Pierre Duhem, Popper’s predecessor

Karl Popper

In a previous post in this blog, I mentioned how Karl Popper defines what is, and what is not, a scientific theory:

A theory is scientific if and only if it is possible to design an experiment that demonstrates that this theory is false.

I also said there that, according to Popper, a scientific theory can never be considered completely confirmed. In other words, we can never be absolutely sure that it is true.

After writing that post, which I published almost one year ago, I have discovered that these two Popper’s fundamental ideas had been anticipated by Pierre Duhem, to whom I dedicated the previous post in this blog.

Popper detailed both these ideas in his book The Logic of Scientific Research, published in German in 1934 and in English in 1959, both versions written by himself. Duhem, however, had anticipated them in 1913, in a letter addressed to Réginald Garrigou-Lagrange, which the latter published in his book Dieu. Son existence et sa nature (1914). By then, Popper was about 12 years old. Did Popper read Duhem? Perhaps not this letter, although other works certainly, since in The Logic of Scientific Research he quotes Duhem five times, usually to show his discrepancy. The problem is that misunderstanding Duhem is quite easy. To avoid it, one should probably read his whole work, which not everybody can do.

Pierre Duhem: Realist or anti-realist?

Pierre Duhem

Pierre Duhem (1861-1916) can be considered one of the last nineteenth-century physicists. Specialist in Thermodynamics, the branch of physics that dominated the second half of the nineteenth century, introduced the idea of the ​​chemical potential at the same time as William Gibbs, expressed in the Gibbs-Duhem equation, which connects the chemical potential with magnitudes such as the volume, pressure, entropy and temperature of a chemical mixture. He is considered one of the creators of physical chemistry and was nominated twice for the Nobel Prize in Physics.

In his scientific work, Duhem confronted Marcellin Berthelot, whose principle of maximum work he opposed. This led to his doctoral thesis being rejected, and he was denied a teaching position at the University of Paris. Duhem was finally shown to be right, as Berthelot’s principle is not generally applicable, for it has many exceptions.

The eye as an argument about evolution

Schematic diagram of the human eye

The vertebrate eye consists of five parts: cornea (a transparent insulating layer); aqueous humor; crystalline lens (a lens surrounded by muscles that make it possible to achieve a variable focal length); vitreous humor; and retina. The light passes through the cornea and the aqueous humor, is focused by the lens, goes through the vitreous humor and impacts on the nerve cells of the retina, which generate electric signals that the optic nerve transmits to the brain, which forms from them an image of the external world, where the light rays came from. The brain even turns the image around, as it is inverted when projected on the retina.

The complex structure of the eye has always been a problem for evolutionists, and an argument for those opposed to the theory of evolution. Darwin, in Chapter 6 of The Origin of Species, whose title is significant (Difficulties of the theory) dealt with the problem of the evolution of the eye in the following words: