It was in 1947 or 1948 that Schrödinger let me know that he was coming to London, and I met him in the mews house of one of his friends. From then on we were in fairly regular contact by way of letters, and by personal meetings in London, and later in Dublin, in Alpbach, Tyrol, and in Vienna.
In 1960 I was in hospital in Vienna, and as he was too ill to come to the hospital, his wife, Annemarie Schrödinger, came to see me every day. Before I returned to England I visited them in their apartment in the Pasteurgasse. It was the last time I saw him.
Our relations had been somewhat stormy. Nobody who knew him will be surprised at this. We disagreed violently on many things. Originally I had taken it almost for granted that he, with his admiration for Boltzmann, would not hold a positivist epistemology, but our most violent clash was sparked off when I criticized one day (in 1954 or 1955 approximately) the Machian view now usually called “neutral monism”—even though we both agreed that, contrary to Mach’s intentions, this doctrine was a form of idealism.212
Schrödinger had absorbed his idealism from Schopenhauer. But I had expected him to see the weakness of this philosophy, a philosophy about which Boltzmann had said harsh things, and against which for example Churchill, who never claimed to be a philosopher, had produced excellent arguments.213 I was even more surprised when Schrödinger expressed such sensualist and positivist opinions as that “all our knowledge… rests entirely on immediate sense perception”.214
We had another violent clash over my paper “The Arrow of Time”,215 in which I asserted the existence of physical processes which are irreversible whether or not any entropy increase may be connected with them. The typical case is an expanding spherical light wave, or a process (like an explosion) that sends particles to infinity (of Newtonian space). The opposite—a coherent spherical wave contracting from infinity (or an implosion from infinity) cannot occur—not because such a thing is ruled out by the universal laws of light propagation or of motion, but because it would be physically impossible to realize the initial conditions.216
Schrödinger had written some interesting papers trying to rescue Boltzmann’s theory, according to which the direction of entropy increase fully determined the direction of time (or “defined” this direction—but let us forget about this). He had insisted that this theory would collapse if there were a method, such as the one I had suggested, by which we could decide the arrow of time independently of entropy increase.217
So far we agreed. But when I asked him to tell me where I was wrong, Schrödinger accused me of unfeelingly destroying the most beautiful theory in physics—a theory with deep philosophical content; a theory which no physicist would dare to harm. For a nonphysicist to attack such a theory was, he felt, presumptuous if not sacrilegious. He followed this up by inserting (in parentheses) a new passage into Mind and Matter: “This has a momentous consequence for the methodology of the physicist. He must never introduce anything that decides independently upon the arrow of time, else Boltzmann’s beautiful building collapses.”218 I still feel that Schrödinger was carried away by enthusiasm: if the physicist or anybody else can independently decide upon the arrow of time, and if this has the consequence which Schrödinger (I think correctly) attributes to it, then, like it or not, he must accept the collapse of the Boltzmann-Schrödinger theory, and the argument for idealism based on it. Schrödinger’s refusal to do so was wrong—unless he could find another way out. But he believed that no other way existed.
Another clash was over a thesis of his—an unimportant one I think, but he thought it very important—in his beautiful book What is Life?. This is a work of genius, especially the short section entitled “The Hereditary Code-Script”, which in its very title contains one of the most important of biological theories. Indeed, the book is a marvel: written for the educated nonscientist it contains new and pioneering scientific ideas.
Yet it also contains, in response to its main question “What is Life?”, a suggestion which seems to me quite obviously mistaken. In Chapter 6 there is a section which begins with the words “What is the characteristic feature of life? When is a piece of matter said to be alive?”. To this question Schrödinger gives a reply in the title of the next section: “It Feeds on ‘Negative Entropy’”.219 The first sentence of this section reads, “It is by avoiding the rapid decay into the inert state of ‘equilibrium’ that an organism appears so enigmatic…”. After briefly discussing the statistical theory of entropy, Schrödinger asks: “How would we express in terms of the statistical theory the marvellous faculty of a living organism, by which it delays the decay into thermodynamical equilibrium (death)? We said before: ‘It feeds upon negative entropy’, attracting, as it were, a stream of negative entropy upon itself.…”220 And he adds: “Thus the device by which an organism maintains itself stationary at a fairly high level of orderliness (=fairly low level of entropy) really consists in continually sucking orderliness from its environment.”221
Now admittedly organisms do all this. But I denied, and I still deny,222 Schrödinger’s thesis that it is this which is characteristic of life, or of organisms; for it holds for every steam engine. In fact every oil-fired boiler and every self-winding watch may be said to be “continually sucking orderliness from its environment”. Thus Schrödinger’s answer to his question cannot be right: feeding on negative entropy is not “the characteristic feature of life”.
I have written here about some of my disagreements with Schrödinger, but I owe him an immense personal debt: in spite of all our quarrels, which more than once looked like a final parting of our ways, he always came back to renew our discussions—discussions which were more interesting, and certainly more exciting, than any I had with any other physicist. The topics we discussed were topics on which I tried to do some work. And the very fact that he raised the question What is Life? in that marvellous book of his gave me courage to raise it again for myself (although I tried to avoid the what-is? form of the question).
In the remainder of this Autobiography I intend to report on ideas rather than on events, though I may make historical remarks where it seems relevant. What I am aiming at is a survey of the various ideas and problems on which I have worked during my later years, and on which I am still working. Some of them will be seen to be connected with the problems I had the great good fortune to discuss with Schrödinger.