"Surely You're Joking, Mr. Feynman!" - unam.

half circles that the particles go around ­­ they'd take a screwdriver, and remove the D's
by hand, fix them, and put them back. At Princeton it was a lot harder, and at MIT you
had to take a crane that came rolling across the ceiling, lower the hooks, and it was a
hellllll of a job.)
I learned a lot of different things from different schools. MIT is a very good place;
I'm not trying to put it down. I was just in love with it. It has developed for itself a spirit,
so that every member of the whole place thinks that it's the most wonderful place in the
world ­­ it's the center, somehow, of scientific and technological development in the
United States, if not the world. It's like a New Yorker's view of New York: they forget
the rest of the country. And while you don't get a good sense of proportion there, you do
get an excellent sense of being with it and in it, and having motivation and desire to keep
on ­­ that you're specially chosen, and lucky to be there.
So MIT was good, but Slater was right to warn me to go to another school for my
graduate work. And I often advise my students the same way. Learn what the rest of the
world is like. The variety is worthwhile.
I once did an experiment in the cyclotron laboratory at Princeton that had some
startling results. There was a problem in a hydrodynamics book that was being discussed
by all the physics students. The problem is this: You have an S­shaped lawn sprinkler ­­
an S­shaped pipe on a pivot ­­ and the water squirts out at right angles to the axis and
makes it spin in a certain direction. Everybody knows which way it goes around; it backs
away from the outgoing water. Now the question is this: If you had a lake, or swimming
pool ­­ a big supply of water ­­ and you put the sprinkler completely under water, and
sucked the water in, instead of squirting it out, which way would it turn? Would it turn
the same way as it does when you squirt water out into the air, or would it turn the other
way?
The answer is perfectly clear at first sight. The trouble was, some guy would think
it was perfectly clear one way, and another guy would think it was perfectly clear the
other way. So everybody was discussing it. I remember at one particular seminar, or tea,
somebody went up to Prof. John Wheeler and said, "Which way do you think it goes
around?"
Wheeler said, "Yesterday, Feynman convinced me that it went backwards. Today,
he's convinced me equally well that it goes around the other way. I don't know what he'll
convince me of tomorrow!"
I'll tell you an argument that will make you think it's one way, and another
argument that will make you think it's the other way, OK?
One argument is that when you're sucking water in, you're sort of pulling the
water with the nozzle, so it will go forward, towards the incoming water.
But then another guy comes along and says, "Suppose we hold it still and ask
what kind of a torque we need to hold it still. In the case of the water going out, we all
know you have to hold it on the outside of the curve, because of the centrifugal force of
the water going around the curve. Now, when the water goes around the same curve the
other way, it still makes the same centrifugal force toward the outside of the curve.
Therefore the two cases are the same, and the sprinkler will go around the same way,
whether you're squirting water out or sucking it in."
After some thought, I finally made up my mind what the answer was, and in order
to demonstrate it, I wanted to do an experiment.