Heisenberg himself may have initially offered explanations which suggested this view. [...]Such explanations [of the Uncertainty Principle], which are still encountered in popular expositions of quantum mechanics, are debunked by the EPR paradox, which shows that a "measurement" can be performed on a particle without disturbing it directly, by performing a measurement on a distant entangled particle.[...]The more modern uncertainty relations deal with independent measurements being done on an ensemble of systems.
This statement is a semantic trap and according to the Delayed Quantum Eraser Experiment is dead wrong... looks good though if stated with "authority".
If I was to give a historical equivalent to certain aspects of quantum theory it would be the Orbits of the Planets according to Ptolemy.
Wikipedia: Deferent and epicycleThe "Universe" is a shell with the fixed stars attached and a number of wanderers (Planets) which moved according to a "perfect" scheme of
epicycles. When discrepancies were found a new "epicycle" was invented to account for the discrepancy. These "epicycles" were "postulates". It seemed a small price to pay for such perfection. Indeed it worked "brilliantly" and predicted the orbits on the shell of our Universe
very accurately... It was so good it must have been right. You just needed a lot of hand tooled variables to make it work with a very high degree of precision according to the times. Does this sound familiar to you?
You cannot make a single measurement on an "ensemble of systems" without apparently collapsing it, once collapsed you need to be able to say just what you really have accomplished here. For a start the answer Heisenberg gave is based on a view of a particle that is not the same as the view of a particle that Neils Bohr or Albert Einstein understood. Bohr proved Einstein was wrong because Einstein was insisting on "local realism". What was not stated is that the acceptance of this position ushered in the concept of "non-local unrealism". Is this position any better? These were early days and as I see it we are still in those early days because this discussion shows that the argument has not advanced beyond this simplistic point of view. It is based on a view of a "particle" being a little "billiard ball" that has neither any divisible character nor extension in space nd is described by the roll of dice. They were also "point particles" and all the maths was centered on this "view".
In order to discuss this point of view all parties must accept the commonly accepted postulates about the "nature" of the quantum, none of which were rooted in realism, they were simple expediencies and were not a rigorous mathematically argued phenomenological "Theory". These are usually stated as an acceptance of a "quantum number"... actually several of them, the principal of which was the principal quantum number N (defining the primary conserved property of the system and was a number that described the "orbit" of an electron in Bohr's Theory). These quantum numbers define conserved states of a quantum system. This is fine up to a point. The states make no allowance for "entanglement" that is a "non-local" influence. It is entirely "revisionist" to suggest that Quantum Theory predicted "quantum entanglement"... it certainly did not but it was the result of experiment on a lab bench that settled the question we have come to understand as "entanglement". This is because of the locality in that assumption of the "billiard ball" point particle. Once and for all the point was no longer tenable and it showed that a single particle actually interferes with itself even across "infinite" space. Recall that the maths related to point particles as sources mathematically "blew up" when it was extrapolated into the sources. Renormalization was required to bring these functions into a common ball park.
This worked very well with quantum electrodynamics but the problem once again turned up with quantum chromodynamics and another level of renormalization was required. By this time some were having doubts that this was the way to proceed because they were all having "deja vu". For one there was Roger Penrose and for another there was David Bohm. Before the answer was found the "differences" were stitched up in endless conferences to settle issues on this "measurement problem" and arrive at a "Standard Model" agreed to by a Committee. It is built like "Topsy"... you just add parameters to the model when it falls short of the correct result. It is my view that an internally consistent methodology had been "agreed on" to remove the "measurement problem" from all issues of quantum reality. Today we do not make those "measurements" because this can lead to inconsistencies and to differences in "interpretation". I am not just stating this to be contrary, it is a very big problem that still lies in the heart of quantum theory that has become "accepted" and in the "too hard" basket to be able to fix so far down the "Quantum Yellow Brick Road" to the Emerald City and the "pay-dirt".
Wikipedia: Measurement problemAs a direct result of this quantum fairyland we can make these weird and "miraculous" statements like this in the popular press...
PhysOrg: Quantum computer solves problem, without runningThere is really nothing "amazing" about the quantum Zeno effect if "particles" are no longer point sources and are resonant harmonic phenomena that will fill a cavity regardless of where a so called "particle" ends up being detected. The question of the moment is what cavity is being filled and what wave is linking all those particles together across space?
QUOTE (Wikipedia: Measurement problem+)
Different interpretations of quantum mechanics propose different solutions of the measurement problem.
