StevieTNZ said:
Nope as in it doesn't align with the thought experiment I'm referring to.
I have had a look at my copy of Sneaking a Look at God's Cards, specifically 15.4 on the Von Neumann chain. Its entirely conventional. Say your measurement gives the position on a pointer. We need to conduct a measurement to determine that position with some apparatus in a regress until we reach the final destination - a conscious observer. The conclusion was the only thing manifestly different was at the consciousness of the observer, so that's when he placed it and you end up with this conscious observer created stuff.
But there is nothing - zilch - in that chain that says we can't say the pointer behaves classically and hence from that point on everything is classical. Its exactly the same nonsense people carry on about in Schrodinger's cat. The particle detector is where the quantum weirdness happens - everything is common sense classical from that point on. And in fact this is precisely what Copenhagen does, which is why the Von Neumann regress is a trivial concern in that interpretation. It assumes the existence of a common sense classical world and that assumption makes all these issues disappear. Its also what the statistical interpretation does.
The cost however is in explaining how that world emerges. That's where decocherence comes in. If you put the selection of a particular outcome just after decoherence by interpreting the improper mixed state as a proper one then you can explain this classical world and there is no issue. Other issues such as the so called factoring problem appear, but they are under active research, and we will need to await what comes out of it, however many think its simply tying up loose ends.
Copenhagen's minor blemish is thus fixed:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html
'Is that true? Is that a sign of a problem of the Copenhagen interpretation?
It is surely true. It's how the world works. However, one may also say that this was a point in which the Copenhagen interpretation was incomplete. They didn't quite understand decoherence - or at least, Bohr who probably "morally" understood what was going on failed in his attempts to comprehensibly and quantitatively describe what he "knew".
However, once we understand decoherence, we should view it as an explicit proof of this fifth principle of the Copenhagen interpretation. Decoherence shows that the states of macroscopic (or otherwise classical-like) objects whose probabilities are well-defined are exactly those that we could identify with the "classical states" - they're eigenstates of the density matrix. The corresponding eigenvalues - diagonal entries of the density matrix in the right basis - are the predicted probabilities.'
As assertion that you can't place the point a specific outcome is selected just after decoherence would be akin to saying an improper mixed state is not formally the same as a proper one. If that was the case it would be big news with many interpretations such as GRW, MW, Decoherent Histories, Ignorance Ensemble all going down the gurgler - not to mention the formalism itself would be in jeopardy.
In fact the G in GRW is Ghirardi, the author of Sneaking a Look at God's Cards. There is a very close connection between GRW and Decoherence:
http://arxiv.org/pdf/quant-ph/0701218v1.pdf
It seems highly unlikely to me his book proves his own interpretation is in trouble - but I suppose one never knows.
This is why I am VERY confident such a proof is in error.
Thanks
Bill
