Let's talk about quantum decoherence in schrodinger's cat gedankenexperiment.

The basic paradox is that the cat's fate depends on a quantum event and the scientist has before him, a superposition of cat-alive and cat-dead states. The question that naturally arises is that why can't the cat inside, collapse this superposition. To the cat, the external universe must be a superposition of all possible states.

Before you say quantum mechanics doesn't apply to macroscopic phenomenon, I'd like you to reconsider why you say that. We say that because of the magnitude of planck's constant is tiny enough to only allow certain particles to exhibit wavy behavior and hence interference patterns in DSlit experiments. Cool, but also remember that the very same wavy particles are forced to assume a particulate nature on observation/measurement/collision. This means that unless some form of coherence is lost in time between origination of a system and its measurement or interaction with environment, coherence is preserved. Thus we shall conclude that in the case the cat box is in a completely isolated box with absolutely no kind of force on it, its constituent particles are truly in coherence with each other and therefore are in a superposition. We cannot escape this fact in any other possible way and now the cat too has the entire external universe in a superposition of umpteen states. Coherence is defined as mainting a definite phase relation throughout a time-slice and true isolation would allow that. Prove me wrong?