand the terms.

 

[lpetrich]

No, not a pope, just the expert round here.

Farsight, your "expertise" on physics seems much like the "expertise" of creationists on evolution.

I know far more physics than you and ben and zig put together. Your lack of physics knowledge is comical. Or should I say tragic.

What "lack of physics knowledge"?

And I will also say this: no sane person would choose to claim that pair production occurs because a photon magically mystically morphs into an electron-positron pair. Now would they? But you would? It's comical, Ziggie. Or it would be if it wasn't so tragic.

Farsight, you ought to read Lactantius, Divine Institutes 3.24. He had exactly your approach to this issue, rejecting round-earthism because everything on the antipodes would be upside down, something he considered to be totally absurd.

But photons do interact with photons. If they didn't, there wouldn't be any point in building a photon-photon collider. Now would there?

They don't interact directly, but instead indirectly, through virtual electrons and other such particles.

It would take me too long to give you that, but I'd be referring to TQFT

Without any effort to demonstrate that electric charge is a topological invariant like winding number.

electromagnetic geometry

Yawn. Another search-engine result link.

 

[lpetrich]

No, I'm not confused. In photon-photon interactions the waves don't just ride over one another and keep going. In simple terms: they displace one another, curling each other up such that each is forever moving through itself displacing its own path into a chiral closed path. Only then we don't call them photons any more.

The only way that can happen is if the photon self-interaction energy was comparable to its kinetic energy. That is an effect that has yet to show up in experiments.

OK? Now take a look at some pictures of the electromagnetic spectrum.

Bzzzt again. Another search-engine result page.

Look at the waveform. Look at the amplitude of that waveform. Well lummee, it's the same for all photons.

That's lame literal-mindedness that would make a fundie proud.

 

[edd]

Phoooey. You don't have the willpower to admit that I gave you a fair answer in this post, or admit that I'm right about the photon-photon interaction.

You're basically claiming that the electron field is actually an aspect of the photon field. Presumably all the other particle fields are also the same (if not, perhaps you'd like to list which ones aren't). None of this is what QED or the standard model says, and your claim that if we understood it better we'd see that is quite untrue.

 

[jhunter1163]

If LaTeX rendering were still enabled, I would draw you all a function showing that as the level of bickering rises in a given thread, the probability of infractions and suspensions tends towards 1. As it is, I will give you an official warning not to personalize your arguments and remain civil and polite. Thank you for your anticipated cooperation.

Replying to this modbox in thread will be off topic  Posted By: jhunter1163

 

[Farsight]

You're basically claiming that the electron field is actually an aspect of the photon field. Presumably all the other particle fields are also the same (if not, perhaps you'd like to list which ones aren't). None of this is what QED or the standard model says, and your claim that if we understood it better we'd see that is quite untrue.

I'm basically claiming that photons interact with photons. And that if they didn't, there wouldn't be much point building a photon-photon collider. And that people who say they don't interact find themselves in a hole and try to save face by saying photons don't interact directly with photons. But it doesn't do them any good. Because photons either interact with photons, or they don't.

Now, is there anybody who still thinks photon-photon pair production occurs because one of the photons mysteriously turns itself into an electron and a positron with which the other photon interacts? Only if it misses, the electron and that positron magically morph back into a single photon that mystically managed to keep on going at the speed of light?

Anybody?


thedopefishlives: I knocked this one out of the park.

 

[Roboramma]

I'm basically claiming that photons interact with photons. And that if they didn't, there wouldn't be much point building a photon-photon collider. And that people who say they don't interact find themselves in a hole and try to save face by saying photons don't interact directly with photons. But it doesn't do them any good. Because photons either interact with photons, or they don't.

So far, as far as I can see, not a single person has said that photons don't interact. They have said that they don't interact directly.

I have some visitors in Shanghai at the moment who don't speak Chinese. When I take them around I help to translate what they are saying to others, and then translate the replies back. Yes, they are interacting with those people, but not directly, because they don't have a mutually understood language.

Others (ben m for instance), have pointed out that according to the mathematics of QED there is no direct photon-photon interaction, but there is an interaction through the intermediary of virtual particles. That you think this isn't actually true of the real world doesn't mean it's not true of the theory, and given that the theory makes testable predictions, it also works, which means that it's at least consistent with the real world.

Your not liking it doesn't change any of that.

 

[thedopefishlives]

Begging your pardon, but no, you did not. If you don't have direct knowledge of what this theory you're promoting predicts as far as the actual expectations of photon-photon interaction, then say so, and then direct me to where I can find this information. If "electrons and positrons" is the best answer the theory you're promoting can give me, then it is an inferior theory; it only gives "qualitative" information, whereas QED gives both "qualitative" and "quantitative" information.

 

[Perpetual Student]

I'm basically claiming that photons interact with photons. And that if they didn't, there wouldn't be much point building a photon-photon collider. And that people who say they don't interact find themselves in a hole and try to save face by saying photons don't interact directly with photons. But it doesn't do them any good. Because photons either interact with photons, or they don't.

