Re: LIGO.
- From: sal <pragmatist@xxxxxxxxxx>
- Date: Thu, 08 Feb 2007 13:50:08 -0500
On Thu, 08 Feb 2007 17:44:25 +0000, Tom Roberts wrote:
dlzc wrote:
Bullion wrote:
What is a wave in space-time?Good question. Would it be resolvable, in some part, in space-only?
No.
The LIGO interferometer mirrors are held apart with constant spacelike
proper distance by the inter-atomic force of their supports and beam
pipes. The lasers measure the distance between the mirrors along a null
geodesic. Their signal is the difference between the lengths of these two
geodesics. They usually describe this as a variation in the distance
between the mirrors (implicitly using c=constant all along the light
path).
Say what? Tom, would you be so kind as to expand that paragraph to
include a definition of "distance" in each place where you used it, and
please explain what you meant by the "length" of each of the geodesics
which are being compared? I'm sorry, but as written, I didn't understand
what you said.
Distance along a null geodesic could mean 3-d _coordinate_ distance of the
endpoints projected into 3-d spacetime, _coordinate_ time difference, or
proper distance (which is zero).
Tom Roberts
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