* The old Copenhagen interpretation was rooted in the philosophical positivism. It claimed that the probabilities are the only quantities that should be discussed, and all other questions were considered as unscientific ones. One could either imagine that the wavefunction collapses, or one could think of the wavefunction as an auxiliary mathematical tool with no direct physical interpretation whose only role is to calculate the probabilities. While this viewpoint was sufficient to understand the outcome of all known experiments, it did not explain why it was legitimate to imagine that the cat's wavefunction collapses once the cat is observed, but it is not possible to collapse the wavefunction of the cat or the electron before it is measured. The collapse of the wavefunction used to be linked to one of two different properties of the measurement:
* The measurement is done by a conscious being. In this specific interpretation, it was the presence of a conscious being that caused the wavefunction to collapse. However, this interpretation depends on a definition of "consciousness". Because of its spiritual flavor, this interpretation was never fully accepted as a scientific explanation.
* The measurement apparatus is a macroscopic object. Perhaps, it is the macroscopic character of the apparata that allows us to replace the logic of quantum mechanics with the classical intuition where the positions are well-defined quantities.[...]The Bohm interpretation tries to solve the measurement problem very differently: this interpretation contains not only the wavefunction, but also the information about the position of the particle(s). The role of the wavefunction is to create a "quantum potential" that influences the motion of the "real" particle in such a way that the probability distribution for the particle remains consistent with the predictions of the orthodox quantum mechanics. According to the Bohm interpretation combined with the von Neumann theory of measurement in quantum mechanics, once the particle is observed, other wave-function channels remain empty and thus ineffective, but there is no true wavefunction collapse.
Wikipedia: Measurement problemThis Bohm Interpretation bridges a gap between theories that sweep old problems under the carpet and an attempt to substitute "dynamics" of a particle with the known apparent statistical behavior of the particle. It does this using an intermediate configuration space to map between the two domains... the theory is obviously highly non-local and solves in physics what was not able to be solved in using quantum theory and the Copenhagen Interpretation.
It goes without saying that Bohmian Mechanics is a half-way house to a physics in higher dimensions, since we are speaking of real particles executing dynamics in a real space that always exists. This space is not coincident with the normal 4D spacetime but is a kind of "quantum space" of its own that exchanges "information" through "harmonic and resonant processes". This is what I have been arguing for in this thread. It is not without physical or experimental justification. As I have previously stated it is very difficult to have a "resonance" in a probability density which is a pure scalar. It is also very difficult to see what kind of "cavity" is resonating unless it has strict bounds in a pure physical sense.
Returning to Quantum Physics, these "quantum numbers" are projections from a Hilbert Space of a hypothetical Riemann Sphere onto a flatspace.
Wikipedia: Quantum numberPlease read about the point that each of these conserved eigenstates are described by a Hamiltonian and confines all energy processes to the "system".
Here an applet shows quantum numbers of "l" and "m" on the Surface of a Riemann Sphere... (Other quantum numbers have a similar derivation)... We have been discussing some of these (especially those for a Photon) previously in this thread...
Spherical Harmonics of the Hydrogen AtomPlease choose Psi+ or Psi- and do not choose "probability" (the projected "density" quantity) but the "unprojected" Psi which indicates "imaginary" phase. The standard explanation does not provide this phase, it provides the "probability" that contains no non-local connections. I can't show you the exact analog of this in higher dimensions but in two dimensional projection the phenomena can be seen here...
QUOTE (Wikipedia: Möbius transformation+)
Stereographic projectionThese images show Möbius transformations stereographically projected onto the Riemann sphere. Note in particular that when projected onto a sphere, the special case of a fixed point at infinity looks no different to having the fixed points in an arbitrary location.
Wikipedia: Möbius transformationThis specific example is not entirely convincing but consider propagating photons as being determined using this "projection method". This image is two dimensional representation (the surface of a sphere and the Cartesian flatspace) and our Universe is apparently three dimensional (plus time) so it would be much more difficult to draw in higher dimensions. This indicates how it may be possible with some imagination to connect different dimensional spaces with our own 4D spacetime. If we are speaking about "dynamics" as we understand them we are certainly dealing with other equivalent 4D spacetimes. This allows a continuum of physics as we know of it in our current 4D space. This is best handled using some kind of String Theory, unfortunately it is very hard to find one of these in the literature. Why should we choose this scheme to view our Universe?... Simply because it works experimentally and tells us more about the geometrical relationships that relate the physics of the quantum realm. Quantum theory says ... don't you worry about all that and just "shut up and calculate". Fine but it leads to a dead end in physics. What is that dead end? A loss of dimensionality... confining our maths to the hyper-surface of a 4-dimensional spacetime. It is a choice that leads to the current situation but without more dimensions we will not be able to proceed.
