La vache du voisin est malade...

C'est pas grand chose mais ça fait toujours plaisir.
(Sagesse populaire)

Bohmian mechanics and the organized skepticism

A few days ago, I read the paper about Bohmian mechanics on the website of the Stanford Encyclopaedia of Philosophy (SEP) [1]. The last time I came across the name of David Bohm [2] was during my stay in Princeton in 2005. I was subletting a house of Princeton University and people in the neighborhood had the habit of leaving on a shelf at the laundry any book they didn’t want to carry along when they were moving out. In one of these, there was a chapter about scientists in Princeton who had been the victims of McCarthy. David Bohm was one of them.

David Bohm had worked on the Manhattan project, he was assistant professor at Princeton University in 1949. After being suspected of being a communist, he was fired from Princeton and he could not find any position in any other American university. He worked in several countries -notably in Brazil- and he eventually settled in London, where he died in 1992.

The exile of David Bohm was actually twofold: not only was he persona non grata in his own country, he was also left out of the international clique of physicists who mattered. Not surprisingly is Bohmian mechanics unorthodox; it is the work of an outcast.

What I realized with the SEP article is that the Copenhagen interpretation of quantum mechanics (QM) is not all there is about QM. David Bohm proposed a causal (deterministic) interpretation of quantum mechanics, the predictions of which are identical with the orthodox QM [3]. Philosophically, however, the two theories are at odds. In Bohmian mechanics the particles have a well defined position and momentum, and the wave function acts as a potential (a so-called pilot wave) that guides the particles. Such an approach was claimed to be impossible, and proved to be so by a famous theorem due to John Steward Bell [4]. Interestingly enough, here is what Bell himself wrote in 1987 about Bohmian mechanics [1]:

But why then had Born not told me of this ‘pilot wave’? If only to point out what was wrong with it? Why did von Neumann not consider it? More extraordinarily, why did people go on producing ‘‘impossibility’’ proofs, after 1952, and as recently as 1978? ... Why is the pilot wave picture ignored in text books? Should it not be taught, not as the only way, but as an antidote to the prevailing complacency? To show us that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice?

This is the story of David Bohm and of his unorthodox theory. Yet another sad example of organized skepticism turned de facto into dogmatic denial.

[1] http://www.science.uva.nl/~seop/entries/qm-bohm/
[2] http://en.wikipedia.org/wiki/David_Bohm
[3] D. Bohm, Phys. Rev. 85 (1952) 166-180.
[4] http://en.wikipedia.org/wiki/Bell%27s_Theorem

Triletters

A few days ago was HMB's birthday. Happy birthday, H!

Nicolas Caritat, ci-devant marquis de Condorcet

Il y a une statue de Condorcet sur le quai Conti à Paris, à coté de l'hôtel des monnaies, dont il a été contrôleur général. Je connaissais un peu Condorcet pour avoir lu sa biographie écrite par les Badinter. J'ai lu, il n'y a pas très longtemps sa "Lettre d'un père proscrit à sa fille" (lien ci-dessous).

Mon sentiment après l'avoir lue a été: "Merde alors, le pauvre vieux!" Ce n'est pas que je plaignais particulièrement sa situation quand il a écrit cette lettre, toute précaire qu'elle eut été (il se terrait dans un grenier, d’où il n’est sorti que pour mourir emprisonné quelques jours plus tard). C'est plutôt ce que cette lettre laisse transparaître de la succession de souffrances intimes qu'a été sa vie.

A mes yeux, cette lettre est une énumération en 10 pages de toutes les recettes qu'une personne hypersensible a mises au point tout au long de sa vie pour ne pas souffrir, notamment de ses rapports avec les autres. Et il transmet ces recettes à sa fille comme un savoir très précieux.

En vrac. A propos du travail: "Rien n'est donc plus nécessaire a ton bonheur que de t'assurer des moyens dependans de toi seule pour remplir le vide du tems, écarter l'ennui, calmer les inquiétudes, te distraire d'un sentiment pénible". Ou encore: "On peut n'être pas maître de ne pas écouter son coeur, mais on l'est toujours de ne pas l'exciter; et c'est le seul conseil que la raison puisse donner à la sensibilité" Un autre: "N'attends, n'exige des autres, qu'un peu au-dessous de ce que tu ferais pour eux". Etc., etc., etc.

(http://books.google.com/books?id=cis0AAAAMAAJ&pg=PA603&dq=Avis+d%27un+proscrit+%C3%A0+sa+fille).

Another one about perspective

There is something odd in what I see from my flat. Until this morning, I thought you could get on the roof through that door...

Perspective

Reminder: these rays are physically all parallel.