And here's the problem: this is an appeal to ridicule and you are going to have to do a hell of a lot better than call QFT names if you seriously want to challenge it.
You sound like you're describing a dog.
What are quarks made of?
- Thread starter Magical Realist
- Start date
And here's the problem: this is an appeal to ridicule and you are going to have to do a hell of a lot better than call QFT names if you seriously want to challenge it.
You sound like you're describing a dog.
Farsight:
There are no photon-photon interactions, by a simple argument.
1)Photons are coupled to fields by the particle's electric charge (see my post #77). Interactions occur because of the coupling.
2)Photons have no electric charge.
3)Therefore, photons do not interact with each other.
If you claim that they do interact, you must claim one of two things: that photons possess an electric charge, or that there is another fundamental interaction whose charge is possessed by the photon. There is no evidence for either.
Also, particle pair production from photons does indeed occur, as a matter of experimental fact. It may seem strange, but it is the case. The simplest example is in Bhabba Scattering. Its a scattering process in which an electron and a positron annihilate into a photon, which then produces an electron and a positron. This can be observed in an experiment:
http://prl.aps.org/abstract/PRL/v59/i3/p266_1
There are no photon-photon interactions, by a simple argument.
1)Photons are coupled to fields by the particle's electric charge (see my post #77). Interactions occur because of the coupling.
2)Photons have no electric charge.
3)Therefore, photons do not interact with each other.
If you claim that they do interact, you must claim one of two things: that photons possess an electric charge, or that there is another fundamental interaction whose charge is possessed by the photon. There is no evidence for either.
Also, particle pair production from photons does indeed occur, as a matter of experimental fact. It may seem strange, but it is the case. The simplest example is in Bhabba Scattering. Its a scattering process in which an electron and a positron annihilate into a photon, which then produces an electron and a positron. This can be observed in an experiment:
http://prl.aps.org/abstract/PRL/v59/i3/p266_1
No I wouldn't.
Farsight, if you want to understand QED's account of scattering processes, then 1) learn linear algebra (matrices and diagonalisation and such), 2) get comfortable with calculus and differential equations, 3) learn classical electromagnetism (you should be able to work with and solve Maxwell's equations for at least some simple problems), 4) learn special relativity, in particular the Minkowski geometric formalism and how it is applied in practice to relativistic theories (you should follow and understand how Maxwell's equations can be expressed in this notation, and understand what it means that they can be written that way), 4) learn the Lagrange and Hamiltonian formalisms including the action principle and Noether's theorem, 6) learn (nonrelativistic) quantum physics (exactly which applications of it you study in detail doesn't matter so much as long as you get a good feel for the subject, except that you should make sure you understand the quantum harmonic oscillator and perturbation theory), and 7) only then get a good textbook[sup]*[/sup] on quantum field theory and start ploughing through it until you, at the very least, have a working understanding of how to do scattering calculations and how to derive Feynman rules. Learning some differential geometry and a bit about matrix Lie groups and algebras along the way will probably be worth the effort too.
There's nothing I or anyone else could say in the space of a forum post that could even come close to an adequate substitute for that. If you want to understand mainstream physics you're going to have to stop looking for quick and easy answers and drop this "if you can't explain something to your grandmother" crap and invest some real work and time and effort learning. And even there you can expect you will probably need some help along the way. It's not easy, but it should be possible if you are motivated and patient enough.
[sup]*[/sup] You probably really want two textbooks: one like Zee that aims at explaining the base concepts, and one like Peskin & Schroeder that will explain how to calculate things. Each is likely to give you insights that you probably wouldn't gain from the other.
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It's not a question of challenging it, it's a question of getting you (and people like you) to see those parts of it that need more work.
It's just a bit of a tease. I quite like rpenner. He puts in some effort, and while he sometimes tries in vain to get one over on me, he isn't abusive. And I've know him long enough to know that when he goes quiet on us, it's because he agrees with me. Or at least I hope so on this occasion. I hope he isn't ill.przyk said:
Mark, with respect, this is wrong. I know this is what all the QED textbooks say, but nevertheless, it is wrong. In electromagnetism we have conduction current, which is the motion of charged particles, and we have displacement current, which is a "time-varying electric field". A photon going past you appears to be "a time-varying electric field". (You'll be aware that I prefer to refer to the electromagnetic field, but let's come back to that another day). A photon is in essence alternating displacement current. You can configure this as a "Dirac's belt" standing wave to create a charged particle, and then you can move it. Displacement current is thus more fundamental than conduction current. And it is also more fundamental than charge. And despite your simple argument, there are photon-photon interactions. The experiments have been done at SLAC. I hope you understand the significance of this: the mediator is more fundamental than the thing it is said to mediate. I need people like you to pick up on this and revise QED and then complete the standard model. Physics needs it.
