Posted:

**Feb 02, 2011 11:44 am**Darkchilde wrote:The cat will be in a superposition of states until the box is opened. This thought experiment was a way by Schroedinger to show his malcontent with the Copenhagen interpretation of QM. However the thought experiment has remained as a way to explain the Copenhagen interpretation.

Now, the major point of the Copenhagen interpretation is measurement. What measurement is, is not defined in this interpretation, and could be anything from a simple observer (like a photon) to measuring equipment. In another thread, I had posted a concise summary of the Copenhagen interpretation, which I am repeating here:

The Copenhagen interpretation was put forth by people like Niels Bohr, Werner Heisenberg, etc. and it is the mainstream one, if I could call it that. It has been named the Copenhagen interpretation because of the location of its main proponents, like Niels Bohr between 1924 and 1927. In the Copenhagen interpretation, the wavefunction describes the state of a quantum system. The solutions to the Schrodinger equation for a specific quantum system are all wavefunctions, and each describes one of the probable states of the quantum system. Each wavefunction has a probability associated with it; until we measure one of the observables (measurable properties of a quantum system), the system does not have any quantum state associated with it.

Not quite. The system does still have a quantum state, as described by the wavefunction. It's just that, until the act of measurement, this state may not be an eigenstate of the operator representing the variable you're about to measure. So the variable doesn't "have" a definite value.

Darkchilde wrote:

When we take a measurement, the system “decides” its quantum state, and the solution of the Schrodinger equation collapses to the specific wavefunction associated with the measurement. According to the Copenhagen interpretation, only the measurement of observables has any meaning, and this measurement “decides” the state of the quantum system.

Yes, immediately after the measurement the system is in an appropriate eigenstate. The choice of this eignestate is where the randomness comes in.