The holometer as constructed at Fermilab includes two interferometers in evacuated 6-inch steel tubes about 40 meters long. Optical systems (not shown here) in each one “recycle” laser light to create a very steady, intense laser wave with about a kilowatt of laser power to maximize the precision of the measurement. The outputs of the two photodiodes are correlated to measure the holographic jitter of the spacetime the two machines share. The holometer will measure jitter as small as a few billionths of a billionth of a meter. Illustration: Fermilab.