NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/astro/13344

Text File | 1992-12-22 | 7.8 KB | 159 lines

Newsgroups: sci.astro
Path: sparky!uunet!well!metares
From: [e-mail] (Tom Van Flandern)
Subject: Re: The Hole Story
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: Whole Earth 'Lectronic Link
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Tue, 22 Dec 1992 06:39:32 GMT
Lines: 147


     My earlier posting of this message was garbled from the mid-point on.
This
is a re-post of the garbled part only.

     [This contains replies to Chris Flatters, Thomas Clarke, Jack Gallimore,
Paul Gilmartin and Benjamin Weiner.]

[conclusion of text to [e-mail] (Chris Flatters):]

>> [TVF]: leaving students in a state of disbelief when they learn about it
>> later in their careers.

     I'm sorry you seem to be in this position yourself.  Please investigate
the matter until you are satisfied, one way or another.  Let me know what
arguments concern you, and I can elaborate or supply details of references.

     Lots of people before you have done this same double-take.  My only
complaint is that the schools don't make more of a point of it.  Perhaps you
will let your own future students know the whole story, so they won't have to
go through this unpleasant process later in their careers.


and [e-mail] (Thomas Clarke) replied:

> I suspect if the sun had a static electrostatic charge then the
> electrostatic field would tend to act from the "true, instantaneous
> position."  No contradiction to special relativity since the field is
> unchanging and nothing is propagating.

     That is the standard GR explanation for why the gravitational field acts
from the true, instantaneous position.

> Conversely, if the sun were radiating gravitational waves (from micro-black
> holes in its core or some such) the graviational waves would appear to come
> from the retarded position.

     Granted.  Gravity waves (which have nothing to do with force) travel at
c, and therefore come from retarded positions, as anything moving at c must
do.  Gravity, by way of contrast, does not.


and [e-mail] (Jack Gallimore,P254) replied:

> No, that's crap.  It takes time for all forces to propagate, even gravity.
> For example, one of the problems in observational cosmology is
> understanding large scale structures (for example, the distribution of
> clusters and voids).  The notion is that you can't have any structure
> arising from gravity that's larger in light-years than the age of the
> universe in years.  This is because gravity also must "propagate" at the
> speed of light.

     Think about what you just said.  You can't have a structure bigger than
10 billion lightyears?  The argument I think you meant to quote was the one
that you can't have structures bigger than galaxies can span at their
peculiar velocities of 1000-3000 km/s over the age of the universe.  But that
argument is irrelevant to our present discussion.

> I'd like to see the reference on the observation you claim to be "true."

     For a history of (unsuccessful) attempts to build theories in which
gravity propagates, see MTW, chapter 7.  GR was the first theory to get
around these problems, and its big breakthrough was getting rid of
propagation.  If anything propagates in the static gravity field, then GR or
SR must fail because observations show that any propagation must be ftl.
According to Laplace and Poincare, the minimum propagation speed must be 10^7
- 10^8 times the speed of light.  With the accuracy of modern data, we can
now revise that minimum to 10^10 c!


and [e-mail] (Paul Gilmartin) replied:

> I'm curious (and naive).  Does the Coulomb potential around a static
> electric charge appear retarded or instantaneous?  In other words, does an
> electric charge in orbit spiral in because of the Poynting-Robertson
> effect?  I know it spirals in because it radiates because of centripetal
> acceleration, but I suppose this is analogous to binary neutron stars
> losing orbital energy to gravitational radiation, which you don't attribute
> to retarded potential.

     Electrons can only have discrete energy levels.  No spiraling is
possible.  There aren't any good fundamental explanations of why this is so,
but it is clear by experiment that it is.  In my forthcoming "Meta Model",
which tries to show (as a by-product of a new, deductive cosmology) how
classical models might yet be built for quantum effects, some sort of a
restoring force (as in a spring) must act to replace any energy the electron
may dissipate. It's a start on answering such intuitive questions, but only a
beginning.


and Benjamin Weiner [temporarily accessible through [e-mail] (Leigh
Palmer)] replied:

> I am perfectly willing to accept your point that the static field has no
> propagation delay.  I would phrase this as: given the distribution of
> masses and their velocities, one can then calculate their future positions
> (Cauchy problem is solved) - and your point is that the "forces" which one
> sees (really curvature of the geodesics) point to instantaneous, not
> retarded, positions, et cetera.  Fine.

     It is nice to have another person join our discussion who is already
familiar with these things.

> Suppose I decide to sacrifice myself for science, and leap into a 10^6
> M_sun black hole, carrying two giant iron spheres.  ...  I decide to send a
> message (say "I'm through OK") to Tom, who is smart enough to stay outside,
> with my iron spheres.  How do I do it?  ...  I wiggle the spheres back and
> forth ...  Exerting EM forces on the spheres, they no longer move along
> geodesics, and produce some kind of disturbance (postulating the existence
> of gravitational radiation) - a perturbation in the metric. Such
> gravitational radiation (assuming its existence) propagates along null
> geodesics - lightlike lines.  It cannot escape the black hole.  My message
> will not reach Tom.

     I don't like mixing gravitational waves with gravitational force.  They
are separate phenomena -- one doesn't cause the other.  I would have conceded
that no waves can get out of the black hole, but not at all that one
shouldn't be able to sense where mass is within the hole before it drops into
the singularity.

     But even without a black hole, it is an experimentally unsolved problem
to learn what would happen if a non-gravitational force moves a mass off its
geodesic path.  Would the new static field exist at infinity instantly, or
after some delay?  If instantly, that seems to act like ftl communication.
(See the current thread in sci.physics, where it seems to be agreed that this
type of ftl communication is not in conflict with observation or experiment.)

     OTOH if the new field is generated with delay, then there is a
discontinuity in the force felt by remote bodies.  A test particle continues
to "feel" and react to the predicted future geodesic path of a mass for a
lighttime interval even after the mass has been moved off that path by a non-
gravitational force.  Then when the new geodesic path information finally
reaches the test particle, the particle begins to react to some future
position of the mass.  As I said, there is a discontinuity in the action.
Either way, something unexpected happens.

     I point out these problems because ultimately, the value of any theory
is to explain and to predict.  Your insightful example reaches into areas
where I think that GR will prove poor at either explaining or predicting.
But that's good -- we're all supposed to be working to get to the next level,
not to glorify past successes.  We can't make progress until we finally see
where the theories we have start to fail.  -|Tom|-

--
Tom Van Flandern / Washington, DC / [e-mail]
Meta Research was founded to foster research into ideas not otherwise
supported because they conflict with mainstream theories in Astronomy.