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From: falk@sun.UUCP
Newsgroups: sci.physics
Subject: Re: A Question
Message-ID: <8597@sun.uucp>
Date: Mon, 27-Oct-86 20:32:43 EST
Article-I.D.: sun.8597
Posted: Mon Oct 27 20:32:43 1986
Date-Received: Tue, 28-Oct-86 18:57:07 EST
References: <230@sri-arpa.ARPA> <572@epimass.UUCP> <2182@ecsvax.UUCP>
Organization: Sun Microsystems, Inc.
Lines: 36

> >     o  Given the old "accellerating-elevator-in-space" experiment,
> >        how can one within the elevator tell the whether he is
> >        accellerating or under the influence of gravity?
> > 
> > You can't tell the difference.  This is the heart of general
> > relativity.
> 
> I've wondered about one "difference" which I once read about.
> 
> Hold a ball in each hand, say 1 meter apart, and level with the floor.
> Then let go of them, and they will "drop" to the floor - mark where
> they hit.  In the accelerating-at-1g-elevator-in-space they will hit 
> exactly the same distance apart.  On the 1-g-surface-of-earth
> they will be slightly closer together because they fall along
> radii converging at the center of mass of the earth.
> 
> What is the loophole here?  Can gravity produce parallel paths
> of the falling balls, or does the elevator test only allow one ball,
> or ... ?  (Please help - I'd hate to discard general relativity
> because of this. :-)


Two other ways:

2) weigh the ball (or time its acceleration) near the ceiling and
   near the floor.  If there's a gravity gradient, you're on a planet, if
   not, you're in an acceleration.

3) Tell the elevator operator "I'll give you this nice ball if you tell
   me if this elevator is accelerating or not"  :-)


-- 
		-ed falk, sun microsystems
			falk@sun.com
			sun!falk