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Natural Science Forum / Physics / Particle Physics / August 2005virtual particle interactions
Can virtual particles interact with eachother? I refer here to pair-production virtual particles of the vacuum, rather than force mediating virtual particles. I was considering whether an electron from a virtual electron-positron pair could bond with a proton from a virtual proton-antiproton pair to make an atom. This would involve emission of a photon, so it seems forbidden, not to mention the short timescale it would have to happen on. But is it the case that absolutely no interactions are allowed at all? Indeed, if one virtual particle exchanges energy with anything, including real particles, doesn't that make it real? What happens to it's partner? Do you get lone virtual particles wandering the vacuum looking for annihilation? Also, if you get a virtual particle pair popping out of the vacuum, and one of the particles is an electron, what really is it's partner? Would it be better to call it a negative energy electron, rather than a positron? How can it be a positron when they don't give off gamma radiation when they recombine? If it really is an electron/positron pair, then what is it that remembers that they must return? What is doing the book-keeping? br > Can virtual particles interact with eachother? I refer here to > pair-production virtual particles of the vacuum, rather than force > mediating virtual particles. Some Frequently Asked Questions About Virtual Particles http://hermes.physics.adelaide.edu.au/~dkoks/Faq/Quantum/virtual_particles.html >> Can virtual particles interact with eachother? I refer here to >> pair-production virtual particles of the vacuum, rather than force >> mediating virtual particles. > >Some Frequently Asked Questions About Virtual Particles > http://hermes.physics.adelaide.edu.au/~dkoks/Faq/Quantum/virtual_part... note all considerations in this FAQ are for force-mediating virtual particles (also I've read this faq before...) The difference I had in mind is that for a two-real-particle interaction, such as electron-electron repulsion, the virtual particles are a component of the system, so are (somehow) a by-product of the electrons (I even did the full QM of it at one stage, though my memory is embarrassingly rusty), whereas in an empty vacuum they are (somehow) a product of "the field". That just seems a bit different to me. As I recall, when the electrons are there, the distortion of their interacting wavefunctions can be equivalent to saying there is an extra particle in the system. But in vacuum, there is no wavefunction to distort, unless the vacuum has its own wavefunction. I suppose it is all "the field", as the electrons are just as much properties of the field as are the virtual photons, and of course the field does the bookkeeping. The only problem left is my visualization! (drat!) br Hi Dr photon ........ you are right the whole situation is a big drat i would say much more bluntly it is a big fraud ed presentation of the existing understanding of any attraction force without some breakthrough idea we will all of us dash in the muddy for the next thousand years!!] and of course all those nonsense ideas about attributing properties to vacuum are just confusion - not leading to anywhere. Einstein started the 'curved space time' that was relay revolutionary but not good enough just see (may be again) my Circlon suggestion ATB Brandan Y.Porat ---------------------- to refine my concern a bit more: When two real particles interact via virtual particles, and the virtual particle undergoes an "unintended" interaction, any imbalance can be carried away by the real particles. But in the vacuum case, if there is an "unintended" interaction, and then the virtual pair recombine, how can the vacuum carry away any imbalance? The imbalance must remain in the field, which implies a residual particle is left after the virtual pair recombine? br > Can virtual particles interact with eachother? I refer here to > pair-production virtual particles of the vacuum, rather than force [quoted text clipped - 22 lines] > > br There is no interaction that happens with "real" particles that does not happen with "virtual" particles. The Feynman diagrams are the same, and at each vertex, the usual set of conservation rules most hold. The only difference is that initial state particles and final state particles must be at least somewhat close to being "on-shell", meaning that their energy and momenta have to conspire to give appropriate masses for those particles. For the virtual-atom case that you mentioned, the initial invariant mass of the vacuum would not come close enough to the invariant mass of an atom+photon final state to be allowed. PD >There is no interaction that happens with "real" particles that does >not happen with "virtual" particles. The Feynman diagrams are the same, >and at each vertex, the usual set of conservation rules most hold. well, I had also heard that, but I was doubting it >The only difference is that initial state particles and final state >particles must be at least somewhat close to being "on-shell", meaning >that their energy and momenta have to conspire to give appropriate >masses