Re: Accelerating rocket/light beam question

Phillip Helbig---remove CLOTHES to reply wrote:
In article <SsednZq3kdk2bObUnZ2dnUVZ_hqdnZ2d@xxxxxxxxxxxxxx>, David
Rutherford <drutherford@xxxxxxxxxxx> writes:

You're saying that in case 1, the beam will not be curved, merely be
deflected downward, while in case 2 it will be curved?

No, the beam _will_ be curved, in _both_ part 1 and part 2, according to
the EP. But according to GR, the beam will neither be curved nor
deflected downward, in part 1.

Of course, since a uniform gravitational field doesn't exist in nature,
we can't solve this problem by observation.

We don't need observation to solve this problem. All we need is logic to
show that the EP and GR are _logically_ inconsistent. It doesn't matter
which one, if either, makes the correct predictions, for the problem I'm
posing, here.

Repeating a portion of the quoted text above:

No, the beam _will_ be curved, in _both_ part 1 and part 2, according to
the EP.

I think we all agree on this point.

But according to GR, the beam will neither be curved nor
deflected downward, in part 1.

Can you give some evidence to back this up? You say "according to GR",
so you should present your evidence in the language of GR.

For a uniform gravitational field, as in this case, there is no
curvature of spacetime. And, according to GR, there is no curvature of
the paths of free-falling bodies or light without the curvature of
spacetime.

I think I see what you are saying: GR attributes the deflection to the
curvature of spacetime, but this curvature of spacetime doesn't exist in
a uniform gravitational field, since we don't observe tidal effects.
Right?

Right, there are no tidal effects, in a uniform gravitational field.
Therefore, no spacetime curvature. Therefore, no `deflection' (I would
say no curvature of the path).

I'm not sure to what extent the concept of a limit is essential to this
discussion. The uniform gravitational field exists only as a limit.
Perhaps it is uniform in this limit in the sense of producing no tidal
effects, but not in the sense of not producing deflection.

What produces the `deflection', in the limit according to GR, if there
are no tidal effects and no spacetime curvature?

I hope I understand your claim. My claim is that, although it doesn't
appear to do so at first (or even second) glance, your claim that GR
predicts NO DEFLECTION in the case of a uniform gravitational field is
wrong. I suspect it has something to do with subtleties involving
limits. Maybe some GR expert (I am not one) can chime in here (at least
a few are regular readers of the newsgroup).

You really don't expect them to agree with _me_, do you :)?

[Moderator's note: I think Dave's claim is now clear (at least to me).
Either it is right or wrong. If right, experts, then state your
agreement. If wrong, explain. To some extent, the situation might be
comparable to some issues involving the redshift, expansion, distances
etc in cosmology---cosmologists get the stuff right, but popular
expositions, even by cosmologists, are sometimes at best confusing and
at worst wrong. -P.H.]

--
Dave Rutherford
"New Transformation Equations and the Electric Field Four-vector"
http://www.softcom.net/users/der555

Applications:
"4/3 Problem Resolution"
"Action-reaction Paradox Resolution"
"Energy Density Correction"
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