Re: Attraction VS geometry


Joe Fischer wrote:
> On Wed, 09 Nov 2005 01:53:16 GMT, Tom Roberts <tjroberts@xxxxxxxxxx> wrote:
>
> >Joe Fischer wrote:
> >> It may even be worse to call it an aspect of geometry, and then
> >> claim that the inertial frame of an object is "falling", but the freefalling
> >> object is not.
> >
> >Using the standard vocabulary, both the LOCALLY-inertial comoving frame
> >of the object and the object itself are in freefall, and each is indeed
> >falling.
>
> To an observer on the surface of Earth, sure, I knew that.
>
> > They are, of course, accelerating relative to an accelerated
> >coordinate system fixed on the surface of the earth.
>
> I want to agree, and I consider you the teacher, but
> I see no need to say the falling object and it's inertial farme
> are accelerating relative to an accelerated coordinate system
> fixed on the surface of Earth.
>
> Yes, I agree there is a relative acceleration, but
> some rational sense but be reflected in statements, and
> if the surface of the Earth has an accelerated coordinate
> system fixed to it, then that has to have some meaning
> other than just to be compatible with "falling" objects
> moving inertally.
>
> >"Freefall" and "falling" merely mean the object in question is not
> >subject to any forces (considering gravity to NOT be a force).
>
> Ok, but why mention gravity in this statement, why
> claim to suscribe to the basic premise of General Relativity
> of inertial motion freefall, and then insinuate that gravity is
> acting on the objects.
> Why not just say the falling objects are in inertial motion,
> and leave it at that?
>
> >You seem to be trying to apply unusual meanings to the words "freefall"
> >and "falling", and get yourself horribly confused. DON'T DO THAT.
>
> No I am not trying, and I am not doing that, if freefall is not
> simply inertial motion, then it is not freefall. I make no other claim
> about what meaning is applied.
>
> >> In the Principle of Equivalence, the "path" is merely undisturbed
> >> motion, but in an explanation, you seem to say there is no attraction
> >> acting on the freefalling object, but there is sone type of action that
> >> resembles attraction acting on the geometry.
> >
> >There is nothing "acting on the geometry", the geometry just _IS_. Of
> >course the geometry must be consistent with the distribution of
> >mass/energy/momentum, in accordance with the Einstein field equation.
> >What you seem to think of "acting" is merely a consistency requirement
> >of GR.
>
> It sounds like this is an attempt to disguise Newtonian concepts
> as part of General Relativity. I think you have said in the past that
> GR is background free, and notw say that the geometry has a goemetry
> that is shaped by the presence of matter/energy/momentum.
>
> >>>... near the earth,
> >>>the geodesic path for a dropped object approches the center of the
> >>>earth,
> >>
> >> Frankly, I don't think you can provide any kind of proof of that,
> >> in fact I believe that a "dropped" object has to be moving away
> >> from the center of the Earth.
> >
> >Measurements and observations indicate otherwise -- objects dropped from
> >rest wrt the surface of the earth do indeed approach the center of the
> >earth, they don't zoom away upwards. Just TRY it.
>
> So now we are back to pure Newtonian gravitation.
>
> >> Oh, I see, you are saying the radius of the Earth is constant,
> >> that the Earth is considered stationary, and a static object.
> >
> >Yes. Of course. Measurements indicate that (for suitable coordinates).
>
> While theoretical physics must user measurements as a guide,
> the measurements are subject to interpretation.
> You stateements seem to insist that applied physics is all there is.
>
> >> This is a good move on your part, it means you will not
> >> have problems with your peers.
> >
> >No, it means I won't have "problems" with MEASUREMENTS AND OBSERVATIONS.
> >This _IS_ supposed to be physics.
>
> And I suppose ALL IS KNOWN about physics, because it has been measured.
>
> >That's your basic problem -- you do not believe that real measurements
> >mean what they clearly do mean.
>
> Of course I believe that real measurements mean what they mean,
> but I also believe that there could be a process that causes all measurements
> to be what that are and what they mean, and that they could not be anything
> other than what they are.
>
> >The radius of the earth is MEASURED to
> >be constant (to high accuracy, anyway). Until you reconcile yourself to
> >measurements, you have no hope whatsoever to understanding any physics.
> ><shrug>
> >Tom Roberts tjroberts@xxxxxxxxxx
>
> I do very well with physics, I have no trouble with measurements,
> but I don't see a need to restrict physics to surveying and engineering,
> without an attempt to interpret the measurements and observations.
>
> While the Divergent Matter model is weird, in it, all measurements
> would be what they are, even if matter expands.
> Things change dimensions with changes in temperature, and
> some things change dimensions when the amount of water in them
> changes.
> I am open minded to any model that can make some sense
> out of all the measurements. I would not relegate a physicist to
> simply be a bookkeeper of measurements.

