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From: matt@oddjob.UUCP (Matt Crawford)
Newsgroups: sci.physics
Subject: Re: A Question
Message-ID: <1529@oddjob.UUCP>
Date: Tue, 28-Oct-86 15:17:19 EST
Article-I.D.: oddjob.1529
Posted: Tue Oct 28 15:17:19 1986
Date-Received: Wed, 29-Oct-86 02:45:49 EST
References: <230@sri-arpa.ARPA> <572@epimass.UUCP>
Reply-To: matt@oddjob.UUCP (Matt Crawford)
Organization: U. Chicago, Astronomy & Astrophysics
Lines: 23

Joe Buck sez:
>In article <230@sri-arpa.ARPA> JDM%SMVL%rca.com@CSNET-RELAY.ARPA writes:
>>    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.

Actually you can tell the difference, as I am sure Joe knows.
Sufficiently sensitive instruments will detect the slight
variations from place to place in a gravitational field.  If the
accuracy of the instrument is known in advance, the elevator can
be made small enough that the variation will be undetectable.
Example: a device which can detect variations of one part in a
million, used inside an "elevator" 3 meters across, will not be
able to distinguish between a 1 g acceleration and the earth the
gravitational field at the earth's surface.
_____________________________________________________
Matt		University	crawford@anl-mcs.arpa
Crawford	of Chicago	ihnp4!oddjob!matt

	Physics are good for you!