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Old August 16th 04, 02:38 PM
Joseph Lazio
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"d" == dkomo writes:

d I found an old PBS documentary on VHS from 1991 called _The
d Astronomers_ at the local public library. One of the programs in
d the series was "Waves of the Future" about gravitational waves. In
d the program Kip Thorne was shown making a bet with one of his
d collaborators on gravity wave theory that these waves would
d positively be detected by 2000.

d I found this both humorous and a touch sad. The program described
d some of the early planning for LIGO (Laser Interferometer
d Gravitational Wave Observatory). Curious, I went to the LIGO web
d site to see what was going on. I found nothing of substance there
d -- just a lot of slick PR.

You don't define "slick PR" but I see links for "Observational
Results," "Publications," "Research Bulletin Boards," "LIGO Email
Archives," .... At least some of these strike me as more than PR.

Of course, you've hit upon a problem not unique to LIGO. If the Web
site isn't slick and flashy, then it's derided as boring and useless.
If it is slick and flashy, then it's derided as just PR.

d So my question is, what are the prospects that gravity waves will
d be detected anytime soon? Is LIGO still having technical problems
d or what? It is now 2004, after all. Other detection labs are being
d built around the world. Are these labs going to have any better
d luck?

There are a host of other gravitational wave laboratories around the
world. The LIGO site has links to VIRGO, GEO600, TAMA300, ACIGA,
LISA, and IGEC.

As for prospects of detection, that's probably a good question to post
on sci.astro.research. In part that depends upon how kind Nature is
to us. I think if a supernova went off in our part of the Galaxy
tomorrow, LIGO would (or should!) detect it. Right now, of course, it
has not detected anything, so the best that one can do is say that the
density of fill in your favorite gravitational wave source is no
larger than some upper limit.

Some will, of course, decry this as adjusting the theory. However,
getting a handle on potential gravitational wave sources is tough.
For instance, just last year the binary pulsar PSR J0737-3019 was
discovered. It's (probably) less than 2000 light years away from us
and yet had gone undetected for the first 35 years of pulsar
searching. Binary neutron star systems are thought to be a prime
candidate for gravitational wave sources as they spiral together.
Finding a binary neutron star system so close to us immediately
boosted the expected signal strength for gravitational waves from
binary neutron star systems.


d Also, what are people's opinions about gravity waves? Is it
d possible that these are a scientific dead end like the decay of the
d proton turned out to be? If gravity waves are never detected, what
d are the implications for the general theory of relativity?

What about PSR B1913+16? This is a binary neutron star system in
which one of the neutron stars is seen as a pulsar. The orbit is
decaying at a rate exactly consistent with that predicted by general
relativity, if gravitational waves are carrying away energy. In a few
years (if not sooner), the orbital decay of PSR J0737-3019 should also
be measurable. (PSR J0737-3019 is a much tighter system, a 2.4-hr
orbit, as compared to PSR B1913+16, an 8-hr orbit, so the rate of
orbital decay should be higher.)

The decay of the orbit of PSR B1913+16 is only an indirect
measurement, of course, but it is a powerful indicator that
gravitational waves do exist.

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