On 12/2/2012 10:43 AM, John Clark wrote:
Now it's usually down is some kind of detector that amplifies the effect of
electron. Neither one has anything to do with destroying the electron.
You don't need to destroy the electrons you just have to arrange things so that the
effect the 2 electrons have on their universes is indistinguishable, then the 2
universes will merge back together and interference is produced. If you fire electrons
at 2 slits and have sensitive detectors mounted near one slit so a record is made of
which slit each of the electrons went through then the universe splits into two each
time a electron is fired and it does not recombine because the 2 universes are
different, one has a record of the electron going through slot X and the other has a
record of it going through slot Y, and so no interference is produced on the
photographic plate. But if there is no detector near a slit or no record kept of which
slit it went through then the universe still splits when it goes through the 2 slits
because the 2 are different, the electrons are on slightly different trajectories, but
when the electrons hit the metal wall there is no longer any detectable difference
between the 2 universes and so they merge back together, but there is still evidence
that the electron went through slot X only and evidence it went through slot Y only and
this produces the interference effect.
>> the walls would not be the same and so the 2 universes would not be
and so they would not merge. However if it was a metal wall the
just join the general sea of free electrons in the metal and there is
even in theory to tell one electron from another. So the walls would
same charge and mass.
> But in an entangled electron pair experiment (EPR type) detecting the
path of one
electron destroys the interference pattern on the other leg.
But also just absorbing one electron destroys the interference on the other
Yes, if one electron is absorbed into the electron sea of a metal and the other electron
is not then obviously the 2 universes remain different and so do not recombine and so no
interference is found.
> To maintain the interference you have to absorb the electron at the focal
a lens so that you not only don't detect the which-way information, you
I don't quite know how a lens enters into this but yes, if the which-way information is
not recorded or the record erased by whatever means then the 2 universes are identical
and merge and a interference pattern is seen.
Apparently I have not explained it in sufficient detail; I thought you probably knew the
experiment and my rough description would be enough to remind you. It's generally
referred to as the Delayed Choice Quantum Eraser and it has actually been performed with
photons rather than electrons: http://xxx.lanl.gov/pdf/quant-ph/9903047.pdf There's also
a web version by the authors with more pictures and explanation and less math:
http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm . But my point is that
you're wrong when you write, "...if the which-way information is not recorded or the
record erased by whatever means then the 2 universes are identical and merge and a
interference pattern is seen." These two cases are different. If the information is not
recorded, e.g. the photon is absorbed or is just let travel off to infinity the
interference is lost. It is only when, by interposing the lens in the right place, the
information is literally erased and the interference pattern is seen.
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