Happy Birthday, APS!

May 20 was the 125th birthday of the American Physical Society (APS).  Founded in 1899 at Columbia University, and later taking over publication of the Physical Review (founded in 1893 at Cornell University) in 1913, the society has expanded both its core early functions (conferences and journal publications) as well as added many other programs in the last century and a quarter.

I joined the APS around 1997, and its Centennial Meeting in Atlanta (1999) was the first national scientific conference I ever attended, and the first one I ever gave a talk at.  That year, the March and April meetings were combined into a grand extravaganza, with (if I recall right) well over 10,000 attendees.  I remember following (by coincidence) at least one Nobel Laureate down an escalator (J. Friedman) and recognizing others in the hallways or meeting rooms.  I presented again at the 2002 March Meeting in Indianapolis, though my findings were shot down by a very prominent scientist in the audience.  That was the second and final time I presented at an APS conference, though in later years I've attended "for fun" on my own time on several occasions, including last year.  I have also attended a number of APS section meetings, as well as the Division of Fluid Dynamics annual meetings.  I once published in an APS journal (Physical Review E), but that was during the end of my time in graduate school.

Since I have not been a practicing physicist for over two decades, I have not been an active APS member, but I am a Life Member of the parent organization and a number of its individual units.  Indeed, I have been an APS member for just over 20% of APS's own lifetime, and just over 50% of my own lifetime!  Many Happy Returns, APS!

Physics Today and fluid mechanics

Back in December, I discussed a couple recent items in Physics Today of great relevance to fluid mechanics.  I remarked that we don't get to see fluid mechanics on the cover of PT very often.  Well, lo and behold, the last couple months have proven me delightfully wrong!  The cover of the April issue featured "Fluid Dynamics of Dry Salt Lakes", referring to a "quick study" article by Beaume, Goehring, and Lasser.  It discusses a theory of groundwater convection as a possible explanation of polygonal patterns on dry lake beds ("salt polygons").  The very next month, the cover features "A Shocking Start to Stars", referring to a piece by Ceccarelli and Codella, on the role of shock waves in the interstallar medium, especially in star formation, and even in synthesizing certain precursor molecules of life itself.

However, I was personally most enthralled by another piece that also appeared in the May issue by meteorologist Tim Palmer, "The real butterfly effect and maggoty applies".  The title seems to have been taken from two earlier efforts, one coauthored by Palmer in 2019 on the real butterfly effect (published in Nonlinearity), and the other a 2002 PT Reference Frame article by Sir Michael Berry on singular limits.  Both these papers seem to have had a strong influence on this article, which mainly deals with weather predictibility, and more generally the predictability of nonlinear systems, including the limits of artificial intelligence-based prediction.  The article is very good, informative, and very readable.  I'd come across the singular limit concept in discussions of aerodynamic lift, where viscosity is the parameter that when taken to exactly zero (and not just a limit approaching zero) results in the impossibility of lift.  Reading Palmer's piece, and then Berry's, has helped me understand that there are other such examples in physics.