How do forces work?
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Yesterday I asked this question on StackExchange: physics.
So far, there haven't been any answers that feel satisfying--although, please look at them yourselves. One of the comments pointed to a 7 1/2 minute video by Feynman, in which he talks around the problem before finally saying he can't provide an intuitive explanation. I don't think it was one of his better efforts. Does anyone on this list have an answer?
-- Russ Abbott _____________________________________________
Professor, Computer Science
California State University, Los Angeles ============================================================ 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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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 |
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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, <[hidden email]> 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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One of the replies to my question on StackExchange was that what really mattered was that something is accelerated. Since acceleration is really(?) a matter of a change in energy of the thing accelerated, perhaps the most fundamental interaction is the transfer of energy from one entity (whatever an entity is) to another. Do we have any reasonable way to talk about how that happens?
-- Russ Abbott _____________________________________________ Professor, Computer Science California State University, Los Angeles On Fri, Apr 19, 2013 at 2:09 PM, Stephen Guerin <[hidden email]> wrote: Along the lines that Lee is mentioning with fields being the first ============================================================ 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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How forces work:
Theres the dark forces and light forces with all persistant and guide your destiny. They push against each other yet somehow balance out. With enough of the dark forces you can choke people you deem incompitent, or shoot lightning from your hands. I hope that helps answers the questions. (I do work on fridays) On Fri, Apr 19, 2013 at 3:47 PM, Russ Abbott <[hidden email]> wrote:
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In reply to this post by Stephen Guerin
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/NeutronDecay 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. --- -. . ..-. .. ... .... - .-- --- ..-. .. ... .... [hidden email] 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 <[hidden email]> 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, <[hidden email]> 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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In reply to this post by Russ Abbott
(bad joke aside): Russ do you have a specific type of force group of forces in mind?
On Fri, Apr 19, 2013 at 3:47 PM, Russ Abbott <[hidden email]> wrote:
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In reply to this post by Russ Abbott
Russ,
Before people knew about magnetism, it must have seemed miraculous that two stones would spontaneously start to move toward (or away from) each other. Now we can say, "Oh, it's just magnetism". But if we think about long enough, we may still wonder how two objects can move toward or away from each other. My question would be, "Does magnetism still seem a bit miraculous, or do you feel your question is answered, at least for magnetism? In either case, what would a satisfying answer look like?" John ________________________________________ From: Friam [[hidden email]] on behalf of Russ Abbott [[hidden email]] Sent: Friday, April 19, 2013 1:50 PM To: FRIAM Subject: [FRIAM] How do forces work? Yesterday I asked this question<http://physics.stackexchange.com/questions/61542/how-do-forces-work?noredirect=1#comment123788_61542> on StackExchange: physics. 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? So far, there haven't been any answers that feel satisfying--although, please look at them yourselves. One of the comments pointed to a 7 1/2 minute video by Feynman, in which he talks around the problem before finally saying he can't provide an intuitive explanation. I don't think it was one of his better efforts. Does anyone on this list have an answer? -- Russ Abbott _____________________________________________ Professor, Computer Science California State University, Los Angeles My paper on how the Fed can fix the economy: ssrn.com/abstract=1977688<http://ssrn.com/abstract=1977688> Google voice: 747-999-5105 Google+: plus.google.com/114865618166480775623/<https://plus.google.com/114865618166480775623/> vita: sites.google.com/site/russabbott/<http://sites.google.com/site/russabbott/> CS Wiki<http://cs.calstatela.edu/wiki/> and the courses I teach _____________________________________________ ============================================================ 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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Thanks for all the answers. To answer John's question first, magnetism doesn't seem miraculous (it's too familiar), but I can't say I understand how it works. It was just that question about magnetism that Feynman was asked as the start of the video in which he danced around the question before saying he couldn't give an intuitive answer.
What would a satisfying answer look like? That's a very good question. Superficially it would be something like a sophisticated version of billiard balls: when one hits another, energy is transferred. But even that doesn't work well when looked at carefully. What happens in detail when one hits another. If the two objects were absolutely solid, how would one "feel" the impact of the other. Would the transfer simply become a primitive? If they were somewhat springy, how does that springyness work? And besides, there must be some surface-like thing that receives the impact and something more internal that absorbs it.
Bruce's QM photon explanation is pretty close to what I'm looking for, but as he notes, it only works for repulsive forces. It also relies on primitives. In that case the emission and absorption of a photon and the associated transfer of energy seem to be primitive actions.
The papers by Hobson look very interesting. They even look like I can read them. I haven't done that yet, though.
As a software person, a good explanation is often something like an API. How does one object interact with another? We know that objects have capabilities (specified by their APIs), and that it's possible for one object to trigger the performance of a capability in another object. We don't ask how the triggering event gets from one to the other. That's magic at a lower level. We just assume that it can happen and that there isn't anything more to say about it at the object level of abstraction.
So I would be (somewhat) happy with an answer that said (a) what the capabilities are (something like a API for elementary particles/fields) and (b) what the non-decomposable primitive actions are, e.g., like emit and absorb.
