If I have seen further it is by standing on the shoulders of giants.

Saturday, December 24, 2011

How Physics Got Weird

Quantum physics has never been more topical. Schrödinger's "dead and alive" cat has entered popular lore, parallel universes have emerged from science fiction to become part of serious scientific speculation, and quantum computers offer the prospect of a leap forward as great again as the leap from the abacus to the classical computer itself. Quantum physicists have even achieved teleportation—although as yet only of photons, not people. So the time is very much ripe for a collection pulling together many of the great scientific papers of the 20th century that comprised the quantum revolution. There have been similar collections before (notably John Wheeler and Wojciech Zurek's 1983 "Quantum Theory and Measurement"), but with Stephen Hawking's name attached, the latest version is likely to reach a much wider audience than its predecessors.

Prospective readers should be warned, though, that the contents are not for the faint-hearted. They are the real thing, written by such luminaries as Max Planck, Albert Einstein, Werner Heisenberg and Erwin Schrödinger, and presented more or less as they were originally published, though with the benefit of introductions setting each section in context. There has been some judicious editing (and some I regard as injudicious, such as the savage cutting of the paper in which Schrödinger published his famous puzzle, in which an unseen cat is paradoxically both alive and dead), but there is very little here that would be an easy read for anyone without a degree in physics. But if you have either the stamina to plow through the whole story, or the inclination to dip in for favorite nuggets, this is the place to find the history behind much of the research making headlines today.

The story starts with Planck's discovery at the beginning of the 20th century of the mathematical law that describes the nature of the radiation emitted by an object as it is heated (bizarrely known as "black body" radiation)—a result that also established that light and other forms of energy came in discrete units (the "quanta" from which the subject takes its name). The collection proceeds through Einstein's 1905 proof that "particles of light"—later dubbed photons—were real, to the application of these ideas to atomic physics and the revelation in the 1920s that the quantum world is stranger than anything that had been imagined.

The discovery of wave-particle duality in 1924 (by Louis de Broglie) and quantum uncertainty in 1927 (by Heisenberg) made quantum physics as much a branch of philosophy as science, stirring arguments that continue to the present day about how to interpret what the equations are telling us. Is it really possible that quantum systems—perhaps even cats—exist in a state of unreality until we look at them and force them to take on one configuration or another? Or are there many, perhaps infinitely many, different realities, in which all possible outcomes of quantum choices are played out simultaneously (the so-called "many worlds" hypothesis)? Is it possible that instantaneous communications link quantum entities across vast spaces, so that actions affecting one particle also instantaneously change the characteristics of a distant counterpart? (Though Einstein called this unsettling prospect "spooky action at a distance," the answer is "yes"; experiments have proved it.)

Against this philosophical debating, hard-core physicists such as Richard Feynman (who is represented here not just by a paper on the work for which he received the Nobel Prize but by his science-fiction-like suggestion that the particles known as positrons are electrons traveling backward in time), Sin-Itiro Tomonaga and Julian Schwinger ignored the philosophy and got on with solving the equations—after they had found the right ones to solve—coming up with a complete, unified description of everything in the universe except gravity. Bringing gravity into the quantum fold remains the Holy Grail of physicists.

There are two serious omissions from the book, which shows signs of having been put together hastily, and one bizarre inclusion. Louis de Broglie's paper introducing the idea that electrons could be treated as waves (which impressed Einstein and led Schrödinger to his Nobel-winning work on quantum theory) is conspicuous by its absence, as is the 1957 paper by Hugh Everett that made the "many worlds" idea, which remains the best resolution of the Schrödinger's cat puzzle, part of mainstream science.

Of course, something has to give, even in a volume this size, but space for these ideas could be found by leaving out the extract from a popular book by George Gamow, which no more deserves a place here than an extract from, say, Mr. Hawking's "A Brief History of Time." It is also inexcusable in a book of this kind to have no index or guide to further reading. And I may be a pedant, but if you are going to use a Shakespeare quotation in the title of a book, you should get it right: The words Shakespeare put in the mouth of Prospero at the end of "The Tempest" are actually "We are such stuff as dreams are made on; and our little life is rounded with a sleep."

That said, on balance "The Dreams That Stuff Is Made Of" is a welcome addition to the quantum library. At $30, it is remarkably good value; but do not be sucked in by the publisher's claim that it "introduces the nonscientific reader to the mind-bending world of quantum physics." Approach this with no knowledge of science and your mind may well get bent, but you are unlikely to get much insight into what is going on.

Source: WSJ - Book Review: The Dreams That Stuff Is Made Of

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