(Alternate titles considered for this post: Ducktoral degree, Send in the ducks, Proof by in-duck-tion, Duck Tales, Duck-ing the issue.)
One of my specializations in optics is the theory of optical coherence, which is the theory that characterizes the random fluctuations of light, and the consequences of said fluctuations. It is typically one of the most difficult optics topics to teach beginning optics students, probably because it combines two challenging bodies of mathematics: wave theory and probability theory. Any teaching tool that can be used to help students visualize and understand the basics is welcome, though such tools are few and far between in coherence.
Enter the ducks! Early this year, some colleagues of mine published a short note pointing out that one can visualize a fundamental result from optical coherence theory, the van Cittert-Zernike theorem, by watching the waves a group of ducks generate when they splash into a pond!
The letter is by W.H. Knox, M. Alonso and E. Wolf, “Spatial coherence from ducks,” Physics Today, March 2010, p. 11; it can be freely read here. Though the letter describes the connection between coherence and ducks, it doesn’t explain what the van Cittert-Zernike theorem is, so I thought I’d fill in a bit of detail with this post!
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