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Thread: Is it true that the concept of force no longer applies?

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    Default Is it true that the concept of force no longer applies?

    Relativity.

    The idea behind force not existing is that the idea of any object existing at any time is really a series of events; example, it is not the force of the sun that acts on the planets, but rather the nature of space-time: the planet is simply moving in the line that the neighborhood (all events near a given event) permits, as gravity is actually a curvature of "space-time."

    "Along the way we show that conservation of four-momentum has an unexpected consequence -- the idea of force at a distance is inconsistent with the theory of relativity. This means that momentum and energy must be carried between interacting particles by another type of particle which we call an intermediary particle. These particles are virtual in the sense that they don't have their real-world mass when acting in this role. "

    http://physics.nmt.edu/~raymond/clas...k/node135.html

    Even two neighboring events could be classifed by means of "intervals" - space-like or time-like. The interval between them is time-like when one body is present at both and space-like if one body could observe both events simultaneously. If a body can travel from one event to another, the interval will be the time between them as measured by a clock. If this is impossible, the interval between them will be the same as the distance between them as verified by an independent observer - but this holds only so long as the events are very near together. Everything in relativity goes from next to next, and there are no relations between distance events, such as distance in space time.

    (Further explained by those numerous examples of a baby being placed in a capsule and supposed sent away from the earth, his "clock" will be different from the terristial beings on earth; if you a light is sent from person A on earth to person B on the sun, anything that happens to A before the light arrives at B and he sends it back, is neither definitely before nor after B receives it, etc. etc. Thus there is no way to tell if two events in space are really simultaneous or not.)

    Thus, the "history" of any event should be seen more like that of a play or an act, as a series of events and movements, rather than as having forces acting upon them, and in general relativity, the notion of "force" doesn't apply at all.

    "In modern particle physics, forces and the acceleration of particles are explained as the exchange of momentum-carrying gauge bosons. With the development of quantum field theory and general relativity, it was realized that "force" is a redundant concept arising from conservation of momentum (4-momentum in relativity and momentum of virtual particles in quantum electrodynamics). The conservation of momentum, from Noether's theorem, can be directly derived from the symmetry of space and so is usually considered more fundamental than the concept of a force. Thus the currently known fundamental forces are considered more accurately to be "fundamental interactions".[6] "

    Thus in a certain sense force is merely a convenient fiction used to explain a series of events, the atom or what have you is taking its most reasonable path, and physics is concerned with what happens, not the supposed reason (force) behind it.

    + YouTube Video
    ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


    sources:

    http://en.wikipedia.org/wiki/Force

    http://en.wikipedia.org/wiki/Fundamental_interactions

    http://en.wikipedia.org/wiki/Geodesic

    These fundamental interactions are better explained by Feynman diagrams

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    My understanding is that all forces with the exception of gravity are mediated by force-carrying gauge bosons (photons, gluons and W & Z bosons) which, because they travel at the speed of light, provide the illusion of "spooky action-at-a-distance".

    Of course, the force of gravity complicates the issue rather a bit, since gravitons have yet to be observed if they exist (PDF link).

    Therefore those magnetic fields with all the lines coming out of the magnets that you see in diagrams aren't really "there" so to speak, but represent a useful abstraction of what's going on.

    In other words, the map is not the same as the territory.
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    "Because an interaction results in fermions attracting and repelling each other, an older term for 'interaction' is 'force'."

    It is difficult to think of force as an antiquated notion or merely a convenience or even not existing at all at least in terms of space-time (all things that have been said about force that i have read). I imagine the mathematics involved in explaining it is very complex. Of course, Newtonian principles are still vaid a great deal of the time and can serve as a "stepping stone" to understanding relativity and it's hard to see how the theories could have been developed through any other way (much like the theory of atoms still is explained in outdated characteristics in the textbooks).

    Really, Newtonian principles have always been sufficient for my purposes, and yet most people do not even understand those very well, so it's easy to see why the abstractions for general relativity haven't been explained very well. Still, any clarity on the subject helps.

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    Here is what nobel prize laureate Frank Wilczek had to say:

    When I was a student, the subject that gave me the most trouble was classical mechanics. That always struck me as peculiar, because I had no trouble learning more advanced subjects, which were supposed to be harder. Now I think I've figured it out. It was a case of culture shock. Coming from mathematics, I was expecting an algorithm. Instead I encountered something quite different --- a sort of culture, in fact. Let me explain.

