Macroscopic Bodies in Quantum Theory

It is shown that if the wave function of a massive body is $\psi =\Sigma c_n{\psi }_n$, where the ${\psi }_n$ are macroscopically distinguishable states, then the observation of interferences between the various ${\psi }_n$ requires inconceivable laboratory conditions (e.g., the experiment may last longer than the lifetime of the universe). It is therefore proposed to interpret $\Sigma c_n{\psi }_n$ as a mixture of states, and not as a superposition. This new interpretation of wave functions is consistent with experience and is free from the paradoxical features of the "orthodox" measurement theory.