Re: LIGO.
- From: "Martin Hogbin" <goatREMOVETHIS123@xxxxxxxxxx>
- Date: Sat, 10 Feb 2007 11:14:16 -0000
"cliff wright" <c.c.wright@xxxxxxxxxxxxxxx> wrote in message news:45cd6bab$1@xxxxxxxxxxxxxxx
Well this is all very interesting but we still appear to have a non
functional, very expensive apparatus here!
Not yet functional! You have not responded to my latest
post about our bet. I want to place a serious bet. We need to
agree some basis on which the winner is decided otherwise it
could end up as an argument as to who has won. I will not
pay up unless I am sure that you would have paid up had you
lost.
Do you want to place a serious bet or shall we cal it off?
Michelson and Morley used an
old cellar and a realtively simple optical interfernometer, in fact they
had to cut their programme short because someone else needed the cellar.
Perhaps, it being in Dublin, a Guiness delivery was expected.
Strange, I always thought that Semantics were to do with the meaning
of language, but I suppose that mathematicians are running out of mames
for ever more abstruse calculations and logical operations.
None of this however more than partially answers my original question.
Though I see someone has phrased it quite well- In effect what are you
actually measuring and how does propagation speed enter the equation?
Electromagnetism had Maxwell, but can Einstein now join his illustrious
company or not?
Tom has carefully answered your question using the correct
technical language because that is the easiest way to do so.
Many words (such as 'energy' or 'momentum') have much more
precisely defined meanings in technical usage than in everyday
speech. You need to find out what the terms Tom has used mean
in order to get your answers.
Maxwell of course had the advantage of already knowing the approximate
velocity of electromagnetic radiation he did not have to assume it.
BTW how is the nature of the "space/time" positioning of the light paths
determined? Or is it assumed that space is substantially "flat" and
unstressed around the mirrors?
I presume that ant "directional" information depends on the time dealy
of signals and therefore the velocity of propagation, but I stand to be
corrected on that.
You are falling into the trap of expecting distance to be
a 'real' pre-defined thing. We can ultimately only define
distance by how we would measure it. Historically, different
methods have been used. In 1889 one metre was defined as
the distance between two marks on a platinum alloy bar kept
in Paris (this is the constant spacelike proper distance Tom
referred to). On this basis, LIGO would measure a variation
in the speed of light.
However, today one meter is defined as the distance travelled
by light in a specified time. In free space, away from gravitation
and other influences, this gives exactly the same result as using the
metal bar would. In the case of LIGO, because the speed of light
is now defined as a constant, we would now say that the length of
metalwork changes. It all depends on how you choose to define
'distance'.
I fully understand that Einstein's original work as regards
"gravitational radiation" has been much "worked on " since his death 50
years ago, but his name keeps coming up.
An quite rightly so. It is still his theory, unchanged, that is used.
It is just that more details have been worked out.
Martin Hogbin
.
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