Re: Is a fact something that has been proven?
- From: "Tracy P. Hamilton" <t_p_hamilton@xxxxxxxxx>
- Date: 9 Jun 2006 09:29:38 -0700
[above snipped accidentally by the %#@$ computer]
This paper reports a "delayed choice quantum eraser" experiment
proposed by Scully and Druehl in 1982. The experimental results
demonstrated the possibility of simultaneously observing both
particle-like and wave-like behaviour of a quantum via quantum
entanglement. The which path or both-path information of a quantum
can be erased or marked by its entangled twin even after the
registration of a quantum.
Well, that's a bit odd -- it seems that the paper is all about a
`quantum eraser' and `quantum entanglement,' and the
abstract is talking about a quantum and its quantum entangled
`twin'. There's nothing there at all about a double slit experiment
involving single electrons!
Until you demonstrate that the content of the entire article cannot
relate to double slit experiments, it's not "a bit odd".
A single electron is not entangled with another, so entanglement simply
cannot apply. QM behavior for multiparticle systems is only observed
when the wavefunctions for individual particles have coherence of
phase. The electron double slit experiment was purposely set up so
that the electrons did not interfere with each other!
In fact here's a statement from
http://www.benbest.com/science/quantum.html which indicates that the
experiment has a close correlation to the double slit experiment: "An
experiment involving circular diffraction, and the famous two-slit
experiment, illustrate the most perplexing behavior of subatomic
particles/waves."
[snip]
A two-body wavefunction is NOT the same thing as a one-body
wavefunction.
It may not be the same thing, but there certainly can be close
correlations made.
No. They both involve QM, and wave functions but that is about it.
Your
"quote" is about the double slit experiment and another experiment
which is ALSO one electron at a time. Of course those are very similar
to each other - the change is double slits vs circular hole.
I don't see this as disingenuous at all. He sees as strong correlation
and has confidence in that correlation.
You can't see the difference between "one" and "two".
Let me continue to look at Rhodes' discussion, just for fun,
to see precisely where he goes wrong. Immediately following
the paragraph that I initially quoted, there occurs the
following discussion:
1.TURN OFF THE ELECTRON DETECTORS AT THE SLITS. Suppose we
take our modified double slit set up -- with electron
detectors at the slits -- and leave everything
intact. But, we will conduct the experiment with the
electron detectors at the slits turned off, so that we
will not actually detect any electrons at the slits.
_The result upon analysis_: an interference pattern at the
back wall. So it seems that mere passage through the
electron detectors at the slits does not affect the
electron, so long as those electron detectors are not
functioning.
So far this is correct. This is indeed what happens in an
actual double slit experiment performed with uncorrelated
electrons. With the electron detectors turned off, an
interference pattern is observed.
Then Rhodes continues:
2.LEAVE THE ELECTRON DETECTORS ON, BUT DON'T GATHER THE
INFORMATION. Suppose we take our modified double slit
set up -- with electron detectors at the slits -- and
still leave everything intact. And we will keep the
electron detectors at the slits turned on, so that they
will be doing whatever they do to detect electrons at
the slits. But, we will not actually look at the count
of electrons at the slits, nor will we record the count
at the slits in any way, so that we will not be able to
obtain any results from these fully-functioning electron
detectors.
_The result upon analysis_: an interference pattern at the
back wall. So it seems that the electron detectors
located at the slits do not themselves affect the
electron, even when the equipment is fully functioning
and detecting (in a mechanical sense) the electrons, so
long as we don't obtain the results of these
measurements.
But this is *completely* wrong.
This is *not* what happens in an actual double slit
experiment done with single electrons. In fact, in such an
experiment, it doesn't matter *at all* whether we actually
record the counts at the slits or don't record the counts at
the slits, or whether we obtain any results at all from the
detectors at the slits.
If you are correct, then why does the Keith Mayes at
http://www.thekeyboard.org.uk/Quantum%20mechanics.htm (I found this
link here:http://en.wikipedia.org/wiki/Double-slit_experiment ) state
this:
"If we repeat the experiment, this time with only one hole open, the
individual photons behave themselves and all cluster round a point on
the detector screen behind the open hole, just as you would expect.
However, as soon as the second hole is opened they again immediately
start to form an interference pattern. An individual photon passing
through one of the holes is not only aware of the other hole, but also
aware of whether or not it is open!
This says nothing about detectors being on or off. You are unable
to tell the difference between the slits and the detectors!
The wave function for the double slit is PSI = psi(1) + psi(2).
The wave function of a single slit is PSI = psi (1).
The probability is | PSI | ^2.
Is | PSI | ^2 the same for these two situations? NOTE: no detectors!
The exercise is left to the student.
We could try peeking, to see which hole the photon goes through, and to
see if it goes through both holes at once, or if half a photon goes
through each hole. When the experiment is carried out, and detectors
are placed at the holes to record the passage of electrons through each
of the holes, the result is even more bizarre. Imagine an arrangement
that records which hole a photon goes through but lets it pass on its
way to the detector screen. Now the photons behave like normal, self
respecting everyday particles. We always see a photon at one hole or
the other, never both at once, and now the pattern that builds up on
the detector screen is exactly equivalent to the pattern for bullets,
with no trace of interference. As if that was not bad enough, it gets
even worse! We do not need place detectors at both holes, we can get
the same result by watching just one hole. If a photon passes through a
hole that does not have a detector, it not only knows if the other hole
is open or not, it knows if the other hole is being observed! If there
is no detector at the other hole as well as the one it is passing
through, it will produce an interference pattern, otherwise it will act
as a particle. When we are watching the holes we can't catch out the
photon going through both at once, it will only go through one. When we
are not watching it will go through both at the same time! There is no
clearer example of the interaction of the observer with the experiment.
