Meeting a friend in the corridor, Ludwig Wittgenstein (1889-1951) said: "Tell me, why do people always say that it was natural for men to assume that the sun went around the earth rather than the earth was rotating?"How clever of Wittgenstein. He is not asking what it would have looked like if the earth were rotating, but what it would have looked like if it had looked as if the earth were rotating. Implying that to look as though the observer is moving with respect to their environment is the same as looking as though the environment is moving with respect to the observer.
His friend said: "Well, obviously, because it just looks as if the sun is going around the earth."
To which the philosopher replied: "Well, what would it look like if it had looked as if the earth were rotating?"
But is that true? As a postgraduate I house-shared with a research assistant who was working on the neurophysiology of perception. Some of his work showed that the world actually looks different dependent on whether the observer is moving with respect to a stationary environment, or the other way round. There are a number of kinaesthetic sensors in the body which respond to bodily motion or rotation, and these interact with the visual sense in various ways. You can fool these sensors in all sorts of ways – for example you can create the illusion of acceleration by tilting their seat backwards, which is how flight simulators like this work. The answer to Wittgenstein’s question could well be “well, it would look exactly like that” – namely, looking as if the earth were moving, rather than the sun.