The problems with decoherence and the many-worlds idea have led
a sizable minority to support a view called GRW theory,
according to Leggett. The concept was put forward in 1986 by
GianCarlo Ghirardi and Tullio Weber of the University of Trieste
and Alberto Rimini of the University of Pavia. In the GRW
scheme, the wave function of a particle spreads out over time.
But there is a small probability that the spreading wave “hits”
a mysterious “something” in the background. The wave function
suddenly becomes localized. Individual particles have only a
small chance of a hit, about once every 100 million years. But
for a macroscopic cat, the chance that at least one of its
roughly 1027 particles makes a hit is high, at least once every
100 picoseconds. The cat never really has a chance to enter any
kind of superposition. Hence, there is no need for decoherence:
the macroscopic state of the cat results from spontaneous
microscopic collapses. A few problems plague this model. One is
that the timing factor that trigge