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Byline: Christopher Lehman-Haupt The New York Times

Title: ``Where Does the Weirdness Go?: Why Quantum Mechanics Is Strange, but Not as Strange as You Think''

Author: David Lindley

Data: Illustrated. 251 pages, Basic Books/HarperCollins; $24

Our rating: Four Stars

``Why do I trust my computer?'' David Lindley asks at the outset of his illuminating new book about subatomic physics. After all, as Lindley points out, his computer is ultimately made up of subatomic particles that depend on the laws of quantum mechanics.

And as physicists have learned over the last century or so, quantum mechanics ``says that at the most fundamental level, the world is not wholly knowable and not wholly dependable.'' He concludes, ``In dealing with individual electrons or the magnetic alignment of individual atoms, I must think not in certainties but in probabilities.''

Of course, his computer works very dependably. But Lindley wonders why. ``Why should an assembly of a trillion weird little quantum objects behave any less mysteriously than its components?'' he asks. ``If we can't trust a single electron to be precisely in one place at one time, how can we trust a throng of electrons to invariably represent the letter `a' on my computer screen and not turn casually into a `z'?''

Why, in other words, does the old world of classical physics continue to operate reliably when it is grounded on the strange world of quantum physics? In short, where does the weirdness go?

To answer, Lindley first describes the specifics of that weirdness. In his book ``Where Does the Weirdness Go?'' he reviews - in particularly clear terms - various forms of Werner Heisenberg's uncertainty principle, which he generalizes as follows: ``The inability to predict, except in terms of probabilities, the outcomes of different kinds of measurements leads inescapably to an inability to obtain at the same time all the information about an object that you might want to know.''

Of course, as Lindley recalls for us, Einstein refused to accept the idea of a world that could be known only by the measurement of its probabilities. He and his followers proposed various alternatives that posited an objective reality independent of whether or how it was measured. But as Lindley shows, these alternatives created more problems than they solved.

The most practical attitude toward the quantum world, Lindley writes, was Niels Bohr's so-called Copenhagen interpretation, which stated that you could know only what you measured and that to speculate about any reality beyond that measurement was useless.

Yet the danger with Bohr's injunction, Lindley writes, was that ``as experimenters became technically more ingenious, they might find places where it became necessary to define with some precision the boundary between the measured and the measuring worlds - the boundary, in other words, between quantum and classical physics.''

After all, at some point in the measurement of a quantum function, you had to stop describing the results in terms of probabilities. To dramatize this point, Lindley invokes the famous paradox proposed by the Austrian physicist Erwin Schroedinger involving an imaginary cat whose life depends on the outcome of a quantum measurement. For if you concluded that the condition of the thing measured was half of one state and half of its opposite, you would have to say that the cat was half-alive and half-dead. Which would be absurd. But how is a cat different from a quantum phenomenon?

Lindley's book has many attractions about it, not least the author's clarity and precision in describing elusive ideas. A theoretical astrophysicist, an editor at Science News and the author of ``The End of Physics,'' Lindley employs amusingly playful metaphors without trivializing his subject. He even expresses compassion for Schroedinger's poor cat, and this may in part explain why his elucidation of the conundrum is the clearest I have come across.

Lindley develops his ideas dramatically, and his book is organized like a theatrical play: ``Act I: Mechanical Failure,'' ``Intermission: A Largely Philosophical Interlude,'' ``Act II: Putting Reality to the Test'' and ``Act III: Making Measurements.'' So I feel as if I oughtn't give away its ending.

The trouble is, not to do so would only cover up that it is the least lucid section of the book. Or maybe, because its material is based on newer discoveries and is therefore less familiar, it requires repeated reading to yield its meaning.

In his introduction, Lindley writes that only in recent years have physicists begun to understand what a measurement really is and by what physical process it makes ``indefinite things definite.''

He continues, ``The answer derives in part from theoretical insights into the behavior of complex systems, which have made it possible to understand how assemblies of many interconnected quantum objects can behave in collective ways that are by no means obvious or easily deduced from the behavior of those single objects in isolation.''

But matters become less clear when he defines the instrumental concept of ``decoherence,'' which apparently explains how complex systems work and which, he admits in an endnote, one cannot really grasp ``without understanding in a more precise way the mathematical properties of wave functions and how measurement probabilities are derived from them.''

Still, Lindley's book teaches forcefully why we must learn to take quantum mechanics at face value and accept that its strange qualities are manageable. As he writes: ``Perhaps that's the most profound lesson of all: In quantum mechanics nature is, at the most fundamental lesson, genuinely unknowable, but despite that, the world at large, the world of which quantum mechanics is the foundation, can be known and understood.''

Lindley concludes: ``Einstein, seeking higher authority for his objections to quantum mechanics, was always saying that `God does not play dice' and that `the Good Lord is subtle, but He is not malicious.' And finally an exasperated Bohr admonished Einstein, `Stop telling God what to do!' ''

Lindley's book makes very clear why Bohr's impatience was warranted.
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Title Annotation:Review; L.A. LIFE
Publication:Daily News (Los Angeles, CA)
Date:Aug 4, 1996
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