Clinton, New York
Perhaps one cannot adequately treat the history of ideas regarding the "collapse" of the wave function in a brief article ("Crossing the quantum frontier", 26 April, p 38), but I was startled to find that Ian Percival and Nicholas Gisin were given credit for ideas that I introduced.
Moreover, no mention was made of the "continuous spontaneous localisation" theory (CSL), arguably the most satisfactory and complete collapse theory at present, introduced by myself and developed in collaboration with Gian-Carlo Ghirardi and Alberto Rimini.
In 1966, David Bohm and Jeff Bub introduced the idea of modifying Schrödinger's equation to incorporate the description of wave function collapse. I showed in the late 1970s how this could be done by making the additional term depend on randomly fluctuating quantitiesthe Brownian motion idea lauded in the articlewhich all subsequent workers in the field have adopted.
CSL is the natural generalisation ...