In 1966, independently of Elliott H. Lieb and Walter Thirring, Dyson and Andrew Lenard published a paper proving that the Pauli exclusion principle plays the main role in the stability of bulk matter. Hence it is not the electromagnetic repulsion between outer-shell orbital electrons that prevents two stacked wood blocks from coalescing into a single piece, but the exclusion principle applied to electrons and protons that generates the classical macroscopic normal force. In condensed matter physics, Dyson also analysed the phase transition of the Ising model in one dimension and spin waves.