Homer said:
So it looks as if you are all a figment of my imagination
Nice one.
Clearly the population of the universe is zero.
Since there are an infinate number of planets in the universe, but only a finite number are inhabited... any finite number divided by infinity is as near to nothing as makes no odds... so any people you meet in your travels are the figments of a deranged imagination.
--- The Hitch Hikers' guide to the Galaxy
The argument from QM (not restricted to wave mechanics btw) seems just a pretext for the more commonly known troubles with phenominalism.
Phenominalism, for those new, proposes that since we experience the universe via sence data, that only the sence data can be considered "real". basically, everything is a kind of illusion and if you don't experience something it dosn't exist.
It can easily get extreme.
One trouble is when you realise that nothing exists but that you make it so. This is trouble as soon as you consider the existance of others like yourself.
Decartes famously suggested that the existance of ones thoughts implied the existance of oneself... and so other things may exist also.
The main problem with the more extreme forms of phenominalism is the persistance of the illusuion that some things have an existance independant of our awareness of them. (Language gets really bogged down here.)
Some have suggested that objects don't go away when we stop looking at them because God is looking at them (and everything else) all the time.
The trouble with this is, who is observing God to keep God existing.
And this, freinds, is the fundamental flaw in all such arguments ...