Testing Einstein's Most Fortunate Thought

Extremely precise measurements of the motion of a fast-spinning pulsar in a triple star system provide one of the strongest tests ever of a simple, but fundamental prediction of general relativity: that gravity affects all objects with the same acceleration, without regard for their composition, density or the strength of their own gravitational field. General relativity has again survived this test, one of the most stringent ever, which strongly constrains many alternative theories of gravity.