[Bill S (OP)]

In Pop Sci literature one often meets references to the wavefunctions of macro systems.  My understanding is that only an isolated system can be described by a wavefunction.  Typically,  macro bodies are not isolated systems.  Decoherence will have taken place,  irrespective of any human intervention.  So it is not appropriate to talk of a wavefunction for any macro system that is not adequately protected from surrounding systems,  or from internal interactions.

Am I on the right track?

[alancalverd]

To the extent that a wavefunction describes the probability of finding something somewhere, the wavefunction of a macro system will be the superpostition of the wavefunctions of its constituents and therefore have a very sharp peak with insignificant amplitudes of its low frequency components.

[Bill S (OP)]

Thanks Alan, so where might one expect decoherence to enter the scenario, given that external influences will effect all but the best protected systems, and internal interactions must be significant in a system with trillions of particles?

[evan_au]

The double-slit experiment shows that light and electrons have a wavefunction.

But the double-slit experiment has also been done with molecules as large as "Buckyballs" (C₆₀), showing that these larger systems also have a wavefunction.

Schroedinger's cat may not appreciate being sent through a double-slit apparatus to see if his wavefunction collapses under this scenario too...

See: https://en.wikipedia.org/wiki/Double-slit_experiment#Interference_of_individual_particles

[Bill S (OP)]

Thanks Evan, lots of interesting stuff in that link that I Was not up to date with.
I'll give the whole thing some more thought before having another shot at the question from my OP. I know I don't have the answer,  but it's important to make sure I'm asking the right question.