Copenhagen interpretation?” and “Is there any alternative theory?”)
Without a definition of observer there can be no mechanism triggered by their presence. Another popular view is that irreversible processes trigger collapse. Certainly wavefunctions *appear* to collapse whenever irreversible processes are involved. And most macroscopic, day-to-day events are irreversible. The problem is, as with positing observers as a cause of collapse, that any irreversible process is composed of a large number of sub-processes that are each individually reversible. To invoke irreversibility as a *mechanism* for collapse we would have to show that new *fundamental* physics comes into play for complex systems, which is quite absent at the reversible atom/molecular level. Atoms and molecules are empirically observed to obey some type of wave equation. We have no evidence for an extra mechanism operating on more complex systems. As far as we can determine complex systems are described by the quantum-operation of their simpler components interacting together. (Note: chao
