## Schroedinger's Rabbits: The Many Worlds of Quantum

*by Colin Bruce*

Washington DC: Joseph Henry Press, 2004, xi + 239 pages, $24.95 (paper)

Reviewed in *Physics In Perspective* by Mark P. Silverman, Trinity College

Each year I receive manuscripts purporting to find either the "flaws"
in Einstein's theory of relativity or the "true" meaning of quantum
mechanics. Besides being generally wrong, the manuscripts have in common
an idiosyncratically quirky use of language. The words sound like
physics words, but are used inappropriately and nonsensically because
the authors have little understanding of what they signify. And so,
when Schroedinger's Rabbits arrived on my desk, I had that depressing
sense of *déjà vu* upon seeing the bright red
subtitle terminate abruptly at the right edge of the book cover with the
word "quantum". Quantum what? Did the author mean quantum mechanics?
Or quantum physics? Or quantum theory? Or quantum number? Or a
quantum of energy? The incompleteness of the phrase was like a chord
unresolved to its tonic - or, less musically, like waiting for the
second shoe to fall.

The syntactical aberration on the cover was not a compositor's error, but perpetuated throughout the book, as in the author's "Principal Puzzles of Quantum", a collection of supposedly paradoxical facts that I believe would qualify for what Gell-Mann once described as "quantum flapdoodle." For example, "Why does the universe seem to waste such a colossal amount of effort investigating might-have-beens, things that could have happened but didn't?" I wasn't aware the universe investigated anything, let alone at the expense of a colossal amount of effort. Could it be that the author has misunderstood what a probability density function is? Such a function gives a quantitative measure of the outcome of an event among a possibly infinite number of events - without tiring the universe out. Here is another PPQ: "Why does reality appear to be the world in a single specific pattern, when the guide waves should be weaving an ever more tangled multiplicity of patterns?" This is a philosophical farrago well meriting Pauli's trenchant remark that it is not even wrong.

More disturbing that the whimsical use of language is the author's attempt to elucidate quantum phenomena by means of heuristic illustrations so outrageously implausible and irrelevant as to be of no instructive value. The book begins with such an example, a fictitious account of a lottery tediously drawn out over ten pages, to give the reader an idea of the Einstein-Podolsky-Rosen paradox, which could have been explained much more succinctly, accurately, and usefully without resort to fairy tales. Further into the narrative, we encounter the author's example of firing chickens through two slits in a brick wall to illustrate the effects of scale on quantum interference. "The scale of the pattern would be incredibly fine," the author assures the reader, "but it would be there." This is total nonsense, a tenacious error arising from the mistaken belief that everything in the universe can be legitimately described by a wave function. This error, together with the misunderstanding of what a wave function is, underlies much of the material in the book.

The very title of the book evokes two of the most egregiously errant misunderstandings of quantum mechanics. The first is the Schroedinger's cat "paradox", whereby the death or survival of a cat, confined to a box with a radioactive source, is linked to the decay or persistence of the unstable nucleus. There is a 50% chance of finding the cat alive and 50% chance of finding the cat dead upon opening the box. From this grisly circumstance a minuscule number of physicists conclude - and all too many science writers repeat - that, prior to an actual observation of the result, the cat is neither alive nor dead but in a linear superposition of both states. There is no sound justification for such an absurd conclusion and consequently no paradox. Cats do not have wave functions; "life" and "death" are not eigenvalues of any quantum mechanical observable; and the entire situation is a far cry from the kinds of systems (superconductors, superfluids, Bose-Einstein condensates) that are capable of manifesting a macroscopic quantum coherence. Technically, the Schroedinger cat nonparadox is an example of an incoherent system characterized by a diagonal density matrix.

The second misunderstanding is to regard each and every potential outcome of observing a quantum system as an actual outcome in a parallel, but disconnected, universe, whereby the total number of such universes compounds continuously and stupendously as there are innumerable quantum choices to be made at every instant. This is the so-called "many-worlds" interpretation of quantum mechanics, which was originally presented as the "relative state" interpretation in the mid 1950s by Hugh Everett III whose purpose was to justify the probabilistic interpretation of the quantum wave function and avoid the issue of wave-function "collapse", i.e. a discontinuous change in the wave function of a system when an observation is made. For the majority of physicists who use quantum mechanics routinely to solve real physical (rather than philosophical) problems, this collapse does not take place in any mechanical sense; rather, it is the well-understood standard procedure by which a state vector (related to, but not identical with, the wave function) is projected onto the eigenstates of an observable (a hermitian operator representing a measurable quantity) to determine the probabilities of the allowable outcomes of an observation. In any event, put Schroedinger's cat together with proliferating universes, and you have Schroedinger's Rabbits, a grotesque Disneyesque caricature of Everett's originally sober, analytical reflections.