Good point! On the other hand, given our right to freely invent
theories of our own liking, the physics community, in its need to
compare the relative merits of competing theories, is more interested
in the economy (simplicity and harmony) of a theory than in its
weirdness per se. Atoms were once considerd as weird, as was atomic
theory of a compact, solid nucleus of protons with electrons flitting
around it (what holds the nucleus together!). Light as particles was
once considered as weird. Radioactivity (unstable atoms proved by the
Curies) was once considered as weird. An expanding universe was once
considered as weird. QM was once considered as weird. So too SR and GR
were considered as weird.

Weirdness is a subjective and time-relative notion that is usually
dropped after one or two generations of physicists living and working
with it. And sometimes that's bad, because physicists can get used to a
weird concept that they take for granted instead of challenging, such
as the case of absolute inertia, which Mach challenged and Einstein
took-up the task of ridding from physics.

Classical physics is not without its own weirdness! Nutation, for one.
Add audio energy of a wave set out of phase to itself and you get less
noise, not more. It took a long time for people to think of short-range
projectile motion as parabolic, though today it seems perfectly natural
(you'd laugh at the bizzare paths gunners once thought that cannon
balls took in space). Action-at-a-distance was once considered as
weird, but people got so used to it, they stopped thinking of it as
weird. In fact, it came to be regarded as quite natural. The
heliocentric model of the planetary system was once considered as
weird. The history of physics demonstrates that the seeming weirdness
of a concept or theory is in itself useless as a predictor of its final
utility.

Demonstrate that the Divergent Matter model is first as predictively
accurate as GR and second that it is also simpler than GR and then
you'll have something to boast about.

While GR is a principle theory and not intended as an explanation of
gravity in mechanical terms, it does integrate space, time,
matter-energy, and motion into one theory. Therefore, it cannot be
fairly written off as merely a bookkeeping of measurements.

>>From the formal point of view, every theory invents its own
explanations: the theorems are *explained* in terms of the postulates!
No theory ever explains its own postulates! Einstein was successful in
what he wanted to accomplish from a formal point of view: He invented a
theory of gravity that replaced Newton's gravitational
action-at-a-distance between particles with a field theory of particle
interaction in which free particles travel on geodesics in spacetime (a
minimization principle).

The notion that the only "true explanations" are both reductionist and
classical mechanical is out of step with QM in the first place. So, the
hope that gravity can be explained in some classical reductionistic,
mechanical explanation is doomed without a radical new foundation to
micro-physics. QM teaches us that the micro world is not "explainable"
in terms of the macro world, but that the macro world, with all of its
classical laws, is a mere epiphenomena of the micro world. (I say this
somewhat tongue in cheek, but only somewhat, because "explanations" are
where one chooses to find them! Because of this truth, arguments on
this forum tend to be both philosophical and doomed from the start to
make any converts. Many technical arguments are given, but ignored,
because of a priori philosophical predispositions against the arguments
"being right.")

.

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