for those particles. this is where I start having problems. This requirement seems to say that there is *almost* no interaction. My doubt was that if they are not exactly "on-shell", then there is some residue which will not be destroyed once the particles re-coalesce, and I was not comfortable with that. I suppose it just keeps ringing around the field like a tiny probability distortion (somehow). >For the virtual-atom case that you mentioned, the initial invariant >mass of the vacuum would not come close enough to the invariant mass of >an atom+photon final state to be allowed. > >PD thanks! just as I suspected... which also goes to say that only *very* minor interactions are permissible. Even something like electron-electron repulsion would hardly be allowed? If two virtual electrons popped up next to eachother and repelled strongly, how could they recombine with their respective positrons again? Wouldn't the momenta be all wrong? Also, if the particles undergo "normal" interactions, why doesn't the electron and positron emit a gamma ray when they recombine? (I know conservation of energy rules it out, but *how* is that kept track of?) br > >There is no interaction that happens with "real" particles that does > >not happen with "virtual" particles. The Feynman diagrams are the same, > >and at each vertex, the usual set of conservation rules most hold. > > well, I had also heard that, but I was doubting it The boundary between "real" and "virtual" particles is arbitrary and fuzzy. There can be no dynamical difference in their behavior. > >The only difference is that initial state particles and final state > >particles must be at least somewhat close to being "on-shell", meaning [quoted text clipped - 3 lines] > this is where I start having problems. This requirement seems to say > that there is *almost* no interaction. Hmm... It does mean there is an additional constraint on the integral, but the strength of the terms themselves is the same as always. Put another way, the higher-order terms in the perturbation series *do* include interaction terms between the virtual particles, and these have the same relative relation/contribution to the higher-order terms as they would if you were considering interactions between real particles. > My doubt was that if they are > not exactly "on-shell", then there is some residue which will not be > destroyed once the particles re-coalesce, and I was not comfortable > with that. I'm not sure why. There are e+e- --> e+e-gamma events, q + qbar --> 3jet events that are all expressions of some residue in the event. As long as the invariant mass of the system is preserved, and energy and momentum and charge and so on are individually conserved, everythings fine. > I suppose it just keeps ringing around the field like a tiny > probability distortion (somehow). No, I don't think the idea of a "spirit in limbo" particle in the final state is a good way to get around it. > >For the virtual-atom case that you mentioned, the initial invariant > >mass of the vacuum would not come close enough to the invariant mass of [quoted text clipped - 4 lines] > thanks! just as I suspected... which also goes to say that only *very* > minor interactions are permissible. I wouldn't characterize it as that, but perhaps it's a matter of degree. > Even something like electron-electron repulsion would hardly be > allowed? If two virtual electrons popped up next to eachother and > repelled strongly, how could they recombine with their respective > positrons again? Wouldn't the momenta be all wrong? Now here is where you're treating the diagrams too literally and too classically. You are supposing that if you have a vertex where a photon decays into an electron-positron pair, and the electron and the positron have opposite momenta (to conserve momentum at the vertex), then they must be heading away from each other and separating in distance. But recall the uncertainty principle, which says the more you know about the momenta, the less you know about their positions. Which means that even if the momenta are in opposite directions, you still don't know whether the particles are heading away from each other or towards each other! You may say, but they were next to each other at the vertex so they *must* be moving away from each other. The response is, but that's applying knowledge of both position and momentum at the same time, and you can't do that in quantum mechanics, only in classical mechanics. (This is Porat's mistake, as well.) > Also, if the particles undergo "normal" interactions, why doesn't the > electron and positron emit a gamma ray when they recombine? (I know > conservation of energy rules it out, but *how* is that kept track of?) Well, essentially by the same rule that the e+e- pair popped out of the vacuum without a gamma in the first place. How you "borrow" energy from the vacuum and put it back in is sort of arbitrary. I personally would prefer to pull energy and momentum from the vacuum in the form of a gamma, which then decays to e+e-, which then coalesces into a gamma, which then gets reabsorbed into the vacuum. For those little "detached" Feynman diagrams that don't have real particles in initial and final states, it's better to start with the