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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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)