The Copenhagen interpretation is the mainstream interpretation of quantum mechanics; it was worked out by Niels Bohr and Werner Heisenberg while collaborating in Copenhagen around 1927. The interpretation attempts to answer some perplexing questions which arise as a result of the wave-particle duality in quantum mechanics.
In the classic double-slit experiment, when light passes through double slits onto a screen, alternate bands of bright and dark regions are produced. These can be explained as areas in which the light waves reinforce or cancel. However it became experimentally apparent that light has some particle-like properties and items such as electrons have wave like properties and can also produce interference patterns.
This poses some interesting questions. Suppose one were to do the double slit experiment and reduce the light so that only one photon (or electron) passes through the slits at a time. In performing the experiment, one will see the electron or photon hit the screen one at a time. However, when one totals up where the photons have hit, one will see interference patterns that appear to be the result of interfering waves even though the experiment dealt with one particle at a time.
The questions this experiment poses are
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The completeness of quantum mechanics (thesis 1) has been attacked by the Einstein-Podolsky-Rosen thought experiment which was intended to show that there have to be hidden variables in order to avoid non-local, instantaneous "effects at a distance".
Of the three theses above, the third is maybe the most problematic from a physicist's standpoint, because it gives a special status to measurement processes without cleanly defining them nor explaining their peculiar effects.
Many physicists and philosophers have objected to the Copenhagen interpretation, both on the grounds that it is non-deterministic and that it includes an undefined measurement process that converts probability functions into non-probabilistic measurements. Einstein's quotes "God does not play dice" and "Do you really think the moon isn't there if you aren't looking at it?" exemplify this.
Many physicists have subscribed to the null interpretation of quantum mechanics summarized by Feynman's famous dictum: "Shut up and calculate!"
A list of alternatives can be found at Interpretation of quantum mechanics.
Criticisms
Alternatives
Further Reading
External Link