Re: Einstein@home post processing of LIGO S4 data

On Apr 23, 4:45 am, Eric Gisse <jowr...@xxxxxxxxx> wrote:
On Apr 23, 1:06 am, Martin Hogbin <goatNOSP...@xxxxxxxxxx> wrote:

Eric Gisse wrote:
http://arxiv.org/abs/0804.1747/

Sucks that nothing was found, but interesting reading regardless.

When does it start to get worrying?

When we have indirect evidence of a continuous wave source [binary
system] that does not show up on a detector of sufficient sensitivity.
For example if we had a detector that had - in theory - the
sensitivity to detect the radiation coming off PSR 1913+16 and there
was no signal within confidence bounds, then there would be a problem.

Absolutely agree. The issue we have, really, is we don't know how many
sources of what size we should expect to see.

Many of the ball-park estimates (which still have error bars that are
a factor of *ten* or so) of likelihood of sources depend on how well
we understand stellar collapse, how much matter is blown away in the
collapse (and therefore how many fall above or below the Oppenheimer
limit), and therefore what the density of black holes is expected to
be -- which in turn drives the projected frequency of black-hole
coalescences, the dominant source for GW searches.

I'm curious now whether anyone has considered whether dark energy
affects these estimates in any appreciable way. I would expect that,
at least qualitatively, dark energy would lower the rate of BH
coalescence via a number of contributing factors -- I just don't have
any idea how much.


That problem would be severe because the question "where the *** is
the energy going?" would have to be asked. It'd be like a regular ol'
antenna having power go in and not appear at a suitably configured
detector. That's the only reason I have full confidence that
gravitational waves exist.



I see the gravitational wave experiments as latter day equivalents
to the MMX.  Not in the sense that the physics is similar but
because current theories predict that something should be detected;
a null result would require some serious rethinking.

I think the comparison is unfair. There is substantial _indirect_
evidence for gravitational radiation. The decay rate for a binary
system is a complicated derivation yet observation matches GR within
some fairly tight bounds over what is now decades of observation.

Also it needs to be remembered that this is a "hard" field - the
deflections being measured are fractions of an atom in size. Plus I
think the endeavor is worthwhile if only from the advances in quantum
optics and vibration damping. I'm really hoping that gravitational
wave astronomy will become an actual field rather than placing bounds
on the stochastic background and such.

This argument is getting weaker now that the S4 run has been analyzed,
but the data corresponding to LIGO's design sensitivity [S5] has not
been processed yet, much less sent off for post processing. Though TBH
I'm not quite sure how they are doing the processing in the sense of
whether or not they are "done" with S4. I think the Einstein@Home
processing should have covered everything in there that could be found
within reason, judging from what I gleaned from the writeup.

I'd rather not be so defensive about this but dollars to doughnuts I'm
going to get replies that say "SO THERE ARE NO GRAVITATIONAL WAVES!
HURR". I'm yet to see an explanation by the people who deny they exist
as to why binary systems [plural is intentional] are observed to decay
as if they do exist. Debate that is informed or at least marginally
interesting is hard to come by since most people here try to pass off
denial and stupidity as education.



Martin Hogbin

.

Quantcast