Advent Calendar of Science Stories 11: Feynman's Plate

I've been trying to keep to a roughly chronological ordering of these stories, but this slow-motion snow storm that was waiting to greet us on our return from Florida made the schools open on a two-hour delay today, which eats the time I usually use for blogging and books stuff. So I'm going to jump forward three hundred years, to a story that I can outsource.

To set the stage, in the aftermath of WWII, Richard Feynman took up a faculty job at Cornell, but between working on the Manhattan Project and the death of his beloved wife, he found that he was completely burned out, and not able to do much useful work. Then, as he relates in his autobiography:

So I got this new attitude. Now that I am burned out and I'll
never accomplish anything, I've got this nice position at the university
teaching classes which I rather enjoy, and just like I read the
Arabian Nights for pleasure, I'm going to play
with physics, whenever I want to, without worrying about any importance

Within a week I was in the cafeteria and some guy, fooling around,
throws a plate in the air. As the plate went up in the air I saw it
wobble, and I noticed the red medallion of Cornell on the plate going
around. It was pretty obvious to me that the medallion went around
faster than the wobbling.

I had nothing to do, so I start to figure out the motion of the rotating
plate. I discover that when the angle is very slight, the medallion
rotates twice as fast as the wobble rate - two to one [Note: Feynman mis-remembers here---the factor of 2 is the other way]. It came out of a
complicated equation! Then I thought, ``Is there some way I can see in a
more fundamental way, by looking at the forces or the dynamics, why it's
two to one?''

I don't remember how I did it, but I ultimately worked out what the motion
of the mass particles is, and how all the accelerations balance to make it
come out two to one.

I still remember going to Hans Bethe and saying, ``Hey, Hans! I noticed
something interesting. Here the plate goes around so, and the reason it's
two to one is ...'' and I showed him the accelerations.

He says, ``Feynman, that's pretty interesting, but what's the importance of
it? Why are you doing it?''

``Hah!'' I say. ``There's no importance whatsoever. I'm just doing it for
the fun of it.'' His reaction didn't discourage me; I had made up my mind
I was going to enjoy physics and do whatever I liked.

I went on to work out equations of wobbles. Then I thought about how
electron orbits start to move in relativity. Then there's the Dirac
Equation in electrodynamics. And then quantum electrodynamics. And before
I knew it (it was a very short time) I was ``playing'' - working, really -
with the same old problem that I loved so much, that I had stopped working
on when I went to Los Alamos: my thesis-type problems; all those
old-fashioned, wonderful things.

It was effortless. It was easy to play with these things. It was like
uncorking a bottle: Everything flowed out effortlessly. I almost tried to
resist it! There was no importance to what I was doing, but ultimately
there was. The diagrams and the whole business that I got the Nobel Prize
for came from that piddling around with the wobbling plate.

I thought of this for today because it came up yesterday on the radio. One of the callers asked a really good question, namely "How do you maintain an interest in science over the course of a long career studying difficult problems?" And, happily for me, I thought of this Feynman story, because one good way to keep going is to just keep playing with stuff.

You don't always have to be beating your head against the biggest, most difficult questions-- sometimes, great stuff comes out of playing around with little problems. Like the question "What is the relationship between the wobble and the spin of a thrown plate?"

Of course, not every playful investigation is going to lead to QED and a Nobel Prize, but even if it does turn out to be unimportant from a physics standpoint, playing with these things can be tremendously rejuvenating. Playing around with sticky tape earlier this year was tremendously helpful to me, not because it led anywhere professionally (though I may yet write an AJP article about that stuff), but because it was fun, and helped me maintain my interest in doing what I do.

So, the story of Feynman and the spinning plate is a useful reminder of the importance of noticing the little things around you, and keeping a playful attitude. Keep looking and thinking and asking questions, because even if they don't lead anywhere directly useful, they help keep you energized and engaged.


(Part of a series promoting Eureka: Discovering Your Inner Scientist, available from Amazon, Barnes and Noble, IndieBound, Powell’s, and anywhere else books are sold.)

(Cornell china plate image from Collectable Ivy. This isn't the same kind of plate Feynman was talking about, but it's what Google came up with in the short time I had to devote to this.)


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Yes and yes. Play and you shall seek; seek and you shall discover.