-- Russ Abbott _____________________________________________ Professor, Computer Science California State University, Los Angeles On Fri, Apr 19, 2013 at 7:06 PM, John Kennison <[hidden email]> wrote: Russ, ============================================================ 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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In reply to this post by John Kennison
I like the question. I wonder what the answer will be? N
-----Original Message----- From: Friam [mailto:[hidden email]] On Behalf Of John Kennison Sent: Friday, April 19, 2013 8:07 PM To: [hidden email]; The Friday Morning Applied Complexity Coffee Group Subject: Re: [FRIAM] How do forces work? Russ, Before people knew about magnetism, it must have seemed miraculous that two stones would spontaneously start to move toward (or away from) each other. Now we can say, "Oh, it's just magnetism". But if we think about long enough, we may still wonder how two objects can move toward or away from each other. My question would be, "Does magnetism still seem a bit miraculous, or do you feel your question is answered, at least for magnetism? In either case, what would a satisfying answer look like?" John ________________________________________ From: Friam [[hidden email]] on behalf of Russ Abbott [[hidden email]] Sent: Friday, April 19, 2013 1:50 PM To: FRIAM Subject: [FRIAM] How do forces work? Yesterday I asked this question<http://physics.stackexchange.com/questions/61542/how-do-forces-work ?noredirect=1#comment123788_61542> on StackExchange: physics. 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? So far, there haven't been any answers that feel satisfying--although, please look at them yourselves. One of the comments pointed to a 7 1/2 minute video by Feynman, in which he talks around the problem before finally saying he can't provide an intuitive explanation. I don't think it was one of his better efforts. Does anyone on this list have an answer? -- Russ Abbott _____________________________________________ Professor, Computer Science California State University, Los Angeles My paper on how the Fed can fix the economy: ssrn.com/abstract=1977688<http://ssrn.com/abstract=1977688> Google voice: 747-999-5105 Google+: plus.google.com/114865618166480775623/<https://plus.google.com/1148656181664 80775623/> vita: sites.google.com/site/russabbott/<http://sites.google.com/site/russabbott/> CS Wiki<http://cs.calstatela.edu/wiki/> and the courses I teach _____________________________________________ ============================================================ 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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In reply to this post by Russ Abbott
Russ,
I think Bruce was using the traditional photon explanation (particles, or particle/waves as primitives) as a setup to introduce the more novel approach of treating fields as primitives. This is more appealing to me and tends to be how we write agent-based models that scale. In fact, one of my rants is that ABM might be better named interaction-based modeling as the models tend to focus on the interactions and not the properties of agents (particles). As one scales up the populations and interactive forces, we tend to convert the interactions to local moving fields (eg pheromone fields around ants, quadtrees in flocking to reduce n^2 interactions to NLogN, etc).
On Fri, Apr 19, 2013 at 9:08 PM, Russ Abbott <[hidden email]> wrote:
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In reply to this post by Gillian Densmore
+2 !
How forces work: ============================================================ 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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In reply to this post by Russ Abbott
leptons-
I think it is all "intermediate vector bosons"... or maybe I just like the way that phrase sounds? -boson
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If everything is fields, how do fields transfer energy from one to another? (I still have to read Hobson papers.)
-- Russ Abbott _____________________________________________ Professor, Computer Science California State University, Los Angeles On Fri, Apr 19, 2013 at 9:33 PM, Steve Smith <[hidden email]> wrote:
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In reply to this post by Steve Smith
hmm:
So what happens if a repulicon and a boson colide? On Fri, Apr 19, 2013 at 10:33 PM, Steve Smith <[hidden email]> wrote:
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Gil-
> hmm: > So what happens if a repulicon and a boson colide? I think it just did... we'll have to see how it turns out... watch for distortions in your field. - Boson ============================================================ 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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In reply to this post by Gillian Densmore
Too bad we don't have Bruce and Ruth here to jury this sideshow, but still!
I was always disturbed by the "rubber sheet" description of Gravitational Forces. In the spirit of circular logic, I was always left wondering when the models of say the sun and a planet or two were set down onto the "rubber sheet" to show how their masses distort the "fabric of time and space", the question always popped up for me... "just what pulls those massive objects down to distort the rubber sheet? Gravity?" Everything you need to know about "Life, the Universe and Everything" can be found in XKCD. I think Randall Munroe has been listening to our conversations here and making fun of us behind our backs! http://xkcd.com/1158/ ============================================================ 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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Steve,
I you are going to destroy an entire morning of mine by tempting me to go to the XKCD website, I am going to return the favor. http://xkcd.com/1162/ -----Original Message----- From: Friam [mailto:[hidden email]] On Behalf Of Steve Smith Sent: Saturday, April 20, 2013 9:38 AM To: The Friday Morning Applied Complexity Coffee Group Subject: Re: [FRIAM] How do forces work? Too bad we don't have Bruce and Ruth here to jury this sideshow, but still! I was always disturbed by the "rubber sheet" description of Gravitational Forces. In the spirit of circular logic, I was always left wondering when the models of say the sun and a planet or two were set down onto the "rubber sheet" to show how their masses distort the "fabric of time and space", the question always popped up for me... "just what pulls those massive objects down to distort the rubber sheet? Gravity?" Everything you need to know about "Life, the Universe and Everything" can be found in XKCD. I think Randall Munroe has been listening to our conversations here and making fun of us behind our backs! http://xkcd.com/1158/ ============================================================ 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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In reply to this post by Stephen Guerin
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. OT, but: I think we failed a test. Maybe we should split the list? Or use wedtech exclusively for physics, programming, etc?
I now simply don't know who is on what list, nor what their interests are. I'm sure Russ wanted Bruce's post, right?
-- Owen
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Yes, I definitely wanted Bruce's post. -- Russ Abbott _____________________________________________ Professor, Computer Science California State University, Los Angeles On Sat, Apr 20, 2013 at 9:47 AM, Owen Densmore <[hidden email]> wrote:
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