Sunday, December 18, 2011

Advent calendar #18: Heisenberg and the microscope

Werner Heisenberg is well known for his analysis of the inevitable uncertainty in observations with a microscope that eventually lead him to formulate the uncertainty principle. Less known is the origin of his obsession with microscopes. In 1923, Heisenberg was heading towards the final oral examination for his doctorate. He passed mathematics, theoretical physics and astronomy just fine, but he run into troubles with experimental physics where he was to be examined by Wilhelm Wien.

Wien had required that Heisenberg did a "Praktikum" (basically a practice in physics experiments), but there was some equipment lacking and Heisenberg wasn't interested enough to find out where to get it. He thus turned towards other things without looking much into the experiments he was supposed to do, for example measuring the splitting of spectral lines by help of an interferometer. Then came the day of the oral exam:
"Wien was annoyed when he learned in the examination that Heisenberg had done so little in the experimental exercise given to him. He than began to ask him questions to gauge his familiarity with the experimental setup; for instance, he wanted to know what the resolving power of the Fabry-Perot interferometer was... Wien had expained all this in one of his lectures on optics; besides, Heisenberg was supposed to study it anyway... But he had not done so and now tried to figure it out unsuccessfully in the short time available during the examination. Wien... asked about the resolving power of a microscope; Heisenberg did not know that either. Wien questioned him about the resolving power of telecopes, which [Heisenberg] also did not know."

(From Jagdish Mehra, Helmut Rechenberg: "The Historical Development of Quantum Theory Vol. 2 - The Discovery of Quantum Mechanics 1925" p. 67)

Wien wanted to fail Heisenberg, but Sommerfeld, in whose exam on theoretical physics Heisenberg had excelled, put in a strong word for Heisenberg. Heisenberg passed the doctoral examination with the lowest possible grade. Many years later Heisenberg would recall
"So one might even assume, that in the work on the gamma-ray microscope and the uncertainty relation I used the knowledge which I had acquired by this poor examination."


  1. Hi Bee & Stefan,

    I guess this only goes to show that each person has their own strengths and weaknesses. One could also say that despite Heisenberg’s poor showing in respect to his experimental competence Sommerfeld helped Wien to look past his own uncertainty.

    “I think that modern physics has definitely decided in favor of Plato. In fact the smallest units of matter are not physical objects in the ordinary sense; they are forms, ideas which can be expressed unambiguously only in mathematical language.”

    - Werner Heisenberg



  2. So one can see, how far someone can reach, even without experimenters knowledge.

    Best Kay

  3. Hi Bee & Stefan,

    Your advent calendar is so precious! thanks. This anecdote is also alluded to in the great book "Einstein Defiant", by E. B. Bolles (

    Would you know of any good resource of online seminars and talks on the history of science? Neither google video nor pirsa give good results.

    I have found some sparse resources like for instance but I am wondering whether you've heard of something more specialized.

    looking forward to tomorrow's anecdote..

  4. NEVER allow a competent theorist into an experimental laboratory. If you do, you will rediscover the Pauli Effect. The University of Göttingen got off easy. Pauli was at Princeton in 1950 when their cyclotron blew.

  5. Although Aristotle in general had a more empirical and experimental attitude than Plato, modern science did not come into its own until Plato's Pythagorean confidence in the mathematical nature of the world returned with Kepler, Galileo, and Newton. For instance, Aristotle, relying on a theory of opposites that is now only of historical interest, rejected Plato's attempt to match the Platonic Solids with the elements -- while Plato's expectations are realized in mineralogy and crystallography, where the Platonic Solids occur naturally.Plato and Aristotle, Up and Down-Kelley L. Ross, Ph.D.

    So, some people do see how self evident flirtations can cognitively exist. This is an inductive/deductive position making itself known. That is the beginning and it really nothing? The synapse of the wondering mind?

    Who makes the rules as to what is observable in the realm of the mind? So logically one asks, how is it possible with all the knowledge available "that nothing exists?"

    If theoretically something is postulated, how much credence does this give to the world in experimental verification? Powers of ten?

    You see, even mathematically our reality may have people who see even further then the microscopes?

    That is just the way it is?:)



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