On 10/21/2019 7:40 AM, John Clark wrote:
On Sun, Oct 20, 2019 at 6:24 PM Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
/> It seems that you think you will just see Young's interference
fringes whatever you do *after* the record is made at the screen.
But that is false,/
Like hell it is! Do you actually think Zeilinger and other
experimental physicists claim they can make a photograph change before
your eyes AFTER it has been taken like something out of Back To The
Future? It was a fun movie but that's not the way things work.
> as has been demonstrated in many experiments.
That statement is worse than false, you're talking logical nonsense.
The photograph itself contains which way information, if the photo has
no interference pattern then you know the photon went through one and
only one slit, and if it does have a interference pattern then you
know the photon went through both slits. So if you have the ability
and really and truly want to destroy the which way information
*_AFTER_* the photon hits the photographic plate (or screen) then you
MUST destroy the photograph too and do so before anybody looks at it.
In 1801 Thomas Young was not a fool and that's why he had no desire to
destroy his screen *_BEFORE_ *he looked at it, and that's why he saw a
interference pattern; but it's true if he had he would have not seen a
interference pattern, he would not see anything at all because there
would be no screen to look at because he destroyed it.
You apparently have still not read Carroll's blog. He discusses exactly
what happens when you erase the welche weg after the photons have hit
the screen, and it doesn't involve erasing the photograph.
In figure 3 of the Xiao-song et al paper, Carroll's example is
equivalent to noting, in the lower half of the figure which spot goes
with which path, but then not partitioning the spot's into different
curves. They add to a flat line as in the upper figure. But after
the fact you can use the recorded information to recover the sinusoidal
distributions.
Brent
/> It does not matter whether you make the choice between
which-way and quantum erasure before or after the photons hit the
screen./
There is one difference and it's a rather large one. If you have no
which way information at all (like Thomas Young) or if you make the
erase/don't-erase decision *_AFTER_* the photon passes the slits but
*_BEFORE_* it hits your photographic plate or screen or electronic
detector (like Zeilinger and other experimentalists in the 21st
century) then your experiment produces data; BUT if you really insist
on erasing all the which way information *_AFTER_* the photon hits
your photographic plate or screen or electronic detector then your
experiment will produce NO data,
If will if you keep track of the erasure result for each point on the
screen. Although I'm curious about the implicit asymmetry in Carroll's
example.
not one bit of it, because you must destroy your photographic plate or
screen or electronic detector. And you can't look at it before you
destroy it because then you would have the which way information.
/>That is what the experiments of Zeilinger and his associates
show. These are the experiments where the decision to erase or not
were made 144 km away from the lab in which the interference
measurement was made./
And why do you think the experimenters thought it was so important to
make the distance between the slits and their detector that long?
Because light is very fast and for practical reasons it takes time for
experimenters to make the erase/don't-erase decision and it takes time
to actually make the erasure, if the distance was as long as 144 km
then even though light moves fast they still had enough time to do all
that BEFORE the photons hit their interference measurement detector.
>> If you place a polarizing filter oriented in the left-right
direction over one slit and a polarizing filter oriented in
the up-down direction over the other slit and shine a light
through both slits and onto a screen you will not see a
interference pattern on that screen because the filters ha ve
encoded information onto the photons about which slit they
went through. However if you then place a third polarizing
filter, this time oriented at a intermediate 45 degree angle,
after the slits but *_BEFORE_* the screen then "the
interference pattern emerges from the apparent
no-interference" because that 45 degree filter has erased the
which way information that was encoded on the photons
*_BEFORE_* any photons hit the screen that you're looking at.
/> That is not the experimental set-up of the Zeilinger et al.
assessment of delayed choice. Read the sources I have quoted......./
Yes Bruce you have quoted sources, but I am not at all impressed. I do
not believe for one nanosecond you understand anything in them and I
doubt if you've spent more than 45 seconds skimming a Wikipedia
article about them.
John K Clark
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