[8] It later received investigation from James Hartle and Stephen Hawking[9] who derived the Hartle–Hawking solution to the Wheeler–DeWitt equation to explain the initial conditions of the Big Bang cosmology.
Hugh Everett's universal wavefunction supports the idea that observed and observer are all mixed together: If we try to limit the applicability so as to exclude the measuring apparatus, or in general systems of macroscopic size, we are faced with the difficulty of sharply defining the region of validity.
For what n might a group of n particles be construed as forming a measuring device so that the quantum description fails?
And to draw the line at human or animal observers, i.e., to assume that all mechanical apparata obey the usual laws, but that they are not valid for living observers, does violence to the so-called principle of psycho-physical parallelism.
Wigner wrote: The state vector of my mind, even if it were completely known, would not give its impressions.