Small reflectors left on the Moon by missions such as Apollo 11 are being utilised by a group of scientists who are aiming laser beams at them in an attempt to test the soundness, or otherwise, of aspects of Einstein’s general theory of relativity.
In the mid-1960s, when NASA asked for suggestions for experiments that could be carried out on the moon, laser ranging was mooted but no one really knew what to do with it. There was a suggestion to look for gradual changes in Newton’s gravitational constant, but this would have meant running the experiment for over 20 years – something no one was prepared to commit to.
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