Ah HA! I *knew* it! :-)

Three American physicists have been awarded the Nobel prize in physics
for the discovery of gravitational waves, ripples in the fabric of
spacetime that were first anticipated by Albert Einstein a century ago.

https://www.theguardian.com/science/2017/oct/03/nobel-prize-physics-discovery-gravitational-waves-ligo

I got a kick out of this because I contributed in a teeny-weenie, small
way to part of the vacuum system design of the LIGO project back in the
mid-90's.


From Wiki:

LIGO operates two gravitational wave observatories in unison: the LIGO
Livingston Observatory (30°33′46.42″N 90°46′27.27″W) in Livingston,
Louisiana, and the LIGO Hanford Observatory, on the DOE Hanford Site
(46°27′18.52″N 119°24′27.56″W), located near Richland, Washington. These
sites are separated by 3,002 kilometers (1,865 miles). Since
gravitational waves are expected to travel at the speed of light, this
distance corresponds to a difference in gravitational wave arrival times
of up to ten milliseconds. Through the use of trilateration, the
difference in arrival times helps to determine the source of the wave.[53]

Each observatory supports an L-shaped ultra high vacuum system,
measuring 4 kilometers (2.5 miles) on each side. Up to five
interferometers can be set up in each vacuum system.

The LIGO Livingston Observatory houses one laser interferometer in the
primary configuration. This interferometer was successfully upgraded in
2004 with an active vibration isolation system based on hydraulic
actuators providing a factor of 10 isolation in the 0.1–5 Hz band.
Seismic vibration in this band is chiefly due to microseismic waves and
anthropogenic sources (traffic, logging, etc.).

The LIGO Hanford Observatory houses one interferometer, almost identical
to the one at the Livingston Observatory. During the Initial and
Enhanced LIGO phases, a half-length interferometer operated in parallel
with the main interferometer. For this 2 km interferometer, the
Fabry–Pérot arm cavities had the same optical finesse, and, thus, half
the storage time as the 4 km interferometers. With half the storage
time, the theoretical strain sensitivity was as good as the full length
interferometers above 200 Hz but only half as good at low frequencies.
During the same era, Hanford retained its original passive seismic
isolation system due to limited geologic activity in Southeastern
Washington.