Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site mtung.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!mtuxo!mtunh!mtung!jhc From: jhc@mtung.UUCP (Jonathan Clark) Newsgroups: net.physics Subject: (yet) More on repulsion and attraction (rather long) Message-ID: <620@mtung.UUCP> Date: Fri, 25-Oct-85 23:43:23 EDT Article-I.D.: mtung.620 Posted: Fri Oct 25 23:43:23 1985 Date-Received: Sat, 26-Oct-85 08:26:33 EDT Reply-To: jhc@mtung.UUCP (Jonathan Clark) Organization: AT&T Information Systems Laboratories, Holmdel, NJ Lines: 110 Messrs Rimey, Anderson, Maxwell (sic), myself and a few others have been discussing the extreme difficulty of translating concepts of QM into classical terms. A few points have arisen in some recent postings which I shall attempt to clarify but will probably just confuse everybody even more. Anyway, here goes... >Re: unstable gluons. Mr Anderson summarizes quite neatly Yukawa's Nobel Prize-winning work which predicted the pion, and reminds us that the heavier the gauge particle, the more rapidly the force it mediates weakens with distance (as an aside, are gravitons supposed to be massless?). While this is true, what I said was also true, viz that the more massive a gauge particle, the smaller is its half-life. Massless particles (photons, neutrinos [these are still massless this week, aren't they?]) do not decay, while heavy ones (pions &c) do, and the heavier they are the faster they break up. His comment about the Uncertainty Principle placing upper bounds on the lifetime of a virtual particle is also quite true, but not relevent as free particles (ones that decay) are not 'virtual'. He also brings up the wave/particle duality of EM (and other varieties of field), which is so distressing to neophyte physicists, and points out that my description should not be strictly interpreted in terms of classical physics. Attempting this will provide some fairly severe headaches and no satisfactory results! It was merely an attempt to provide a classical-type picture of a mechanism, and the analogy breaks down very quickly. In addition, he correctly points out that the momentum of a virtual particle bears very little relation to anything obvious. The only rule of Nature here seems to be that the more unlikely a phenomenon is then the shorter period of time it lasts. > What is unusual is that like-charged and oppositely-charged > particles pick up one or the other, exclusively. Well they don't really, actually. See below. Mr Maxwell's question of: > is there some sort of intuitive explanation for why like- > or unlike-charged particles "pick up" a photon with one or > the other momentum exclusively? does not have a satisfactory (aethsetically pleasing) answer, I'm afraid. The answer is... 'because it is more likely to happen that way'. Imagine, if you like (help, here I go with the dubious analogies again!), that an electron in an EM field (ie in the Universe) is rather like a molecule in a gas (or a liquid). It is continuously absorbing and emitting ('real' and 'virtual') photons, and thus its energy, momentum and direction of travel are constantly changing. Doesn't this sound like Brownian motion? Now remember Mr Anderson's point about the momentum of a 'virtual' particle being able to have any value, but for a limited period of time. Well, in this limited period of time the 'virtual' photon has a certain probability of interacting with another particle. The closer the other particle is, the higher the probablity if interaction. These particles (they are 'virtual' if they are reabsorbed by the source, 'real' if they interact with another particle) have a certain distribution of energy and momentum, according to some set of probabilities. As to why particles with like signs repel each other, you might hypothesize that the other particle disturbs the probablities in such a way that it emits more particles with a momentum vector which if absorbed by the other particle would cause it to move away. A particle of unlike sign has the opposite effect. The whole business balances out over the Universe, leading to the results we observe (think once again of the contrast between the motion of individual molecules of a gas and the large-scale motion). Then again, you might hypothesize something completely different. If this sounds like a simple (sic) electron has an awful lot of things going on at once, well it does. But an electron is generally moving fairly fast, so its clock runs really slowly :-) ! Bear in mind that QM treats the electric charge as infinite, not some small number. The reason that we don't measure it as infinite is that there is intense 'virtual' pair production in the energy field surrounding the charge. These particles are preferentially created with the unlike charge near the particle, and the like charge away from it. This has the effect of spreading the measurable charge out in space. The degree of 'virtual' particle production is just one of the fundamental constants of the Universe. For an analogy to this, think of Steven Hawking's work on the evaporation of black holes which follows a similar mechanism. -- Jonathan Clark [NAC]!mtung!jhc Personally, I doubt that a truly random walk would be interpreted as such. -- Jonathan Clark [NAC]!mtung!jhc My walk has become rather more silly lately.