
LIGO's vibration isolation system - lisper
https://www.ligo.caltech.edu/page/vibration-isolation
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andrepd
10 to the minus _19_! It's mind boggling. Semiconductor process nodes
constantly boggle my mind, and yet they sit at a cool 10 to the minus 9. These
vibrations are smaller relative to a CPU transistor than a CPU transistor is
to me.

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topquark
LIGO scientist here. The way this is presented can be a little deceptive - the
isolation is very frequency dependent. At high frequencies (>10Hz), the
pendulums and blade springs in the suspension isolate the mirrors very well,
so they are moving by only these small amplitudes (10^-19 meters). But at low
frequencies (<1Hz) the isolation ratio is essentially 1, so the amplitude of
the mirror motion is roughly the same as that of the ground (about 10^-6
meters).

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idanoeman
Yes, which makes sense physically. If the earth's rotation slowed by a
constant velocity, in order to damp that motion the mirrors would have to
displace themselves in the opposite velocity. Of course, there's no room for
them to do so, so damping such low frequencies is not possible.

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jonknee
> LIGO's mirrors must be so well shielded from vibration that the random
> motion of the atoms within the mirrors and their housings can be detected.

It's just simply amazing to me that this is possible.

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Animats
That's impressive. They didn't have to put it in orbit to get sufficient
vibration isolation. The eLISA team must be so frustrated about this.[2] Their
gravitational wave detector is in orbit at the L1 point, and their test masses
just float in space. But they're not quite ready to turn everything on; that
happens in early March.

XKCD: [1]

[1] [http://xkcd.com/1642/](http://xkcd.com/1642/) [2]
[https://www.elisascience.org/](https://www.elisascience.org/)

~~~
jessriedel
LISA and LIGO aren't in competition. They are very different projects trying
to be sensitive to very different frequencies. (Likewise, Hubble isn't
competing with ground-based arrays of radar antenna even though both are
looking for electromagnetic waves.)

Furthermore, the only satellite currently in orbit is the LISA pathfinder
mission, which is just a testbed for some of the requisite tech. It is
incapable of detecting gravitational waves.

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natch
The multiple pendulum systems sound really cool. I wish they would put up more
images, and high resolution ones, to show what is going on from different
angles.

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iamcreasy
A Video. We need a video!

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leeoniya
i think a video of a system that achieves 10^-19 vibration sensitivity would
be stiller - far stiller - than a still photograph

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sreejithr
Not a video of the equipment working. More of a 3D video explaining stuff
would be awesome.

~~~
leeoniya
/s

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ascorbic
This is the sort of thing that makes me proud to be human.

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dnautics
what about molecular motions of the mirrors themselves?

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lololomg
That averages out over the timespan involved in gravitational wave detection.
The waves detected by LIGO are on the order of 100 Hz while molecular
vibrations are many orders of magnitude higher.

~~~
JabavuAdams
Ah! This is a key point! Thanks.

