LIGO movie!!
Mar. 1st, 2006 09:45 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
nibotThe NSF has sponsored the production of a 20-minute video about LIGO (the project I am working on).
The results are hilarious! Watch it here: http://www.ligo.caltech.edu/einstein.ram
The results are hilarious! Watch it here: http://www.ligo.caltech.edu/einstein.ram
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no subject
Date: 2006-03-02 07:37 pm (UTC)no subject
Date: 2006-03-07 06:30 pm (UTC)no subject
Date: 2006-03-08 05:34 pm (UTC)you can see some pictures, etc: http://nibot.livejournal.com/tag/ligo (in reverse chronological order)
The facilities have been there for a number of years now. What they mean by "up and running" is that most of the bugs have been worked out, so that we're now operating at a sensitivity where it is conceivable that we would detect gravitational waves. Now we're running in "science mode" (looking for gravity waves) rather than engineering mode/"commissioning" (getting everything working properly, identifying noise sources, etc).
thanks for the redirect
Date: 2006-03-09 12:11 am (UTC)you have had so many adventures (no tent-sleeping at cern, heh) and it's neat to read about them (and todd matthews -- compelling writer) and see the pix. there's just so much out there ordinary people don't know about.
re ligo -- is curvature of the earth an issue at 4 kilometers?
Re: thanks for the redirect
Date: 2006-03-10 06:46 pm (UTC)Re: thanks for the redirect
Date: 2006-03-10 06:36 pm (UTC)hmm. I doubt the curvature of the earth matters at all over 4 km.
The earth's radius is 6378 km according to Google, which gives a circumference of 2πr = 40074 km. Therefore 4km represents one tenthousandth of the circumference of the earth, or an angle of 0.002859 degrees. So if you extended a line out from a point of tangency, after 4km it would be (6378 km)*Sin[0.00289] = 0.636 meters above the surface.
The ligo beam is, however, straight, and I'm told the beam enclosure is straight too. Actually the beam of light curves ever so slightly due to Earth's gravity, but this isn't important.
Re: thanks for the redirect
Date: 2006-03-10 07:08 pm (UTC)todd matthews is the guy you referenced on your 2005 post with that straaaange Hanford Site photo -- "Todd Matthews' Atomic Postcard (http://www.wahmee.com/hanford.html) is a great description of the place."
and your last comment above makes me wonder ... at what distance would the 'curve due to gravity' become an issue? but nevermind, you have a great weekend!
Re: thanks for the redirect
Date: 2006-03-10 07:13 pm (UTC)The 25 inches doesn't matter because they built the pipe in a straight line instead of just laying it on the (curved) surface of the earth.
Bending of light due to gravity is so slight, I think it mainly becomes observable when beams spend a long time passing by very massive objects, like when you're looking at a star that appears near the sun.
Re: thanks for the redirect
Date: 2006-03-10 07:19 pm (UTC)Re: thanks for the redirect
Date: 2006-03-27 11:56 pm (UTC)I came across your postings and wanted to make a comment about the curvature of the earth issue.
The curvature does indeed matter and 4km is about what you can achieve. Perhaps there would be a factor of 2 in the possible arm length but not much more. The reason for this limitation does not lie in the bending of the light due to the earth's gravity but rather in the curvature itself. In order to isolate the interferometer optics from seismic they are suspended by pendulums (in the case of LIGO it is single pendulums, for Advanced LIGO it will be quadruple pendulums derived from the suspensions of the British-German GEO600 interferometer). Now these pendulums hang naturally towards the center of gravity. With a separation of a few km between the so called input test mass and the end test mass this effect leads to an angle between these two masses. Although the angle appears to be rather small it does need to be corrected. This is done via electronic feedback to the test masses, which is inherently not noiseless. In fact, LIGO has glued little magnets to the rear sides of the mirrors (or test masses) and exerts the required feedback forces via electro-magnetic coils opposing these magnets. The noise comes mainly from the readout and derivation of the control signals, from the control electronics, and from the current drivers for these coils.
I hope that makes sense and was helpful. The difficulty with these instruments is obviously that the expected gravitational-wave signals are so tiny that literally every noise source has to be taken into account.
Re: thanks for the redirect
Date: 2006-03-28 01:58 am (UTC)By the way, who are you?
Re: thanks for the redirect
Date: 2006-03-28 04:27 am (UTC)