BOOK REVIEW

Events of 1905

Secrets of the Old One: Einstein, 1905. Jeremy Bernstein. vii + 200 pp. Copernicus Books, 2006. $25.

It's About Time: Understanding Einstein's Relativity. N. David Mermin. xvi + 192 pp. Princeton University Press, 2005. $35.

Every generation rewrites Shakespeare, finding new meanings in his tragic heroes, his plays within plays, his depictions of love and betrayal. So it has been—and will remain—for Einstein, as physicists continue to explore the depths of his work in quantum theory and general relativity. Einstein's reasoning is very much with us, from the laboratory production of Bose-Einstein condensates, through the observatory's glimpses of gravitational lensing, to the abstractions of string theory and the outer reaches of cosmology. For historians and philosophers of science, Einstein remains a figure of endless fascination—what he thought about the real and the objective in science, how he sorted out the shifting politics of his very long day: pacifism, militancy against Nazism, the atomic bomb, McCarthyism. No doubt our current concerns weigh on us as we try over and over to discern how this extraordinary figure fit into the changing culture that surrounded his life, which spanned the years from 1879 to 1955. A hundred years after his staggering series of papers in 1905, Einstein's works also remain points of departure for many architects, artists and musicians.

A wide public with various levels of technical background would like to know what it was that Einstein did in his physics. Over the course of 2005, we had dozens of books about Einstein and relativity. Just out are new ones by two of our most engaging physicist-writers, Jeremy Bernstein and N. David Mermin. Bound by a common interest in relativity (in the works reviewed here, mainly special relativity), they have aimed their books at different audiences. Both are excellent—for very different reasons.

Before continuing, I should confess that I think most popularizations of science actually do more harm than good. Why? Because in my view the single most important feature of scientific work is not this or that specific result. Instead, what physics in particular does so beautifully—and what science more generally accomplishes—is the linking of diverse phenomena, the binding together of a myriad of predictions and explanations.

What nearly all popularizations do is systematically undermine the progressive reasoning that links principles, conventions, experiments and laws. Bad science writing splinters the most interesting feature of science, its long run of connected argumentation, into isolated metaphors that last just long enough to evoke a particular result. Black holes are said to be like huge funnels; quantum electron orbits, to resemble diffuse clouds. This problem of shattered connectedness is bad enough. Adding to the difficulty is that many science writers (or scientists writing for the broad public) feel caught: Either insert a new metaphor or two per sentence, or introduce a mathematical apparatus that loses the vast majority of the audience from the first page.

Is there any passage between these twin dangers? There are at least two, but both are formidably difficult to navigate. One way to proceed is to find a felicitous metaphor and stick with it—using the conceit to display the interconnectedness of the phenomena that at first glance appear scattered within a scientific domain. The best popular physics book written in the last half century, in my view, is of this kind—Richard Feynman's QED: The Strange Theory of Light and Matter, which has an absolute minimum of mathematics and a single guiding image. Feynman is nonetheless able to lead the reader through the connections between reflection, refraction and a dozen more complex physical phenomena. On my short list of other really good popular science books that actually let you follow reasoning from one sector of the world to another are Steven Weinberg's 1977 book The First Three Minutes and Brian Greene's much more recent The Elegant Universe (1999). Such ventures (and the list beyond these is not very long) give up the disconnected-metaphor approach and so require real concentration to read. It is not accidental but instead exactly the point of a good systematic popularization of physics that one cannot just dip in and read sections in an arbitrary order.

A second kind of wide-angle science writing that I also quite like—when it too avoids the metaphor-a-minute approach—embeds the science in a larger picture. Richard Rhodes does this nicely in his remarkable history of the Manhattan Project. James Gleick does it beautifully in his biography of Feynman and in his study of chaos. In other words, the effort in this second kind of writing is to situate specific, illustrative pieces of the science rather than to focus on the interconnections worked out in detail. Let's call this an embedded rather than a systematic approach.

Jeremy Bernstein shines at this strategy of embedment, particularly in his biographical sketches—the striking series of portraits of physicists he has given us over the years in The New Yorker, in which he humanizes figures like Hans Bethe while keeping their ideas lucid and central. My favorite work of Bernstein's may be less widely known: his hard-hitting analysis of the infamous tapes of the captured German nuclear scientists at Farm Hall. Slicing through their vacuous claims to have understood the physics of nuclear weapons from the get-go, Bernstein dissects the conversations, skewering apologetics and obfuscations. For example, he shows that the captured scientists often conflated fast and slow fission neutrons and that anyone who confuses the two has not understood the sine qua non of explosive chain reactions.

When wearing his research hat, Cornell's David Mermin is a theoretical physicist, but his ferocious drive to find the simplest explanations of physical concepts has echoed far beyond work in his research specialty. For example, it was Mermin's extraordinarily simple explanation of Bell's inequality that taught several generations of physicists and philosophers of science the range and depth of what John Bell had done. In particular, Mermin made the depth of Bell's contribution transparent: The results of quantum observations that ground the inequality could be grasped in their entirety without the details of the theory of quantum mechanics; the correlations between distant effects simply make it necessary that any theory, canonical quantum mechanics or any putative alternative, would have to be nonlocal.

Bernstein's and Mermin's styles differ too. If you have read even a single one of Bernstein's sketches, you will recognize his style immediately: a mixture of conceptual presentation, telling anecdote and personal reminiscence. In his new book, Secrets of the Old One, he uses this approach to good effect. Einstein himself stands just outside—or, more precisely, before—Bernstein's story. But stories, including some I've never heard, appear right and left, many based on Bernstein's discussions with leading physicists who knew Einstein well (especially the physicist-philosopher Philipp Frank), and others based on Einstein's letters and other writings.

