Most liquids when chilled contract by about 10 per cent. Water does too, but only down to a point. Once it is within whispering distance of freezing, it begins—perversely, beguilingly, extremely improbably—to expand. By the time it is solid, it is almost a tenth more voluminous than it was before. Because it expands, ice floats on water—“an utterly bizarre property,” according to John Gribbin. If it lacked this splendid waywardness, ice would sink, and lakes and oceans would freeze from the bottom up. Without surface ice to hold heat in, the water’s warmth would radiate away, leaving it even
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