So I have been quoting quite a number of recent results which come as a surprise to many from the literature recently. Have a look there are lots more. The "old ways" have a flaw and yet there appears to be no way to proceed. Your quote was "The more modern uncertainty relations deal with independent measurements being done on an ensemble of systems". The language used suggests that Bell's Inequality "debunks" all other interpretations of "non-classicality". My view is that you can be still highly non-classical and still develop theories that are non-local yet work within the framework of spacetime... but not without added dimensions (and other spacetimes). This immediately "debunks" the Copenhagen Interpretation in favor of "hidden variable" theories that can be shown to be "complete". These result in different "systems". As I have said that the collapse of these "ensembles" is a argument in its own right to seek alternative reasons why the Universe is non-local yet behaves locally in so many other ways. To me this is simply the way higher nearby dimensions project and connect into our "flatspace". Perhaps this is the appearance of "Many Worlds" but it is not a "no World" interpretation.
Cheers
Confused2
1st October 2006 - 10:01 AM
Hi Good_Elf,
QUOTE (me+)
1/ Why is the result of the 2 slit experiment not completely predictable when the photon can pass freely through the slits without being detected, I'll call this the two slit interference result.
2/ Why does detection of the photon at one or other slit (as it passes) change the statistical outcome from double slit to that of a single slit (That's the easy one?)
3/ Detecting (later) which slit the photon passed through apparently changes the experiment from a 2 slit interference experiment to a single slit experiment.
If the answers to 1/ and 2/ do not predict the answer to 3/ then our answers to 1/ and/or 2/ are wrong. We need to keep refining our answers to 1/ and 2/ until they predict 3/
Unfortunately answers to 1,2, and 3 have to fit in with everything else we know about reality.
QUOTE (Good_Elf+)
[To: Why is the result of the 2 slit experiment not completely predictable?]
1/ It is completely predictable ... just plug in the "exact" relationships that will be measured and that will be the "exact" solution.
QUOTE (Good_Elf+)
[To:The result (shown) is absolutely predictable. I just don't see analogue for the Uncertainty Principle here. ]
Well this is very hard to show but it is in the measurement of the system that you will have uncertainty
To clarify your PoV I introduced a question about quantum tunneling. This is because the answers to 1,2 and 3 ought to be consistent within the thread and also consistent with other well known phenomena.
It would be perfectly valid to suggest that tunneling is a different sort of quantum effect and subject to different quantum rules. At first sight I have to admit that any explanation of quantum tunneling would appear to be incompatible with either of the statements I have quoted. Perhaps you can clarify the point .. perhaps not.
This is a very difficult problem .. to explain it I see no disgrace in going round several times or even failing altogether.
-C2.
Confused2
1st October 2006 - 01:52 PM
Imagine you have two potential wells divided by a lowish potential barrier. We introduce an electron into (say) the left hand well .. leave to simmer .. where is the electron?
C2.
Good Elf
1st October 2006 - 04:24 PM
Hi Confused2,
QUOTE (C2+)
Unfortunately answers to 1,2, and 3 have to fit in with everything else we know about reality.
Believe me, I have very carefully considered these points and I am well aware that they are in total agreement with everything that is known about these issues (to the limit of my understanding of the issues). Clearly only photons that are unobstructed will pass through the slots, it is essential that you do not detect any photons used to create an interference pattern "prematurely". The "detection" of a particular photon will prevent the same photon interfering with itself. A "detection" will be where the photon is "absorbed" so it will no longer partake in the final interference pattern. I disagree with the interpretation you have there for item 3. In this case I have a point of emphasis and "nit picking" on my part. Anything which strips the qubit from a free photon reduces it to a "ballistic" particle and it will not diffract (will no longer carry the phase information it originally was carrying from the source). Of course for most photons this does not happen since it is usually absorbed by a secondary target. In the case of
entangled photons this can be illustrated by noting that an observation on one photon is an observation on the other photon simultaneously... along the wavefront at "infinite speed"... the phase velocity. If you then determine the "position" of one of the photons it destroys the interference pattern (this phase information) .... completely.
QUOTE (Good Elf+)
[To: Why is the result of the 2 slit experiment not completely predictable?]
1/ It is completely predictable ... just plug in the "exact" relationships that will be measured and that will be the "exact" solution.
Exact solutions are mathematically exact and undisturbed. Any measurement or observation will change the systems. You will not know the exact path of an individual photon but the bosonic system is the wave aspect of it and it is as "exact" as things will ever become because the "boson" is a single state. Remember you do not "see waves" you need to detect them. You are referring to "particles" and I am not. I am thinking about the surface of the sea and seeing a trough propagating as a soliton.
QUOTE (C2+)
Imagine you have two potential wells divided by a lowish potential barrier. We introduce an electron into (say) the left hand well .. leave to simmer .. where is the electron?
