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Re: Particle Position



Hi all-
Jim Green asks:
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We all understand that the position and momentum of a particle must satisfy
the Heisenberg Uncertainty Principle. But what does this mean? Is it
that _I_ can not know x & p with better precision? --- that the
infinitesimal _particle_ "knows" exactly where it is and how fast it is
going but an observer can not -- ie that the particle does indeed have an
exact locations and velocity, but the observer just can't know what it is?
OR does it mean that the particle is of finite size such that it takes up
a space of delta x?

Consider a particle in a 1 d box -- say of length L: How many locations
along L can the particle occupy? Assume any needed additional information.

Likewise, consider a 3 d box of sides L: how many places in the box can the
particle occupy?

Just me over here in my little corner.
************************************
Here is a hint.
It is now experimentally verified that a beam of electrons that passes
through two slits interferes with itself. One can watch the interference pattern
grow with time if the interval between electrons is sufficiently large (this is
the experiment that was suggested by Feynman). I saw a movie of this experiment
at a colloquium a year or two ago.
So in order for Jim's question to have meaning, he has to tell us what
he means by a "particle".
Regards,
Jack


"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography