Merged Relativity+ / Farsight

[Farsight]

I don't think sol said that the electron field is an aspect of the electromagnetic field, so I don't think all you are claiming is settled.

No, but what is settled, is that photons interact with photons.

Remember that this latest round of discussion arose because I started a thread called Turning light into matter, reporting on some news a couple of weeks back. Then some "moderator" merged it into this thread, and the naysayer custodians of ignorance crawled out of the woodwork to try to shout down what I said in my last paragraph. Here it is on page 43:

"Note thought that the article says 'From quantum electrodynamics it can be found that photons cannot couple directly to each other'. That's wrong. Pair production doesn't occur because pair production occurs, instead two photons interact. Recognition of this is the arguably the most important aspect of this news. It may lead to an important advance in physics".

To be absolutely honest edd, I think one has to be ******* crazy to say that photons don't interact with photons in a photon-photon collider. And I'm sick to the back teeth of arguing about it.

 

[Perpetual Student]

Having glanced over some recent posts in this thread, I think there might be an overemphasis on whether the interaction between photons in QED is "direct" or not. While of course I understand what people mean when they say it is not direct, I don't think the distinction is particularly useful.

In the 1-loop effective action you get in QED from integrating out the electron, there IS a direct photon-photon interaction. It's true that coupling arises in the computation due to the interaction of photons with virtual electrons, but so what? In the end, photons scatter off photons - that's the experimentally observable fact. Everything else is interpretation or semantics.

You are correct, but have missed the point, which is that Mr. Duffield denies the QED description of photon - photon interactions, solely based on his own incredulity.

 

[ctamblyn]

You already have the equations for classical electromagnetism too. That doesn't stop you believing in cargo-cult nonsense like electrons and positrons throwing photons at one another.

The Standard Model is extremely successful. That's the justification for my provisional acceptance of it. Oh, and I do mean the Standard Model, not the caricature of it you've been bashing.

Now, what is your justification for all the crackpottery you've presented in this thread, like your theory (inspired by similar ideas from Williamson and van der Mark, and Qiu-Hong Hu) that electrons are twisted photons, and that protons are trefoil knot configurations of single photons (and so on)? How about some justification for your belief in the numerological arguments of Andrew Wiles? And where is your justification for believing in the numerological derivation of the fine structure constant in terms of kissing numbers? Why should anyone accept any of this, when you have been unable to develop any of these ideas into something empirically testable?

And I'm still waiting for you to answer these earlier questions:

1. http://www.internationalskeptics.com/forums/showthread.php?p=10048237#post10048237
2. http://www.internationalskeptics.com/forums/showthread.php?p=10048083#post10048083

 

[ctamblyn]

...the naysayer custodians of ignorance...

The preferred term is "self-appointed defenders of the orthodoxy".

 

[edd]

Try to talk physics, Clinger. Everybody here knows that I've got maths A level, did more mathematics during a computer science degree followed by ad-hoc self-teaching, and that I've done private tutoring. Trying to slag me off on my mathematical abilities won't stop it being a photon-photon collider.

* You have never disavowed the atrociously wrong lack of units in Worsley's formulae.
* a CV fight is not going to go down your way
* No one has disagreed with photon photon colliders working as everyone expects.

 

[Farsight]

a CV fight is not going to go down your way

No, but a physics fight is. Like it just did. Because as is crystal clear, I know more physics than the rest of them put together. Now, like I said, the photon-photon interaction is settled. Photons interact with photons. And if anybody wants to talk about something else, start a thread. Not that anybody will. Guys like ctamblyn are only here to make sure there's no critical thinking about physics on JREF. They are the "self-appointed defenders of the orthodoxy" who crawl out of the woodwork to close down discussions, and are otherwise quite happy for JREF to be a physics-free zone.

 

[edd]

You think what you're saying is accepted physics? What universities do you think teach physics acceptably? Genuinely interested if there are any.

 

[phunk]

Can somebody have a word with Phunk please?

Can't explain it yourself?

 

[ben m]

No, but a physics fight is. Like it just did. Because as is crystal clear, I know more physics than the rest of them put together. Now, like I said, the photon-photon interaction is settled. Photons interact with photons. And if anybody wants to talk about something else, start a thread. Not that anybody will. Guys like ctamblyn are only here to make sure there's no critical thinking about physics on JREF. They are the "self-appointed defenders of the orthodoxy" who crawl out of the woodwork to close down discussions, and are otherwise quite happy for JREF to be a physics-free zone.

Imagine someone who spent 7 years believing in UFOs, alien abductions, reptoids, and Martian canals. Imagine that person finding his opponents are comfortable with the statement "there is life out there somewhere". To what extent can this person claim to have been right all along about a settled mainstream question?

 

[Perpetual Student]

..., I know more physics than the rest of them put together. ...

