I know I am not qualified to join this discussion, but may I say just one thing?
As we struggle with our data from our accelerators n' stuff, we bring to bear models from our experience . metaphors. The language of your discussion is full of such metaphors, and full, also, of expressions of pain that these metaphors are not only incomplete -- all metaphors are incomplete - but that they are incompletete in ways that are essential to the phenomena you are trying to account for. Now, it seems to me, that this conversation is like the conversation that would ensure if we were to see a unicorn drinking out of the fountain at St. Johns, but did not have the mythology of unicorns, or even the word, unicorn, to bring to bear. We would instantly start to apply incomplete models. "It's a whacking great horse!" One of us would say. "Yeah, but, it's got a narwhale tooth sticking out of its forehead." Nick From: Friam [mailto:friam-boun...@redfish.com] On Behalf Of Steve Smith Sent: Sunday, April 21, 2013 1:40 PM To: stephen.gue...@redfish.com; The Friday Morning Applied Complexity Coffee Group Subject: Re: [FRIAM] How do forces work? S - I'd like to think Gil and I could take credit for running Bruce off with our Light/Dark Boson/Lepton nonsensery but I think he's hardier than that! Carry On! - S Aya, it turns out Bruce recently unsubscribed from FRIAM. I hope you guys on the list are happy with your signal to noise ratio ;-) Just kidding...keep it up. Anyway, Bruce, as I had hoped, had a nice response, albeit offlist. If you want to respond to this thread, please cc: Bruce. I copy his response below. //** Bruce Sherwood response offlist Feynman diagrams give one visualization of "forces". In this picture, consider two electrons moving near each other. With a calculable probability, one of the electrons may emit a photon, the "carrier" of the electromagnetic interaction, and this electron recoils. The other electron absorbs the photon and recoils. At least for electric repulsion, this is a nice way to think about the interaction, but it has obvious problems for talking about attraction. The exchanged photon is a "virtual" photon which unlike unbound photons has mass. At the individual "interaction vertices" (emission event and absorption event) momentum and energy need not be conserved, but for the two-electron system momentum and energy are conserved. For the strong (nuclear) interaction, the interaction carrier is the gluon. It is thought that the gravitational interaction is carried by a "gravitron" but we have no direct evidence for this. The weak interaction is mediated by the W and Z bosons and is so similar to electromagnetism that one speaks of the "electroweak interaction". A key example is neutron decay, and here is the story: http://matterandinteractions.wordpress.com/2012/05/25/neutron-decay/ Or, if you have an up-to-date browser and a graphics card with GPUs, here is a central animation from that article: http://www.glowscript.org/#/user/Bruce_Sherwood/folder/Pub/program/NeutronDe cay On the other hand, the March 2013 issue of the American Journal of Physics has a very interesting and perhaps important article by Art Hobson on the modern (last few decades) perspective on quantum mechanics. Maybe this is familiar to you, but it wasn't to me. The basic idea he reviews is that everything is fields; there are no particles. Here is what seems to me a key paragraph in the conclusion: Thus Schrodinger's Psi(x,t) is a spatially extended field representing the probability amplitude for an electron (i.e., the electron-positron field) to interact at x rather than an amplitude for finding, upon measurement, a particle. In fact, the field Psi(x,t) is the so-called "particle." Fields are all there is. There is a popular science book by Rodney Brooks on the subject: At amazon.com search for "Fields of Color: The theory that escaped Einstein". Brooks was a student of Schwinger, a major contributor to quantum field theory. Here are related references, dug out by Stephen: http://physics.uark.edu/Hobson/pubs/05.03.AJP.pdf http://arxiv.org/pdf/1204.4616 http://henry.pha.jhu.edu/henry.hobson.pdf I've finished the Brooks book. It's not very well written and much of it is taken up with material that is familiar to physicists (but needs to be there for the nonphysicist reader). The main message is however very clear. He feels that it is deeply unfortunate that the quantum field theory (QTF) developed especially by Schwinger has been way underappreciated by the physics community in general, and the Feynman emphasis on particles (and particle exchange) has had unfortunate consequences. He makes a convincing case that for several decades the big names (Weinberg, Wilczek, etc.) have all worked within the QTF framework. He stresses that wave-particle duality is a mistake which unnecessarily makes quantum phenomena more paradoxical than they need be. I checked with a powerful theorist colleague at NCSU who agrees with the basic thrust of these arguments, though he's not comfortable with the phrasing, "There are no particles." He says that all reputable quantum field theory texts spend a lot of careful time defining what is meant by a "particle" in this context. Bruce P.S. The Kindle version of the Brooks book had badly mangled format, but a few days ago Amazon updated my copy so that it now looks good. **// Bruce Sherwood response offlist BTW, the book I recommended to Bruce was by Rodney A. Brooks. I was surprised he was writing on QFT and was excited as I assumed it would have a lucid explanation as he tends to write well. The book actually isn't as great as I had hoped. I had assumed it would be the same Rodney Brooks we know from the Alife/robotics world from MIT. Turns out there's another Rodney A. Brooks that was in Cambridge, MA with Schwinger who had a career at NIH and then retired to New Zealand. Oh well. --- -. . ..-. .. ... .... - .-- --- ..-. .. ... .... stephen.gue...@redfish.com 1600 Lena St #D1, Santa Fe, NM 87505 office: (505) 995-0206 tollfree: (888) 414-3855 mobile: (505) 577-5828 fax: (505) 819-5952 tw: @redfishgroup skype: redfishgroup gvoice: (505) 216-6226 redfish.com | simtable.com On Fri, Apr 19, 2013 at 3:09 PM, Stephen Guerin <stephen.gue...@redfish.com> wrote: > Along the lines that Lee is mentioning with fields being the first > class objects, Bruce Sherwood may be able to illuminate some of the > current thinking in Quantum Field Theory and how interpretations are > made with respect to forces. > > Bruce? > > -Stephen > > On Fri, Apr 19, 2013 at 1:36 PM, <lrudo...@meganet.net> wrote: >> Russ asks: >> >>> Is there a mechanistic-type explanation for how forces work? For example, >>> two electrons repel each other. How does that happen? Other than saying >>> that there are force fields that exert forces, how does the electromagnetic >>> force accomplish its effects. What is the interface/link/connection between >>> the force (field) and the objects on which it acts. Or is all we can say is >>> that it just happens: it's a physics primitive? >> >> I have the impression that the best you can say is that fields act on fields; fields are (the >> only) first-class objects, and what you're calling "objects" are at best second-class--they >> are epiphenomena of fields (or, of *the* field). >> >> There is (or was when I last tried to look into this, about 40 years ago) a concept of >> "current" (which I suppose is a generalization of our familiar "electric current", but if so >> is such a generalization that I was unable to see the connection at all) which was in some way >> involved with interactions of fields. Maybe a Google search on current and Jakiw would turn >> up something useful, but probably not. >> >> ============================================================ >> FRIAM Applied Complexity Group listserv >> Meets Fridays 9a-11:30 at cafe at St. John's College >> to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
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