A Twist on Schrödinger's Cat Paradox
Here are a couple of things that are very rarely explained in QM pedagogy but which are very helpful in understanding Shroedinger&#x27;s cat:<p>1.  The wave function does not exist in physical space, it exists in <i>configuration</i> space.  Configuration space is the same as physical space only in the one very special case of a single non-entangled particle.  The intuitions of physical space do not generally carry over into the general case of configuration space.<p>2.  In order to produce interference you have to split up the wave function into two pieces and then bring those pieces back together again with a phase change.  But since the wave function exists in configuration space, &quot;bringing it back together again&quot; becomes increasingly difficult as the number of entangled degrees of freedom grows.  As a practical matter, it is effectively impossible to do this once the number grows beyond a few hundred (this is why building quantum computers is hard).  But an actual macroscopic observer consists of O(10^23) degrees of freedom, and is also entangled with their environment.  This is the reason that large systems behave classically and don&#x27;t exhibit interference.<p>3.  Whether or not a system is in a superposition is not a physical fact about the system, it is a consequence of the measurement you choose to make.  A vertically polarized photon (for example) is in a superposition relative to a measurement axis rotated away from the polarization axis.  For a more complicated system, the measurement axis, like the wave function itself, is in <i>configuration</i> space.  But we can only do measurements in <i>physical</i> space.  This is the reason that in order to see interference in an entangled system it is necessary to do multiple physical measurements and look at the correlations between them.  Doing those kinds of measurements on actual macroscopic objects is <i>way</i> beyond the current state of the art, and may well be impossible even in principle.  But this is the sort of thing that is contemplated in the theory behind these experiments.  This is the reason that single particles are used as stand-ins for Wigner&#x27;s friend.