Which way do carousels move?
As I walked towards UNESCO for the second day of the opening event of IYL2015, I discovered two carousels on different sides of the Seine, moving in opposite directions – counter-clockwise on the right bank and clockwise on the left bank, just northwest of the Eiffel tower.
It reminded me of spectacular quantum physics experiment where a beryllium ion was prepared in a superposition state with itself, with “50 percent probability of being in a “spin-up” state in its initial position and an equal probability of being in a “spin-down” state in a position as much as 80 nanometers away, a vast distance indeed for the atomic realm. In effect, the atom was in two different places, as well as two different spin states, at the same time” (Scientific American, 1996). This beryllium ion is such a spooky illustration of the quantum world, “an atomic analog of a cat both living and dead”, i.e. “Schrödinger’s cat”, and was part of the motivation for the Nobel prize in physics 2012, shared by Dave Wineland and Serge Haroche.
This association to Schrödinger’s cat fitted very well into the morning session, with a number of the quantum magicians on stage. First Bill Phillips took the stage, entertaining the audience with ever-popular liquid nitrogen experiment, as an introduction to the extremely low temperature achieved by the atomic cooling and trapping community, and the spectacular precision experiments made possible.
Serge Haroche talked about decoherence – which explains why real cats can not behave like the mythical Schrödinger’s cat. He also demonstrated how an atom could be trapped in light, enabling him to count photons 4, 3, 2, 1, 0.
The thread of entanglement carried into the afternoon, when Alain Aspect talked about how he now does with atoms what he did with light in the milestone experimental tests of Bell’s inequalities, published in 1982. Aspect presented his work at the ICAP in Göteborg the same year. During the APS reception after the IYL2015 opening event, a told me how the 1982 ICAP talk had been one of the high-points of his career (a second was to present the work at CalTech, with Richard Feynman in the audience, who had approved).
He also told me how Norman Ramsey, as chairman, had supported him when he was nervous before his ICAP presentation. We talked a bit about Norman as a physics hero to both of us. I remember how Norman supported me, when I was nervous for my first session chairing (1986), with him as a speaker. I also remember the ICAP in Florence 2000, where I met him taking a cold drink when he had abandoned his attempt to see all posters, after three hot afternoon hours!
The IYL2015 is about much more than spectacular atomic physics, and I will come back to other topics in later posts. (See also reports e.g. from SPIE, APS, as well as a report from UNESCO executive council the following day.) The Swedish IYL2015 site is found at ljus2105.se
Which way do carousels move?
The question of carousel “spins” has been with me for a number of years, following a question in Jan 2008 in the Exploratorium Teacher Institute mailing list.
In the first chapter of my trigonometry book, there is a question “Which way do merry-go-rounds turn, clockwise or counterclockwise?”. The answer, without any explanation, is “counterclockwise”. Is this true? and if so, why? (my favorite answer so far is “because that’s the way the horses face”). This sparked no end of debate in class. One girl said she spent her summer at the Santa Cruz Boardwalk and swears that theirs goes clockwise. Any theories out there?
Kim Greco, El Molino High School, Forestville
After looking at carousel photos, finding only counter-clockwise moving carousels in my first attempt, I approached roller-coaster designer Werner Stengel. This is part of his reply:
Soll ein Karussell im oder gegen den Uhrzeigersinn drehen? Diese Frage hat Anton Schwarzkopf schon vor über 40 Jahren an mich gerichtet. Damals war meine Antwort: Herr Schwarzkopf lassen sie die Bayernkurve gegen den Uhrzeigersinn drehen, weil alle mir bekannten Karusselle so drehen und damit das Publikum beim Ein- und Aussteigen es so gewohnt ist. Bis heute kenne ich nur Karusselle, die gegen den Uhrzeigersinn drehen, abgesehen von den auch manchmal außerplanmäßig rückwärts fahrenden Karussellen Musikexpress und Enterprise.
I looked into early patent drawings, finding a reasonably equal mixture of carousel CW and CCW rotaion – and also learned that most British carousels move clockwise. I continue to look for the “spins” of carousels I encounter, and was trilled to find both types so close to each other that morning in Paris.
(I was less thrilled to find my camera battery low after taking too many photos on the first day! Thus, the carousel photos on the page are not from Paris, but from Tusenfryd, Oslo, one reversed)