The Diósi-Penrose model's central assumption is that gravity causes the quantum superposition to collapse. If an object is in a superposition of two quantum states with different spatial positions, it implies a gravitational instability, which spontaneously collapses the wave function, with a time constant inversely proportional to the gravitational self-energy of the difference between the mass distributions of the two superposed states (Figure ). Suppose we have a system in a state  that is a superposition between stationary states A and