Sunday, December 22, 2002

Richard Feynman, the virtuoso physicist with an unmatched insight into the quantum world, once famously remarked that “Nobody understands quantum mechanics.” Despite this disturbing situation, physicists were able to use the counterintuitive results of quantum mechanics to construct the panoply of devices, from nuclear bombs to lasers, MRI machines and electronic computers, that characterized the astonishing technological progress of the 20th century.
Barry Parker, for 30 years a physics professor at Idaho State University and author of a dozen popular science books, provides in Quantum Legacy: The Discovery that Changed our Universe (Prometheus Books, $29, 282 pages) a sprightly and intelligible account of quantum physics and what it has wrought.
The first part of Mr. Parker’s book is a conventional historical account of the development of quantum theory, brought to life by numerous anecdotes. The theory began as a desperate mathematical maneuver by Max Planck to explain the spectrum of so-called “black-body” heat radiation. Defying the well-established principles of classical physics, Planck suggested that matter and radiation did not interact in a smooth and continuous way, but rather only via discontinuous finite packets, or “quanta,” of energy. This idea was soon extended by Albert Einstein to explain several more otherwise incomprehensible phenomena, and later by Niels Bohr to provide a quantitative explanation of the spectrum of the hydrogen atom.
In the 1920s, this “old” quantum theory, a hybrid of classical ideas and ad-hoc rules, was superseded by the more sophisticated and far reaching quantum mechanics associated with the names of Schrodinger, Born, Heisenberg and Dirac. The new theory showed how matter and radiation possessed both particle-like and wave-like properties. This meant that in principle nature could only be described statistically, a dramatic departure from the classical view that the need sometimes to use statistics was simply a consequence of limitations on the human ability to calculate everything precisely.
This idea scandalized Einstein. In a long debate with Bohr, Einstein showed that assuming quantum mechanics was the ultimate description of reality showed that it implied that particles, no matter how far apart from each other, must be able to “communicate” instantaneously, contradicting a basic assumption of physics. In the 1980s, experiment showed that this scandalous situation was in fact true.
The second part of the book describes the practical consequences of the quantum revolution, including lasers, nuclear energy, DNA and molecular biology, and solid state devices like the microchips at the base of today’s computers hardware. Mr. Parker stretches to include a long chapter on the history of computing, much of which has nothing to do with the quantum devices that make computers work so quickly. He might have done better to discuss some of the open problems of quantum mechanics with which today’s researchers are struggling, rather than leaving the impression that the theory’s paradoxical underpinnings were resolved back in the 1930s by Bohr’s “Copenhagen Interpretation.”

Some of the different ideas being explored by current researchers are discussed in The Universe Next Door: The Making of Tomorrow’s Science (Oxford University Press, $26, 191 pages) by Marcus Chown, a British astrophysicist turned bestselling science writer. One particularly unorthodox approach was put forth 45 years ago by Hugh Everett in his PhD thesis, and has gained more adherents in recent years. This “Many Worlds” interpretation differs from Bohr’s approach in explaining the probabilistic nature of quantum mechanics.
According to Everett, the universe is continuously splitting into different universes, each of which is described by a different possible states. This picture is most popular among some of the scientists attempting to build a quantum computer, a device which could theoretically operate far more rapidly than current computers by exploiting the ability of atoms to occupy different states at the same time. Noone has yet built such a machine, but they are being worked on very seriously.
Taking the Many Worlds theory further, it implies there are infinitely many duplicates of you in the infinitely many replicating universes, each of whom is enjoying (or suffering) a different life. Unfortunately, you can’t all get together to compare notes.
Two other “dispatches from the frontier of the imagination,” as Mr. Chown calls his colorful but seriously researched pieces, discuss the idea that time flows in different directions in different parts of the universe and that electrons, hitherto firmly established as elementary particles, might sometimes split. Others deal with the greatest mystery of the universe, which is the nature of the vast quantity of “missing mass” or “dark matter” that has not yet been observed but that cosmologists calculate is needed to account for the observed rate of expansion of the universe.
One theorist suggests that most of the universe consists of refrigerator-sized black holes, each weighing about as much as the planet Jupiter. Others postulate the existence of a “mirror universe” made up of matter that does not react to the electromagnetic and nuclear forces that control the behavior of the normal matter, and is therefore invisible to us. Chown rounds out his book with some researchers’ speculations on the possible interstellar origin of life and the existence of highly advanced alien civilizations.

A similar range of unconventional ideas can be found in Tom Siegfried’s Strange Matters: Undiscovered Ideas at the Frontiers of Space and Time, (Joseph Henry Press, $24.95, 224 pages) Mr. Siegfried writes on science for the Dallas Morning News, and his book was inspired by the fact that by following their mathematical equations to their logical conclusions has often led physicists to predict and later discover previously unforeseen phenomena, such as the anti-matter foretold by Dirac’s equation for the electron in the 1920s.
Mr. Siegfried searches out scientists who are making similar intellectual forays today. Interestingly, he cites a completely different set of people than does Mr. Chown, even though they are in the same field and their thoughts run in similar directions.
Mr. Siegfried’s breezy account includes a healthy dose of exposition of current physical theories, but focuses on the unconventional implications some have drawn from them. These include the possibility that quarks, the fractionally charged constituents that combine to form protons, neutrons and other so-called hadrons, but cannot be pried out of them, may under certain circumstances form “strange matter.”
Some researchers want to examine seismic records to detect evidence that the earth is being bombarded by quark nuggets, millimeter-sized clumps of strange matter weighing four tons each. Mr. Siegfried suggests that you wouldn’t want one of these as a pet rock. Discussing different ideas about the nature of the missing mass that supposedly pervades the universe, he cites possibilities including WIMPs (weakly interacting massive particles), Q-balls (“superparticles” that formed in the hot, dense phase of the newly-created universe and are still lurking somewhere) and WIMPZILLAs monstrous versions of the previously mentioned WIMPs.
Mr. Siegfried also reviews a range of theorists trying to describe the world mathematically using many dimensions more than the conventional four (three of space and one of time)and concludes with a summary of the ongoing philosophical debate over whether the uncanny ability of humans to derive models of physical reality from abstract mathematical reasoning shows that e mathematics, and our brain’s ability to use it, reflects reality, or whether the “physical reality” we perceive is simply an artifact of the mathematics we invent.

Jeffrey Marsh has written widely on scientific topics and public issues ranging from nuclear strategy to social policy.

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