Einstein Was Uncertain About Uncertainty
Last week, in an unprecedented feat of quantum mechanics, Harvard physicists were able to use a cloud of Bose-Einstein condensate to stop a pulse of light and then resuscitate the light at a different location. “That’s the sort of stuff we find really sexy in this business,” Eric A. Cornell, from the National Institute of Standards and Technology, said admiringly.
David Lindley’s new book about the development and impact of Werner Heisenberg’s uncertainty principle has some of that same sex appeal. Though this book’s only suspense revolves around exactly when each of its principals will receive his Nobel Prize (Max Born got a late one in 1954), it provides a useful précis of the mind-blowing progress of physics in the early 20th century.
Mr. Lindley is a sufficiently good explicator to summarize how an understanding of the atom begat nuclear physics, which led to quantum mechanics, special relativity, matrix algebra, matrix mechanics and so on. That he breaks this down, step by step — and casts it in terms accessible to lay readers, yet not too oversimplified for more sophisticated ones — is reason enough for “Uncertainty” to be worthwhile.
Mr. Lindley’s clear explanations brings to mind one great scientist’s remark, cited here, that any physicist worth his salt ought to be able to explain his research to a barmaid. By contrast, Mr. Lindley says, Niels Bohr had trouble making even other physicists understand what he meant. One of this author’s better ideas is to translate passages of typically vague and bewildering Bohrian prose.
In a book that is wisely short-winded, Mr. Lindley also analyzes tensions among the important theorists and innovators in these fields. And when his book’s subtitle calls this friction a “struggle for the soul of science,” it is not being excessive.
“Uncertainty” examines the critical juncture at which classical scientific methods became obsolete and the most radical theories began to be outside the realm of proof. He explains how “a gap had opened up between what a theory said was the full and correct picture of the physical world and what an experiment could in practice reveal of that world.” This was a schism so deep and troubling that it meant two fundamentally different ways of approaching science.
At some point the debate became a battle of personalities as well as of scientific principles. And while Albert Einstein, Niels Bohr, Werner Heisenberg, Ernest Rutherford, Max Planck, Erwin Schrödinger, Wolfgang Pauli and their colleagues were not prone to conventional catfights, they did have claws. As Pauli once said to Heisenberg, the irreverent young physicist who made waves in more ways than one: “It’s much easier to find one’s way if one isn’t too familiar with the magnificent unity of classical physics. You have a decided advantage there, but then lack of knowledge is no guarantee of success.”
What Heisenberg had done to prompt such malice was to come up with an idea too sexy to stay confined to the physics world. As Mr. Lindley points out, the Heisenberg uncertainty principle is now freely bandied about in nonscientific contexts, from literary theory to television dialogue. He cites an instance when Heisenberg was glibly name-dropped on “The West Wing,” in an anecdote about a film crew’s changing an event simply by observing it.
If Heisenberg’s idea “has become a touchstone, a badge of authority, for a certain class of ideas and speculations,” Mr. Lindley says, perhaps that is because it can be used to make scientific truth sound less than all-powerful. Treated that way, “the uncertainty principle makes scientific knowledge itself less daunting to the nonscientists and more like the slippery, elusive kind of knowing we daily grapple with.”
But the real uncertainty principle is more precise than that. It states that while some phenomena produce a definable range of possible outcomes, it is impossible to infer from the outcome which single unique event actually produced it. This has evolved, Mr. Lindley says, into “a practical, workaday definition of the uncertainty principle that most physicists continue to find convenient and at least moderately comprehensible — as long as they choose not to think too hard about the still unresolved philosophical or metaphysical difficulties it throws up.”
But in Heisenberg’s day, as “Uncertainty” elucidates, science’s superstars were not inclined to overlook those unresolved difficulties. Heisenberg prompted great resistance from Einstein, who by 1927 was the great old man of the physics world (his own biggest ideas had arrived with staggering impact in 1905) and found at least one of Heisenberg’s scientific papers to be “dégoûtant,” or disgusting.
“Heisenberg has laid a large quantum egg,” Einstein complained. It does not escape Mr. Lindley, nor has it escaped other scientists writing about this conflict, that the man whose theory of relativity was so counterintuitive might better have been inclined to give the oddness of Heisenberg’s theory the benefit of the doubt.
As for Bohr, whose machinations with Heisenberg have prompted so much speculation (as in Michael Frayn’s play “Copenhagen”) and whose influence led to changes in Heisenberg’s thinking, Mr. Lindley examines the evidence and decides that “the simple explanation is not necessarily wrong.” In his opinion, and in a book more finely attuned to scientific progress than to the personalities behind it: “Heisenberg changed his mind, in short, because he saw that Bohr offered a better way forward. He was a pragmatist. There is no reason to believe he was insincere.”
Einstein, Heisenberg, Bohr and the Struggle for the Soul of Science
By David Lindley
257 pages. Doubleday. $26.