Fermi to Dyson: 'With 4 parameters I can fit an elephant'

mmbronstein · x · 2026-08-31

In 1953, physicist Freeman Dyson showed Enrico Fermi graphs demonstrating that his theory agreed with experimental results. Fermi was unimpressed, criticizing Dyson for lacking both physical intuition and rigorous mathematical methodology.

When Dyson defended his work based on its agreement with experiments, Fermi asked how many adjustable parameters he had used. 'Four,' Dyson replied.

Fermi smiled, quoting Johnny von Neumann: 'I remember my old friend Johnny von Neumann used to say that with four parameters I can fit an elephant, and with five I can make his trunk move.' This anecdote is often cited to criticize overfitting and model tuning lacking physical meaning.

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