Uncertain Principles

What did Bohr really do? Indeed. That might be a good lead for a general studies class or a week un-learning common misconceptions about QM based on the language derived from the Bohr model (saying orbits instead of orbitals, or any mention of a quantum jump between energy levels). Unless your chemistry faculty were really careful (having learned something about the Wigner-Eckart theorem in pChem class), your students could come in with as many misconceptions about QM as they might have about motion.

Epistemology:
Bohr came up with a model (one I like to call proto-QM because it is entirely unrelated to actual QM) that got one answer correct and just about every other answer wrong. This can be extremely stimulating to experimental physicists, who get quite bored spending a G$ to measure the width of the Z only to establish that the number of leptons is 3 to three or more sig figs. That model, or more importantly its many flaws, revived spectroscopy ... which continues to this day in what you do.

My main complaint about the article is the statement about "soon superseded". More than a decade of struggle, albeit with a World War in the middle, is not "soon". Just look at all that Bohr and Sommerfeld did to try to make it work. (Relativistic elliptical orbits!) The flash of insight that Heisenberg had could only come when you are so frustrated with the problems that you finally decide that everything you know is wrong.

Bringing Heisenberg to tears was probably the incident where Bohr might have made his greatest contribution. If you have never looked at the Uncertainty (unfocused) Principle paper, dig it up (or look in Cassidy's book) and read the note added in proof. Heisenberg had made a major, elementary physics error in proposing a "microscope" analogy (one that is still made today). Bohr saw it in a preprint and Heisenberg fixed it just before publication. (The referee and/or editor must not have noticed it.) That key idea might have been lost if Bohr had taken a different tack.

That would be a prime example of how his insistence on an "integrity of thought" helped improve the clarity of what QM was all about.

Posted by: CCPhysicist | May 3, 2008 12:05 PM