The following is Serge's account of Dyson's account of Fermi's opinion of QED [1]:
'''
“When Dyson met Fermi, he quickly put aside the graphs he was being shown indicating agreement between theory and experiment.
His verdict, as Dyson remembered, was “There are two ways of doing calculations in theoretical physics. One way, and this is the way I prefer, is to have a clear physical picture of the process you are calculating. The other way is to have a precise and self-consistent mathematical formalism. You have neither.”
When a stunned Dyson tried to counter by emphasizing the agreement between experiment and the calculations, Fermi asked him how many free parameters he had used to obtain the fit. Smiling after being told “Four,” Fermi remarked, “I remember my old friend Johnny von Neumann used to say, with four parameters I can fit an elephant, and with five I can make him wiggle his trunk.” There was little to add.”
'''
[1] Segre G., Hoerlin B. The Pope of Physics: Enrico Fermi and the Birth of the Atomic Age. Henry Holt and Co, 2016 ISBN 9781627790055
This quote is from Oliver Consa's 2020 paper: "Something is rotten in the state of QED".
Since we're trading Dyson anecdotes, here's a similarly awkward one, about how Dyson met Wolfgang Pauli for the first time [0]:
> I remember the very first time I met [Pauli] at a conference in Zurich. He was talking with a whole group of people about Julian Schwinger, who had just come to Switzerland. Schwinger was a brilliant young American who had done some very fine work. He was a rival of Feynman; they were the two geniuses then. Pauli was saying that Schwinger told us all this stuff that actually made sense, not like that nonsense Dyson has been writing. At that point I came walking up with a friend of mine, Markus Fierz, who was also a Swiss scientist. With a twinkle in his eye, Fierz came up to Pauli and said, “Please allow me to introduce you to my friend, Freeman Dyson.” Pauli said, “Oh that doesn’t matter. He doesn’t understand German.” Which of course I did. That was a good beginning and we were friends right from the very first day.
I recall that fitting example from undergrad physics. Nowadays, with deep learning going on with billions of parameters being fit, it probably makes somewhat more sense to recall that bit of humor.
''' “When Dyson met Fermi, he quickly put aside the graphs he was being shown indicating agreement between theory and experiment.
His verdict, as Dyson remembered, was “There are two ways of doing calculations in theoretical physics. One way, and this is the way I prefer, is to have a clear physical picture of the process you are calculating. The other way is to have a precise and self-consistent mathematical formalism. You have neither.”
When a stunned Dyson tried to counter by emphasizing the agreement between experiment and the calculations, Fermi asked him how many free parameters he had used to obtain the fit. Smiling after being told “Four,” Fermi remarked, “I remember my old friend Johnny von Neumann used to say, with four parameters I can fit an elephant, and with five I can make him wiggle his trunk.” There was little to add.” '''
[1] Segre G., Hoerlin B. The Pope of Physics: Enrico Fermi and the Birth of the Atomic Age. Henry Holt and Co, 2016 ISBN 9781627790055
This quote is from Oliver Consa's 2020 paper: "Something is rotten in the state of QED".