It has long (since ~ '84) seemed to me that what all one really needs
is a way to "kill" off relatively small branches. Imagine there were a
slight non-linearity whereby when there are two branches that are
sufficiently similar, and one of the branches has a large enough
amplitude relative to the other one, then physics in the small branch
gets modified in big enough way as to kill off living creatures like
ourselves. This would seem to imply that creatures like us only
survive in the branches with large relative amplitude, which would
seem to imply experimental verification of the squared-amplitude
probability law for QM.
I was very interested in studying this topic when I was a grad student
in physics and philosophy of science back in '81-84. But as Nicholas
notes, philosophers don't take many worlds seriously (or didn't till
recently). And physicists didn't think it an appropriate topic for
non-senior folks. Had I been encouraged more, I would have pursued
this research idea in much more depth. As it is, I likely won't get
around to doing physics again for quite some time.
Robin D. Hanson hanson@hss.caltech.edu http://hss.caltech.edu/~hanson/