X-Message-Number: 14170
From: "John Clark" <>
Subject: The Identity Of Indiscernibles 
Date: Tue, 25 Jul 2000 12:15:23 -0400

Yvan Bozzonetti in  #14147 Wrote:

    >If (say) two atoms are widely separated in space, then they
    > ARE distinguishable both in principle and in practice.

How? If we were talking about apples and oranges it would be easy to tell if
I switched them around, but I claim I instantly exchanged two carbon atoms.
Prove I didn't.

    >If I recall well, space coordinates are included in the quantum state

How could it be, the more you know about the coordinates of a particle the
less you know about its velocity. If you know exactly where something is
right now you'll have absolutely no idea where it will be an instant from now.
What quantum mechanics describes is the wave function, and that's
much more abstract than just coordinates, it's not even a probability,
it's the square root of a probability.

    >so that two objects at two different places can't be in the
    >same quantum state.

Actually,  two fermions at the same place can't be in the same quantum state.

It's called The Pauli Exclusion Principle and it tells us that  2 identical 

can not be in the same orbit in an atom. It's the reason chemistry is the way it
is and

it's the reason matter is not infinitely compressible, it's why everything 
doesn't collapse
into a point.

    >Only bosons are able to pile up at the same place


     >and so may be indistinguishable

Fermions are indistinguishable too. If two things are distinguishable that means
if I

exchange their positions a detectable change will happen in the system. There is

way you could tell if I exchanged the position of two electrons so they're 

In essence this means that electrons don't have scratches on them to tell one 

      John K Clark        

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