Whereas the consistency of Everett's scheme lay in his demonstration that no experiment in any branch of the splitting universe can ever reveal any other branch of the universe, the author of Rabbits claims that experimental evidence in support of the many-worlds interpretation has been obtained from optical experiments with a Mach-Zehnder interferometer. I have investigated quantum phenomena over much of my career by means of quantum interferometry, radiofrequency and microwave spectroscopy, coherent laser spectroscopy, atomic beams, magnetic resonance, and nuclear decay and, for what it is worth, can tell you that no experiment - interferometry or otherwise - has proven or can prove the many-worlds interpretation of quantum physics. Indeed, to the extent that one is dealing with an interpretation of quantum theory, in contrast to an alternative to quantum theory, the mathematical formalism underlying the many-worlds view, if applied correctly and consistently, must be identical to that in any textbook on standard quantum mechanics.

Besides the obfuscation of basic quantum phenomena through inappropriate examples, unclear exposition, and seriously flawed interpretations, Rabbits exudes an unjustified and irritating arrogance by presuming that the reader who fails to appreciate and accept the preposterous views of the author is a kind of anti-scientific troglodyte who should join the Flat Earth Society. "Read this book - or join the Flat Earth Society," proclaims, as well, the editor of The Joseph Henry Press in a foreword to the book, where he tells us condescendingly: "You see, there's this town called Oxford, in a kingdom known as England, where modern magicians with odd-sounding names...are coming up with fantastic notions like entanglement,...multiple universes, and teleportation." One of the listed names is indeed odd, as it is of a physicist from Austria, not Oxford, who, according to the author of the book, repudiates entirely the many-worlds view. Moreover, none of those "fantastic ideas," as far as I am aware, was devised at Oxford. Schroedinger and Einstein first worried about entanglement; the American Everett came up with multiple universes, and IBM scientists first conceived of teleportation (...in order to raise stock prices, some have said). Whether the first experimental achievement of teleportation occurred at Cal Tech or at Innsbrück may be open to some debate; in any case, it did not occur at Oxford.

If the choice is between the philosophy expounded in Rabbits or membership in the Flat-Earth Society, it is worth keeping in mind that Flat-Earthers at least have their feet on the ground; their belief is informed by what they can see. Many-worlders, if indeed there really are any, believe in something intrinsically not observable. The author, however, proposes a test which anyone who is a true-blue many-worlder should be avid to try:

"If you believe in many-worlds, there is an infallible way for you to get very rich. All you need to do is buy a single ticket in a big-money lottery and wire yourself up to a machine that will kill you instantly and painlessly if your ticket does not win....If you believe in many-worlds, then you believe that there is a literally infinite number of versions of yourself in universe-variants that are diverging all the time. After the lottery is run, and the machine has killed you (in an infinite number of worlds)...then all the versions of you still alive will be extremely rich."

Anyone foolish enough to take the many-worlds interpretation of quantum theory seriously should be encouraged to try the experiment and win a posthumous Darwin Award. I highly doubt anyone will. Assuredly, no Flat-Earther is likely to do so.

In the 1995 American film comedy, Billy Madison, starring Adam Sandler as a ne'er-do-well who returns to school so he can inherit his father's business, there is a scene where a frustrated teacher tells Billy:

"What you've just said is one of the most insanely idiotic things I have ever heard. At no point in your rambling, incoherent response were you even close to anything that could be considered a rational thought. Everyone is the room is now dumber for having listened to it. I award you no points, and may God have mercy on your soul."

As a teacher myself, I could never say such a thing to a student, but I believe I would have no difficulty saying that to the author and editor of this book. There are numerous better books for the nonspecialist to read to learn about conceptual and philosophical issues arising from the strange behavior of quantum particles.

### About the author

Mark P. Silverman is Jarvis Professor of Physics at Trinity College. He wrote of his investigations of light, electrons, nuclei, and atoms in his books *Waves and Grains: Reflections on Light and Learning* (Princeton, 1998), *Probing the Atom* (Princeton, 2000), and *A Universe of Atoms, An Atom in the Universe* (Springer, 2002). His latest book *Quantum Superposition* (Springer, 2008) elucidates principles underlying the strange, counterintuitive behaviour of quantum systems.