Frank Close has a question. "If you step off the top of a cliff, how does the Earth down there 'know' you are up there for it to attract you?" It's a question that has taxed many illustrious minds before him. Newton's law of gravitation first allowed such apparently instantaneous "action at a distance", but he himself was not a fan, describing it in a letter as "so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it".
Today we ascribe such absurdities to fields. "The idea of some physical mediation – a field of influence – is more satisfying," says Close, a physicist at the University of Oxford. Earth's gravitational field, for example, extends out into space in all directions, tugging at smaller objects like the moon and us on top of ...
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