Science has taught us, against all intuition, that apparently solid things like crystals and rocks, are really almost entirely composed of empty space. And the familiar illustration is the nucleus of an atom is a fly in the middle of a sports stadium, and the next atom is in the next sports stadium. So it would seem the hardest, densest, solidest rock is really almost entirely empty space broken only by tiny particles so widely spaced they shouldn’t count. Why then do rocks look and feel solid, and hard, and impenetrable? As an evolutionary biologist, I’d say this: our brains have evolved to help us survive within the orders of magnitude of size and speed which our bodies operate at. We never evolved to navigate in the world of atoms. If we had, our brains probably would perceive rocks as full of empty space. Rocks feel hard and impenetrable to our hands precisely because objects like rocks and hands cannot penetrate each other. It’s therefore useful for our brains to construct notions like solidity and impenetrability because such notions help us to navigate our bodies through the middle-sized world in which we have to navigate. Moving to the other end of the scale our ancestors never had to navigate thought he cosmos at speeds close to the speed of light. If they had our brains would be much better at understanding Einstein.
— Richard Dawkins, spoken at TED Conference