Werner Heisenberg (1901–1976)

> Babelio : https://www.babelio.com/livres/Heisenberg-La-partie-et-le-tout/240288

> L'histoire de la physique atomique nous est contée dans un langage accessible et élégant.
Un livre d'une grande humanité, plus historique que scientifique et c'est justement là tout son intérêt : ce livre fait le lien entre sciences, histoire et philosophie.
Les questions de sens, de conscience, de responsabilité sont posées avec une clarté tout en gardant une grande densité à la réflexion, captivant.
—Danieljean (Babelio)

> LA PARTIE ET LE TOUT, par Werner Heisenberg, trad. Paul Kessler, Albin Michel. Paris, 1972, 333 pp. — AU-DELÀ DE LA SCIENCE ET DES SENS — LA SCIENCE n'a pas cette belle certitude hautaine qu'on lui attribue généralement, et les phrases telles que "la science nous apprend que… ” ne peuvent le plus souvent que recouvrir une somme d'incertitudes et d’approximations, car si, pour le profane, la science équivaut au réel, le savant est, quant à lui, de plus en plus conscient qu'il "fait” le réel.
[…]
LE TÉMOIGNAGE D'UN SAVANT
Avec Werner Heisenberg, nous atteignons au cœur même de ce monde de la physique moderne que nous n'avons abordé jusqu'ici que de façon tangentielle. Heisenberg, on le sait, a été, avec Einstein, Max Planck, Bohr , Dirac et Pauli, l'un des théoriciens les plus audacieux de la physique théorique au cours des cinquante dernières années. On lui doit la formulation de ces fameuses "relations d'incertitudes" auxquelles Einstein, têtu, ne put malgré tout opposer que son célèbre "Dieu ne joue pas aux dés".
Ce qui est intéressant avant tout, dans l'autobiographie de Werner Heisenberg, de 1920 à 1965, ce sont les à-côtés humains de cette grande aventure de la physique moderne, les discussions, les rencontres, les incertitudes. La découverte aussi que ce qui était un jour certitude est le lendemain remis en question, reformulé. Ne prenons ici à témoin que l'exemple de l'atome. Tout le monde « les savants les premiers » pensait avoir bien compris comment était constitué l'atome. On pouvait même en faire un dessin : une forme définie à l'intérieur de laquelle des électrons suivraient des trajectoires comparables à celles du système solaire. Or, cela n'est devenu qu'une pieuse imagerie ne correspondant plus à rien de réel, devant l'incertitude quant à la nature même des électrons, ondes électroniques ou particules ?
"Quand nous descendons au niveau atomique, le monde objectif de l'espace et du temps n'existe plus, et les symboles mathématiques de la physique ne se rapportent qu'à des possibilités, et non à des faits" (Heisenberg).
De même est soulevée, de façon assez spectaculaire, la relativité de l'observation scientifique, par la réflexion suivante d'Einstein à Heisenberg : "Seule la théorie décide de ce que l'on peut observer."
Il faut lire ce livre pour prendre conscience de la constitution de cet univers de la science où le possible et le prévisible jouent un si grand rôle : également, pour y voir comment les savants sont amenés à se poser, en rapport avec leur démarche, des questions touchant les réalités politiques, religieuses, sociales, etc.
Un récit passionnant qui se lit comme un roman et qui nous apprend plus, sans doute, sur la physique moderne que beaucoup de livres scolaires. J'en profite pour souligner l'intérêt tout particulier de cette collection intitulée "Les savants et le monde" d'Albin Michel, dont le livre de Werner Heisenberg est le dernier rejeton. (Jean-Claude DUSSAULT)
—La presse, 25 novembre 1972, D. Arts et lettres, (p. 3)… (lisätietoja)

REVIEW OF THE BOOK AS A WHOLE

Really, the title should have warned me that I was unlikely to get along with this book - but it doesn't actually say, Physics and Metaphysics. I have very little time for metaphysics; it's day is long since past (couple of millenia, at least) and it is really only of historical interest to those concerned with understanding nature. Far too much of the book is spent on either; comparing quantum mechanics (QM) with Western metaphysics or pondering unanswerable conundrums, like, "does anything exist when it isn't being observed?" and "what type of reality is really real?" What science does (with increasing precision over time) is attempt to explain the contents and behaviour of nature, not whether it is "dogmatically objective" or some other type of objective or subjective or, who knows, subjunctive or conjunctive or metastatically cancerous...

This comparison with western metaphysics is as profitless as the later (80s-90s) fad for comparison with "eastern philosophy." Metaphysics, regardless of hemisphere did not lead to nuclear reactors and smart phones, so any apparent correspondences are vague, incomplete and of no practical use.

Heisenberg seems inconsistent at times, which is a bit naff in a book on science or philosophy, let alone both. For instance, he states categorically that no human observer is actually necessary in QM but later seems to tacitly assume the opposite. He's also wrong about a few things, but only in the light of 50 years' worth of further scientific investigations.

I also don't know who the intended audience is; he assumes quite a bit of knowledge of both physics and metaphysics - certainly too much of the former for a non-physicist audience now or then and too much of the latter for present-day non-philosophy students.

Probably the only really valuable insight I got from the book was the point that General Relativity isn't a limiting case or approximation of (or to) any other physical theory: it famously can't be integrated into any current quantum theory but it can't be derived from any other classical theory either, not can any other classical theory be derived from it: It just stands there in majestic aloofness. It has done since it was first published and still does now.

The other segment of interest to me was the final chapter on the influence of science in general and modern physics in particular on contemporary society - here's where I think general philosophical thought might profitably be focused, along with close examination of recent history.

The book also seems badly organised; why does the chapter on alternatives to the Copenhagen Interpretation of QM not follow immediately after the chapter on the Copenhagen Interpretation itself, for instance?

I find it difficult to recommend this book to anybody: if you want to become familiar with the central concepts of QM, The Character of Physical Law by R.P. Feynman is enormously better. Einstein's own book is a much better introduction to Relativity theory (especially if you can remember school algebra). If you are interested in the philosophy of science, this book won't help. It's too out of date to work as an introduction to the state of contemporary fundamental physics. The only bits that seem to remain really relevant are the thoughts about the use of language in science and the thoughts on science's impact on society at large.

Below the line: more or less chapter by chapter thoughts whilst reading.
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Insufficient room in the status update field so I'm gonna have to post my thoughts here as I go along.

Despite the lack of mathematics, I already can't recommend this for non-physicists: I think they'd be terribly confused and horribly lost by the end of Chapter 2. On the other hand, this might be very good for current physics undergrads who've done an atomic physics course already.

Interesting errors and confusions in Chapter 3:Conservation of energy: Heisenberg states that initially this was believed to be true only statistically for quantum systems but in fact turned out to be exactly true always. This is not correct; conservation of energy can only be said to hold to the accuracy given by - fanfare! - The Heisenberg Uncertainty Principle! One of the bizarre consequences of this is the phenomenon of quantum tunneling, which was unknown at the time of publication.

Heisenberg states that quantum mechanical experiments consist of three parts, an initial set up in terms of classical physics, an unobservable part only describable in terms of what we would now call the probability wave-function, and a measurement only describable in terms of classical physics. Only the middle part of this is correct; it is entirely possible to describe an experimental set-up in quantum terms and also the measurement of the result in quantum terms, too. (The middle bit is indeed not describable in any normal sense.) Take the photon double-slit experiment. The emission of the photons can be described quantum mechanically but so can their reception at the detector if you use photo-multiplier detectors, for example.

Ah! I hear you cry, but the real observation is by the human eye, when the flash from the photo-multiplier hits the retina!

Sorry - the optic nerve is a receptor of quanta, too. The whole system is describable quantum mechanically.

Heisenberg then goes on to more or less follow my argument in a vague way. (It's enormously easier to make it precise in the light of half a century's technological advances.)

And here's something really important that we agree on. The human observer is not in any way an essential part of the system. The idea that the entire universe stopped being just a cloud of probabilities the day a sufficiently astute observer appeared is not in any way required by or implicit in the Copenhagen Interpretation.

...and we're only about 1/6th the way through...

Chapter 4: Waffling comparison of ancient Greek philosophy and quantum mechanics. The most important thing here is the bit where he explains the difference i.e. QM is based on experiment where-as ancient Greek philosophy is based on yabbering on without having a clue.