math and decide later how to draw the diagram. PD did you ever hared me saying that we can know momentum and position at the same time???!! i never said that i only said that the HUP can be bypassed by other knowledge while there is no need at all to know momentum and position at the same time in order to know much more than you imagine!!! see for instance my model in my site i show there the geometric structure of the nuc *without length scale* and i say 'not proportional!! we can know for instance the relative positions of particles as you can know the relative positions of buildings in your street without telling what is the length scale there and i keep on bringing a simple example that you never answered me : if we know the Deuteron is composed of a Proton and a neutron--- can we say that they are located one next to the other?? while we know they can be separated and combined not too difficultly and many other facts about them so can we say: if they are one next to the other than can we assume with a highest probability that the shape of the deuteron is something longish?? will you answer me that question once and for all in order of making some advance beside the QM mumbling that you dont stop dashing in ? and without admitting that(once and for all) all your above discussion is one big mumbling??? IE not admitting to say: 'we have no green idea what is making any attraction force ??!!! btw the spell checker fount about 20 mistakes in my post .... and probably there are still more .(:-) TIA Y.Porat ------------------------ Learn how to use "did", Porat! Hi Shakespeare thank you but what about virtual particles interaction?? ATB Y.Porat ---------------------- > did you ever hared me saying that we can know momentum and position at > the same time???!! [quoted text clipped - 14 lines] > if we know the Deuteron is composed of a Proton and a neutron--- > can we say that they are located one next to the other?? No, not definitively. In fact, there is substantial overlap in their probability distributions. Got a problem with that? > while we know they can be separated and combined not too difficultly > and many other facts about them > so can we say: > if they are one next to the other than can we assume with a highest > probability that the shape of the deuteron is something longish?? Probably, but not necessarily in the shape of two balls sitting side-by-side. > will you answer me that question once and for all > in order of making some advance beside the [quoted text clipped - 11 lines] > Y.Porat > ------------------------ not necessarily in the shape of two balls sitting side by side?? 1 did you ever heard from me 'two balls???!! never it i snot two balles it is each of them a longish shape!! can you suggest for me a shape of 3 quarks (3 remember??) making a 'ball'?? btw what is your 3d education ??....... so listen carefully to old Porat even the nucleid is a longish shape a linear shape of sub particles connected linearly !1 will you remember that?? and who told you that first?? 2 can you suggest something else about the geometric shape of the Deuteron?? if yes than welcome !! go on and we will see about your suggestion just here. (and you will learn about the little difference between being a creator and being a criticizer) 3 a Little suggestion: get to my site and become a bit more wiser about the geometric structure of the nuc it is a 10 years work of some unknown crackpot.. 4 let there be no mistake i respect you personally!! no cynicism.! you are of the much better people here. yet even for you there are a lot of news *and surprises* to come. TIA Y.Porat -------------------- Stop using "did" wrong, Porat! 1 i dont know what is wrong with my 'did' 2 are you aware that you are disturbing the *physics discussion???* or may be you do it on purpose ??? hope not.......... TIA Y.Porat ----------------------------- > 1 > i dont know what is wrong with my 'did' "do" is an auxiliary verb, thus followed by the infinitive and not the participle. It's used for confirmation of an action, not for the placement in time. So stop putting the past participle after "did". Do that with "have", "had", "is", "was", etc. > 2 are you aware that you are disturbing the *physics discussion???* hardly so we may conclude that you are disturbing by trivialities *on purpose*!!! and let everyone know it !! keep well Y.Porat ---------------------- did you ever hear-ed for me describing the nucleid as a ball?? just have a look at my site i describe the nucleid as a chain of orbitals!! so if a chain of orbitals than ...... some of the external ones are overlapping for the proton and the neutron but : the main body of the proton and neutron in the Deuteron are side by side!! Got me ??? that gives more substantiating to my 'chin of orbitals theory as well got it ?? now at the bottom line that you forgot and is crucially important and innovative : can we bypass the UHP in this case and know something about the shape of the Deuteron??!! (in spite of its extremely small dimensions??) TIA Y.Porat ---------------------- You are a coward, Draper, and you do not mean the words you say. That makes you a disingenuous coward. Nobody can trust you. Androcles |
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