 As a particularly vivid example illustrating common-cause inferences from very limited knowledge of the state of the universe on a final value surface consider the detection of gravitational waves in 2016, which, physicists concluded, were emitted by two colliding black holes. If we wanted to derive the black hole event within General Relativity from knowledge of the data on a complete final value surface, we would have to know the precise state of the universe in a sphere with a diameter of many, many light-years—something that is obviously impossible for us to know. Instead researchers inferred the black-hole event from the two signals detected locally in the LIGO detectors in Washington and Louisiana, arguing that the extremely strong correlations between the signals detected at both detectors simultaneously are evidence for the colliding black holes as the signals’ common cause.