Wednesday, February 22, 2012

Uncertainty Principle Is NOT Due To Measurement Uncertainty

I just came across this report, and I've yet to read closely the actual paper (so I'm going out a bit on a limb here talking about something I haven't fully read yet). But still, it is consistent with what we know about the Heisenberg Uncertainty Principle (HUP).

As I've stated earlier on the misconception of the HUP, it has very little to nothing to do with the act of measurement, or how accurate our measurement is. It is an INHERENT property of QM and the nature of the so-called particles that we are trying to measure. One can examine the single-slit diffraction to satisfy oneself of this.

A new paper in Nature Physics confirms this further.

This probabilistic nature of particles means there will always be imprecision in any quantum measurement, no matter how little that measurement disturbs the system it is measuring.

"This has nothing to do with error or disturbances due to a measurement process, but is a basic fundamental property that every quantum mechanical particle has," Sulyok told LiveScience. "In order to describe the basic uncertainty together with measurement errors and disturbances, both particle and measurement device in a successive measurement have to be treated in the framework of quantum theory."
So there!

I'll post the exact reference to this paper later today.

Edit: exact reference: J. Erhart et al., Nature Physics Online  doi:10.1038/nphys2194.

Zz.

1 comment:

Joey Dumont said...

"In order to describe the basic uncertainty together with measurement errors and disturbances, both particle and measurement device in a successive measurement have to be treated in the framework of quantum theory."

In my Quantum Mechanics class, we had a discussion about the "measurement problem" in the Copenhagen interpretation of QM. When considering both the instrument and the system to be measured as quantum systems, if the measured system's state is a linear combination of eigenstates, then the "needle" on the instrument must also be in a superposition of eigenstates.

In other words, the needle must be in two places at once. If I recall correctly, this problem arises from the choice of the wavefunction for the instrument in the Copenhagen itnerpretation.

This problem is solved in Bohmian mechanics, as the instrument's wavefunction can assumed to be very localized in phase space, hence not interfering with the particle's wavefunction.

Another part of the problem is related to the wavefunction collapse, but I'd have to review my notes for that one.

Anyway, the point I'm trying to make is that if the researchers try to consider both systems as quantum, they'll run into problems.