The Magic of Reality by Richard Dawkins Page A

and me. I’ve said that solid matter is made of atoms ‘packed’ together, but ‘packed’ means something rather odd here because the atoms themselves are mostly empty space. The nuclei of the atoms are spaced out so far apart that, if they were scaled up to footballs, any pair of them would be 15 kilometres apart with only a few gnats in between.
    How can this be? If a rock is almost entirely empty space, with the actual matter dotted about like footballs separated by kilometres from their neighbours, how come it feels so hard and solid? Why doesn’t it collapse like a house of cards when you sit on it? Why can’t we see right through it? If both a wall and I are mostly empty space, why can’t I walk straight through the wall? Why do rocks and walls feel hard, and why can’t we merge our spaces with theirs?
    We have to realize that what we feel and see as solid matter is more than just nuclei and electrons – the ‘footballs’ and the ‘gnats’. Scientists talk about ‘forces’ and ‘bonds’ and ‘fields’, which act in their different ways both to keep the ‘footballs’ apart and to keep the components of each ‘football’ together. And it is those forces and fields that make things feel solid.
    When you get down to really small things like atoms and nuclei, the distinction between ‘matter’ and ‘empty space’ starts to lose its meaning. It isn’t really right to say that the nucleus is ‘matter’ like a football, and that there is ‘empty space’ until the next nucleus.
    We define solid matter as ‘what you can’t walk through’. You can’t walk through a wall because of these mysterious forces that link the nuclei to their neighbours in a fixed position. That’s what solid means.
    Liquid means something similar, except that the mysterious fields and forces hold the atoms together less tightly, so they slide over each other, which means that you can walk through water, although not so fast as you can walk through air. Air, being a gas (a mixture of gases, actually), is easy to walk through because the atoms in a gas whizz about freely, rather than being tied to each other. A gas becomes difficult to walk through only if most of the atoms are whizzing in the same direction, and it is the opposite direction to the one in which you are trying to walk. This is what happens when you are trying to walk against the wind (that’s what ‘wind’ means). It can be difficult to walk against a strong gale, and impossible against a hurricane or against the artificial gale hurled out behind a jet engine.
    We can’t walk through solid matter, but some very small particles such as the ones called photons can. Light beams are streams of photons, and they can go right through some kinds of solid matter – the kinds we call ‘transparent’. Something about the way the ‘footballs’ are arranged in glass or in water or in certain gemstones means that photons can pass right between them, although they are slowed down a bit, just as you are slowed down when you try to walk through water.
    With a few exceptions like quartz crystals, rocks aren’t transparent, and photons can’t pass through them. Instead, depending on the rock’s colour, they are either absorbed by the rock or reflected from its surface, and the same is true of most other solid things. A few solid things reflect photons in a very special straight-line way, and we call them mirrors. But most solid things absorb many of the photons (they aren’t transparent), and scatter even the ones that they reflect (they don’t behave like mirrors). We just see them as ‘opaque’, and we also see them as having a colour, which depends on which kinds of photons they absorb and which kinds they reflect. I’ll return to the important subject of colour in Chapter 7, ‘What is a Rainbow?’ Meanwhile, we need to shrink our vision to the very small indeed, and look right inside the nucleus – the football – itself.
    The tiniest things of