on 30 June 2007
Quantum systems behave in strange ways: If a water tap was a quantum system, the water might have only two possible temperatures, hot and cold, and nothing in between. Adding up water from a hot and a cold tap wouldn't end up with lukewarm water, but with water in a superposition: As soon as you put your finger in it, the water instantly becomes either hot, or cold, but nothing in between. Opening one tap further would not influence the resulting temperatur, but the chances of the water being hot or cold when you measure it.
Sounds confusing? It certainly is. Quantum theory is a very precise, widely-applicated theory that is in extremly good agreement with experiments. But some central concepts of this theory, which forms the heart of modern physics, are yet strangely vague. We do not yet know what exactly constitutes a measurement. We do not exactly understand what a "superposition of states" actually means, especially since it cannot be directly observed almost by defintion: With every observation, the system jumps into one state, randomly, as it appears.
While the mathematics underlying quantum physics are not that difficult to grasp once you've had your first year calculus and linear algebra classes, the world it describes is completely different from the one we seem to experience every day. We, therefore, cannot "understand" quantum physics by finding every day analogies. We need new concepts - and most textbooks on quatum physics downplay just how strange and problematic these concepts are.
Jim Baggott's book first gives a concise introduction to quantum physics that fills about half the book. It is scientifically sound, keeps the maths to a minimum and is therefore quite accessible to laypeople and undergraduate students of physics alike. It does not, however, spare a future physicist from working through a textbook like J. J. Sakurai's "Modern Quantum Mechanics" (which I recommend wholeheartedly).
The second part of the book discusses the interpretation of quantum theory - the meaning of its central concepts, if it describes reality or is "only a theory", if the is true chance (and the world "indetermined"), if there is instant causation, or even a cause following its results (possible billions of years later). These questions once have been thought as being purely philosophical (in the 1920s, e. g. inspiring the discussion of the Einstein-Podolsky-Rosen paradox); but different answers have been shown to have different observable results (Bell's theorem); and crucial experiments have been performed by Aspect and others, which shed light upon possible interpretations. By now, technical applications such as quantum cryptography are being developed.
You won't find much on the recent developements in this book, since it was written in the early 90s (Bouwmeeste's, Ekert's, and Zeilinger's "Physics of Quantum Information" or Bertlmann's and Zeilinger's "Quantum (Un)Speakables" would be my recommendations, or even Baggotts more recent books on the subject). But to get a basic oversight over the questions discussed, to get a basic understanding of quantum theory concepts and ideas, Baggott's book is still one of the best on the market.
I would recommend it not only to students of physics or chemistry, but also to students of philosophy, and to anyone truly interested in one of the most central and strange fields of modern science. It is not the most up-to-date book on the subject, but by far one of the most concise, reliable and accessible.