Re: 4
From: Mike (eleatis_at_yahoo.gr)
Date: 02/14/05
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Date: 14 Feb 2005 12:29:27 -0800
Sam Wormley wrote:
> St. M wrote:
> > An accelerating spaceship gives the
> > astronauts the sensation of weight. Can
> > we say that this accelerating motion
> > simulates gravity or is it real gravity
> > that is being produced?
> >
>
> No experiment can tell the difference in a closed environment...
I guess you are pretty sure you know all the kind of experiments that
can be performed.
That is locally, not "closed". This terminology you are using is not
correct. Accelerated motion and gravitational free-fall are
indistinguishable locally, that is in a infinitesimally flat region of
curved spacetime. Coordinate based experiments, such as laser ranging
for instance, can differentiate between accelerated motion and
gravitational free-fall unambiguisly. Same can be achieved using
inertial sensors such as test masses attached to spings.
That is, the EP in GR is a postulate. It is a principle that cannot be
verified experimentally but the theory can be corroborated
experimentally by measuring its predictions, i.e. the Universallity of
Free Fall (UFF).
When people say that the EP has been confirmed experimentally they
really mean its predicted effects have been demonstrated to hold to a
high accuracy, in the order of some parts in a trillion or so and
increasing.
It is important though to understand that this experimental
corroboration does not imply the EP is a law of nature, such assertion
would be a logical fallacy. It simply corroborates the theory using the
EP postulate in its axiomatic basis.
One could further assert that all experiments that claim to confirm the
weak EP version of GR actually confirm the EP version of Newton
(equivalence of inertial and gravitational mass) while only corroborate
GR. What about that?
Mike
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