Prout's hypothesis that all atomic weights are whole numbers was defended with ad hoc patches for 85 years — because chlorine's fractional weight couldn't be chemically resolved — until isotopes, which are chemically indistinguishable, were discovered; there was no way to know in advance that this stubborn anomaly pointed to something real.

Dwarkesh recounts Lakatos's example of Prout's hypothesis: an 85-year 'hostile' verification loop where the anomaly (chlorine's 35.5 weight) couldn't be resolved until isotopes were discovered, showing there's no ex ante rule for knowing which anomalies matter. ✦ AI generated

Dwarkesh Patel · Dwarkesh Podcast · 2026-04-07 · original ↗

So you have 85 years before we realize what an isotope is, where the verification loop is actively hostile against the correct theory. You just need this remnant to be defending… There's no ex ante reason it's the preferred theory.

verbatim transcript · starts at 29:52