Mass distribution width. The width of the mass distribution has been under discussion since Diósi's initial proposal. In ref. , for instance, Diósi equaled it to 10 - Å, a typical nuclear size. Penrose proposed that stationary-state nuclear wave functions, which are about 10 -2 to 10 - Å, provided a natural basis for mass distributions as long as their spreading in nonbonding systems was limited by a Newtonian gravitational potential. We agree that the nuclear wave function describes the mass distribution and, for molecules, in particular, it is automatically bound by the Born-Oppenheimer potential. This is indeed the approach we employed in all simulations of this paper, with the parameters of Table .