Bachelier was no Einstein
It's been fun following David Warsh's series on the history of economic thought (I got a bit behind and only now read this one ... so now I'm obviously going to see what I can do about Black-Scholes in the information equilibrium framework).
Although this quote by Warsh from Davis and Etheridge:
[Bachelier] defined Brownian motion – predating Einstein by five years ...
doesn't make much sense to me. Brown 'defined' Brownian motion (a physical process) by observation. Einstein's contribution was to connect Brownian motion directly to atoms thereby confirming that atoms exist [1]. There is no sense in which Bachelier came up with the idea of Brownian motion first (it was observed) or predated Einstein's result about atoms in his 1905 paper.
...
Footnotes:
[1] Einstein's "annus mirabilus" papers (from 1905) are paradigm shifting because of the way they take theoretical models "seriously" in a modern sense. In 1928 Dirac writes down a relativistic Schrodinger equation that has an additional solution with the opposite charge. Before Einstein, this might have been taken as a mathematical curiosity or irrelevant solution. After Einstein, we get Dirac taking the solution seriously and proposing the existence of antimatter. Einstein's papers from 1905 have us taking the theoretical constructs of atoms, photons and Lorentz symmetry seriously.