Quantum Epistemology

henry.pha.jhu.edu/Marburger.pdf

 

The link above offers a perspective on quantum physics that I had not fully considered.  It asks, how do we “know” anything about that which we cannot see directly, but must rely on instruments, such as Geiger counters?

Two excerpts follow (emphasis added):

It is not true that the underlying stuff sometimes behaves like a wave and sometimes like a particle.  It always behaves like itself, but we sometimes choose to measure one property, sometimes another.  When we choose to measure momentum, we find momentum clicks.  When we choose to measure position, we find position clicks.

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Why all the talk about waves and particles?  That has to do, in part, with the different kinds of detectors.  You can make an apparatus that triggers a momentum detector consistently at the same value p – so its histogram just has one tall bar reaching to 100% at p.  It is a fact of Nature that the same apparatus will trigger an array of position detectors in a wave pattern with a definite wavelength precisely equal to h/p, where h is the tiny “Planck’s constant”.  (Multiple trials have to be run to generate the histogram. See the figures on the next page.)  The wave is not in the underlying stuff, it is in the spatial pattern of detector clicks.  We do not – cannot – measure waves in the underlying stuff.  We can only measure detector clicks.  But when we hear the click we say “there’s an electron!”  We cannot help but think of the clicks as caused by little localized pieces of stuff that we might as well call particles.  This is where the particle language comes from.  It does not come from the underlying stuff, but from our psychological predisposition to associate localized phenomena with particles.  That predisposition is reinforced by the fact that in large scale Nature there are particles whose trajectories we can trace to an accuracy limited by the size of Planck’s constant.  This is how the Copenhagen Interpretation frames the wave versus particle issue.

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On The Copenhagen Interpretation of Quantum Mechanics

Symposium on "The Copenhagen Interpretation: Science and History on Stage"

National Museum of Natural History of the Smithsonian Institution

John Marburger Director, Office of Science and Technology Policy

March 2, 2002