Merged Relativity+ / Farsight

[Ziggurat]

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.

Beats me. I never complained.

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.

You are indeed confused. But that, ultimately, is your problem, not mine.

Photons interact indirectly with other photons. I'll give you a simple example. Suppose you have two balls, A and B, and you tie each of them to different ends of a spring. The two balls are coupled to each other, and if you shake one of them, it will make the other ball shake because of that coupling (or "interaction").

Suppose you take a third ball C, tie it to the end of a second spring, and tie the other end of that second spring to ball B. Now ball B and ball C will interact with each other. If you shake ball B, then ball C will shake as well.

Now, do ball A and ball C interact with each other? Yes, they do: if you shake ball A, that will make ball C shake. Do they interact directly, that is, is there a spring tied between ball A and ball C? No, there is not. If you shake ball A, then the direct interaction between A and B will make B shake, and the direct interaction between B and C will then make C shake. The interaction between A and C exists, but it is indirect, it requires ball B to act as an intermediary.

Photons interact with each other, but not directly.

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?

You keep accusing other people of not knowing physics, and claiming that you do. And yet, these other people can actually predict the correct quantitative answer, while you cannot.

Physics. You keep using that word. I do not think it means what you think it means.

 

[Farsight]

...If I understand correctly, what they try to do is predicted by QED and is not a direct interaction between 2 photons...

Sorry mate. You've stumbled into an argument wherein some people say that QED says that photons don't interact with photons. I'm saying they do, that the photon-photon collider experiment will prove it, and that some people misunderstand what QED says.

...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...

You have confused yourself. See above, and try reading back through the thread, starting from post #1713 on page 43. Note that we've been talking about a photon-photon collider, and that lpetrich said this: Photons don't have direct interactions with each other. Period. Full stop.. Then I said photons do have direct interactions with each other. Then ben m said Not according to Maxwell's Equations. Nor according to QED. Not according to the Standard Model of Particle Physics. They defend the orthodoxy that photons don't interact with photons, and therefore that photon-photon pair production occurs because one of the photons magically spontaneously morphs into an electron and a positron. It's a tautology. It's a nonsense.

 

[Kwalish Kid]

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.

It is a sad feature of this board that they seem to misunderstand the relationship between argument and arguer.

In the case of Farsight, he is not offering an argument in anything but the most basic sense that he is offering a collection of sentences, one (or more) of which is purported to be a conclusion supported by the other sentences. However, Farsight is not offering an argument in the sense that he is presenting this supposed support in good faith. That is, he is not actually engaging in producing evidence, he is merely engaging in presenting what superficially appears to be evidence. When asked for further clarification, he merely reacts obfuscation, often through attacking the character of the questioner.

This is an observation germane to a discussion of Farsight's argument. That is, it is a comment about the pattern of argument presented and its content, even though it is identifying Farsight's behaviour in this argument. This is similar to identifying a collection of dark energy in the Bullet Cluster: one can identify the patterns and reasonably attribute the patterns to a cause not necessarily apparent in one particular observation.

However, I suspect that this board still does not support this analysis of arguments. So be it.

So, please clear up my confusion. Do photons interact with photons?

This is a great example of a question that Farsight has asked many people and that many people have given him a straight answer. Here, for example, is a great one, though I'm sure this board has many as well: http://www.thephysicsforum.com/high...5908-turning-light-into-matter.html#post14107 However, Farsight has ignored these straight answers, and he will undoubtedly ignore this one because it relies too heavily on the actual physics as practiced.

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.

Farsight may be a singular example of the Clarke idea that a sufficiently advanced technology is indistinguishable from magic; that is, Farsight may be so muddled that he cannot actually see science at work. This is tragic, but it need not encourage people to granting him charity that he does not deserve in the face of his insults and deceptive activity.

 

[ctamblyn]

...
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.
...

We've been waiting for evidence for this claim of yours - that all fundamental particles are somehow excitations of the electromagnetic field - since this thread started, almost four years ago. Do you ever plan to cast your theory in a form which can be compared quantitatively with experiment?

Also, since you've returned to this thread, I'll remind you that I'm still waiting for answers to this and the last three points in this.

 

[Farsight]

...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?

The validity of QED isn't the issue, the interpretation is. Feynman said "it works, but nobody knows why it works". You can see a reference to that at the end of this. Hence this little contretemps about whether photons interact. I say they do. Other people say QED says they don't and find they've dug themselves into a hole, because we're talking about a photon-photon collider.

 

[Farsight]

Photons interact indirectly with other photons.

So photons interact with photons. Good. We're getting there.

I'll give you a simple example. Suppose you have two balls, A and B, and you tie each of them to different ends of a spring. The two balls are coupled to each other, and if you shake one of them, it will make the other ball shake because of that coupling (or "interaction").