    Newton's second law of motion, F = ma, is the soul of classical mechanics. Like other souls, it is insubstantial. The right-hand side is the product of two terms with profound meanings. Acceleration is a purely kinematical concept, defined in terms of space and time. Mass quite directly reflects basic measurable properties of bodies (weights, recoil velocities). The left-hand side, on the other hand, has no independent meaning. Yet clearly Newton's second law is full of meaning, by the highest standard: It proves itself useful in demanding situations. Splendid, unlikely looking bridges, like the Erasmus Bridge (known as the Swan of Rotterdam), do bear their loads; spacecraft do reach Saturn.

    The paradox deepens when we consider force from the perspective of modern physics. In fact, the concept of force is conspicuously absent from our most advanced formulations of the basic laws. It doesn't appear in Schrdinger's equation, or in any reasonable formulation of quantum field theory, or in the foundations of general relativity. Astute observers commented on this trend to eliminate force even before the emergence of relativity and quantum mechanics.

    In his 1895 Dynamics, the prominent physicist Peter G. Tait, who was a close friend and collaborator of Lord Kelvin and James Clerk Maxwell, wrote:

    "In all methods and systems which involve the idea of force there is a leaven of artificiality...there is no necessity for the introduction of the word 'force' nor of the sense−suggested ideas on which it was originally based."...

    To anyone who reflects on it, it soon becomes clear that F = ma by itself does not provide an algorithm for constructing the mechanics of the world. The equation is more like a common language, in which different useful insights about the mechanics of the world can be expressed. To put it another way, there is a whole culture involved in the interpretation of the symbols. When we learn mechanics, we have to see lots of worked examples to grasp properly what force really means. It is not just a matter of building up skill by practice; rather, we are imbibing a tacit culture of working assumptions. Failure to appreciate this is what got me in trouble.
    From his book: Fantastic Realities. 49 Mind Journeys And A Trip To Stockholm (World Scientific, 2006). [Most of this quote can be found here.]

    Scientist and philosopher of science, Max Jammer noted:

    [The eliminability of force]...is not confined to the force of gravitation. The question of whether forces of any kind do exist, or do not and are only conventions, ha[s] become the subject of heated debates....

    In quantum chromodynamics, gauge theories, and the so-called Standard Model the notion of 'force' is treated only as an exchange of momentum and therefore replaced by the ontologically less demanding concept of 'interaction' between particles, which manifests itself by the exchange of different particles that mediate this interaction.... [Jammer (1999) The Concept of Force , p.v.]
    as Noxion and the Wiki article point out.

    [I have to say that there are just as many problems associated with this 'new view' of forces as there were with the classsical version, but I won't go into what they are here.]

    However, the contrary opinion (that the concept of force is alive and well, and rightly so, in Physics) is argued very forcefully in this recent paper:

    Wilson, J. (2007), 'Newtonian Forces', British Journal for the Philosophy of Science 58, 2, pp.173-205.

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    If magnetic fields don't exist, why do iron filings align and clump themselves into 'lines'?

    Are gravitational fields an abstraction?
    I have read that certain areas of the Earth's surface display higher or lower 'gravitational force'.

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    No one is denying that fields explain why the phenomena you mention occur; it's the ontologiocal status and causal efficacy of such things that is up for grabs (in view of the fact that a 'field' is a mathematical construct, and as such can move/arrange nothing at all).

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    Field = an area affected by a force.

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    Lynx:

    Field = an area affected by a force
    Well, that seems to separate forces from fields, since that latter appears to be a consequence of the former.

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    Quote Originally Posted by Rosa Lichtenstein View Post
    Well, that seems to separate forces from fields, since that latter appears to be a consequence of the former.
    Yes... fields do have some properties of their own, namely distance and permeability, which, if relevant, form part of an equation.

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    Well, thanks for posting those quotes, Rosa. That is basically what I was trying to say and thought some people here might like to hear the discussion. (Physics is not my field and when I first heard this I was also given somewhat of a "shock.")

    The second quote actually makes sense to me, and I'll try and convey it whenever I bring up the issue.

