Re: Critical size (or Mass?) of the particle at which Macro transitions to Micro (Ref: Double Slit Experiment)

The book has a good detail of the experiment though I will just brief
the concept here...
This is the variation of the double slit experiment...wherein there is
a light source and the light is impinged onto a beam splitter that will
send the beam one way or the other. This beam is in turn focused onto a
screen by reflectors placed on either side...the book has a diagram
that makes it very clear to understand this setup. Now something called
as "downconverter" are placed in the path of the beam from the
reflector to the screen. What this will do is to take an input as one
photon and produces 2 identical ( twin) photons...The twin photon is
called as idler photon. By detecting the idler photon, we can clearly
know if the photon has travelled through the right reflector / left
reflector without disturbing/detecting the path of the original
photon...When the idler photon was detected and hence indirectly it was
known if the photon travelled through the left / right relfector, to
the surprise there was no interference pattern observed!! The
explanation for this given is that out of the many possible different
history paths, one history path has gained significance because of the
fact that it got observed and hence the probability wave got
collapsed...so no interference was observed. When the idler detector
was removed, interferece pattern appeared!! ( again the origin photon
was not disturbed!)

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