A short piece about order and disorder in snow, cut from the final version of the book.
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Picture the world in halves. In one half is the human urge to know, and furthermore to structure our knowledge with observations of cause and effect, with generalisations and categories, order and regularity. It is a half of light and clarity, and our ambition is to make it bigger.
In the other half of this world stand the awkward objections to our human sense of understanding – the wilder, darker realms of exception and irregularity, of disorder, chance, randomness, mess and muddle, where God appears to play dice in the dark. This unruly half is reluctant to submit to the dreams of tidy minds.
For a brief, bewitching illustration of the tussle between them, consider snow.
* * *
Snow hardly falls in the low hills of southern England. Where I live, you might wake now and then in mid-winter to discover a dusting of whiteness, soon gone. Only once in a while will you catch a proper snowfall. But then, if it’s the right kind of cold, you’re in luck; this is the moment.
Now, as you sense the heavy quiet that you know with your eyes shut says ‘snow’, hold out a gloved hand (wool is good), tempt a snowflake to settle and, if the right one should oblige and stay a while before dissolving, then sometimes with surprising ease you can discern its elaborate hexagonal shape.
This shape – maybe 100 times wider than thick – obeys the laws of physics, naturally. Those six-sides begin with a structure determined by the lopsided arrangement of one hydrogen and two oxygen atoms in each molecule of water. As more water molecules chance on each side of the hexagon and also crystalize, the characteristic arms of the snowflake grow and reach into the air to catch still more molecules and crystals, creating the classic six-armed or six-sided snowflake.  This emerging architecture is known as a growth instability, as the first lumps and bumps build on themselves.
But physical law so far described is clearly not so prescriptive that it demands the same result every time. Although there is an underlying structure and process, snowflakes are famously unique.
To look at them, you wouldn’t think so. In March 2018, southern England had an unusual spate of snowy weather; then, on March 17th, a blitz of the biggest, most perfect, six-sided crystals I’d ever seen. I felt an urge to stop passers-by to insist they gaze at these millions of astonishing events, never seen before, never to be seen again.
But it’s hard to believe: in all the snowflakes in all the world in all time, can it be true there have never been others quite like these, never a match between any two anywhere? Depending how we define ‘alike’, it can. If we limit ourselves to the arrangement of water molecules and not their composition (which would add variation to an absurd degree as not all single water molecules are alike); and then say that we’re talking about complex crystals rather than those with a very small number of molecules (which can in fact be alike), then the number of possible permutations for any one snowflake is greater than the number of atoms in the universe.
Nonetheless, we can try to bring our own sense of order to this profusion – and we do. The images below are from the KKHY Global Snow Classification – named after its originators’ initials – of an impressive 121 different types (Eskimos might need more words for it) arranged in seven general levels.
These various types have features called columns, bullets, sectors, needles, branches, plates, and so on .
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Classifying snow is both a rigorous and charming enterprise, and tougher than it sounds: it means gathering samples from often-inhospitable places all over the world.
The classifying goes beyond mere description. We can even say where and in what weather each of the 121 types is most likely to fall, which altogether begins to sound like a cradle-to-grave story of how snowflakes turn out. Except – to bring us back to the singular object of attention on your glove (or scarf) – that even if we stood in an exclusive blizzard of nothing but P3c ferns, we would be clueless about what detail to expect of any P3c fern in particular. Even the same turns out not to be the same . Human order stops at the border with a riot of unpredictability – a border it will never cross.
So, on one side, we see law; elegant, sublime, tidy and disciplined, like the physics of the six-sided structure of the snowflake. We also find our own order in the elaborate classification of types. From the other side, we see near anarchy, buzzing with diversity and confusion, a blizzard of detail, with the thought that no two snowflakes are alike and the realisation that we will never tell the precise story of their differences .
My perspective in The Hidden Half is from the unruly side. Not because the perspective from the other, orderly side is somehow wrong. Simply because the former is often overlooked, and we need to see both.
From the perspective of this second, noisy, irregular half, we could lose ourselves in wonder at the path of experience of the flake resting on your glove; at how, where and what moments the drama of this precise arrangement – poised-but-dying – began, unfolded, grew like itself and no other, and how it’s possible for the torrent of all snowflakes in all time to do likewise, but uniquely.
And so, as our snowflake melts, and the story written into its detail fades, we know we can categorise and classify, describe laws of cause and effect, observe structures and processes, we can do all this with amazing cleverness, yet still we cannot tell how even one damn snowflake turns out like itself.
Can’t nail medown, says the snowflake, with a mischief that revels in life’s scope for disruption. For people too, it is as the writer Alfred North Whitehead once said: ‘We think in generalities, but we live in detail’ . My question is, are we so seduced by the often-beautiful and satisfying tidiness of our ideas that we forget how prodigiously awkward life can be.
 Strictly speaking, a snow crystal. Flakes can be bundles of several crystals.
 The KKHY classification, devisedby Katsuhiro Kikuchi, Takao Kameda, Keiji Higuchi and Akira Yamashita, was published in the journal Atmospheric Research, Volumes 132–133 October–November 2013. Their system builds on an earlier, formerly-standard classification of 80 types described by C Magono and CW Lee in 1960, reminding us that there’s no objective way to classify snow. The form of order we see is not dictated by nature but chosen.
 It’s not just the origin of the detail that’s mysterious; apparently, it’s not altogether clear why snow crystals change from columns to plates to columns again as humidity and temperature change.
 For a superb account of the orderly level of nature and society, see Philip Ball’s Critical Mass – how one thing leads to another. Similarly, for the wonderful story of how we have discovered many probabilistic social regularities, Helen Pearson’s The Life Project is terrific.
 The Education of an Englishman. Atlantic Monthly, Vol. 138 (1926)
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