PD Smith

Sky in a Bottle

Times Literary Supplement, 4 August 2006

Peter Pesic, Sky in a Bottle (MIT), 262 pp., £16.50.

Review by P. D. Smith
The question of why the sky is blue has perplexed philosophers, scientists and children alike since the beginning of history. Physicist and musician Peter Pesic finds it “strange and beautiful that such simple questions lead to such deep realizations about the nature of the universe”. Indeed, his fascinating journey into the history of light and colour shows that attempts to answer this apparently simple question involve “the secrets of matter and light, the scope of the universe in space and time, the destiny of the earth, and deep human feelings.”

Among those who have applied their intellects to explaining why the sky is blue was Leonardo da Vinci. He believed that “minute, imperceptible particles” were attracted by solar rays which then “seem luminous against the deep, intense darkness of the region of fire that forms a covering above them”. He was one of the first to try to capture an “artificial sky” in a bottle. In the eighteenth century, Swiss geologist and meteorologist Horace de Saussure was enraptured by the deep blue of the Alpine sky. It held “in its grandeur and its dazzling purity, an element of death and infinite sadness”, wrote Saussure, who created a “cyanometer” with 52 hues to measure the blue of the sky. Like da Vinci, he tried to create sky in a bottle using a saturated solution of copper sulphate and ammonia: “For both men, this quest would have concerned the same desire to bring to earth, to capture in a bottle, the mysterious hue that had astonished them on the heights.”

But it was physicist John Tyndall who came closest to explaining the mystery and recreating the wondrous blue of sky in a bottle using photochemical reactions in 1869. Even Ruskin – a sceptic as far as science was concerned – was impressed: “To form, ‘within an experimental tube, a bit of more perfect sky than the sky itself!’ here is magic of the finest sort.” Rather remarkably, as Pesic shows, “the visionary artist saw more clearly than the sober scientist.” For although Tyndall clung on to the idea that particles in the air create blue sky, Ruskin grasped that air molecules themselves were responsible. This was confirmed by Einstein’s 1910 paper on opalescence, showing that the colour of the sky is caused by gas molecules scattering the sun’s light. Einstein’s paper provided further evidence for the existence of atoms. As Pesic concludes, “the quest to understand the sky and its color leads inward, for the sky cannot be blue if atoms are not real. Gazing at the sky, we confront the most beautiful proof of atomic theory.” From mountaineering to mathematics, Sky in a Bottle offers a memorable survey of the many attempts to cast light on this intractable yet beguiling problem.