It is still a fairly astounding notion to consider that atoms are mostly empty space, and that the solidity we experience all around us is an illusion. When two objects come together in the real world - billiard balls are most often used for illustration - they don't actually strike each other. 'Rather,' as Timothy Ferris explains, 'the negatively charged fields of the two balls repel each other ... [W]ere it not for their electrical charges they could, like galaxies, pass right through each other unscathed26.' When you sit in a chair, you are not actually sitting there, but levitating above it at a height of one angstrom (a hundred millionth of a centimetre), your electrons and its electrons implacably opposed to any closer intimacy.