According to the classic quantum theory, an observer who opens the box will cause a collapse of the wave function, which describes the whole situation into one of the two possible states, a live or a dead cat. In order to avoid the very problematic idea of the collapse, Everett had raised the idea of the parallel many worlds, where two worlds are created; one contains a live cat, the second - a dead cat. The observer is duplicated too, as well as all other objects in the world, so in one world the observer sees a live cat, while in the second she sees the dead cat. There is no relation between the two worlds since the split. This solution is difficult to accept, but some physicists are holding it seriously, since it resolves other serious difficulties in Quantum Theory (such as Prof. Lev Vaidman from Tel Aviv University, see Vaidman 1996).  

David Albert from Columbia University, proposed at 1988 the Many Minds Interpretation (MMI), as a different approach to MWI. Michael Lockwood joined him in 1996. According to MMI, the multiplication of worlds takes place only in the mind space, not in the physical space. The observer may have many minds, each mind ‘gets’ a different result of the observation. Each new observation in a quantum superposition state creates a new split of minds, where the number of possible results dictates the number of newly created minds. There is no linkage between the minds, but all of them are associated with the same physical body. One mind sees a live cat, the second – a dead cat. This schizophrenic interpretation is also very difficult to accept as the normal observer situation.

In this short paper I propose another interpretation, which might be easier to accept. Leibniz described the universe as a collection of Monads, where each Monad is a world in itself. The Monads have no “windows”, they can not interact with other Monads, and the coordination of all Monads is taken care of by the nature harmony. I’d like to argue that the MWI idea can be supported by Leibniz Monads, where the multiple worlds’ infrastructure is already defined. The split of a world as a result of observing a superposition is made by associating different branches of results with existing monads, and not by creating new worlds, neither physical nor mental. The number of Leibnizian Monads is infinite; hence there is no problem to populate any number of different results.
                                        
The Leibnizian infrastructure eliminates the redundancy of physical or mental worlds. For one Monad the cat will be live, for another Monad – dead. Since there are no windows for the Monads, the natural harmony will take care for the gaps between the different perspectives of the universe, as being perceived by the Monads. As Leibniz explained in the Monadology (item 57): And as the same town, looked at from various sides, appears quite different and becomes as it were numerous in aspects; even so, as a result of the infinite number of simple substances, it is as if there were so many different universes, which, nevertheless are nothing but aspects [perspectives] of a single universe, according to the special point of view of each Monad.

The MWI interpretation strongly contradicts the Occam’s razor principle, which can be phrased as “entities should not be multiplied beyond the necessary”. The MMI interpretation reduces the multiplications to the mental dimension, but also contradicts the razor. The Leibniz utilization proposed here does not require any multiplication beyond what already exists.
 

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Bibliography

Albert, D. Z. [1992]: Quantum Mechanics and Experience, Harvard University Press, Cambridge, MA.

Albert, D. and Loewer B. [1988]: Interpreting the Many Worlds Interpretation, Synthese 77: 195-213.

Deutsch, D. [1985]: Quantum Theory as a Universal Physical Theory, International Journal of Theoretical Physics, 24, pp 1-41

DeWitt, B. S. [1971]: The Many Universe Interpretation of Quantum Mechanics. In Foundation of Quantum Mechanics, Academic Press, New York, reprinted in DeWitt and Graham (eds), 162-218

Everet, H. [1957]: Relative State Formulattion of Quantum Mechanics. Reviews of Modern Physics, 29:454-462

Everet, H. [1973]: The Theory of the Universal Wave Function. In DeWitt and Graham (eds).
Lewis, David. [1986]: On the Plurality of Worlds. Basil Blackwell

Lockwood, M. [1996]: ‘Many Minds’ Interpretations of Quantum Mechanics. British Journal of Philosophy of Science; 47: 159-188

Page, D. N. [1995]: Sensible Quantum Mechanics: Are Only Perceptions Probabilistic? University of Alberta preprint

Skyrms, B. [1976]: Possible Worlds, Physics and Metaphysics. Philosophical Studies, November 1976, 30(5):323-332

Vaidman, Lev. [1996]: On Schizophrenic Experience of the Neutron, or Why We Should Believe in the Many Worlds Interpretation of Quantum Theory. International Studies in the Philosophy of Science, 12: 245-261