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    I thought it was a given that Newtonian and other classical mechanics are an "incomplete" picture of the universe, a "special case" so to speak. For example, Newtonian mechanics is just fine for plotting the courses of space probes and rockets because they cannot approach significant fractions of the speed of light, where Relativity comes into play. It's entirely possible to plan a space mission using Relativistic maths, but Newton's approach is easier and accurate enough for the job.

    In a purely Newtonian universe, one can accelerate as much as one has reaction mass to do so. However, we do not live in a Newtonian universe, so as one approaches the speed of light additional factors, unpredicted by Newton, come into play. Hence the "incompleteness". It also turns out that there are objects with enormous masses (black holes, neutron stars etc) as well as objects travelling at enormous energies (cosmic rays) throughout the known universe, hence also the "special case" aspect.
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    Lynx:

    Yes... fields do have some properties of their own, namely distance and permeability, which, if relevant, form part of an equation.
    And yet, how can a mathematical object like a field make objects move (i.e., create a force)?

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    Noxion:

    I thought it was a given that Newtonian and other classical mechanics are an "incomplete" picture of the universe, a "special case" so to speak. For example, Newtonian mechanics is just fine for plotting the courses of space probes and rockets because they cannot approach significant fractions of the speed of light, where Relativity comes into play. It's entirely possible to plan a space mission using Relativistic maths, but Newton's approach is easier and accurate enough for the job.
    This is the standard view, but Newtonian mechanics cannot be a special case on Relativity Theory since many of the concepts employed by the former are totally different from those used in the latter -- for example, 'mass', 'time' and 'space' -- and of course, 'force'.

    And, it is possible to use Newtonian theory to explain all the anomalies that Einstein's theory supposedly explains far batter, for example the perihelion of Mercury, and equally accurately.

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    Quote Originally Posted by Rosa Lichtenstein View Post
    This is the standard view, but Newtonian mechanics cannot be a special case on Relativity Theory since many of the concepts employed by the former are totally different from those used in the latter -- for example, 'mass', 'time' and 'space' -- and of course, 'force'.

    And, it is possible to use Newtonian theory to explain all the anomalies that Einstein's theory supposedly explains far batter, for example the perihelion of Mercury, and equally accurately.
    But GR has stood up to decades of tests. Obviously these Newtonian explanations are insufficient.
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    Noxion:

    But GR has stood up to decades of tests. Obviously these Newtonian explanations are insufficient.
    No one 'important' has bothered to test Newton's theory, that's the only difference.

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    Quote Originally Posted by Rosa Lichtenstein View Post
    And yet, how can a mathematical object like a field make objects move (i.e., create a force)?
    Fields are real world objects that lend themselves to mathematical analysis - perhaps you are referring to the (imaginary) lines of force?

    Fields don't make objects move, but they can affect the lines of force, by diverting and concentrating them. Flux density is an often used term. The magnitude of the force is represented by the number of lines of force per given area.

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    Lynx:

    Fields are real world objects that lend themselves to mathematical analysis - perhaps you are referring to the (imaginary) lines of force?
    In that case, what are fields made of? If they are made of nothing, how are they different from nothing? If they are made of something, what holds them together but other forces? In that case, you'd be explaining force by means of force, and thus going round in circles.

    Fields don't make objects move, but they can affect the lines of force, by diverting and concentrating them. Flux density is an often used term. The magnitude of the force is represented by the number of lines of force per given area.
    Once more, how can fields do this if they are made of nothing? And if they are made of something, then other forces (of cohesion, resistance, etc.) come into play, as noted above.

    In that case, you'd have forces changing the motion of bodies.

    But, forces are not made of anything; so how can they affect the motion of bodies?

    This is in fact the classic problem posed by Leibniz, to which no one has been able to think of an effective answer. There isn't much on-line on this, but the following partly explains the background:

    http://www.garybanham.net/LECTURES_f...ALECTURE16.pdf

    And several related issues are explained by one of my old teachers:

    "As significant as his critique of Descartes' mechanics was Leibniz's attack on Newton's account of force. In the Principles, Newton limited himself to describing interactions between bodies in terms of general mathematical laws. This limitation was both a strength and a weakness. Newton succeeded in making the complexities of nature amenable to mathematical description only by simplifying the phenomena: by treating material particles as if they were infinitely hard yet infinitely elastic, concentrated at points, capable of exchanging any amount of force all at once, connected by forces operating instantaneously at a distance, and so on. Leibniz complained that this made Newton's system an idealised abstraction, which could not possibly be true of the real world. In reality, nothing was absolutely hard or elastic, nothing happened instantaneously, and every causal interaction was mediated by a complex mechanism. In general terms, Newton would have agreed with Leibniz's comment. He too believed in underlying mechanisms, but he refused to speculate about them in the Principles (his famous, 'I do not invent hypotheses')....

