GEO600 is a gravitational wave detector located near Sarstedt, a town 20 kilometres (12 mi) to the south of Hanover, Germany.

In 1977 the Department of Physics and Astronomy of the University of Glasgow began similar investigations, and in 1980 started operation of a 10-metre (33 ft) prototype.

The two groups combined their efforts in 1989 – the project GEO was born, with the Harz mountains in northern Germany considered an ideal site.

[8][9] In 2001 the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI) in Potsdam took over the Hannover branch of the MPQ, and since 2002 the detector is operated by a joint Center of Gravitational Physics of AEI and Leibniz Universität Hannover, together with the universities of Glasgow and Cardiff.

[14] GEO600 uses many advanced techniques and hardware that are planned to be used in the next generation of ground based gravitational wave detectors: A further difference to other projects is that GEO600 has no arm cavities.

The first observation of gravitational waves on 14 September 2015 was announced by the LIGO and Virgo interferometer collaborations on 11 February 2016.

[25] This claim was made by Craig Hogan, a scientist from Fermilab, on the basis of his own theory of how such fluctuations should occur motivated by the holographic principle.

[28] A similar remark was made in a GEO600 paper submitted in October 2007 and published in May 2008:[29] in the region between 100 Hz and 500 Hz a discrepancy between the uncorrelated sum of all noise projections and the actual observed sensitivity is found.It is a very common occurrence for gravitational wave detectors to find excess noise that is subsequently eliminated.

According to Karsten Danzmann, the GEO600 principal investigator,[25] the daily business of improving the sensitivity of these experiments always throws up some excess noise [...].

We work to identify its cause, get rid of it and tackle the next source of excess noise.Additionally, some new estimates of the level of holographic noise in interferometry show that it must be much smaller in magnitude than was claimed by Hogan.

From September 2011, both VIRGO and the LIGO detectors were shut down for upgrades, leaving GEO600 as the only operating large scale laser interferometer searching for gravitational waves.

[31] Subsequently, in September 2015, the advanced LIGO detectors came online and were used in the first Observing Run 'O1' at a sensitivity roughly 4 times greater than Initial LIGO for some classes of sources (e.g., neutron-star binaries), and a much greater sensitivity for larger systems with their peak radiation at lower audio frequencies.