See above. Photons do not possess any charge. And note that there is evidence for a direct photon-photon interaction, whilst there is no evidence that a single photon all on its own spontaneously morphs into an electron-positron pair. As I said to przyk, QED "works" because the leading portion of the photon behaves like a partial positron. Take a positron and cut it in half: ∩. Take an electron and cut it in half: U. String them together: U∩.MarkM125 said:
I'm sorry Mark, but an electron and a positron can not annihilate into a single photon which then spontaneously turns into an electron and a positron all on its own. Bhabba scattering is merely modelling the resemblance between half an electron and half a photon.MarkM125 said:
But you did: the reaction $$\gamma \gamma \,\rightarrow\, e^{+} e^{-}$$, is composed out of more primitive interactions, one of which is $$\gamma \,\rightarrow\, e^{+} e^{-}$$. One 511KeV photon morphs into an 511KeV electron and a 511Kev positron? Spontaneously like worms from mud? All on its own? How does that happen? Magic? Pray do tell.
Whoa. I understand classical electromagnetism. You don't. That's why we're having this little discussion.przyk said:
Are you kidding me? I know special relativity better than anybody else here. I understand it. I know why the measured speed of light is always the same. You don't. You accept "definitions" and "postulates" without understanding why they apply. Grrrr. This is not looking too good przyk. I dread to think what I'm going to read next.przyk said:
For God's sake przyk, I'm the only one around here who has read the original Maxwell. I'm the only one who understands what he was on about with his vortices and his screw. You don't.przyk said:
So, like you concede this little argument then? With go learn some physics. Because you can't defend your tautological magic that tramples all over conservation of energy, momentum, angular momentum, charge, de dah de dah. Przyk, you are so easy to beat.przyk said:
Let's just recap shall we?
Pair production occurs because pair production occurs is garbage.
Now go and fix it.
What Mark wrote down is 'how it is'. They're no photon-photon interactions regardless what you say. What you say is generally irrelevant bullshit. The probability that you're going to get physicists to agree with anything you say is nil. Bullshit isn't a term that has any scientific value.
Sure, that's true.
Once again, fine. The electric field in an EM wave satisfies Maxwell's equations in vacuum, with solutions that vary sinusoidally. When EM waves interact with charged particles, a force is exerted called "radiation pressure". In response to an E and B field, the particle moves according to the Lorentz Force Law:
$$F = qE + q(v \times B)$$
Therefore, for q = 0, there is no interaction. So, classical theory also predicts no interaction between electromagnetic radiation (photons). In QED, the interaction term is $$-i q A_{\mu} \psi$$, sp when q = 0, no interaction. All of physics, classical and quantum, resoundingly states: uncharged particles do not interact with photons. As photons are uncharged (you agreed with this), they do not interact with each other.
This doesn't follow. The concept of the electric field was introduced by Faraday to explain the interaction between charged particles. What we call more "fundamental" doesn't really change the physics.
Speaking of tautologies: "There photon-photon interactions because there are photon-photon interactions." Nothing in the above even supported this statement, whether it is right or wrong. You're simply stating it. If you could offer an explanation for (a) Why my reasoning is incorrect and (b) Why photons must interact with photons, I'll be happy to read it.
Link? I find that odd, considering SLAC's Monte Carlo simulator GEANT4 doesn't seem to include photon-photon interactions.
Again, a question of what is "fundamental". It may be an interesting philosophical question, but it doesn't affect physical predictions. It doesn't change the fact that in all branches of physics, uncharged particles do not interact electromagnetically.
Just saying that its true isn't going to convince me. Since you haven't provided experimental data on this, its essentially your word against the entire community of physicists and authors.
"Half an electron" and "Half a photon" aren't known to exist. No electron or photon has ever been detected in halves. If I'm wrong, go ahead and link to the paper that shows that I am.
How old are you? Twelve?
You repeatedly assert that you understand physics better than, apparently, anyone alive. I don't buy it. Any idiot with a keyboard and an internet connection could say that.
And don't pile on how you've read the original Maxwell or Einstein or [insert whatever celebrity]. Physics is not Bible study. You have never gone into any of these theories in anything more than the most superficial detail. You have zero demonstrated functional understanding of these theories. While you beat your chest here about how great your understanding of electromagnetism is, hundreds of thousands if not more engineers are actually doing stuff with it that you could never do. Time and time again you try to argue a case and the best you can do is quote an authority figure and simply assert how we should understand it and assert that we should believe it that way. You never do an independent analysis of your own. You do not understand physics.
Why? You've done nothing to convince me that you have a promising research direction to follow.
(And if you supposedly understand physics better than I do, wouldn't you be better placed to "fix it" than I, mere mortal, am?)