    "Much later, in his Specimen of Dynamics (1695), Leibniz tried to give an account of the mechanism which mediated exchanges of force between colliding bodies. In real collisions (unlike Newton's idealisations), there had to be a finite period during which one body slowed down and the other picked up speed. This implied that bodies had a certain size, and were not absolutely hard or elastic, since the only conceivable mechanism for transfer of force was that bodies were first squashed together, and then gradually sprang back from each other once all the kinetic energy had been taken up. However, as soon as it is accepted that transfer of force between every day objects must be mediated by a mechanism, there is no point at which you stop needing smaller and smaller sub-mechanisms. At no level can you suddenly say that force is transferred directly.

    "Elasticity is itself a phenomenon requiring explanation in terms of pushings of particles. At the first instant of impact, the outermost particles of each colliding body push against their neighbours, and these in turn push against their neighbours, and so on right through each body. But then each of these pushings needs to be explained by the compression of sub-particles, and so on to infinity. The conclusion Leibniz drew was that, ultimately, forces were not really transferred at all. All action was, as he put it, spontaneous. The energy required for a body's motion on the occasion of an impact, had to be drawn from its own resources, since it could not actually take up any energy from bodies impinging on it....

    "An even more significant aspect of the theory was its abandonment of the traditional notion that matter was essentially inert. Leibniz saw that if the only function of matter was as a passive carrier of forces, then it had no role to play in scientific explanation. Its only role would be the metaphysical one of satisfying the prejudice that forces must inhere in something more substantial than themselves. He maintained that matter was nothing other than the receptive capacity of things, or their 'passive power', as he called it. Matter just was the capacity to slow other things down, and to be accelerated rather than penetrated (capacities which ghosts and shadows lack) -- in other words, inertia or mass, and solidity. So, taking also into account 'active powers' such as kinetic energy, Leibniz reduced matter to a complex of forces. In this he was anticipating modern field theory, which treats material particles as concentrated fields of force –- an anticipation duly recognised by its founder, the Italian mathematician Ruggiero Giuseppe Boscovich (1711-87)." [Ross (1984) Leibniz, pp.40-44.]

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    Quote Originally Posted by Rosa Lichtenstein View Post
    In that case, what are fields made of? If they are made of nothing, how are they different from nothing? If they are made of something, what holds them together but other forces? In that case, you'd be explaining force by means of force, and thus going round in circles.
    Fields are comprised of 3 dimensional space. They are a consequence of a distance parameter in an equation. If I hold a magnet in my hand, the magnetic field extends into 3 dimensional space, and is affected by the medium present within that space.

    I cannot answer to the rest of your post. By my understanding, lines of force are used to represent the magnitude and distribution of force over areas of space. By some (or most?) accounts, it is just a representation!

    Read this?

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    Lynx:

    Fields are comprised of 3 dimensional space. They are a consequence of a distance parameter in an equation. If I hold a magnet in my hand, the magnetic field extends into 3 dimensional space, and is affected by the medium present within that space.
    This seems to mean that fields are mathematical objects after all!

    I cannot answer to the rest of your post. By my understanding, lines of force are used to represent the magnitude and distribution of force over areas of space. By some (or most?) accounts, it is just a representation!
    Maybe so, but representing what exactly?

    Thanks for the link, but that seems to confirm my suspicion: forces and fields are mathematical, not physical, entities.

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    Quote Originally Posted by Rosa Lichtenstein View Post
    This seems to mean that fields are mathematical objects after all!
    The math describes relationships, for example:
    A particle passing through a magnetic field of 1 Tesla at 1 meter per second carrying a charge of 1 Coulomb experiences a force of 1 Newton, according to the Lorentz Force Law.
    Maybe so, but representing what exactly?
    Representing what can be observed or measured.
    Thanks for the link, but that seems to confirm my suspicion: forces and fields are mathematical, not physical, entities.
    Well, topographic lines don't physically exist, but they can represent the slope and elevation of geographic features. They provide numbers able to describe physical objects.

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