Re: Double slit experiment questions

David Wimp wrote:
> In a double slit experiment where "which path" information is provided
> and one particle is sent through at a time, do all particles go through
> one slit or the other or do some go elsewhere?
> What happens if a detector is placed in one of the slits but not the other?

You are actually asking a lot of overlapping questions here, and they
are not all the same but not very different. You will tend to get
better
responses if you don't "shotgun" this way.

In the double slit experiment, if you obtain information about which
slit, then the two-slit diffraction pattern does not result. What does
result depends on exactly how you get the "which slit" information.

For example: If you close one slit, then the diffraction pattern
changes
to a one slit pattern. If you put a detector near one slit such that
you
can tell which slit the particle goes through, then you get two one
slit
patterns added rather than the double slit pattern.

If you ask "do all particles go through one slit or the other" then you
run right into the heart of quantum mechanics. The answer is, you
can't ask those sorts of questions. What happens is, the wave function
evolves and tells you (through the usual mechanism of QM) what to
expect at each observation. That depends on the details of the entire
set of available paths to the observation, including such details as
whether there is a detector there or not.

A good introductory explanation of this can be found in Feynman's
book "QED: The Strange Theory of Light and Matter" which is
available from Amazon for $10.85 plus shipping.
Socks

.

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