Why an electron... why not a photon? The only difference is the group velocity and the phase velocity have the same speed... the speed of light. The effect is the same though... the photon or the electron "wave" explores the entire cavity and occupies it. You want me to tell you where the spin quanta is centered around... a still point is it not? An eye of the Hurricane.
http://ist-socrates.berkeley.edu/~cywon/Quantum.htmlThe electron and the photon can and will interfere with itself and in the case of an electron it can also interfere with other electrons as well but pairs of electrons are "Cooper Pairs" which are "bosons" when you add up the quantum numbers and are "special" as we all know.
Pretty colors represent phase... 30 Kepler Periods of an electron in a "circular orbit".
Motion of a Circular Orbit Wave Packet (electron)Cheers
Confused2
3rd October 2006 - 03:06 PM
Hi Good_Elf,
We could argue about whether your pictures are better than my pictures .. but unless we can actually see what's going on .. we're no further forward.
Re 3/ I hope we're talking about the same experiment ..!
http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9903/9903047.pdfDiscussed on wiki here
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraserI hope it's OK with you if I try to chase up the points that lead to differences of interpretation.
Firstly .. of entanglement .. I see it as being very similar to sending the same Christmas card to two .. if they know this they can open their card on (say) christmas moring and instantly know what card the other person has .. can you give any evidence to refute this Pov?
Spin.. 'the eye of the storm'. Tricky! If we go back to our view of an em wave .. I get the impression you see it as continuous whereas as I see it as a superposition of many photons. Strangely we both seem to see the basic two slit experiment as confirming the conflicting PoV's. Am I right?
QUOTE
Anything which strips the qubit from a free photon reduces it to a "ballistic" particle and it will not diffract (will no longer carry the phase information it originally was carrying from the source).
As I understand it .. if I place a detector on one slit .. the photons going through the other slit seem to know the detector is there and give a diffraction pattern rather than an interference pattern .. they detect the detector without the detector detecting them .. if you see what I mean. Yes/no?
Why an electron in a potential well?
I find it easier to visualise. Assuming we're happy with two separate zones for the electron to be in .. We could draw a Gauss type sphere round one zone .. would it contain a charge of half an electron .. or something else? Do you see a current flowing between the two halves?
-C2.
Confused2
3rd October 2006 - 04:19 PM
Christmas moring ? Too late to edit this and a few other typos .. sorry about them.
Good Elf
4th October 2006 - 08:08 AM
Hi Confused2,
QUOTE (C2+)
Christmas moring ? Too late to edit this and a few other typos .. sorry about them.
Typos have a strict one hour time limit ... after that PhysOrg will not allow edits anymore.
I find this particularly difficult when an image on the web has shifted "locale".
The "pretty picture" does not show "exactly" what you were discussing but I hope it indicates the potential for path induced self-interference. DCQE Experiment has been designed to "eliminate" those kind of complications (well designed experiment). Naturally in the real world reflections along paths is very possible and will occur in many instances. I have discussed reflections and their implications elsewhere.
Perpetual motion?, Cyclic photon reflections QUOTE (C2+)
Firstly .. of entanglement .. I see it as being very similar to sending the same Christmas card to two .. if they know this they can open their card on (say) Christmas moring and instantly know what card the other person has .. can you give any evidence to refute this Pov?
Sorry... This is not correct. First...They are "enantiomorphic" and the "detection" of one "Tweedledee twin" decides the fate of the other "Tweedledum twin" no matter how far they are separated. This has been conclusively shown by the Bell's Inequality Experiment. The question you pose is were they always in these states right from the start? Firstly... It is not possible to send a message by this means, though the "detection" of one photon "sets" the state of the other photon, it is unable to choose the state of the first photon.
The next point is is the correlation between the two photons changeable after the photons leave the source? This has been convincingly shown by Aspect's variation of the experiment by changing the state of the polarizers while the photon or particle is still in flight but after the period when the photon was created but at a time when communication of the change in the polarizer state would need to communicate FTL. The state of the polarizer determines the result of both photons so there is no connection to locality in the experiment. This rules out a local hidden variable and rules in Bohm Mechanics with non-local hidden variables.
QUOTE (Does Bell's Inequality Principle rule out local theories of quantum mechanics?+)
[...]At the time Bell's result first became known, the experimental record was reviewed to see if any known results provided evidence against locality. None did. Thus an effort began to develop tests of Bell's Inequality. A series of experiments was conducted by Aspect ending with one in which polarizer angles were changed while the photons were `in flight'. This was widely regarded at the time as being a reasonably conclusive experiment confirming the predictions of QM.
Three years later Franson published a paper showing that the timing constraints in this experiment were not adequate to confirm that locality was violated. Aspect measured the time delays between detections of photon pairs. The critical time delay is that between when a polarizer angle is changed and when this affects the statistics of detecting photon pairs. Aspect estimated this time based on the speed of a photon and the distance between the polarizers and the detectors. Quantum mechanics does not allow making assumptions about where a particle is between detections. We cannot know when a particle traverses a polarizer unless we detect the particle at the polarizer.
Experimental tests of Bell's Inequality are ongoing but none has yet fully addressed the issue raised by Franson. In addition there is an issue of detector efficiency. By postulating new laws of physics one can get the expected correlations without any nonlocal effects unless the detectors are close to 90% efficient. The importance of these issues is a matter of judgment.
The subject is alive theoretically as well. Eberhard and later Fine uncovered further subtleties in Bell's argument. Some physicists argue that there are assumptions in derivations of Bell's Inequality and that it may be possible to construct a local theory that does not respect those assumptions. The subject is not yet closed, and may yet provide more interesting insights into the subtleties of quantum mechanics.
http://math.ucr.edu/home/baez/physics/Quan...inequality.html Unfortunately Wikipedia this time is not one of those references that contains an adequate discussion I could recommend of this problem and might be "gilding the lily".
The strength of emotion that is pushing this issue can be seen in this reference...
Experimental tests of Bell's inequalityI would add that it isan excellent primmer and does point out a lot of the shortcomings of the present theory. But it does go overboard in this section toward the end..
QUOTE (Experimental tests of Bell's inequality+)
It is not difficult to see why most physicists are confident in their expectations for these experiments. Quantum mechanics is a spectacularly successful theory producing extraordinary predictions many of which have astounding accuracy far surpassing anything possible with classical physics. One can easily understand Bell's skepticism about the detection efficiency loophole.
...it is hard for me to believe that quantum mechanics works so nicely for inefficient practical set-ups and is yet going to fail badly when sufficient refinements are made[6].
How can a theory that has been so spectacularly reliable and successful suddenly falter because of improved detector efficiency? That is one way to look at things and the way most physicists do.
An alternative view focuses on how extraordinary these predictions are and on how convoluted and improbable a theory quantum mechanics is. Locality is the most powerful simplifying assumption in physics. Without it any event in the universe can influence any other and physical theories become problematic if not impossible. How is it that the universe violates locality but only does so in obscure and difficult experiments that we have yet to achieve? One would expect that a universe containing the complexity required for non-locality would be spectacularly nonlocal. One would hardly expect a theory like relativity that is local at its core to be one of the two dominant theories in such a universe. Of course the universe does not have to live up to our expectations but simplicity and elegance have often been a guide to deeper and richer physical theory and these predictions of quantum mechanics are about as far from simplicity and elegance as one can get.
Bell proved that the configuration space model of quantum theory cannot be mapped into physical space except with an explicitly nonlocal model such as Bohm's[7].
I would also add that this is the conclusion of many others as well... Bohmian Mechanics is the solution... non-local hidden variables.... Translation: Hidden Dimensions. This is also backed up with experiments such as the Delayed Choice Quantum Eraser Experiment and of course the Aharanov-Bohm Experiment (or the Aharanov-Cashir Experiment or other variants that show that there are "global" aspects to some apparently local phenomena.
QUOTE (C2+)
Spin.. 'the eye of the storm'. Tricky! If we go back to our view of an em wave .. I get the impression you see it as continuous whereas as I see it as a superposition of many photons. Strangely we both seem to see the basic two slit experiment as confirming the conflicting PoV's. Am I right?
Of course... it is at the heart of all these phenomena. You still appear to want to distinguish between photons in a bosonic state when you know they all occupy the same state when they can. The reason why entanglement works has always been known and it is that there are two speeds of light... the Group Velocity and the Phase Velocity. The velocity of light along the wavefront is"infinite" and this can technically be demonstrated with a simple laser pointer. This means that for whatever reason, the photon wavefront can shrink almost instantly even if it covers galaxies... all the while the velocity in the direction of propagation remains just the local speed of light (in a vacuum).
QUOTE (C2+)
Why an electron in a potential well?
You see a "well" I see a "shell" or "cavity"... a dimensional shell or cavity that defines the boundaries of harmonic spaces "beyond our normal three dimensions" and "our time".
QUOTE (C2+)
As I understand it .. if I place a detector on one slit .. the photons going through the other slit seem to know the detector is there and give a diffraction pattern rather than an interference pattern .. they detect the detector without the detector detecting them .. if you see what I mean. Yes/no?
Not if they are "entangled"... that makes them "special". For "unconnected" photons ... you are right there is now a single slit diffraction pattern... but two simultaneously entangled photons on the one wavefront ... quite a different matter.
QUOTE (C2+)
I find it easier to visualize. Assuming we're happy with two separate zones for the electron to be in .. We could draw a Gauss type sphere round one zone .. would it contain a charge of half an electron .. or something else? Do you see a current flowing between the two halves?
Umm... what are your "zones"? No... there are no fundamental charges only topological charges. What is "seen" depends on the frame of reference and how it is measured. Electrons are a difficult object and have a very small non-local cross-section in our "three dimensional" world (if any).
Cheers
Confused2
4th October 2006 - 11:13 AM
Hi Good_Elf,
QUOTE (Good Elf+)
I would also add that this is the conclusion of many others as well... Bohmian Mechanics is the solution... non-local hidden variables.... Translation: Hidden Dimensions. This is also backed up with experiments such as the Delayed Choice Quantum Eraser Experiment
Hm. I had rather hoped we could consider the Delayed Choice Quantum Eraser Experiment in sufficient detail to find out what it actually shows and how it shows it.
From
http://math.ucr.edu/home/baez/physics/Quan...inequality.htmlQUOTE
Three years later Franson published a paper showing that the timing constraints in this experiment were not adequate to confirm that locality was violated. Aspect measured the time delays between detections of photon pairs. The critical time delay is that between when a polarizer angle is changed and when this affects the statistics of detecting photon pairs. Aspect estimated this time based on the speed of a photon and the distance between the polarizers and the detectors. Quantum mechanics does not allow making assumptions about where a particle is between detections. We cannot know when a particle traverses a polarizer unless we detect the particle at the polarizer.
It seems the jury remains out on this.
It is certainly valid to state our assumptions and test them on the DCQE. I have to admit I am still not clear about the assumptions you are making.
QUOTE (->
| QUOTE |
Three years later Franson published a paper showing that the timing constraints in this experiment were not adequate to confirm that locality was violated. Aspect measured the time delays between detections of photon pairs. The critical time delay is that between when a polarizer angle is changed and when this affects the statistics of detecting photon pairs. Aspect estimated this time based on the speed of a photon and the distance between the polarizers and the detectors. Quantum mechanics does not allow making assumptions about where a particle is between detections. We cannot know when a particle traverses a polarizer unless we detect the particle at the polarizer.
|
It seems the jury remains out on this.
It is certainly valid to state our assumptions and test them on the DCQE. I have to admit I am still not clear about the assumptions you are making.
1/ Why is the result of the 2 slit experiment not completely predictable when the photon can pass freely through the slits without being detected, I'll call this the two slit interference result.
2/ Why does detection of the photon at one or other slit (as it passes) change the statistical outcome from double slit to that of a single slit (That's the easy one?)
3/ Detecting (later) which slit the photon passed through apparently changes the experiment from a 2 slit interference experiment to a single slit experiment.
For 1/
GE:- The result can be precisely known so the 'how random' doesn't arise.
For 2/
We agree this result..
QUOTE (me+)
As I understand it .. if I place a detector on one slit .. the photons going through the other slit seem to know the detector is there and give a diffraction pattern rather than an interference pattern .. they detect the detector without the detector detecting them ..
But we lack an explanation for 2/ .
And of 3/ I'm not sure about your assumptions.
--------------------------------
Of other bits of 'stuff'..
QUOTE (my question+)
Spin.. 'the eye of the storm'. Tricky! If we go back to our view of an em wave .. I get the impression you see it as continuous whereas as I see it as a superposition of many photons. Strangely we both seem to see the basic two slit experiment as confirming the conflicting PoV's. Am I right?
QUOTE (Good_Elf's reply+)
You still appear to want to distinguish between photons in a bosonic state when you know they all occupy the same state when they can.
Sorry , I don't understand this answer. My 'superposition' would assume the use of the correct statistics but I feel the wave can be fully analysed as 'photons' (which would give us a probability distribution in time and space) .. your answer remains unclear.
QUOTE (Good_Elf+)
The reason why entanglement works has always been known and it is that there are two speeds of light... the Group Velocity and the Phase Velocity.
I suspect your 'two speeds of light' are strangely similar to my 'not knowing where a photon is without detecting it'. Do either or both (potentially) give us a hand-waving way of getting information back from an apparently later event to an earlier event? This would seem to be the issue we need to examine in the
delay part of the DCQE. Do you want to go into this?
QUOTE (Good_Elf+)
there are no fundamental charges only topological charges. What is "seen" depends on the frame of reference and how it is measured. Electrons are a difficult object and have a very small non-local cross-section in our "three dimensional" world (if any).
Maybe come back to this another day.. enough problems already.
Best wishes,
C2.
Confused2
4th October 2006 - 11:27 PM
I found this very interesting .. I will need to read it several times before I have any idea quite what it means
BELL’S THEOREM : THE NAIVE VIEW OF AN EXPERIMENTALIST
http://arxiv.org/ftp/quant-ph/papers/0402/0402001.pdf-C2.
