The Detection of Gravitational Waves

The detection of gravitational waves is challenging researchers since half a century. The relative precision required, $10^{-21}$, is difficult to imagine, this is $10^{-5}$ the diameter of a proton over several km, using masses of tens of kg, or picometers over millions of km. A theoretical description of gravitational radiation and of its effects on matter, all consequence of the General theory of Relativity, is given. Then the astrophysical phenomena that are candidates for gravitational wave emission are discussed, considering also amplitudes and rates. The binary neutron star system PSR1913+16, which provided in 1975 the first evidence for energy loss by gravitational radiation, is briefly discussed. Then comes a description of the experimental developments, starting with ground based interferometers, their working principles and their most important sources of noise. The Earth wide network that is being built describes how these instruments will be used in the observation era. Several other detection techniques, space interferometry, pulsar timing arrays and resonant detectors, covering different bands of the gravitational wave frequency spectrum complete these lectures