MadSci Network: Physics

Re: A problem with theHeisenberg uncertainty principle

Date: Sat Aug 30 15:03:23 2003
Posted By: Dwayne Rosenburgh, Senior Electronic Engineer
Area of science: Physics
ID: 1062260108.Ph

In quantum mechanics, the uncertainty principle states that, for isolated 
systems involving small distances and momentum it is impossible to know, 
exactly, the instantaneous position and momentum of the particles.  I 
think that your quandary can be addressed by examining how do we “know” 
something.  In general, we know things as a result of mental (via 
philosophy, theory, calculation, etc.) or physical (via observation, 
experimentation, etc.) processes.  If we are doing calculations, we shall 
be able to make predictions only of the probable behavior of particles.  
If we try experimentally, for example, to determine whether radiation is a 
wave or a particle, we find that an experiment which forces radiation to 
reveal its wave character strongly suppresses its particle character, and 
vice versa.
[References: Elmer Anderson.  1971. Modern Physics and Quantum Mechanics.  
Philadelphia: Saunders.
Eisberg, Robert, and Robert Resnick.  1974.  Quantum Physics of Atoms, 
Molecules, Solids, Nuclei, and Particles.  New York: John Wiley & Sons.]

Therefore, as I see things, it does not matter if you are doing an 
experiment or doing a calculation.  In either case, you are attempting to 
know something about a particle.  The uncertainty principle says that we 
cannot, simultaneously, precisely, know everything about the particle.  We 
must express the particle in terms of probabilities.  Therefore, we cannot 
measure or calculate the speed with certainty.  We can say that speed is x 
m/s, with a probability of, say, 0.9.  There most likely is a definite 
(certain?) speed associated with the particle – we just cannot know it, by 
calculation or measurement.

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