Good Elf
5th October 2006 - 03:53 PM
Hi Confused2,
QUOTE (C2+)
I found this very interesting .. I will need to read it several times before I have any idea quite what it means
BELL’S THEOREM : THE NAIVE VIEW OF AN EXPERIMENTALIST
http://arxiv.org/ftp/quant-ph/papers/0402/0402001.pdf
I will read this article before I continue... thanks for that. I will reply tomorrow. I note that Aspect's view is that our Universe is "non-local"... I agree.
Cheers
Confused2
5th October 2006 - 05:17 PM
Hi GE,
Can you help?
http://arxiv.org/ftp/quant-ph/papers/0402/0402001.pdfObviously don't trust me on this notation but
Equations (2)
P+(a) = P-(a) = 1/2
P+(b) = P-(b) = 1/2
Individually .. + or - equally likely
Eq (4) I reckon is a typo for (a,b) and then makes perfect sense
The source emits EITHER ++ OR --
QUOTE
"In conclusion, the quantum mechanical calculations suggest that although each
individual measurement gives random results, these random results are correlated, as
expressed by equation (6). For parallel (or perpendicular) orientations of the polarizers, the
correlation is total ( EQM = 1)."
Can't fault that.
QUOTE (->
| QUOTE |
"In conclusion, the quantum mechanical calculations suggest that although each
individual measurement gives random results, these random results are correlated, as
expressed by equation (6). For parallel (or perpendicular) orientations of the polarizers, the
correlation is total ( EQM = 1)."
|
Can't fault that.
2.3. Difficulty of an image derived from the formalism of Quantum Mechanics
As a naive physicist, I like to raise the question of finding a simple image to understand
these strong correlations. The most natural way to find an image may seem to follow the
quantum mechanical calculations leading to (3). In fact, there are several ways to do this
calculation. A very direct one is to project the state vector (1) onto the eigenvector
corresponding to the relevant result. This gives immediately the joint probabilities (3).
However, since this calculation bears on state vectors describing globally the two photons, I do not know how to build a picture in our ordinary space.
Now I seem to be totally drunk on naivity. I give you a chicken that lays EITHER two brown eggs OR two white eggs. Once you know the colour of one egg you always know the colour of the other (unless the chicken fowls up).
I take my naivity on to the end of section 2. replacing any controversy with the words "it's a chicken". Can you see where I'm going wrong?
Best wishes,
-C2.
younghand
5th October 2006 - 09:23 PM
Hi all
First time poster so go easy
QUOTE (C2+)
As I understand it .. if I place a detector on one slit .. the photons going through the other slit seem to know the detector is there and give a diffraction pattern rather than an interference pattern .. they detect the detector without the detector detecting them .. if you see what I mean. Yes/no?
This has probably been theorized before but I didn't find any posts. So here goes.
Maybe the photons has to know its destination before it can leave the emitter? How can I put this.. Imagine a photon sitting on the tip of the emitter ready to be fired. It cannot leave the emitter until it knows where its going. What Im thinking is a "how can I say" information particle that originates from the screen travels through one of the slits to interact with the photon. Now the photon has the information it needs and knows where its destination is and can leave the emitter, following the path of the info particle back to the place on the screen it came from.
This way the photon doesn't have to know if the other slit is open or not. The info particle knows if it came from a interference pattern or not and passes that on to the photon. This would also work if a detector was looking at one of the slits as it would change the instructions of the info particle on its way to the photon.
The info particle would have to be traveling backwards in time proportionate to the photon traveling forwards in time. So to us it would seem instantaneous.
Well what you think ?
Good Elf
6th October 2006 - 03:04 AM
Hi Confused2, younghand et al,
QUOTE (C2+)
Obviously don't trust me on this notation but
Equations (2)
P+(a) = P-(a) = 1/2
P+(b ) = P-(b ) = 1/2
Individually .. + or - equally likely
Eq (4) I reckon is a typo for (a,b ) and then makes perfect sense
The source emits EITHER ++ OR --
He he he... typos... Yquantum is always warning about them. It does not matter who you are you will always make them. I have made quite a few myself. I have noted that when I have made them and I am unable to correct it (after an hour) it is easy to see that people who read these posts must either be very few or are not thinking too closely about it all from the number of responses I am getting. Alternatively they get the "drift" and realize it is a typo. Yes you are right with the above. Note though this is a transcript of a talk given by Aspect and not one of his "peer reviewed" papers. That is the benefit to having interested "well wishing peers".
elves do not have such things so you must "beware"... He he he.
Orthogonal polarizers at any angle of setting will have a 50/50 (P=1/2) chance of passing an
arbitrarily polarized photon. However there is a 1:1 correlation between orthogonal polarizers passing "entangled" photons and zero correlation when they are parallel. That is just what "entanglement" actually means.
