Structures of Matter
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Matter in the universe can exist in many kinds of structure. Water drops and atomic nuclei were mentioned under the heading of surface tension.
Below nuclei in size are particles such as protons and neutrons. These appear to be "made" of quarks and gluons, which, like the electrons around a nucleus, are unimaginably small. The idea of shape and size has not been applied to these mysterious objects. Nobody even knows why all electrons are identical to the nth degree, even when they are created at distances where they cannot apparently communicate with some of the existing ones. On the other hand, non-locality is a feature of quantum mechanics.
The electron cloud around a nucleus is unlike the nucleus in that it is controlled entirely by the long range electro-magnetic force, though both are controlled by the laws of quantum mechanics. Without those laws the world would be formless. In effect the wave nature of the particles determines the size of small objects. Some ancient Greeks thought there was a kind of musical harmony that described the world, and quantum mechanics is something like what they sought. The size of an organ pipe determines the wavelengths of the sounds that are emitted. Quantum mechanics is the other way around - the waves determine how big things are. From the hydrogen atom to the longest string of DNA, the size of objects is determined by the same rules.
The spacing of atoms in all substances is fixed in the same way, so that solids and liquids cannot have any old density. Densities don't vary all that much - from liquid hydrogen (89 kg/m3) to osmium (22580 kg/m3) the range of density is a factor of about 250. Most of that is accounted for by the ratio of atomic weights, 190 to 1, leaving only about 1.33 for atomic spacing to account for.
The universe contains much larger structures than molecules - such as planets and stars. These are organized into arrangements such as the solar system and galaxies, and even groups of galaxies, all of which are controlled by the weakest known force - gravity. It has a long range, but even a baby can pick up a toy against the pull of the earth, whose mass is about 6 X 1024 kg, or 6000000000000000000000000 kg.
Nature makes blobs of many sizes, but seldom does two different things in exactly the same way. Here is a list of some of the known blobs of matter in increasing order of size -
Quarks+electrons - protons+neutrons - nuclei - atoms - molecules - crystals - neutron stars - planets - stars - galaxies - galaxy-groups - inter-galactic clouds.
Our world is endlessly fascinating. At every level of magnitude it is rich with detail, providing in infinite supply of material for those lucky enough to be able to conduct research. And for the rest of us, it is also interesting at every level of difficulty, so that we can all enjoy it, whether we want explore nature deeply or just enjoy the visual beauty it provides. We don't need to understand aerodynamics and evolution to marvel at the soaring buzzard or the wandering albatross. But if we do look further, more knowledge will enrich our knowledge and our feelings about the natural world. Unlike a fractal picture, the world behaves differently at ever level, yet they are all related, like the parts of a piece of music. Nobody yet has a theory of everything, or even knows how close they are to it. But the search is fascinating, and it enriches the world.
Books
The Cambridge Guide to the Material World Rodney Cotterill - C U P
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