Almost a century past, has the Copenhagen Interpretation (CI) undergone any modification? In other words, has any of its underlying principles been reformulated since?

The notable (usual) examples that come to mind when one brings up CI, can be among the followings:

  • Collapse of the wavefunction (often considered as too hand-wavy as the concepts of collapse and the necessaity of "wave" mechanics in QM are questionable)
  • Physical distinction of "observation", "interaction" and "measurement" of quantum systems.
  • Decoherence of the superposition of states and Bohr's correspondence principle
  • etc.

Please feel free to touch upon any of the above aspects of CI.


1. I have no idea what is the difference between observation and measurement of a quantum system. If you want to test a certain observable, you measure it.

2. About the so-called collapse of the wave-function, this issue was widely investigated and there is some progress about it. An well-know issue about the collapse is that appears at the interaction with a classical apparatus of measurement - a pointer, a bubble or aglomeration of ions in a chamber, etc. The joint system, microscopic and macroscopic, has a total macroscopic mass, or other macroscopic features. Now, the Feynman path integral tells us clearly what happens when the action function of an object increases very much in comparison with the elementary action ħ - e.g. due to the mass increase.

3. Decoherence and collapse are two different things. There is no clear evidence that the former is the cause of the latter as Zurek thought.

4. The mechanism of the entanglements is today in general clear.


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