An extension of "Popper's experiment" can test interpretations of   quantum mechanics
  Karl Popper proposed a way to test whether a proposed relation of a quantum-mechanical state to perceived reality in the Copenhagen interpretation (CI) of quantum mechanics - namely that the state of a particle is merely an expression of ``what is known'' about the system - is in agreement with all experimental facts. A conceptual flaw in Popper's proposal is identified and an improved version of his experiment (called ``Extension step 1'') - which fully serves its original purpose - is suggested. The main purpose of this paper is to suggest to perform this experiment. The results of this experiment predicted under the alternative assumptions that the CI - together with the above connection of the state function with reality - or the ``many-worlds'' interpretation (MWI) is correct are shown to be identical. Only after a further modification (called ``Extension step 2'') - the use of an ion isolated from the macroscopic environment as particle detector - the predictions using the respective interpretations become qualitatively different. 
R. Plaga (Max-Planck-Institut fuer Physik)