Really, this is a rubbish example. Photons aren't balls on springs, they have an E=hf wave nature.

Suppose you take a third ball C, tie it to the end of a second spring, and tie the other end of that second spring to ball B. Now ball B and ball C will interact with each other. If you shake ball B, then ball C will shake as well.

It gets worse.

Now, do ball A and ball C interact with each other? Yes, they do: if you shake ball A, that will make ball C shake. Do they interact directly, that is, is there a spring tied between ball A and ball C? No, there is not. If you shake ball A, then the direct interaction between A and B will make B shake, and the direct interaction between B and C will then make C shake. The interaction between A and C exists, but it is indirect, it requires ball B to act as an intermediary.

Uhhn. It's a trash analogy. We're not getting there, are we?

Now, let's try it another way. You have a photon-photon collider. You put photons in. You get electrons and positrons out. Now, in this photon-photon collider, what are the photons interacting with?

Duh!

 

[MRC_Hans]

Deleted

 

[Hlafordlaes]

The validity of QED isn't the issue, the interpretation is. Feynman said "it works, but nobody knows why it works". You can see a reference to that at the end of this. Hence this little contretemps about whether photons interact. I say they do. Other people say QED says they don't and find they've dug themselves into a hole, because we're talking about a photon-photon collider.

Thank you for your response. Indeed, I find quite a few articles on Nature Photonics hinting at the possibility of a photon-photon collider, and light into matter.

Where I buck against the idea is ~ again, with my simple understanding ~ how could massless particles ever collide? Seems an oxymoron. Would that not produce reactions in a room full of light going in many directions? Has this effect ever been observed?

(I'll stop soon and not interrupt those more knowledgeable; curiosity has the best of me for the passing moment.)

 

[Farsight]

There's things like physicists tie light in knots and tying light in knots. The photons don't so much "collide" like billiard balls, they interact with each other, or with themselves, because of their wave nature.

 

[ben m]

Where I buck against the idea is ~ again, with my simple understanding ~ how could massless particles ever collide? Seems an oxymoron. Would that not produce reactions in a room full of light going in many directions? Has this effect ever been observed?

Nothing oxymoronic about it.

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 (i.e., much less than the electron rest energy). It can happen in principle, but with an event rate of zero in any practical experiment. A photon/photon elastic scatter at 3 eV has a lower cross section than virtually anything you can think of---solar neutrinos reactions, for example, have HUGE cross sections (on anything, including other neutrinos) compared with photon-photon elastic scattering.

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. That reaction, when allowed, has a cross section comparable with ordinary Compton scattering! (But those aren't the energies you're dealing with in an ordinary "roomful of light")

 

[ben m]

There's things like physicists tie light in knots and tying light in knots. The photons don't so much "collide" like billiard balls, they interact with each other, or with themselves, because of their wave nature.

Nope! As usual, you're wrong wrong wrong.

I was on the committee, years ago, supervising an undergrad thesis on this topic (knotted light). I actually asked the student this specific question---"Wow, it looks like there's something nonlinear going on"---thinking that there was a nonlinear medium involved. The student assured me that that was not the case, it was just a funny initial condition for 100% linear wave equations, and that they were searching for better visualization tools in order to avoid making this mis-impression.

The "knots" are just a description of the complicated intensity/polarization maps in these beams. THERE ARE NO LIGHT-LIGHT INTERACTIONS HERE. It's just a propagating laser beam with a funny-looking intensity/polarization profile. No interactions. None.

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.

ETA:

Laser beams: Knotted threads of darkness

Jonathan Leach1, Mark R. Dennis2,3, Johannes Courtial1 & Miles J. Padgett1

Abstract
Destructive interference may lead to complete cancellation when light waves travelling in different directions cross, and in three-dimensional space this occurs along lines that are vortices of electromagnetic energy flow. ... A direct consequence of the linearity of Maxwell's equations for the electromagnetic field is that the intensity pattern in free space is static, so our optical vortices are stable in both space and time.

No interactions, just wave interference. No nonlinearities, just Maxwell's equations. Like I said.

 

[ben m]

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

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. 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.

 

[Ziggurat]

So photons interact with photons. Good. We're getting there.

We've always been there, Farsight.

Really, this is a rubbish example. Photons aren't balls on springs, they have an E=hf wave nature.

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.

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?

 

[Hellbound]

Yet you want us to abandon QED in favor of your "theory". Why on earth would any sane person choose to do so?

Objection!

Assumes facts not yet in evidence.

