Some people used to believe that the Earth is in the centre of a nest of spheres, containing the moon, all the planets and the sun, as well as several layers of heaven.

Others imagined it as a flat disc supported by a turtle, or an elephant.

Still others imagined it simply as a flat disc, with the sky as a pierced dome over the disc, and light from beyond the dome shining through the holes as stars.

Mental models are useful. They help us explain what’s going on and to work out what we should do in response to events. Often we can get by with such models for a long time – even if sometimes we have to bend the observable facts to fit the model we prefer.

A point comes though, where the facts get bent so far as to become ridiculous.

Then we need to adopt a better model.