ROBERTO, 26 YEARS

I was involved in one discussion with Richard Feynman - not one-on-one mind you, but in a small group. It was, as one of the others in the group once wrote, “like being on hallowed ground.”
The occasion was a physics teachers conference in November, 1987 - his last professional meeting just three months before his death - and he was obviously quite weakened by the illness and treatments. He had been on a panel discussion about what should be included in teaching high school physics - and was accompanied by Caltech’s David Goodstein, whom I knew well.
At the conclusion of the conference, there were a dozen or so of us (Feynman and Goodstein included) standing around at the front of the auditorium chatting about the events of the meeting. He was, as usual, exuberant - charming us all with his wit - in every meaning of the word. It was then that Robert Wild (who had been my freshman physics teacher) handed Feynman a long copper tube and dropped an object down the tube. And the object fell v-e-r-y s-l-o-w-l-y through the copper tube. “Ah, it must be magnetic,” said Feynman gleefully of the falling object - something we all knew as it was a fairly common lecture demonstration showing how a falling magnet would induce eddy currents in the copper tube, which in turn would create a magnetic field which would then slow the magnet’s fall. And he dropped the magnet several more times, playing with it like a kid with a new toy, delighting in the interplay of interesting ideas that the demonstration evoked.
Then someone asked “the question”: “What would have happened had the tube been one of the new superconductors rather than copper?” And everyone just stopped! We were faced with a brand new question that no one had ever asked before - and we were in the presence of Richard Feynman. [NOTE: This was 1987, just after the discovery of the high Tc copper oxide superconductors earlier that year.] Feynman chimed in, “I don’t know anything about the new superconductors, so let’s assume it is just an ordinary superconductor.” Game on.
The discussion that followed was priceless - as we all speculated on what would happen, offering arguments and counter arguments. “It would never get inside the tube since it would levitate,” someone said. “No, it would be unstable,” said another. “One could always force it inside,” I offered, “levitation is just a balance of forces.” “Then it would just come to a stop inside the tube - or maybe pop back out,” someone else said. “Or maybe oscillate inside the tube,” said another. Then David Goodstein entered the discussion with, “Once inside the tube, it would be in freefall.”
“Of course!” Feynman responded gleefully - having just had a new insight into an interesting new physics question. (And everyone else said, “Of course” as well - whether they understood it or not!) “It would slow as it entered, be in freefall inside, then be ejected at the other end!”
It was exhilarating - a conversation I will remember forever. On the entire four hour drive home, I could think about nothing else. Why did Goodstein say what he did - and why did Feynman so quickly agree? (I’m pretty sure all the rest of us agreed because Feynman did.) What was really going on physically that made that answer correct?
The short answer, of course, which requires some assumptions that were never stated, was this: Since the magnetic field cannot penetrate the superconductor, any induced currents would just surface currents - and since the tube would be resistanceless, those currents could not dissipate any energy. So the magnet could not lose any energy as it fell - so would be in freefall! Brilliant. But what was really going on?
.
I spent much of the next year looking at the very subtle conditions associated with this problem, what the induced currents in the tube would be like, what forces on the magnet they would create, how the Faraday effect and the Meissner effect would be in play - and how their effects were different. That led to talks that I gave - and a paper. It drove the discussion in my advanced topics in solid state physics course, because to understand the details required understanding both superconductivity and magnetism.
All progress in both science and education depends on the questions asked. And being a part of that discussion with Richard Feynman was indeed like being on hallowed ground.