On Sun, Oct 20, 2019 at 8:32 AM John Clark <[email protected]>
wrote:
On Fri, Oct 18, 2019 at 6:31 PM Bruce Kellett
<[email protected]> wrote:
_> if you erase or not the welcher weg information 'before' the
signal photon hits the screen, then presumably some, presently
unknown physics, could send this information to the screen and
influence the result there._
So you admit it. If you continue to insist Many Worlds do not exist
then to explain an experiment that has been performed many times you
must postulate new physics and mess with Schrodinger's Equation.
Not at all. The results of the experiment are easily explained
within the structures of conventional quantum mechanics, whatever
interpretation one wishes to adopt. There is nothing mysterious here.
There is a lot of mystery here! In 2007 entangled photons were sent 89
miles between La Palma and Tenerife, the decision to erase or not to
erase was made in less time than it took for light to travel those 89
miles and hit the detector:
Quantum Spookiness Spans the Canary Islands [1]
The last potential loophole, the freedom of choice loophole, was
pretty much closed in April 2018. That loophole says that maybe your
measurement settings that chose between erase and don't erase are not
really random after all, there might be a deterministic process that
makes the choice and misleads us:
Quantum entanglement loophole quashed by quasar light [2]
They state that:
_"Arguably the most interesting assumption is that the choice of
measurement settings is “free and random,” and independent of any
physical process that could affect the measurement outcomes. As Bell
himself noted, his inequality was derived under the assumption “that
the settings of instruments are in some sense free variables, say at
the whim of experimenters, or in any case not determined in the
overlap of the backward light cones.”_
So to close this loophole they didn't use a standard random number
generator to make the choice to erase or not erase the information in
the short amount of time it takes light to travel those 89 miles
before (yes BEFORE) the photon hit their detector; instead they used
the light from a distant quasar to make the decision, so if its a
conspiracy to mislead us (as Superdeterminism says) it's a grand
conspiracy indeed. They conclude:
"This experiment pushes back to at least 7.8 billion years the most
recent time by which any local-realist influences could have exploited
the “freedom-of-choice” loophole to engineer the observed Bell
violation"
It seems that the fundamental problem here is that you are confusing
tests of Bell's inequality on entangled particles with delayed choice
experiments. These are different things.
If you decide to erase or not to erase after the photon passes
the slits but before it hits the photographic plate then to explain
the results you've either got to embrace Superdeterminism, backward
causality or Many Worlds.
_> No, you have got it wrong here. No need for any of this. _
That's it? That's all you've got to say? If you have a explanation for
all the odd stuff coming from the 2 slit experiment that has been
bedeviling scientists for a century, a explanation not involving
Superdeterminism, backward causality or Many Worlds then please
enlighten a poor mortal such as myself.
If you are confused by this, then read the explanations that we have
offered, by Carroll or Wikipedia.
[...]
Because the choice to erase or not to erase is delayed until long
after the photon has passed the slit, it could be made a billion
years after it passed the slit, and the decision could be made one
nanosecond before the photon hit the photographic plate, but it must
be BEFORE or you will see nothing new or interesting.
Exactly what do you think that you will see in that case? and why do
you think it uninteresting?
[....]
_> Yes, of course you do: you just select the subsets of photons
that were quantum-erased by passing the left polarizer
(respectively, the right polarizer) to see the interference
patterns emerge from the apparent no-interference blob._
Ah Bruce.....in that case you are very obviously erasing the which
way information BEFORE it hits the screen or photograph that you're
looking at!
You will have to explain that to me. I pass the photon through the
slits and entangle it with some spin state that will be spin-up for
the left slit, and spin-down for the right slit. I store these
particles for a billion or so years until long after the original
photons have hit the screen and have been recorded photographically. I
then decide to measure my stored "which-way particles". If I measure
them in the up-down basis, I can tell which slit the photon went
through, so I do not see any interference. However, if I measure my
stored particles in an orthogonal basis, such as the left-right basis,
I have quantum erased the which-way information, so I do see
interference by selecting either the left- or right- polarized
particles. The decision of which to measure was clearly made *after*
the original photons hit the screen, so it is not erasing the
which-way information *before* they hit the screen.
You say you are not an expert on this.....I think that has become very
clear.....
