Advanced Ligo: Labs 'open their ears' to the cosmos
22 Sep 2015 10:03:25 UTC
Topic 198241
(moderation:
http://www.bbc.com/news/science-environment-34298363
Quote from the article:
... Supercomputers will be sifting constantly the data for patterns that match the expectations from simulations - and even for those signals that stand out as so unexpected they may hint at something that goes totally beyond current understanding...
... no word about us Volonteers :-(
Arthur
I know I am a part of a story that starts long before I can remember and continues long beyond when anyone will remember me [Danny Hillis, Long Now]
Advanced Ligo: Labs 'open their ears' to the cosmos
)
Fair enough, it is a high level description. The graphic shows the AEI Atlas cluster there. A supercomputer on it's own terms. To be exact : Bruce Allen et al is part of the LIGO Continuous Wave Group and thus E@H is being used for that type of signal mode.
For me I think that if LIGO performs even half as expected there will be a plenty of glory to go around .... :-)
Recall the Michelson-Morley experiment. A null result* with profound implications to this day. If LIGO fails to catch a wave, when it is working as expected, then that will have savage importance for our understanding of the universe too. I'm all for a definitive answer either way, then go from there .... 'cos that is how you do science ! :-) :-)
Cheers, Mike.
* By the measure used to assess 'aether wind' it was expected to yield a value some 20 times what was actually revealed. And that was explicable by error analysis upon the apparatus at the time ie. consistent with no aether wind. No aether really, or a superfluous concept in Einstein's mind. I think of LIGO as Michelson Morley Version II ..... Version I looked for a first-derivative/velocity component, LIGO is seeking a second derivative/acceleration effect ( roughly ).
Let's not do a Lord Kelvin, circa 1900, and say :
[ I think it is mildly amusing that Planck was the first to deduce the quantum nature of things by studying ( as requested by his employer ) how to predict the power rating of these new fangled gadgets called 'light globes' .... sometimes tripping over a pesky tree root can be the best outcome ! :-) ]
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
RE: Recall the
)
So... I was watching a talk by Scott Ransom (some years ago) and he went on, or spoke at length, about how the models are accurately matching pulsar pulses to their predicted time to the fraction of a second down to something like 14 decimal places.
Ok, so we've got the ultra deep field with "gravitational lensing."
Why, if there were any wave, coming from any direction, at any frequency, can we get down to fractions of a second to 14 decimal places... and the models that predict the next blip are right on time from hundreds of light years away?
How many decimal places are we supposed to have to go before we see a little interference?
I understand that we would need an array to understand the nature of the wave, but doesn't the complete lack of interference in a single metronome's signal make you go, "hmmmmmmm."
You have indeed hit the very
)
You have indeed hit the very moot point. How quiet is too quiet ? I don't really know .... but that's never stopped me discussing these things before .... :-)
On the one side you have well proven radiation at source. The various pulsar systems have been terrific in demonstrating - to very high degree - that aspect. And in outstanding agreement with classic GR. With LIGO we want to show reception at great distances. This is the antenna response for the two GW polarisations and their sum { courtesy of Peter Saulson's primer on the topic : "Fundamentals Of Interferometric Gravitational Wave Detectors" which I suggest you all rush out and buy a copy today ! :-) } :
... the puckered parts of the right hand peanut are the null directions ( with respect to interferometer axes ). But overall a single IFO is described as pretty much omnidirectional hence, as you say, one needs separated near-simultaneous coherent reception to deduce a sky direction back to source. But the world turns and transits a path around the Sun etc. So it ought not be quiet all the time for a given source.
I would guess that one tricky variable is whether or not spacetime is 'lossy' for it's waves. AFAIK they are not expected to be. Does a distant sphere surrounding some GW source have all GW power from said source pass ultimately across it's surface ?
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal