We must not, in other words, describe only the two balls, but also all that is around them: the table and any other material objects – and the space in which they are immersed during the time that elapses between the start of the shot and the end of the process. Space and time are the gravitational field, Einstein’s ‘mollusc’: we are also including the gravitational field, that is to say, a piece of the mollusc, in the process. Everything is immersed in Einstein’s great mollusc: here, imagine that you are slicing a small, finite portion of it, like a piece of sushi, which encompasses the
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