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From: dgary@ecsvax.UUCP
Newsgroups: net.physics,net.astro.expert
Subject: pulsing quasars and the like
Message-ID: <2631@ecsvax.UUCP>
Date: Fri, 1-Jun-84 20:02:43 EDT
Article-I.D.: ecsvax.2631
Posted: Fri Jun  1 20:02:43 1984
Date-Received: Tue, 5-Jun-84 19:37:59 EDT
Lines: 30


For some time I have been reading about rapidly pulsing objects and how this
puts an upper limit on their size.  That is, since no signal can propagate
faster than light, the period of oscillation of a body cannot be less than
the light transit time.

I'm confused by this, and I offer a thought experiment to explain why.
Imagine an immense pool of water with a couple of flags at either end.
Suppose I disturb the water in the center of the pool so that waves
cause the flags to move up and down.  A distant observer can see that
the flags are moving almost in unison.  Can this user then infer that
the pool is of a certain limited size?

Or, more to the point, imagine a spherical body in space light years across.
A signal travelling at less than c but consisting of high-frequency pulses
travels from the center of the body
and reaches the perimeter 'simultaneously' in all directions, causing said
perimeter to pulsate in unison.

I'm not suggesting a mechanism, just asking if this isn't somehow possible.
If we're talking about objects more or less at rest with respect to us,
I don't see how simulaneity considerations really enter into it.

So, does the period of pulsation really place an upper limit on size??

Confusedly,
D Gary Grady
Duke University Computation Center, Durham, NC  27706
(919) 684-4146
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