We must, however, note that not all atoms in the medium are displaced by the superposition; only those creating the left/right states are displaced. Thus, we split the iron atoms into two sets: those in the system (which includes the NS = 10 14 atoms/mol that have different positions in the superposition) and those in the environment (all remaining atoms that remain in the same position). With such a split, the difference in mass distribution that appears in (3) is where S and E stand for system and environment. Eq. ( ) implies that only the system's gravitational self-energy contributes to the Diósi-Penrose collapse time. Therefore, we should replace Nat with NS in (8) . Using the fitting proposed in Table ,  = 24.9 a0 -2 for the atomic radius Rat = 2.26 Å. The result is shown in Figure . According to the Diósi-Penrose model, the state superposition occurring in a 1 kg piece of iron would last about 1 s. This is a surprising result, meaning that if the Diósi-Penrose model is correct, quantum coherence could survive for a long time for macroscopic systems.