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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