I found this little book by chance in a local second-hand bookshop. I feel bad for the person that sold (or had to sell) this little treasure. Anyway, reading this booklet is like being driven around in a fancy and fast car by an expert driver. Smoothly cruising over nice roads surrounded by gorgeous landscapes, only interrupted by short spurts of high speed driving, executed just as professionally… This is a physics book for the non-physicist about a wide variety of subjects. With a little effort you will be richly rewarded with new insights about thermodynamics, randomness, determinism, black holes, irreversibility, the relationship between mathematics and physics and lots more. David Ruelle, a physicist, writes concisely and vividly about all these subjects. This is not a recent book, there are no URL’s in the notes! But what David Ruelle wrote in 1990 is still very relevant today.
I will elaborate on some stuff I liked but let me mention my surprise that Ruelle still seemed in awe about the work of Freud. Maybe that was understandable, in France, and 15 years ago. Today all this sounds rather dated, but I liked the two last sentences of the notes and therefore put them among the quotes you can read in the sidebar of my blog.
David Ruelle’s description of the interplay between mathematics and science: “If you study physics you soon must face the apparent paradox: your control over a physical object that you can hold in your hand is less than your control over a mathematical object without material existence.” (Digressing a bit, this also explains why I liked doing science on a computer). He then strongly advises to know and explain the operational issues involved before extrapolating form any experiment to a general statement about the probabilistic or deterministic nature of physics (or nature, in general). The discussion about the relationship between determinism and free will is just as interesting: do the ideas of Laplace put a limit on free will (only our own free will, not that of others, as noted by SchrÃ¶dinger). Ruelle typically manages to summarize, I quote: “What allows our free will to be meaningful notion is the complexity of the universe or, more precisely our own complexity. ”
The author discusses the origin and development of “chaos theory” where he points to a number of French scientists deserving more widespread recognition such as Hadamard, Duhem and PoincarÃ©. He also describes his own contributions with a lot of candor, kudos! In addition he gives a sobering account about how chaos theory, renamed non-linear science, became a fad and on how this, undeservedly, made the whole field disreputable in the eye of many scientists outside the field.
Ruelle likes thermodynamics, who doesnâ€™t 😉 and I particularly liked his account on irreversibility. The mainstream opinion among physicists is a probabilistic one, in other words, there is nothing special about the ‘arrow of time’: the actual path particles follow forward is just overwhelmingly more likely than the backward direction. This conflicts with the opinion of I. Prigogine, where the direction of the arrow of time does matter, a position which I favour. Time reversibility, simply changing particles velocities from positive to negative, can easy be done in a thought experiment, but I am not convinced there is a simple equivalent in the physical world. Should we not know the exact velocity before we can reverse the sign? But David Ruelle, although disagreeing with Prigogine, attributes these differences to philosophical prejudice and not to physical evidence. I can live with that. Again, I like this kind of candor as so many other texts simply ignore this problem or I. Prigogine’s ideas. Davdid Ruelle concludes: “But in due time things have to be settled by careful comparison of mathematical theories and physical experiments.” I can live with that too!
Anyway I plan to read/reread more on this subject, suggestions are welcome.