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From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: sci.physics
Subject: Re: Accelerating elevator
Message-ID: <546@mcgill-vision.UUCP>
Date: Sat, 8-Nov-86 04:34:10 EST
Article-I.D.: mcgill-v.546
Posted: Sat Nov  8 04:34:10 1986
Date-Received: Mon, 10-Nov-86 05:21:31 EST
References: <230@sri-arpa.ARPA> <572@epimass.UUCP> <2182@ecsvax.UUCP> <1388@trwrb.UUCP>
Organization: McGill University, Montreal
Lines: 59

In article <1388@trwrb.UUCP>, galins@trwrb.UUCP (Joseph E. Galins) writes:
> If the elevator is accelerating, then after a long, long time its
> speed will reach the speed of light then pass it.

Not if current theories are correct.

> I know that the problem here has to do with the fact that F=mA is
> false when the speed approches 'c'.

Well, this depends on how you interpret the symbols.  As I recall, if
you interpret m as relativistic mass then it is true.

> In fact F approches infinity near 'c'.

Really?  Where does the energy to exert such a force come from?

> So with a constant (or even increasing but finite) force, wouldn't
> the acceleration necessarly slow down as the rider approched 'c' and
> hence notice that he was in an elevator?

Yes, EXCEPT that as the rider views it, the acceleration is constant.
Time dialation, remember.  It's the outside observer that sees
acceleration as slowing down.

> In other words, with a constant acceleration eventually you would be
> going at a speed of 'c' with no more acceleration therefore losing
> the 'gravity' feeling.

(1) You can't reach c.
(2) The rider still feels the acceleration as proportional to the
force; it's just the observer with respect to whom the elevator is
moving near c (the "stationary" observer) that sees the acceleration
slack off.

> Then is it impossible to simulate gravity via acceleration for a
> 'long' period of time?

Not so.  The only difference between "gravity as created by a mass" and
"gravity as created by acceleration" (I use the quotes because gravity
*is* acceleration, but I don't see any simple, brief, and more accurate
way of putting it) is the structure of the field (ie, parallel versus
converging lines of force....).

Note another difference.  If the elevator rider measures his velocity
with respect to "the universe", whatever that means, he will find it to
be steadily increasing.  The guy on the planet will not.

For "the universe", picky theorists may substitute, say, the background
black-body radiation (a suspiciously absolute frame of reference, if
you ask me!).

					der Mouse

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