[extropy-chat] Seth, 4 forces and urk

[scerir]

From: "Hara Ra" 
> 3) Even if we ever determine the relation 
> between the initial BCs and final BCs, 
> there is still the problem of observability. 
> Note each cm^3 of air has 10^19 molecules in it, 
> and any way of finding out the details will change 
> them beyond recovery. Can you spell 'heisenberg'?

Not sure I get your point. But even when HUP has 
a physical meaning (that is not always, see *) 
if we really need to know the 'true' state of 
a physical system (not just in the trivial case in 
which the physical system is already in an eigenstate) 
we can measure it. The 'weak measurement' technique 
exploits quantum uncertainty. In this case quantum 
detectors are so weakly linked to the experiment 
that any measurement moves the detector's pointer 
by less than the level of uncertainty. There is 
a price to pay for these delicate readings, they 
are inaccurate. But while this might appear to make 
the whole process pointless, when repeated many 
times, the average of these weak measurements 
approximates to the 'true' value of the observable 
to be measured. (But what is the 'urk' in the subject
line?).
 
s.

* In general given a pair of non-commuting observables A and B, 
belonging to an Hilbert space H, the quantity delta A delta B 
can either vanish, or become arbitrarily close to zero, if at least 
one of the two observables (A or B) is bounded. Suppose B is the 
bounded observable and suppose A possesses a discrete eigenvalue. 
In this case the variance of the observable A becomes null 
in correspondence of the proper eigenvector associated to 
the discrete eigenvalue and the indeterminacy relation assumes 
the form 'delta A delta B = zero' since delta B is always finite 
for a bounded B. Not to mention here the 'delta E delta t' relation, 
in which 'delta t' is about 'our' clock time and 'delta E' is 
about 'its' energy!