Secrets of the Old One truly is a book aimed at a wide audience. It should be no trouble to read for anyone who enjoys sophisticated, often witty writing about science. There are a few moments when more technical comments will fly by—a beautiful side remark about the relative dimensions of the magnetic and electric fields is pregnant with meaning. When a point is central, Bernstein slows to explain it with enormous clarity: the random walk, the Doppler shift, ether experiments, the twin paradox. Then, around these scientific explorations, Bernstein wanders in the best essay style through relevant stories of Viennese cafes and American basement laboratories. (Mermin's text—more on this in a moment—is a step up the ladder of demands that can be made on an audience.)

Bernstein aims to cover the basics of Einstein's theory of special relativity, Brownian motion and the quantum of light, and he treats each neatly. Beginning with relativity has advantages for Bernstein: In a way, at least in the retelling, it requires the least technical background to understand—and Bernstein uses this physical simplicity to advantage by beginning with explanations even of the Pythagorean Theorem, which Einstein so admired as a child. Bernstein discusses the Lorentz transformations, making them plausible in their Einsteinian form, and introduces to good effect the space-time diagrams of the great mathematician and mathematical physicist Hermann Minkowski. Bernstein has a nice and simple discussion of how Einstein used the random walk to treat the erratic movements of colloidal particles as evidence for the physical reality of atoms. And he cleanly introduces Einstein's notions about the quantum of light, the only one of his ideas that Einstein himself called "revolutionary."

Within Bernstein's reasonable and self-imposed constraints of target audience, emphasis and level, I wished for one last chapter: a discussion of connections among Einstein's great works of 1905. The papers have an intense stylistic unity, a feature Gerald Holton has long emphasized. They generally begin with an asymmetry that deeply troubled Einstein (and practically no one else). For example, it bothered him tremendously that Maxwell's equations ("as they are usually understood") gave two different explanations for the generation of a current in a coil as it approached a magnet—one explanation if the magnet was "at rest" and the coil in motion; another explanation if the reverse were the case. Einstein's papers ended with a resolution of the asymmetry and, inevitably, a suggestion of very concrete experimental predictions (such as the photoelectric effect, the motion of electrons in electromagnetic fields or a quantitative account of the wanderings of suspended Brownian particles).

But my imaginary last chapter could go even further. Einstein has long been seen as an heir to Ernst Mach—to Mach's razor-sharp critique of "metaphysical" notions such as "absolute space" and "absolute time." Less philosophically well known was Einstein's fascination with the program of Ludwig Boltzmann's development of statistical mechanics. It was toward Boltzmann's intellectual world of the statistical study of atoms and molecules that Einstein first turned his theoretical research—in 1902, three years before the "miracle year." My imaginary last chapter could explore how Einstein's fascination with statistical fluctuations joined the light-quantum paper to the Brownian-motion paper; and it could explain how the quantum of light helped carve out a thinkable way in which light could move without an underlying ether. On this reading, Einstein's light-quantum paper is the leading vertex of an arrow, joined on one side via fluctuations to Brownian motion and on the other to an etherless electrodynamics of moving bodies. But maybe I'm gilding the lily—Bernstein has gone far in brief, accessible style. That is more than enough.

Now let's move on to Mermin's It's About Time. From the title forward, Mermin's exposition heads for only a portion of Einstein's 1905 year. As his title suggests, Mermin's argument is that Einstein's contribution to special relativity revolves around his reformation of time. Light quanta and Brownian motion do not enter into his discussion—nor does the long experimental history of ether-drift experiments or the complex theoretical inquiry by Hendrik Lorentz, Henri Poincaré and others into the physics of the electron.

There are two things remarkable about Mermin's book. First, it consistently switches back and forth between different frames of reference. This way the reader really understands how extraordinary the theory is—that different points of view can capture one and the same phenomenon while giving it different descriptions. Now, the uninitiated might think this was an obvious thing to do. After all, the theory of relativity, as its name advertises, is precisely designed to give an account of the world that is not dependent on a particular choice of inertial reference frame. But in fact I can't think of another account (other than one remarkable place where Einstein himself does it) where the view from multiple reference-frame perspectives is so consistently kept front and center. Second, the book starts and finishes with collisions—looked at from different frames of reference. As a start, this very clever stratagem conveys the fecundity of switching reference frames. As a finish, it leaves the reader with a clear understanding of the most famous equation in all of modern science, E = mc ².

Back in 1905—in his first relativity article—Einstein used the more-than-metaphor of coordinated clocks along train tracks. It served him well for a lifetime. Mermin too uses trains, clocks and light signals to enormously good effect, constantly switching between points of view, explaining real physics clearly. My only regret is that I was never lucky enough to watch Mermin do this at the board. I imagine some of the more complex diagrams gain in force by watching their elements laid down in sequence. Then there's a second approach—introduced by Minkowski in his eponymous diagrams. About midway through the book, having conveyed crucial ideas, Mermin introduces the idea of space-time geometry: how the x and t axes look in different frames of reference, and how this new geometry alters the way we define simultaneity, length and much else. Indeed, Mermin pursues spacetime with diligence all the way through a myriad of results and resolved "paradoxes."

It's About Time is a book that should join the very best systematic popular expositions of science written in the last 50 years. Secrets of the Old One is one of the best scientist-sketches and adds to Bernstein's long list of such successes. Hats off—Bernstein and Mermin. They have written excellent popular books, in very different styles, ones that stand out on a subject, Albert Einstein, about whom there is no shortage of excellent writing.

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