[Paleopsych] SW: On the Concept of Force

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Theoretical Physics: On the Concept of Force

    The following points are made by Frank Wilczek (Physics Today 2004
    1) 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.
    2) 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 Schröedinger'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.
    3) In his 1895 Dynamics, the prominent physicist Peter G. Tait, who
    was a close friend and collaborator of Lord Kelvin (1824-1907) and
    James Clerk Maxwell (1831-1879), 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."(1)
    4) Particularly striking, since it is so characteristic and so
    over-the-top, is what Bertrand Russell (1872=1970) had to say in his
    1925 popularization of relativity for serious intellectuals, /The ABC
    of Relativity/:
    "If people were to learn to conceive the world in the new way, without
    the old notion of "force," it would alter not only their physical
    imagination, but probably also their morals and politics.... In the
    Newtonian theory of the solar system, the sun seems like a monarch
    whose behests the planets have to obey. In the Einsteinian world there
    is more individualism and less government than in the Newtonian."(2)
    The 14th chapter of Russell's book is entitled "The Abolition of
    Force." (3,4)
    References (abridged):
    1. P. G. Tait, Dynamics, Adam & Charles Black, London (1895)
    2. B. Russell, The ABC of Relativity, 5th rev. ed., Routledge, London
    3. I. Newton, The Principia, I. B. Cohen, A. Whitman, trans., U. of
    Calif. Press, Berkeley (1999)
    4. S. Vogel, Prime Mover: A Natural History of Muscle, Norton, New
    York (2001), p. 79
    Physics Today http://www.physicstoday.org
    Related Material:
    The following points are made by Ian Shipsey (Nature 2004 427:591):
    1) The fundamental particles called quarks exist in atom-like bound
    states, such as those constituting protons and neutrons, the quarks
    held together by the strong force. The heavier varieties of quark,
    such as the bottom quark, can disintegrate to produce other, lighter
    particles, and the pattern of the decay rates is constrained, but not
    determined, in the theory of fundamental particles, the so-called
    "standard model". That pattern, especially the part involving the
    bottom quark, is sensitive to new physical phenomena. But although
    accurate measurements of the rates have been made, the window on new
    physics has been obscured. This is because the binding effect of the
    strong force between quarks modifies the decay rates: unless
    correction factors can be accurately worked out, the data cannot be
    fully interpreted for signs of any physics that is as yet unknown.
    This has been the case for almost 40 years.
    2) The standard model describes all observed particles and their
    interactions. Particles interact by exchanging other particles that
    convey force. For example, in an atom, electrons bind to protons by
    swapping photons. This is the electromagnetic force, described by the
    theory of quantum electrodynamics (QED). In a proton, two types of
    quark, called "up" and "down", are bound together so tightly, by
    exchanging particles called gluons, that this is known as the "strong
    force". Its associated theory is quantum chromodynamics, or QCD. In
    the standard model there is a third force, the "weak force", which is
    the mediator of radioactive beta-decay. Another example of the weak
    force in action is the decay of a heavy bottom quark into an up quark,
    through the emission of a W particle (which then itself decays to an
    electron and an anti-neutrino).
    3) Despite its success, the standard model leaves many questions
    unanswered. For example, although the observable Universe is made of
    matter and there is no evidence for significant quantities of
    antimatter, equal amounts of both should have been created in the Big
    Bang. When matter and antimatter meet, they annihilate each other: if
    a small asymmetry between matter and antimatter did not exist at the
    time of the Big Bang, there would be no matter in the Universe today.
    So how did that asymmetry arise?
    4) If heavy particles that existed in the early Universe decayed
    preferentially into matter over antimatter, that could have created
    the matter excess. In the standard model, two types of quark, bottom
    and strange, do decay asymmetrically. But this effect alone is far too
    small to account for the asymmetry. However, there are many theories
    that predict the existence of other, massive particles that could
    readily produce the asymmetry. And because of the connection between
    asymmetry and mass, these theories also address other puzzles, such as
    why electrons are almost 10,000 times lighter than bottom quarks.
    Nature http://www.nature.com/nature
    Related Material:
    The following points are made by E. Buks and M.L. Roukes (Nature 2002
    1) In 1948, Hendrik Casimir (1909-2000) calculated that the quantum
    fluctuations of an electromagnetic field, so-called zero-point
    fluctuations, give rise to an attractive force between objects(1).
    This force is a particularly striking consequence of the quantum
    theory of electrodynamics(2). Casimir's calculations were idealized --
    he considered two perfectly conducting parallel plates at
    absolute-zero temperature -- but there are implications for more
    realistic objects. For example, Kenneth et al.(3) have extended these
    considerations to real-world materials.
    2) Their work follows that of Boyer in 1974, who also studied the case
    of parallel plates but with one plate perfectly conducting and the
    other having infinite magnetic permeability (permeability is a measure
    of the material's response to an applied magnetic field). For this
    special case Boyer found that quantum fluctuations induce a force with
    the opposite sign, causing the plates to repel each other(4). Kenneth
    et al (3) extend understanding of the Casimir force phenomenon to the
    more general situation of realistic "dielectric" materials that are
    characterized by both their electrical permittivity (a measure of the
    material's response to an applied electric field) and their magnetic
    permeability. Their numerical results show that repulsive forces can
    arise in the general class of materials with high magnetic
    3) Although the Casimir effect is deeply rooted in the quantum theory
    of electrodynamics, there are analogous effects in classical physics.
    A striking example was discussed in 1836, in P. C. Caussee's L'Album
    du Marin (The Album of the Mariner)(5). Caussee reported a
    mysteriously strong attractive force that can arise between two ships
    floating side by side -- a force that can lead to disastrous
    consequences. A physical explanation for this force was offered only
    recently by Boersma (1996), who suggested that it originates in the
    radiation pressure of water waves acting differently on the opposite
    sides of the ships. His argument goes as follows: the spectrum of
    possible wave modes around the two ships forms a continuum (any
    arbitrary wave-vector is allowed); but between the vessels their
    opposing sides impose boundary conditions on the wave modes,
    restricting the allowed values of the component of the wave-vector
    that is normal to the ships' surfaces. This discreteness created in
    the spectrum of wave modes results in a local redistribution of modes
    in the region between the ships, with the consequence that there is a
    smaller radiation pressure between the ships than outside them.
    References (abridged):
    1. Casimir, H. B. G. Proc. Kon. Ned. Akad. 51, 793-795 (1948).
    2. Bordag, M., Mohideen, U. & Mostepanenko, V. M. Phys. Rep. 353,
    1-205 (2001).
    3. Kenneth, O., Klich, I., Mann, A. & Rezen, M. Phys. Rev. Lett. 89,
    033001 (2002).
    4. Boyer, T. H. Phys. Rev. A 9, 2078-2084 (1974).
    5. Caussee, P. C. L'Album du Marin (Mantes, Charpentier, 1836).
    Nature http://www.nature.com/nature

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