Some interesting points are raised, though; "What's a particle?" is a very hard question to answer in QM. "It's a probability wave packet," isn't a very good answer; it's a form of energy is better (except, what's energy?). Today you might get, "it's a resonance in a field." Leading straight on to, "What's field?" Well, it's something emitted by particles that controls how they interact with each other... This is just wave-particle duality all over again, with waves disguised as fields.

He also expresses the views that the ultimate quantum theory would take the form of a single equation that would yield solutions representing the fundamental particles and the forces between them and that in fact there will turn out to only be one kind of particle that is truly fundamental. The former is the approach taken by current Guess the Lagrangian approaches to the problem and the latter is adopted in string theories (all 10^500 of them...).

Chapter 5: Physics vs. Metaphysics: Physics wins! Or summat.
Is there such a thing as objective reality? Yes! OK - I can agree with that. But I don't really understand when he starts trying to distinguish between types of objective reality. I mean, in science you get successive different theories of the behaviour of objective reality but that doesn't seem to be what is being discussed. It doesn't seem to be the old causality vs. indeterminacy chestnut, either. Colour me baffled - and not caring much, either.

Chapter 6: Relation of QM to other sciences.
Here Heisenberg seems to be groping after a coherent general philosophy of Emergent Behaviour without quite getting there; seems more in the Emergent camp than the Reductionist camp, anyway. One interesting comment is that biology requires physics/chemistry plus "history." The history allows for evolutionary theory by way of genetics. But one could view "history" as actually being emergent from physics by way of the 2nd Law of Thermodynamics, a connection he does not make.

He also discusses the main theories of physics in relation to each other: Newtonian mechanics is an approximation to Special Relativity which assumes an infinite speed of light. It is also an approximation to QM assuming an infinitely small Planck's Constant. Thermodynamics can be understood as a statistical theory of particles and can be derived from either QM or Newton's Laws. But General Relativity sits there looking lonely and mean, yet beautiful, and defying all attempts to integrate it into any other aspect of physics as any kind of limiting case or emergent theory.

The error regarding the description of QM experiments in terms of classical physics is repeated.

Chapter 7: Relativity.
Einstein's book will give you a clearer understanding of Special Relativity and the Principle of Equivalence but you will need to know some (school) algebra. On the other hand, that is a whole book about the same length as this one, not one lecture/chapter. A point re-iterated through out the chapters so far is the use by physicists of ordinary language in specialised ways. This is essential as it turns out that "ordinary" concepts like space and time, on closer examination turn out to be much more subtle and complex phenomena than is readily appreciated in daily life. I think one of the later chapters goes into this in depth.

Heisenberg emphasises that General Relativity is not on a strong experimental footing; it wasn't then but it is now. Some of the cosmological questions raised have been answered, others haven't and recently new and even more freaky ones have been found.

Chapter 8 seems (as far as I can tell) to come down to, "Does the particle exist when you're not looking?" Well, that question isn't any more answerable than the question in classical physics, "Does that brick exist when you're not looking?"
"Looking" here means doing anything in order to verify the existence of the particle/brick. Assuming something doesn't exist when you're not "looking" is essentially Solipsistic/Cartesian and denied by the persistence of macroscopic objects.

The Everett Many Worlds Interpretation hadn't been thought up yet, so isn't discussed. The main focus is on "hidden variables" notions.

I'm getting impatient for this to be over...

The remainder:
A chapter surveying the contemporary state of sub-atomic physics. Of course, it's out of date. Most interesting now for it's speculation that the number of types of truly elementary particles will drop, possibly to one. What happened between then and now is that the number went up for some time, then dropped again as quark-theory was verified and recently went up by one again with the discovery of a "Higgs-like boson." Given the current experimental evidence/hypotheses/theories in cosmology, one would think the number will more likely go up rather than down in the immediate future.
Chapter on language in science and physics in particular in relation to "every-day" language. Perhaps the most obvious pervasive theme of the book.
Final chapter on the effects of modern physics and nuclear physics in particular on society at large and it's mode of thought. More interesting than almost the entirety of the rest of the book.… (lisätietoja)