Ben Goertzel writes about:
> The questions I have regard the replacement of the Coincidence Counter (from
> here on: CC) in the  above experiment with a more complicated apparatus.
> What if we replace the CC with one of the following:
> 1) a carefully sealed, exquisitely well insulated box with a printer inside
> it.  The printer is  hooked up so that it prints, on paper, an exact record
> of everything that comes into the CC.  Then,  to "erase" the printed record,
> the whole box is melted, or annihilated using nuclear explosives, or
> whatever.

The CC is not what is "erased".  Rather, the so-called erasure happens
to the photons while they are flying through the apparatus.  Nothing in
the experiment proposes erasing data in the CC.  So I don't really see
what you are getting at.

> What will the outcome be in these experiments?

It won't make any difference, because the CC is not used in the way you
imagine.  It doesn't have to produce a record and it doesn't have to erase
any records.

Let me tell you what really happens in the experiment above.  It is
actually not so mystical as people try to make it sound.

We start off with the s photon going through a 2 slit experiment and
getting interference.  That is standard.

Now we put two different polarization rotations in front of the two slits
and interference goes away.  The web page author professes amazement,
but it is not really that surprising.  After all, interference between two
photons would typically be affected by messing with their polarizations.
It is not all that surprising that putting polarizers into the paths
could mess up the interference.

But now comes the impressive part.  He puts a polarizer in front of the
other photon, the p photon, and suddenly the interference comes back!
Surely something amazing and non-local has happened now, right?

Not really.  This new polarizer will eliminate some of the p photons.
They won't get through.  The result is that we will throw out some
of the measurements of s photons, because if the p photon got eaten
by its polarizer, the CC doesn't trigger as there is no coincidence.
(This is the real reason for the CC in this experiment.)

So now we are discarding some of the s photon measurements, and keeping
some.  It turns out that the ones we keep do show an interference pattern.
If we had added back in the ones we discarded, it would blur out the
interference fringes and there would be no pattern.

The point is, there is no change to the s photon when we put the polarizer
over by p.  Its results do not visibly change from non-interference
to interference, as the web page might imply.  (If that did happen,
we'd have the basis for a faster than light communicator.)  No, all
that is happening is that we are choosing to throw out half the data,
and the half we keep does show interference.

The only point of the CC, then, is to tell us which half of the data
to throw out of the s photon measurements.  Destroying the CC and all
of the other crazy things you suggest have nothing to do with the
experiment.  The CC is not what is "erased" and it does not create a
permanent record.  It is only there to tell us whether a p photon got
through its polarizer or not, so that we know whether to throw away
the s photon measurement.

Hal Finney

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