When we try to look at the spread-out photon wave, it collapses into a
definite particle, but when we are not looking it keeps its options
open."
You need to understand what a physicist means by observer: a person who
sets up a measuring apparatus that physically interacts with the
system. You need to understand the basics of QM before taking the word
of some expert on metaphysics. For example, Wheeler proposes it is US
who created the universe, because we are intelligent beings who
observe! Do you really want to advocate that?
Another good read is here:
http://www.lifesci.sussex.ac.uk/home/John_Gribbin/quantum.htm
Once you've read this, please reflect on why Ross Rhodes
(bottomlayer.com) has been persuaded to say what he has said about the
detectors not being central to quantum theories strange "measurement
effect". It's not the detectors that sway the outcome, but the
intelligent observers themselves having knowledge of that which
happened quantumly.
Falsified easily.
[snip quote based entirely on this misunderstanding]
So, what we have here is an explanation of the Copenhaen interpretation
and it depends on intelligent beings having knowledge of an occurance.
Ross Rhodes didn't invent the Copenhagen interpretation of quantum
mechanics, but he certainly knows much about it.
In NO case is an interference pattern formed at the back
wall when the electron detectors are on. That's because
the electron detector influences the motion of the electron.
So you assert.
I tell you what. You run the experiment without a detector but with
the person
obtaining knowledge of which slit it went through. As stated above, we
can run the
experiment with the experimenter not looking at the results until long
after the experiment but with the detector on during the experiment.
No interference pattern is ever observed when there is even
the *possibility* of the experimenters measuring the path
that the electrons actually follow through the experimental
apparatus.
Do you have evidence that this is true?
It doesn't matter at all what the experimenters actually know about those paths.
But who set up the detectors? Those people with intent to measure
quantum things which happened, and they could always peak at the data
somewhere down the road.
So the cause would be after the effect. Again, a possibility in
coherent (linked) systems, but not in the double slit experiment.
The experiment done with single electrons in fact differs
critically from the experiments done with two quantum
entangled photons.
It differs in the following obvious way: there are two
photons involved, and these have initially, a common,
correlated two-body wavefunction. The detection of one of
the two photons at some later point in time in the `quantum
eraser' type experiments can thus be used to *deduce*
information about what has to have happened to the other of
the two photons, without necessarily destroying an
interference pattern.
This means that an entirely different analysis is required
for such experiments.
But there are definitely correlations which relate to the double slit
experiments. Here's another excerpt from
http://www.lifesci.sussex.ac.uk/home/John_Gribbin/quantum.htm
"But then Chiao and his colleagues ran the same experiment with
polarising filters in front of each of the two slits. Any photon going
one way would become "labelled" with left-handed circular polarization,
while any photon going through the other slit is labelled with
right-handed circular polarization. In this version of the experiment,
it is possible in principle to tell which slit any particular photon
arriving at the second screen went through. Sure enough, the
interference pattern vanishes -- even though nobody ever actually looks
to see which photon went through which slit.
Now comes the new trick -- the eraser. A third polarising filter is
placed between the two slits and the second screen, to scramble up (or
erase) the information about which photon went through which hole. Now,
once again, it is impossible to tell which path any particular photon
arriving at the second screen took through the experiment. And, sure
enough, the interference pattern reappears! "
This represents a close correlation to the double slit experiments when
it comes to the measurement effect. I don't know how you're getting
that it's unrelated.
It is a SINGLE particle experiment where there are detectors AND an
eraser.
The net effect is the same as if there were no {detectors plus eraser}.
That is the whole point of an eraser - to remove the effect of the
detector. When the knowledge is erased is it erased from a human
intelligence? No - because the human never knew the result because of
the way the experiment is set up!
We shall need to theoretically
describe the interactions of both photons with the
experimental apparatus to say what will happen in various
configurations.
I don't see what the problem is, though, when it comes to the
measurement effect and how it works similarly in both experiments.
That is abundantly clear. How many wave functions have you actually
computed in your lifetime?
[snip]
But it remains the case that all that is important in the
theoretical analysis is the interactions of the pair of
photons with the experimental apparatus itself. The state of
knowledge of the thinking observers is completely irrelevant
to the results of the experiment.
Then I suppose the Copenhagen interpretation of quantum theory is just
nonscience then. . . *rolls eyes*
Perhaps it is your understanding that is faulty?
We do not need to take into account the thoughts of the
experimenters when we do experiments in quantum mechanics.
I am not sure you've looked deep enough into this, because you don't
seem to understand the implications.
ROTFL!
[snip]
If I were you, and I wished to preserve my credibility, I
would modify my signature.
The signature stands. At this point, the credibility problem is with
you.
Did mind come before matter in the universe or matter come before mind?
Chapters 1 and 2 have your answer:
http://www.bottomlayer.com/bottom/reality/Intro.html
There's no answer to the question posed to be found on that
website. Instead there is a farrago of error and deception.
David
Or maybe you just don't like the implications of quantum theory. . .
Here's a suggestion: use google scholar to search for David E Kahana,
and see what fields he has published research in, and whether he might
know a little bit of QM. He is not going to toot his own horn as
authority, but there are experts on talk.origins even if you don't have
the wits to recognize them.
[snip signature credulously citing of something Ave1 agrees with, with
no background to evaluate its correctness]
Credulous - I can't think of a more apt adjective.
Tracy P. Hamilton
.
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