 The evaporation of black holes has another startling consequence that raises far-reaching philosophical and physical problems for our current picture of quantum field theory and particle physics: it implies that baryon and lepton number need not be conserved. Suppose a neutron star composed of ∼1057 baryons collapses to form a black hole. After evaporation, the resultant baryon number is essentially zero, since it is overwhelmingly likely that the black hole will radiate particles of baryon number zero. (The radiation is not energetic enough to produce baryons, until, perhaps, the very late stages of the evaporation.) This issue seems not to have agitated researchers in either the particle physics or the general relativity community so much as the idea of non-standard quantum evolution even though conservation of baryons and leptons are surely principles as well entrenched as that of the unitarity of quantum  evolution.[18]  One could perhaps argue that they are even more entrenched, since our empirical evidence for the conservation principles is simple and immediate in a way that our evidence for standard evolution is not: one simply counts particles before and after an observed interaction—interpretational questions arising from the Measurement Problem in quantum theory and a possible “collapse” of the wave function do not bear on it. (See the entry  Quantum Mechanics.)  