Back in 1983 or so I was a graduate student in physics at UC Santa Barbara. I was having lunch with friends on the lawn of the UCen (student center). One of our fellow physics students came running up and told us Richard Feynman would be speaking in ten minutes at the Institute for Theoretical Physics at Ellison Hall!
We ran as fast as we could and barely made it in time to hear Feynman speak.
Feynman said he had been wondering if there was a way to do quantum mechanics without complex numbers. He wondered if he could make a version of the Schrödinger equation with no imaginary numbers.
He realized it indeed was possible. All you needed was negative probabilities. He looked around the room as we looked utterly mystified as to what that might mean. He said it really is not so bad.
"Look, suppose you have three apples in your hand. I take five from you. But then I give seven back to you. What's the big deal!?"
It was memorable how he was able to even think of that question. And then to come up with such a radical solution. And I am not even sure he considered it worth publishing!
He was mobbed by people wanting to talk to him and I stayed away. Until everyone else had left and he was just standing there. I went over and asked him if he had heard of someone named Ed Fredkin.
He snapped back wanting to know why I was asking. I asked what he thought of Fredkin's ideas.
"Fredkin? Fredkin!? That nut? That crank? His ideas are totally stupid and crazy! Why would you ask me about such ridiculous ideas!?"
I said nothing and just smiled at him. Then, after a pause, Feynman went on to say, "Well I said that about the last idea Fredkin had. But it turned out he was right.'
You might wonder who is Fredkin. Have you seen the movie "War Games"? There was an eccentric computer scientist who lived on his own private island. The young heroes had to find him and convince him to help them. Or else the world would be destroyed in a nuclear holocaust they started by accident.
That character was Ed Fredkin.
Ed Fredkin was also my undergraduate thesis advisor at MIT. But that is another story.
-- Robert Bernstein 11/2/18