Farsight, I really think it would help your cause if you remind people what you mean by "understand". In the past you've been good enough to admit that this "understanding" of yours vanishes if someone takes away your ability to quote celebrity scientists or link to Wikipedia pages. This means your usage of the word "understand" differs very much from that of a scientist's usage.
When you say "I understand" I think what you mean is "I'm very content with the picture I've painted for myself". Perhaps if you learn about some of the subjects przyk mentioned, you might be able to see how your notion of "understanding" something measures up to a scientists notion.
Hi MarkM125. Haven't much time today. Did you read my post #90 addressed to rpenner where I further explained about the 'plasmonic' field as the more fundamental 'bridging field' via which the photonic and electronic features/fields energies 'merge' and 'couple' etc before resonance features re-emerge as distinct photon or electron types?
This perspective can explain how the e-m energy content in both electrons and photons can interact in a composite energy context.
Also, I would like to point out that the 'scattering' you mentioned occurs in particle accelerators where e-m energy INPUTS beyond the actual 'colliding particles' themselves, so the scattering event centre has more energy in it above the quotient just provided by 'particles' scattering. So naturally we can have greatly increased energy levels transiently which would differentiate eventually into pair products. But the e-m energy didn't all come 'spontaneously' from the photon, it also came from the accelerator input/energy process/reservoir (which is by some called e-m energy, or photonic exchange particle energy?).
This is why no SINGLE photon of average energy content in 'free space' conditions (where NO external energy inputs are involved) has ever been observed to spontaneously create electron-positron pairs, let alone pairs of higher energy than the single average-energy photon under study. Yes?
I hope this helps the discussion along by pointing to the 'bridging' insights in this which might in future prevent some of the 'apples and oranges' exchanges/misunderstandings which I read in this discussion at times.
Well, I have to be going again. See you all again tomorrow, hopefully!
Hi MarkM125. Haven't much time today. Did you read my post #90 addressed to rpenner where I further explained about the 'plasmonic' field as the more fundamental 'bridging field' via which the photonic and electronic features/fields energies 'merge' and 'couple' etc before resonance features re-emerge as distinct photon or electron types?
This perspective can explain how the e-m energy content in both electrons and photons can interact in a composite energy context.
Also, I would like to point out that the 'scattering' you mentioned occurs in particle accelerators where e-m energy INPUTS beyond the actual 'colliding particles' themselves, so the scattering event centre has more energy in it above the quotient just provided by 'particles' scattering. So naturally we can have greatly increased energy levels transiently which would differentiate eventually into pair products. But the e-m energy didn't all come 'spontaneously' from the photon, it also came from the accelerator input/energy process/reservoir (which is by some called e-m energy, or photonic exchange particle energy?).
This is why no SINGLE photon of average energy content in 'free space' conditions (where NO external energy inputs are involved) has ever been observed to spontaneously create electron-positron pairs, let alone pairs of higher energy than the single average-energy photon under study. Yes?
I hope this helps the discussion along by pointing to the 'bridging' insights in this which might in future prevent some of the 'apples and oranges' exchanges/misunderstandings which I read in this discussion at times.
Well, I have to be going again. See you all again tomorrow, hopefully!
There was a clownish fellow who was banned that used/employed/typed slashes and who never had much time, so he would pop in a drops some inane comment to 'help' the conversation and then say he must be on his way until tomorrow. Golly! You sound just like that guy. Is that weird or what?
OK, that is just plain funny! Farsight, it appears to me that brucep has probably forgotten more physics than you ever knew.
RealityCheck. Came back as Undefined.
Magical Realist
Valued Senior Member
Mark125, you stated:
Now I'm just a layman mind you, but I was wondering if that was true how do we explain the phenomena of interference? Do the waves actually interact but not the photons? Or is it merely an illusion that the waves are interacting in this case?
Now I'm just a layman mind you, but I was wondering if that was true how do we explain the phenomena of interference? Do the waves actually interact but not the photons? Or is it merely an illusion that the waves are interacting in this case?
Interference occurs because the photon (or electron) is described by a wavefunction which passes through both slits, and interferes as any wave does. That is, when waves overlap, you add their amplitudes at every point. Remember, the pattern can be created by firing a single photon at a time.
What I'm referring to above are electromagnetic interactions between photons. Of course, photons do interact in some ways - for example, gravitationally. However, because the photon possess no charge, no EM interactions between photons occur. So, they don't interact in this way, or through the weak or strong interaction, and gravity is negligible on these scales. Therefore, Farsight would need to introduce a new interaction to explain his proposed $$ \gamma \gamma $$ interactions at vertices.
Magical Realist
Valued Senior Member
That's interesting about the single photon. I had forgotten about that. Tks for the clarification!
If you've never seen the double-slit experiment performed with individual photons yourself, here's a video of it being performed:
http://www.youtube.com/watch?v=MbLzh1Y9POQ