Quote:
Originally Posted by Warren Platts
To say that it's the case that a particle never really has both a definite position and a definite momentum is pure metaphysics. There is not even in principle a way to decide whether positions and momentums are really discrete or not. ... The poor particle physicist, on the other hand, must of necessity be forever ignorant of the true nature of his or her chosen subject matter.  |
This is a mis-characterization of Heisenberg. The HUP allows quantum observables to be measured to any degree of accuracy. And there are several observables that can be measured without any discernible "observer effect". For example, you can make repeated identical photon polarization measurements and you will get the same answer each time. The photon is not disturbed by such measurements.
The EPR Paradox, in fact, was created to demonstrate that quantum theory was "incomplete" as you describe. Unfortunately, EPR came to the wrong conclusion on this point; they did not know about Bell's Theorem and the Aspect experiment - both of which came decades later.
So it is not just semantic or metaphysical to say that particles do not have simultaneous values to some observables. It is a physical reality (per Bell's Theorem etc.) that either they don't have such simultaneous attributes, or there exist non-local (i.e. faster than the speed of light) forces of which we are otherwise unaware. It is not clear that either of these alternatives have preferential footing currently. However, the general belief is that reality is shaped by the "context" of an observation... i.e. that reality is contextual. If reality was fully observer independent by classical standards, then it would need to be non-contextual.
So the usual general conclusion is: classical observer independence of particle attributes is ruled out by physical experiment.