Wednesday, 14 December 2011

The Quantum Universe

The Quantum Universe: Everything that can happen does happen by Brian Cox and Jeff Forshaw
Daily Telegraph, 22 October 2011
More than 10,000,000,000, 000,000,000 transistors are manufactured each year. For an idea of the magnitude of this number, it is roughly 100 times greater than all the grains of rice consumed annually by the people of planet Earth. This astonishing fact about the fundamental building block of all electronic devices is buried deep within The Quantum Universe, the latest book from Brian Cox and Jeff Forshaw.The very first transistor computer built in 1953 had just 92 transistors, but today more than 100,000 can be bought for the cost of a single grain of rice and there are around a billion of them in a mobile phone. It is easy to see why Cox and Forshaw believe the invention of this device was “the most important application of quantum theory”, while the theory itself is “the prime example of the infinitely esoteric becoming the profoundly useful”.

It is esoteric because the theory describes a reality in which a particle can be in several places at once and moves from one place to another by exploring the entire universe simultaneously. The American physicist Richard Feynman unveiled a piece on the quantum universe, but nevertheless cautioned: “I think I can safely say that nobody understands quantum mechanics. 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.”
Heeding this advice and sticking to the maxim that “following the rules is far simpler than trying to visualise what they actually mean”, Cox and Forshaw set out to “demystify quantum theory”. If they do not entirely succeed, it says more about the size of the task they have set themselves than its execution. The word “quantum”, they warn at the outset, is at “once evocative, bewildering and fascinating”. Having written a narrative history myself with that one word as a title, I know exactly what they mean.
Peppered with diagrams and equations, The Quantum Universe is not an easy read. We encounter Planck's constant (nature’s own axe for chopping up energy and much else besides); the principle of least action; the wave function; the uncertainty principle; electron standing waves; the exclusion principle; semiconductors; Feynman diagrams; quantum electrodynamics; the Higgs boson and the standard model of particle physics. The reader is made to work along the way and for those prepared to do so there is much to learn. Why, for example, empty space isn’t empty but is a seething maelstrom of subatomic particles.
While they sidestep the question of its interpretation and the decades-long debate between Albert Einstein, Niels Bohr and others, for Cox and Forshaw there is no better demonstration of the power of the scientific method than quantum mechanics. Nobody could have come up with the theory without the aid of detailed experiments, and the physicists who came up with it were forced to suspend and then discard their previously held beliefs to explain the evidence that confronted them. In an attempt to convince any sceptical readers about the power of quantum mechanics, the authors turn to the death of stars and the Chandrasekhar limit as they champion curiosity-driven research.
The sun is a gaseous mix of protons, neutrons, electrons and photons with the volume of a million earths that is slowly collapsing under its own gravity. This compression heats the core to such temperatures that protons fuse together to form helium nuclei. The fusion process releases energy that increases the pressure on the outer layers of the star, thus balancing the inward pull of gravity. And so it will go on for the next five billion years until the sun runs out of material to fuse and ends up as a super dense ball of nuclear matter in a sea of electrons known as a white dwarf. It’s a fate that will befall more than 95 per cent of the stars in our galaxy. Though the highlight of the book is confined to the epilogue, Cox and Forshaw show how it’s possible to approximately calculate the largest possible mass of these stars.
The detailed and more complex calculation was originally published in 1931 by the Indian astrophysicist, and future Nobel laureate, Subrahmanyan Chandrasekhar. It led to two remarkable predictions: white dwarf stars exist and they cannot have a mass greater than 1.4 times that of the sun. Astronomers have catalogued some 10,000 white dwarves and the largest recorded mass is just under 1.4 solar masses. Depending on four of nature’s fundamental numbers – Planck’s constant, the speed of light, Newton’s gravitational constant and the mass of the proton – Chandrasekhar’s limit is a stunning triumph of the scientific method. “The eternal mystery of the world is its comprehensibility,” Einstein wrote. “The fact that it is comprehensible is a miracle.”