The Quantum Universe: Everything That Can Happen Does Happen By Brian Cox and Jeff Forshaw, Allen Lane, Rs 699

Where’s the moon when you aren’t looking at it? If you think the earth’s satellite can’t but be in the sky no matter whether you look at it or not, you’re in good company. Albert Einstein thought as much. Even after proving such facts that space can warp and time can stretch, he found the moon’s existence being contingent upon one’s looking too much to bear. As one who famously declared that the most incomprehensible thing in this universe is that it is comprehensible, Einstein, in the later part of his life, was desperately trying to comprehend the then emerging science — quantum mechanics (QM). His desperation has been succinctly depicted by Abraham Pais in his highly acclaimed biography of Einstein, Subtle is the Lord: The Science and Life of Albert Einstein. Pais begins his account by recalling a midday stroll both Einstein and he took from the Institute for Advanced Study to their quarters for lunch. He was startled when Einstein stopped him midway to ask if he, too, believed that the moon wasn’t there in the sky when he wasn’t looking at it.

The poser was aimed at exposing the apparent absurdity of QM. According to this new branch of physics, no object exists until it is detected. More precisely, it exists at many places at once before being spotted. As if the act of detecting ‘creates’ it. Before Einstein it was the Austrian Nobel laureate, Erwin Schrödinger, who poked fun at this bizarre picture of reality through an imaginary cat locked up in a sealed vault. The feline’s fate, said Schrödinger, was tied to a Rube Goldbergesque contraption. Alongside it the vault contained some amount of a radioactive substance, a hammer and a vial of potassium cyanide. Radioactivity, essentially the disintegration of particles into smaller fragments, is a process governed by QM, which means that no one can predict (no failure of a human, it’s not predictable in principle) exactly when a particle will break apart. QM allows one only to calculate the probability of that particle disintegrating — or not disintegrating — at a given time. Now, if a particle does decay in the vault, it causes the hammer to strike the potassium cyanide vial; the poison spreads; the cat dies.

What happens if the vault remains sealed for an hour? Common sense has it that the particle in question has either decayed, or not; the hammer has struck the vial, or not; and the cat is either dead, or alive. But, as said earlier, QM flies in the face of common sense. The particle is and isn’t broken apart; ditto for the potassium vial; so the cat is both dead and alive! No wonder Richard Feynman, another physicist, cautioned his students, saying, “I think I can safely say that nobody understands QM. Do not keep asking yourself, if you can possibly avoid it, ‘But how can it be like that?’ Nobody knows how it can be like that.” Feynman, Pais and all those belonging to the young generation thought it better to contribute to the new physics than to fret about its meaning. Einstein, with the zeal of an old guard, chose the latter option. And hence his problem with the moon.

Brian Cox, a well-known TV presenter and physics professor at Manchester University, and Jeff Forshaw, also at the same institution, are on their second venture in popular science after Why Does E=mc2. And relativity’s sequel is QM, which they set out to demystify. An ambitious goal indeed.

While digging up the history of their subject the authors tread the beaten track, recounting the bewildering experimental results that shattered the existing paradigms. However, their non-conformist take on the essentials of QM differs from the run-of-the-mill fare. Instead of the cat-in-the-box, or all those almost worn-out examples to portray quantum weirdness, they plunge deep into the subject. Among the many realms of quantum reality they explore are how an electron behaves both like a particle and a wave; why a particle doesn’t have a fixed location and a velocity at a given time; why you can sit on a chair without falling through it; why any vacuum, instead of being really empty, is a seething cauldron in which innumerable particles are perennially popping in and out of existence.

However, for all their attempts to simplify those mysterious phenomena, Cox and Forshaw may not win many readers. Reluctant to discuss those apparent absurdities superficially, they adopt a somewhat novel technique. To explain things by invoking the wavy nature of particles they employ the imagery of a clock face. A clock with a single hand, that is. The trick works because such a clock depicts the various phases of a wave easily. The trick was first employed by Feynman in 1985 when he wrote QED: The Strange Theory of Light and Matter (popular exposition of quantum electrodynamics, the research that earned him a Nobel prize). However, Cox and Forshaw make use of the trick much more extensively than Feynman did, explaining many a phenomenon that other popular titles on QM avoid. The feat comes at a price though. Often, there’s deluge of clock faces spanning page after page in which even an avid reader may get lost.

To show that QM, rather than a mere mind sport, is a hugely useful theory, the authors highlight many of its successes. For example, researchers’ prediction of how an electron will behave in the vicinity of a magnet has matched experimental results up to 12 decimal places. That’s as accurate as measuring the distance between your rooftop and the moon to within a few millimetres. The authors also discuss ‘the most important invention of the 20th century — the transistor’, which couldn’t be made without the knowledge of QM. The invention, now lurking in every computer or mobile phone, has shown that QM is ‘the prime example of the infinitely esoteric becoming the profoundly useful.’

The authors end their paean to QM with ‘one of the greatest demonstrations of scientific reasoning’. They elucidate what Nobel laureate Subrahmanyan Chandrasekhar had done in 1931, calculating the destiny of certain stars. Those fireballs are caught in an eerie tug-of-war. Their huge mass exerts immense gravity which tries to squeeze them small. But squeezing causes its atoms to fuse together, an act that releases heat. The heat, in turn, tries to swell the stars’ size. Between gravity and heat, which wins? Depends on the mass a star starts its life with.

Going against the then-current wisdom, thereby infuriating many a stalwart of the era, Chandrasekhar showed that there was an upper limit (now known after him) of mass for a star to become a so-called ‘white dwarf’, a superdense ball of nuclear matter intermingled with a sea of electrons. Stars less than 1.4 times our sun’s weight are all destined to become such dwarves. How could Chandrasekhar conclude this? Through QM, of course. Astronomers have catalogued about 10,000 white dwarves, and none of them are more massive than what the Chandrasekhar limit foretells them to be.

That QM’s unerring rule extends from the tiniest to the largest of objects in the universe, Cox and Forshaw claim, is ‘spine-tingling’. They couldn’t more right.