You have demonstrated that you are an avid reader about physics, but you have also clearly shown that you have not undertaken a serious study of the subject (including the mathematics) and consequently have only a superficial knowledge laced with serious misunderstandings and great confusion. Unfortunately, your prodigious reading has lead you to a have an intense sense of unjustified confidence about your own comprehension of the subject.
Regarding the current question about photon interactions, unless you are able to produce and comprehend the relevant QED equations, you are not qualified to hold any opinion on the subject worthy of consideration by me or any one else here.

 

[sol invictus]

You are correct, but have missed the point, which is that Mr. Duffield denies the QED description of photon - photon interactions, solely based on his own incredulity.

That's probably the case, but I think it's interesting to consider whether a "direct" versus "indirect" coupling has any real meaning. I think someone gave an example of a mass A connected by a spring to mass B, which is connected by another spring to mass C. The idea was that A is directly connected to B, but indirectly connected to C. But mass A is directly connected only to the end of the spring, which is connected to the part of the spring next to it, which... is connected to B. So how is the connection between A and B any more direct than that of A to C?

I think something analogous is true of QED. The physical "truth", such as we understand it, is that the wavefunction of a photon is in fact affected by that of other photons (i.e. photons can scatter off photons). We can calculate that effect using perturbation theory through a series of diagrams, and it's true that in those diagrams it's virtual electrons that cause it (although incidentally, when a photon scatters off a charged particle there's a virtual photon in the leading diagram, so how exactly is that "direct" either?).

We can also show that in a world without electrons or other charged particles, photons would not affect each other. But we do not live in that world. In our world, photons scatter off photons in a specific way. Photons scatter off electrons in a different, but equally specific way. I don't really see how one is more "direct" than the other, although I'd be happy to have it explained to me.

 

[ctamblyn]

That's probably the case, but I think it's interesting to consider whether a "direct" versus "indirect" coupling has any real meaning. I think someone gave an example of a mass A connected by a spring to mass B, which is connected by another spring to mass C. The idea was that A is directly connected to B, but indirectly connected to C. But mass A is directly connected only to the end of the spring, which is connected to the part of the spring next to it, which... is connected to B. So how is the connection between A and B any more direct than that of A to C?

I think something analogous is true of QED. The physical "truth", such as we understand it, is that the wavefunction of a photon is in fact affected by that of other photons (i.e. photons can scatter off photons). We can calculate that effect using perturbation theory through a series of diagrams, and it's true that in those diagrams it's virtual electrons that cause it (although incidentally, when a photon scatters off a charged particle there's a virtual photon in the leading diagram, so how exactly is that "direct" either?).

We can also show that in a world without electrons or other charged particles, photons would not affect each other. But we do not live in that world. In our world, photons scatter off photons in a specific way. Photons scatter off electrons in a different, but equally specific way. I don't really see how one is more "direct" than the other, although I'd be happy to have it explained to me.

A comparison you might draw is between photons and gluons. In the QED you have the related facts that the Lagrangian has no cubic terms in the electromagnetic field, there are no three-photon vertices in the Feynman diagrams, and photons are neutral. In QCD you have a Lagrangian with cubic and higher terms in the gauge field, there are three- and four-gluon vertices in the Feynman diagrams, and gluons carry colour. I think it is reasonable to describe the difference in terms such as "photons do not interact directly whereas gluons do".

 

[Perpetual Student]

A comparison you might draw is between photons and gluons. In the QED you have the related facts that the Lagrangian has no cubic terms in the electromagnetic field, there are no three-photon vertices in the Feynman diagrams, and photons are neutral. In QCD you have a Lagrangian with cubic and higher terms in the gauge field, there are three- and four-gluon vertices in the Feynman diagrams, and gluons carry colour. I think it is reasonable to describe the difference in terms such as "photons do not interact directly whereas gluons do".

Great point! The "direct interaction" among gluons compared to that of photons (both force carrying bosons) makes the case that photon-photon interactions are "indirect" in a very real sense.

 

[sol invictus]

A comparison you might draw is between photons and gluons. In the QED you have the related facts that the Lagrangian has no cubic terms in the electromagnetic field, there are no three-photon vertices in the Feynman diagrams, and photons are neutral. In QCD you have a Lagrangian with cubic and higher terms in the gauge field, there are three- and four-gluon vertices in the Feynman diagrams, and gluons carry colour. I think it is reasonable to describe the difference in terms such as "photons do not interact directly whereas gluons do".

In the classical QED Lagrangian there are no 4-photon interactions - but in the quantum effective Lagrangian there are.

Anyway I think you may be missing my point. I don't really care about Lagrangians and Feynman diagrams. Those are just technical tools. What I care about is physical reality, and I don't see a way to distinguish between "direct" and "indirect" interactions using experiments.

 

[DeiRenDopa]

In the classical QED Lagrangian there are no 4-photon interactions - but in the quantum effective Lagrangian there are.

Anyway I think you may be missing my point. I don't really care about Lagrangians and Feynman diagrams. Those are just technical tools. What I care about is physical reality, and I don't see a way to distinguish between "direct" and "indirect" interactions using experiments.

Leaving aside what 'physical reality' is (are gluons real, for example?), much of the recent sub-thread has been about Farsight's claims that his ideas about electromagnetism, photons, electrons etc are 100% consistent with QED. For that topic, 'direct' vs 'indirect' is important.

 

[ben m]

What I care about is physical reality, and I don't see a way to distinguish between "direct" and "indirect" interactions using experiments.

Maybe there is: I would imagine that in a degenerate bath of electrons, like a white dwarf, indirect photon-photon coupling via electrons would be suppressed but direct coupling would not. I think.

 

[lpetrich]

But do note that the electron is always 511keV with unit charge. That's a kind of quantum.

So what?

What I'm saying is you don't have to throw out the whole of QED just because you've found out that photons interact with photons.

Write out the extra term(s) that you think ought to be added to the QED Lagrangian to account for direct photon-photon interactions. You seem to be claiming that there is no such thing as indirect photon-photon interactions, indirect interactions like charged particles' electromagnetic interactions with each other.

You just fix the interpretation, wherein you now say the photon field and the electron field are but two aspects of the electromagnetic field.

Pure hooey. A gauge quantum field (the photon) != a Dirac quantum field (the electron).

I give a bit of background, referring to people like Maxwell and Kelvin and Atiyah.

Pure book-thumping, complete with misunderstanding those quotes.

I'm not just some "my theory" guy making stuff up.

Are you running away from your own theory? That's what your "not my theory" claims seem like to me.

You already have the equations for classical electromagnetism too. That doesn't stop you believing in cargo-cult nonsense like electrons and positrons throwing photons at one another.

Seems like projecting the classical particle limit onto quantum field theory. That's asking for trouble.

Everybody here knows that I've got maths A level, did more mathematics during a computer science degree followed by ad-hoc self-teaching, and that I've done private tutoring. Trying to slag me off on my mathematical abilities won't stop it being a photon-photon collider.

Then why complain about math in physics? The math is there for VERY good reasons? Your anti-math physics is a throwback to Aristotelian physics, it must be pointed out.

(your arguments as theologian-like)

You are all dismissal, lpetrich.

For very good reasons.

No, but a physics fight is. Like it just did. Because as is crystal clear, I know more physics than the rest of them put together.

Need I say more?

 

[ctamblyn]

In the classical QED Lagrangian there are no 4-photon interactions - but in the quantum effective Lagrangian there are.

Anyway I think you may be missing my point. I don't really care about Lagrangians and Feynman diagrams. Those are just technical tools. What I care about is physical reality, and I don't see a way to distinguish between "direct" and "indirect" interactions using experiments.

If you're talking about integrating out the electron degrees of freedom to get a theory of directly-interacting photons, OK, but surely you then have a theory with no electrons? And once you started colliding photons at energies of ~2m_e and above you'd find that the effective field theory was no longer so useful, wouldn't you? (These are not rhetorical questions, I'm genuinely interested to know.)

Although it is interesting, I'm not sure how relevant this is to the real issue under discussion here. Farsight believes that you can have a theory in which electrons are self-interacting photons (somewhat analogous to glueballs, I guess, but somehow with a single photon), and that the sort of photon-photon scattering mentioned in the article under discussion is evidence for the type of photon-photon interactions which would make his model more plausible, and indicate that there is something wrong with QED.

 

[sol invictus]

If you're talking about integrating out the electron degrees of freedom to get a theory of directly-interacting photons, OK, but surely you then have a theory with no electrons? And once you started colliding photons at energies of ~2m_e and above you'd find that the effective field theory was no longer so useful, wouldn't you? (These are not rhetorical questions, I'm genuinely interested to know.)

Yes to both. My point there was to show that even the presence of absence of a direct coupling in the Lagrangian depends on which Lagrangian you mean.

Although it is interesting, I'm not sure how relevant this is to the real issue under discussion here. Farsight believes that you can have a theory in which electrons are self-interacting photons (somewhat analogous to glueballs, I guess, but somehow with a single photon), and that the sort of photon-photon scattering mentioned in the article under discussion is evidence for the type of photon-photon interactions which would make his model more plausible, and indicate that there is something wrong with QED.

Right, well, that's obvious nonsense for many reasons, one being that the photon collider we are discussing was proposed because QED predicts that it will work.

 

[sol invictus]

Maybe there is: I would imagine that in a degenerate bath of electrons, like a white dwarf, indirect photon-photon coupling via electrons would be suppressed but direct coupling would not. I think.

I'm not sure about that, but it's certainly the case that the coupling between photons one gets in QED is very different from the coupling one gets between gauge bosons (say) a non-Abelian gauge theory, and depends on the charges, masses, spins, and multiplicities of the charged states in the theory. For example, for photon energies well below the mass of the electron (which is the lightest charged particle and hence the most important at low energies) the coupling is very small, so that the force one photon exerts on another falls off exponentially with distance for distances larger than the electron Compton wavelength. None of those statements apply to "direct" couplings like in a non-Abelian gauge theory.

So maybe one could say that the defining characteristic of an "indirect" coupling is a Yukawa-type (i.e. exponentially suppressed) force at long distances.