occasional meanderings in physics' brave new world

Name:
Location: New Zealand

Marni D. Sheppeard

## Monday, July 16, 2007

### Home Sweet Home

All right, so I came straight to the office, but that's close enough.

Following up on results from GRG18, Carl Brannen has a post with a tentative prediction, "Suffice it to say that I expect that the gravity wave people will eventually detect gravity waves, but that these will not correlate to any simultaneous astronomical events." That is to say, the $\sqrt{3}$ factor which often arises in discussions is used in a comparison between the (faster) GWs and standard model particles. Now if this was true maybe one could search for events in the detector data, corresponding to nearby objects such as GRB 070201, for which one has a precise prediction for the arrival time, but no, oh dear, maybe the detector wasn't operating then. 800 kpc is nearby in universal terms, but still some distance compared to the age of human technology. Hmmm. Yes, this could be tricky to sort out!

In general, something like the proposed Southern Hemisphere AIGO telescope will be necessary to pinpoint locations in the sky, via triangulation with respect to the Northern Hemisphere telescopes (which unfortunately lie almost in a plane).

CarlBrannen said...

Thanks for the "attaboy". I'm going to keep on writing articles more or less like that one. I hope that they have more pictures, though.

As far as a gravity wave experiment determining the arrival direction, I assumed it could not be done. I've never seen it listed in the literature that I recall. I know that the detectors are directional, but I think of them as very crude devices with resolutions at their low visibility limit measured in radians.

If you could get a sort of general direction, a wonderful test (for a faster than light gravity wave theory) would be to look for evidence of some nearby gravity wave source, but presumably at a higher frequency than it currently beats. Knowing the distance to the source, and the rate at which the frequency changes, voila, you get the speed of gravity.

I should probably admit that I took two classes from Joe Weber (a wonderful man, he died quite recently), who, uh what's the right word here, "jump started" the gravity wave industry. One was on general relativity, the other was a class that covered a lot about things like the "fluctuation dissipation theorem", which turns out to be so important in gravity wave detectors.

A great book on Joe Weber, and the technology (and sociology) of the gravity wave industry is Gravity's Shadow.

July 16, 2007 5:55 PM
Kea said...

Hi Carl

As far as a gravity wave experiment determining the arrival direction, I assumed it could not be done.

Oh, it could be done with AIGO on line, which might happen in the next decade or two, although funding is yet to be decided. We saw an analysis on this at GRG18.

July 17, 2007 11:03 AM
CarlBrannen said...

Kea, at my age "decade or two", plus a little margin for excessive optimism, starts to get problematic. My next post is going to be on the subject of QFT for qubits, something that is used more or less explicitly in the dmfound paper. I found a reference at arXiv.

QFT on qubits is a lot simpler than the way I was taught. It basically amounts to ignoring spatial considerations.

July 19, 2007 6:20 PM