On 6/17/2018 3:51 PM, Bruce Kellett wrote:
From: *Brent Meeker* <[email protected]>
On 6/17/2018 12:05 AM, Bruce Kellett wrote:
The fact that energy spectra of atoms and the like are discrete does
not change the fact that energy eigenvalues are a continuous set of
delta functions on the real line. And generally, when one is
measuring atomic spectra one determines energies by the deviation
occasioned by a prism or diffraction grating. In other words, one
actually measures a position on a screen, or a wavelength, which is
also a position measurement.
Yes, it's interesting to consider what measurements are /not/
position measurements. We can distinguish colors, so is that a
direct energy measurment. And we have calorimeters. Is there a
direct measurement of momentum?
It has been suggested that all measurements ultimately boil down to
position measurements. Colour vision is the result of distinct
receptors in the retina that are at different positions, and the light
from distant objects is focused at different positions by the lens in
the eye.
But the lens doesn't send one color to one photoreceptor and another
color to a different photorecptor. It focuses a spot of light on
several photorecptors and the one with the right pigment fires its
neuron. So it is energy detection.
I don't know enough about the physics of calorimeters as used in HEP
to comment here. But if temperature changes are measured by bimetals
or strain gauges, position comes into it in an essential way.
Most work by measuring a voltage. But you miss the point. Those
position measurements are not essential in the QM sense. They are just
changing one classical value into another. Temperature is the first
classical level.
Brent
I don't know of any direct, non-position-dependent, measure of momentum.
It is an interesting question, but somewhat beside the point of
determining why our current classical perceptions of position
correspond to the stable quantum eigenvalues -- an evolutionary
explanation might explain the correspondence, but not why classical
position is the way it is.
Bruce
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