Max Tegmark in his paper “Many worlds in context” http://arxiv.org/abs/0905.2182(adsbygoogle = window.adsbygoogle || []).push({});

Argues that …. .“Everett’s MWI is simply standard QM with the collapse postulate removed, so that the Schrödinger equation holds without exception”. He also argues that from this we can deduce that not only microscopic-superpositions are inevitable, but also that macroscopic-superpositions (say of a cat being dead and of being alive) are perfectly legitimate quantum states.

However, the assumption that macroscopic superpositions are valid seems puzzling to me. The well known Schrödinger’s cat scenario gives:

|psi> a|up>|cat alive> + b|down>|cat dead>.

But is this really viable? cats are very complicated Can a cat really be in a macroscopic pure quantum state like |cat Alive> just because we can write it on the page as a bra vector? Is it the intention that the state vector of the cat can be explained as the tensor product of states of all the particle states that make up the cat?

|cat alive> = |molecule 1> ⊗ |molecule 2> ⊗ |molecule 3> ⊗.......

If instead we suppose the pure cat state to be an energy eigenstate, then would it not be in a stationary state. Its only dependence on time being through some phase factor which makes no physically distinguishable difference - surely a cat in this state would be in a frozen state (i.e. |cat dead> )?

If the cat was said to be in a mixed state then, for this interpretation is it the implication that it would need to be an "improper mixture" with some off diagonal terms persisting in the off diagonal terms of the density matrix in some basis?

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# Everett's interpretations and Macroscopic quantum states

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