 

[DeiRenDopa]

You have confused yourself. See above, and try reading back through the thread, starting from post #1713 on page 43. Note that we've been talking about a photon-photon collider, and that lpetrich said this: Photons don't have direct interactions with each other. Period. Full stop.. Then I said photons do have direct interactions with each other. Then ben m said Not according to Maxwell's Equations. Nor according to QED. Not according to the Standard Model of Particle Physics. They defend the orthodoxy that photons don't interact with photons, and therefore that photon-photon pair production occurs because one of the photons magically spontaneously morphs into an electron and a positron. It's a tautology. It's a nonsense.

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.

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?

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

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?

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

 

[steenkh]

Sorry mate. You've stumbled into an argument wherein some people say that QED says that photons don't interact with photons. I'm saying they do, that the photon-photon collider experiment will prove it, and that some people misunderstand what QED says.

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?

 

[Reality Check]

Sorry mate. You've stumbled into an argument wherein some people say that QED says that photons don't interact with photons.

Sorry, MetalPig , but you have stumbled on a argument where Farsight is writing misinterpretations that stray close to lies.
No one here is saying that photons don't interact with photons.
Everyone except Farsight is saying that QED says that photons don't interact directly with photons.
Everyone is saying that QED says that photons can interact indirectly with photons via transforming into virtual particles. Farsight denies that photons can form virtual particles but does not realize that he is denying that photons interact even indirectly!

Farsight has said that photons do interact directly with photons which does not happen in either Maxwell's equations (classical electromagnetism) or QED.
See: Farsight: Do photons have direct interactions with each other?
Asked 28 May 2014.

The rest of his reply is a repeat of that inability so far to understand that photons do not directly interact in physics (no charge = no EM forces between them ) and that QED allows them to indirectly interact.

 

[Reality Check]

The validity of QED isn't the issue, the interpretation is. Feynman said "it works, but nobody knows why it works".

Farsight - Feynman did not say that imaginary quote.
Feynman said "On the other hand, I think I can safely say that nobody understands quantum mechanics"
If you want to paraphrase what he said then it would be 'it works but it is useless to ask how can it be like that' (single quote to emphasize that this is not an actual quote !).

P.S. Farsight: What is the charge of a photon? What does this mean for Maxwell's equations for the interaction between two photon?
First asked 27 May 2014

 

[Reality Check]

A photon–photon collider in a vacuum hohlraum

The ability to create matter from light is amongst the most striking predictions of quantum electrodynamics. Experimental signatures of this have been reported in the scattering of ultra-relativistic electron beams with laser beams1, 2, intense laser–plasma interactions3 and laser-driven solid target scattering4. However, all such routes involve massive particles. The simplest mechanism by which pure light can be transformed into matter, Breit–Wheeler pair production (γγ′ right arrow e+e−)5, has never been observed in the laboratory. Here, we present the design of a new class of photon–photon collider in which a gamma-ray beam is fired into the high-temperature radiation field of a laser-heated hohlraum. Matching experimental parameters to current-generation facilities, Monte Carlo simulations suggest that this scheme is capable of producing of the order of 105 Breit–Wheeler pairs in a single shot. This would provide the first realization of a pure photon–photon collider, representing the advent of a new type of high-energy physics experiment

is saying that photon-photon interactions producing massive particles has already been observed. Their proposal would create Breit–Wheeler pairs (electron + positron) from photon-photon interactions.

Evidence of photon-photon interactions has already been seen as in the Wikipedia article that Farsight has cited many times !
Two-photon physics

Experiments
Two-photon physics can be studied with high-energy particle accelerators, where the accelerated particles are not the photons themselves but charged particles that will radiate photons. The most significant studies so far were performed at the Large Electron–Positron Collider (LEP) at CERN.

and in the references in the above paper.

 

[ben m]

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, with y-axis linear polarization) aimed at each other starting at t=0. It's the incoming beams of a photon collider!

E(x,y,z,t) = {0, A*sin(-kx - wt) + B*sin(mx - nt) , 0}
B(x,y,z,t) = { 0,0, A/c*sin(-kx - wt) - B/c*sin(mx - nt) }

where wavenumbers are k = w/c, m=n/c, w and n are frequencies in rad/s, A and B are amplitudes in V/m.

Uh oh! By writing it this way I have neglected to include "photon-photon scattering". According to you, this is wrong---there should have to be a nonzero-amplitude waves emerging in the y and z directions, and Maxwell's Equations should tell me so. If you are right, i.e. if Maxwell's Equation include photon-photon scattering, this would be an approximate solution but not an exact one. If you are right, the correct solution must include both the incoming beams and their off-x-axis scattered output.

So, what a great opportunity to show off. Go ahead, I've handed you an equation that you claim, citing your extra-special non-math intuition, is not a solution to Maxwell's Equations. Go ahead, do the math. Plug the "photon collider" fields into the simple equations and tell me what should be coming out.