Re: Double Slit variant
From: Thomas Trotter (thomastrotter2005_at_juno.com)
Date: 11/19/04
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Date: Fri, 19 Nov 2004 19:29:24 +0000 (UTC)
blake.winter@houghton.edu (Blake Winter) wrote in message news:<87423d2a.0411121006.3602e941@posting.google.com>...
[snip]
> In other words, we change the probability
> distribution on the experiment in the left by placing a detector in
> each slit. From conservation laws, we can then figure out which slit
> the photon on the right went through. Then the probability
> distribution on the right should no longer correspond to the usual
> double slit pattern.
>
> This seems reasonable to me (as in, I don't see why my conclusion is
> wrong). However, it does seem to violate locality in a noticeable
> way, because by measuring the probability distribution on the right,
> we can tell whether a measurement of which slit is made on the left
> without comparing our data from the right with the data from the left.
> This would open the possibility of sending real information faster
> than light, which seems like a bad thing. So my conclusion would be
> offhand that this couldn't happen, but I can't actually figure out
> quantum mechanically why this wouldn't work. Are there any ideas?
Send the light to the left through 1 slit. Send the light to
the right through 2 slits. You'll get no interference on the left
and interference on the right. Then do it the other way around.
Same result, reversed. A single slit produces a single wave and,
thus, no interference. A double slit produces two waves which
interfere with each other. No useful information is passed between
the left and right sides, because no signal or disturbance of any
sort is passed between the left and right sides. That's really all
there is to it.
Now, there are all sorts of ways to complicate things so that it
*seems* like one side is affecting the other, but it's just a
result of the way the data is processed.
Quantum entanglement really has nothing whatever to do with
causal influences between the entangled entities themselves.
Their relationship is purely correlational -- the analysis
of common properties (from a common source) via a common
observational context.
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