On Mon, Dec 3, 2012 at 3:26 PM, meekerdb <meeke...@verizon.net> wrote:

> > That's where you're wrong; read the paper more carefully.  If you record
> the which-way the interference is lost. [...] The interference pattern
> occurs *only* if the which way information is *erased*

Nope, you've got it exactly precisely backwards yet again. I quote from


" If the experimenters know which slit it goes through, the photon will
behave as a particle. If they do not know which slit it goes through, the
photon will behave as if it were a wave when it is given an opportunity to
interfere with itself. "

Or you don't like Wikipedia

*" *when we don't know which slit the photons are going through, we get a
wave interference pattern. When we do know which slit each photon traveled
through, no interference pattern."*

*Or maybe* you prefer this:

"One can set up a measurement to "watch" which slit a photon goes through.
It can be determined that the photon went through one slit and not the
other.  However, once this is kind of measurement is set up, the photons
will  no longer collectively produce a nice pattern of bright and dark
spots.  Instead they will strike the screen in one big bright spot, as if
there were only one slit instead of two."

Or perhaps this:


"If one neglects to observe which slit a photon passes through, it appears
to interfere with itself, suggesting that it behaves as a wave by traveling
through both slits at once. But, if one chooses to observe the slits, the
interference pattern *disappears*, and each photon travels through only one
of the slits."

*Actually you don't need other people to tell you this you can figure this
out on your own; if you only have one slit then obviously you know which
slit the photon went through and there is no interference pattern. But if
you have 2 closely  slits then you don't know which slit the photon went
through and you get a interference pattern.

  John K Clark



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