  In quantum theory, it is widely accepted that all experimental results must
agree with theoretical predictions based on the Copenhagen interpretation.
However the classical system in the Copenhagen interpretation has not been
defined yet. On the other hand, although ongoing research of decoherence is
trying to elucidate the emergence of the classical world, it cannot answer why
we observe one of eigenstates in observed system. These situations show that
the relation between what we observe and physical law has not been elucidated.
Here I elucidate the relation by developing Everett's suggestion. Further, from
this point of view, I point out that today's brain science falls into circular
argument because it is trying to assign what we observe in the brain to process
of the subjective perception, and I suggest the future research line in brain
science.
