On Sun, 25 Dec 2005 09:14:20 -0500 Les Schaffer <schaffer at optonline.net>
writes:
> Chris Doss wrote:
>
> >That's not a mechanism -- that's an improved
> >predictive model. The question is "why does matter
> >cause space to 'curve'?", i.e., "why is there
> >gravity?", "why does matter have this occult
> >property?"
> >
>
>
> i'd split the difference here. no previous theory i know of ever
> suggested a clock should run more slowly deeper in a gravitational
> field
> (a quick result from the equivalence principle), though Gauss DID
> wonder
> if large scale triangulation would show interior angles adding up to
> 180
> degrees. a theory which -- on top of making clock synchronization
> and
> simultaneity practical realities -- ties our clocks and rulers to
> matter
> and energy is a more down-to-earth theory than we had previously.
>
> although it doesnt qualify as a mechanism in the way i think Chris
> means, its nice to have a dynamic, field oriented model for gravity,
> even if gravity waves arent exactly of blinding intensity in this
> part
> of space-time. finding wave equations -- be it for the photon
> (electromagnetism), the electron, the graviton, and so on -- seems
> always to advance our understanding. such a theory for gravity
> suggests
> that binary star systems will evolve due to emission of
> gravitational
> radiation via such waves. (google: Taylor Hulse PSR B1913+16
>
<http://en.wikipedia.org/w/index.php?title=PSR_B1913_plus_16&action=edit>
> )
>
> as to general relativity and the notion of a force, many physicists
> are
> fond of the expression "tidal interaction" or "tidal force" for
> gravity's action. this in honor of the observation that although
> free
> fall in space makes us feel weightless, body parts closer to earth
> are
> pulled away from body parts farther away from the earth's center. in
> a
> similar fashion, body parts seperated spatially but equidistant from
> earth's center are pulled closer together. the ocean's tides are a
> prime
> example of this effect. it is this tidal effect which is central to
> GTR.
> the notion that there is no gravity force because everything just
> falls
> freely in curved space-time is only one piece of the puzzle. a much
> clearer way to visualize GTR is to take an initially spherical cloud
> of
> mases and let them free-fall. watching the distortion of the
> spherical
> geometry gives a nice picture of the curved spacetime near massive
> objects. [if jks took relativity with Wheeler, he's heard all about
> this.]
>
> by the way, Nature on Wednesday published a paper that verifed
> E=mc^2 to
> several parts in 10 million (a factor of 55x over the previous
> accuracy
> winner, electron/positron annhilation experiments). in the same
> issue,
> Freeman Dyson discusses S. Chandrasekhar theory of the death of
> "heavy"
> stars (stellar astrophyics plus general relativity plus QM) and Ed
> Witten waxes prophetic on string theory, with, however, a caveat on
> unified theories:
>
> In fact, there are ample reasons why one might doubt whether
> Einstein's vision is achievable, or at least achievable in the
> foreseeable future. Crucial clues may be hopelessly out of reach.
> When looking back at Einstein's own work, most physicists would
> say
> that many of the most important clues for a unified field theory
> —
> involving strong and weak nuclear interactions, the role of gauge
> theory and the world of elementary particles — were simply not
> known
> in Einstein's day.
And Einstein thought that a unified field theory would take the form of a classical field theory, not unlike Maxwell's electrodynamics or Einstein's own theory of general relativity, rather than a quantum field theory. In fact it was Einstein's hope that a unified field theory would supersede quantum mechanics, which he had always disliked as a physical theory. However, as the theory of electroweak unification showed, a unified field theory, if one is possible, will almost certainly take the form of a quantum field theory.
>
> Moreover, even if we could somehow find the unified field
> theory, it
> is not at all clear whether we could determine that it is right.
> From a simple combination of Planck's constant, the speed of
> light,
> and Newton's gravitational constant, one can construct a natural
> unit of length — the Planck length. First defined by Max Planck a
> century ago, this length is so fantastically small that if it, or
> something close to it, is fundamental in
> physics, then some of the most important phenomena may be
> permanently beyond our experimental reach.
>
> in my opinion, though superstring/brane theory offers a possible
> escape
> from "failure to renormalize", the nicer results right now at the
> intersection of quantum field theory and general relativity are work
> on
> black hole energetics and thermodynamics (hawking et al, the penrose
> process, Wikipedia not bad here) -- and yes, string theory has a
> take on
> these topics -- along with first order quantum field theory in
> curved
> spacetime (my favorite result is the Unruh effect:
> http://en.wikipedia.org/wiki/Unruh_effect ), and quantum geometries
> (smolin et al, is area quantized?
> http://www.phys.lsu.edu/mog/mog21/node11.html ). though not yet (and
> maybe never) amenable to experimental verification, they have the
> kind
> of down and dirty feel to them that reminds me of einstein's
> speculations on time, simultaneity, and equivalence of mass and
> energy,
> all of which took years to really gel into a cohesive,
> experimentally
> verified whole.
>
>
>
> les schaffer
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