Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!ut-sally!ut-ngp!melpad!reality1!james
From: james@reality1.UUCP (james)
Newsgroups: sci.physics
Subject: Re: Accelerating elevator
Message-ID: <78@reality1.UUCP>
Date: Tue, 18-Nov-86 00:59:37 EST
Article-I.D.: reality1.78
Posted: Tue Nov 18 00:59:37 1986
Date-Received: Tue, 18-Nov-86 08:53:43 EST
References: <230@sri-arpa.ARPA> <572@epimass.UUCP> <2182@ecsvax.UUCP> <1388@trwrb.UUCP> <546@mcgill-vision.UUCP>
Reply-To: james@reality1.UUCP (james)
Organization: F.B.N. Software, Austin TX
Lines: 57

IN article <546@mcgill-vision.UUCP>, mouse@mcgill-vision.UUCP (der Mouse) wrote:
> In article <1388@trwrb.UUCP>, galins@trwrb.UUCP (Joseph E. Galins) writes:
> > 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.

Hmmm...  I take it you mean that if the rider measures acceleration in terms
of the gravity the rider feels, then it is constant.  But if the rider
measures acceleration in terms of the observer that was left behind?  I
guess it all depends on how you want to define acceleration maybe?  After all,
since the rider can't see the observer recede faster than the speed of light,
eventually the change in velocity between the rider and observer would have
to fall off.

> 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.

Huh?  Are you suggesting that the observer could view the rider as having no
acceleration even while the rider viewed acceleration?  I would think the guy
on the planet would still measure the _velocity_ as increasing, but the
acceleration as decreasing...

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

Ah, but absolute relative to what?  :-)

One other thing that confuses me about all of this.  The rider takes off from
the planet at relativistic speeds, and the observer on the planet sees the
rider "suffer" time dilation: the rider appears to move more slowly through
time.  I think I see where this comes from.  But what does the rider see of
the planet?  Since the planet is also receding relativisticly from the rider,
the rider observes the planet suffering the same fate: time dilation by the
same factor as the planetary observer measured.

Now, when the rider arrives at the destination, the rider must conclude that
the rider's clocks are *ahead* of the planet's, since the rider clearly observed
the planet's clocks "slow down".  Similarly the planetary observer must also
conclude that the rider's clocks are *behind* the planetary clocks.  Clearly
I'm missing something rather fundemental, but it seems to me that I have to be
able to view the situation from both the rider's standpoint and the planet's
and get the same answers (that's what relativity is about in this example?).
When the rider returns to the planet, every cutsey story says the rider is
much "younger" than the contemporaries left behind because of time dilation.
Yet somehow I much account for the fact that the rider observed the rider's
contemporaries age slower than the rider as the rider left the planet...

Not very well put, but I think the dilema is stated.  My high school physics
isn't letting me in on the secret...
-- 
James R. Van Artsdalen    ...!ut-ngp!utastro!osi3b2!james    "Live Free or Die"