Now, is there anybody who still thinks photon-photon pair production occurs because one of the photons mysteriously turns itself into an electron and a positron with which the other photon interacts? Only if it misses, the electron and that positron magically morph back into a single photon that mystically managed to keep on going at the speed of light?

Anybody?




thedopefishlives: I knocked this one out of the park.

You keep missing the point. We all know that the quantum world defies our macro-world intuition, but the key point is that it makes exquisitely accurate quantitative predictions. Your photon-photon interaction picture may satisfy the simpleminded; however, without quantitative predictions it is utterly useless. QED is a successful theory because it describes and predicts behavior accurately; in contrast, you've got nothing! Welcome to the real world of physics.

 

[ferd burfle]

Electrons and positrons. I'm not putting up "my theory", I'm saying the reality that underlies QED is not understood. Guys like lpetrich will tell you that photons don't interact with photons. In your photon-photon collider. Duh! And that you shouldn't listen to me. It's total nonsensical garbage from a bunch of naysayers defending an orthodoxy of ignorance that is nothing other than the science of stupid

For those of you keeping score at home, here we have numbers 17 and 28, for a combined score of 30 points.

http://math.ucr.edu/home/baez/crackpot.html

ETA: Farsight, I am not calling you a crackpot but when your arguments can be found on this list you might want to consider a different approach.

 

[steenkh]

1) You put photons in. They collide. With each other. Not with something else. 2) They won't.

So you admit that your theory is indistinguishable from real science? That is interesting.

But people will appreciate that pair production occurs because photons interact with photons, not because pair production occurs. Spontaneously. Like worms from mud. Like magick. Woo!

I think people will appreciate that real science can make quantitative predictions that you cannot. In other words, your ideas are worthless.

 

[ben m]

Relativity+ / Farsight's thread

And don't think for one minute that a photon-photon interaction somehow turns on like some magic switch once you exceed some particular energy.

I didn't say it does. I said the cross section scales as something like (E/me)^4. Not a magic switch, just a standard QED prediction. The weak interaction does the same sort of thing.



(I "asked around", as you suggested so helpfully, and I can correct my "something like" to the actual QED prediction: the scaling is E^6/me^8 when E

 

[Farsight]

So far, as far as I can see, not a single person has said that photons don't interact. They have said that they don't interact directly.

OK, so do photons interact with photons or not? Yes or no?

I have some visitors in Shanghai at the moment who don't speak Chinese. When I take them around I help to translate what they are saying to others, and then translate the replies back. Yes, they are interacting with those people, but not directly, because they don't have a mutually understood language.

Robo, spare me the lame analogy. We've been talking about a photon-photon collider. Not a photon-Robo collider.

Others (ben m for instance), have pointed out that according to the mathematics of QED there is no direct photon-photon interaction, but there is an interaction through the intermediary of virtual particles. That you think this isn't actually true of the real world doesn't mean it's not true of the theory, and given that the theory makes testable predictions, it also works, which means that it's at least consistent with the real world.

Sigh. In the real world we'll have something called a photon-photon collider. A photon-photon collider. Not a photon-virtual particle collider. Those virtual particles are virtual. They aren't real particles. Geddit? Uhhnnnn, don't tell me, you think virtual particles are short-lived real particles that pop into existence. Like magic. Then pop, more magic. Uhhhnnnn, it's like that movie.

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Begging your pardon, but no, you did not blah blah whine whine squeak squeak.

Oh, yes I did. BENGGGG! Out-of-the-paaaaaark.

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You keep missing the point. We all know that the quantum world defies our macro-world intuition...

It only defies our macro-world intuition when you cling to the science of stupid and mince around bleating that it surpasseth all human understanding.

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For those of you keeping score at home, here we have numbers 17 and 28, for a combined score of 30 points.

http://math.ucr.edu/home/baez/crackpot.html

ETA: Farsight, I am not calling you a crackpot but when your arguments can be found on this list you might want to consider a different approach.

Who are you? Everybody who knows anything about physics knows that Baez's crackpot index doesn't have a readout. So you don't know if you're Einstein, leading edge, maverick, slightly weird, or raving. And everybody also knows that the later questions get nasty, just like the people who refer to it instead of talking physics. Troll.

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So you admit that your theory is indistinguishable from real science? That is interesting... I think people will appreciate that real science can make quantitative predictions that you cannot. In other words, your ideas are worthless.

Yeah, well I think people will appreciate that photons interact with photons, and that you're just another po-faced naysayer who doesn't know any physics.

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I didn't say it does. I said the cross section scales as something like (E/me)^4. Not a magic switch, just a standard QED prediction. The weak interaction does

We'll come onto the weak interaction some other time.

(I "asked around", as you suggested so helpfully, and I can correct my "something like" to the actual QED prediction: the scaling is E^6/me^8 when E << me.)

Yeah, whatever. Now, let's see if you've learned anything today. Do photons interact with photons? Yes or no? Here's a clue: photon-photon collider.



Now, is there anybody who still thinks photon-photon pair production occurs because one of the photons mysteriously turns itself into an electron and a positron with which the other photon interacts? Only if it misses, the electron and that positron magically morph back into a single photon that mystically managed to keep on going at the speed of light?

Anybody?