Max-Born-Institut Berlin (MBI)

interpretation
the Ψ function
On 24 November 1954, Albert Einstein wrote to his friend Max Born: “I was very pleased to
hear that you have been awarded the Nobel Prize – even though somewhat belatedly – for
your contributions to the present quantum theory. After all, it was particularly your rigorous
statistical interpretation of the description that decisively clarified our thinking. This seems to
me to be quite clearly the case in spite of our inconclusive correspondence on this subject.”
Born and Einstein had been close friends since 1913, that is to say roughly since Born’s time
in Berlin, but – as indicated by Einstein’s allusion in this letter – they had never been able to
agree upon a joint interpretation of quantum theory.
Born describes the origin of his idea of a statistical significance of the wave function, for which
he was awarded the Nobel Prize, in his speech of acceptance and in his autobiography. I quote
from the latter: “I was guided here by a remark of Einstein’s about the significance of the
intensity of light (i. e. of an electromagnetic wave) from the aspect of the photon. This intensity
must represent the number of photons, but the latter was, of course, to be regarded statistically
as the mean of a certain photon distribution. Einstein had made some profound considerations
of the statistical nature of this distribution ... I was very familiar with these considerations
and they led me directly to the conjecture that the intensity of the de Broglie wave,
i.e. the square of Schrödinger’s wave equation, had to be regarded as the probability density,
as the probability of a particle being present in a volume unit”.
This is still the approach that we take in physics today. Born’s statistical interpretation was also
the starting point for the Copenhagen interpretation of quantum mechanics, which has survived
up to the present day in a variety of forms. Nevertheless, the interpretation of the wave
function even today remains an unsolved physical and above all epistemological problem which
we have carried over in our baggage from the physics of the twentieth century into our work
in the twenty – first century. The collapse and Everitt interpretations are current versions of
these attempts to synchronize our powers of imagination oriented to classical physics with the
concepts of quantum theory.
Einstein was surprised that Born received the Nobel Prize so late. In his memoirs, Born himself
wrote on the subject: “My statistical interpretation of the Ψ function was merely the first step
in our understanding of the relation between particles and waves in atomic physics. Even if the
vast majority of physicists accepted this interpretation, there were always those for whom this
was not the case including ... Planck, Einstein, de Broglie and Schrödinger, .... This may well
be the explanation of why I only received the Nobel Prize for my work 28 years later”.
Max Born • Paul Corkum 49