Re: What causes time dilation?
From: Edward Green (spamspamspam3_at_netzero.com)
Date: 08/29/04
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Date: 29 Aug 2004 04:53:00 -0700
"Old Man" <nomail@nomail.net> wrote in message news:<FuGdnVs954KCCrPcRVn-pw@prairiewave.com>...
> "hunkahunkaburninluv" <some@where.come> wrote in message
> news:2p75lgFhs9v9U1@uni-berlin.de...
> > First, I am not a physicist. I do desktop publishing as a profession, but
> am
> > an avid sci-fi reader.
> >
> > Two related questions. What causes time to slow down as a ship approaches
> > the speed of light? Is there any possibility that we could create the
> effect
> > on a stationary object? Imagine a room in which time was slowed down to
> say
> > 1% normal. One year might in it might equal 100 years.
>
> Sure you can do that by modification of the space-time
> metric, that is, by increasing the curvature of space, for
> some limited region of space. For, example, see to it
> that the gravitational field is increased in that special
> room of yours.
>
> Actually, a field isn't required. All you need is a huge
> amount of gradient-free, negative gravitational potential.
> You can do that by constructing a massive spherical
> shell about yourself. Then, through peepholes in the
> shell, you can watch time fly by on the shell's outer
> surface, all in weightless comfort.
That's a very cute idea, Old Man.
You could use that as a refrigerator: Say your peach is ripe. You
just pop it in your massive spherical shell, and, a week later, when
you want to eat it, you take it out, a few minutes older. Better than
a refrigerator.
I wonder somewhat about the physics of watching time fly by, though.
If a some light at frequency f came down your peephole, would its
frequency on receipt be slowed by the same factor?
No, I guess that's not so: light climbing out of a gravity well is
red-shifted -- i.e., _not_ speeded up to the frequencies we would
expect for its particular spectral transmission. It carries the
stigmata of its slow birth. So I guess the reverse is true, and light
falling in would be blue shifted to the internal observer. Which does
solve a queueing problem for all the light which would otherwise be
waiting around to fall in your peephole. Not to mention the even more
significant precognition problem for light climbing out.
> However, for a large factor in time-rates between you
> and those on the surface, the people on the surface
> would be living (?) in a huge gravitational field. So, lets
> put them out in space, almost an infinite distance away.
> Then the ratio in time rates between you and them is
> given by
>
> delta_t (you) / delta_t (them) = sqrt[ 1 - 2 M / R c^2 ]
>
> where M and R are the mass and radius of the shell,
> and G is the universal gravitational constant. Note that
> your time approaches zero (their time approaches infinity)
> as the mass of the shell, M, approaches that of a black-
> hole of radius, R, but everyone lives in free-fall comfort.
>
> See: "Gravity: An Introduction to ... " by J.B. Hartle
> ISBN 0-8053-8662-9
Should be banned by the GR technicians, of that is an example of its
teachings: it was clearly comprehensible! :-)
(P.S. He asked about kinematic time dilation, not gravitational. But
yours was a lovely answer anyway ;-).
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