Wikipedia: Photon entanglementClearly "screw" related to each other... exactly. To clearly illustrate how this relates to other properties of a particle such as an electron (fermion) consider the Stern-Gerlach Experiment as indicated in the footnote.
Wikipedia: Stern–Gerlach experimentI call your attention particularly to the section "Sequential experiments". While not photon entanglement these spin states can be entangled too. You can see that electron spin polarization occurs in all three orthogonal planes "simultaneously". Remember that objects in three dimensions plus time can only spin in one plane (e.g. a Top) but in six dimensions any object can spin in three
"fixed" orthogonal planes all at once (I stress
fixed), add in the three degrees of freedom we seem to be living in and you have 9 linear dimensions plus time... "String Theory" and ten dimensions in all. Add an extra dimension (or more) if you want to allow "String Transport" and that makes 11 dimensions. My only "beef" with this view is the
connection between each group of three spatial dimensions.
QUOTE (younghand+)
This has probably been theorized before but I didn't find any posts. So here goes.
Maybe the photons has to know its destination before it can leave the emitter? How can I put this.. Imagine a photon sitting on the tip of the emitter ready to be fired. It cannot leave the emitter until it knows where its going. What I'm thinking is a "how can I say" information particle that originates from the screen travels through one of the slits to interact with the photon. Now the photon has the information it needs and knows where its destination is and can leave the emitter, following the path of the info particle back to the place on the screen it came from.
Yes.. I have mentioned it when I was referring to the Delayed Choice Quantum Eraser in this thread..
QUOTE (Good Elf+)
I think you really have thought about this one and the analysis is "spot on". This seems to me as if we have the dual nature of photons coming to the fore. When the "event" is in motion according to our "external" concept of time, because of the Delayed Choice Quantum Eraser Experimental Result it is "painting" a single final view of the total event on the "hyper-surface" of our Universe once and for all time. This is just the "cosmic artist" using "his" timeless brush to paint this event into the framework of our Universe, the "artist" moves only at the speed of light but the individual event is "timeless" and "unchanging". The word "artist" is just a literary artifice... do not take this literally .. he he he!
Perpetual motion?, Cyclic photon reflectionshttp://forum.physorg.com/index.php?showtop...ndpost&p=115910The photons "must" know just where they end up if viewed "outside of time" (C2 and StevenA will remember this point from an earlier posts elsewhere). In a dynamic Universe this is quite an interesting revelation. Such determinism is only possible if you "admit" to "Non-Local Supplementary Parameters Theories" (Translation: Non-Local Hidden Variable Theories)... One of which is Bohmian Mechanics that Aspect himself finds "attractive"... The EPR-Bohm Experiment. The big problem with Quantum Mechanics and its interpretation is the assumption of "locality". All 4D Theories of the Universe require "locality". QM is a 4D theory... Locality is "violated". Bohmian Mechanics is not a 4D Theory... it contains "at least" extra hidden parameters. String Theorists will maintain that these extra parameters are "linear dimensions" interpreted using a "configuration space". There are other interpretations one of which is Loop Quantum Gravity where these "dimensions" may only be parametric and added into spacetime to further characterize it but not physical "dimensions" (Zephir holds this view). Heim's Theory is a variant on this schema. Lee Smolin is pushing for the LQG view. I find this unacceptable since they are all simply "models". You just add in parameters to remove any perceived discrepancies.
Bohmian Mechanics "adapts" to providing an intermediate space that will have some "real" physical interpretation (a quantum "place" where particles actually go when unobserved, not actually part of our "spacetime"). Quantum Mechanics provides nothing in this "gap" and is found "wanting" in being unable to answer some very tricky questions as I have already stated in this thread... this is not my opinion it is a long standing problem with the theory and those who disagree point to the wonderful successes with local interpretations of QM and ignore the "measurement problem". Those who say this usually point to chaos and anarchy if a non-local view is accepted even though a number of experiments do point to it. I totally disagree.
Now I will continue on with a story here...
QUOTE (C2+)
Hm. I had rather hoped we could consider the Delayed Choice Quantum Eraser Experiment in sufficient detail to find out what it actually shows and how it shows it.
I am having the same problem, you are asking too many questions for me to cover all bases. I "wave my arms" sometimes because we have discussed all this before elsewhere.
QUOTE
I have to admit I am still not clear about the assumptions you are making.
I hope there are no unwarranted "assumptions". If you can could you point out the assumptions for me since I am trying to assume nothing "extra" but attempting to do away with quantum postulates.
QUOTE (->
| QUOTE |
| I have to admit I am still not clear about the assumptions you are making. |
I hope there are no unwarranted "assumptions". If you can could you point out the assumptions for me since I am trying to assume nothing "extra" but attempting to do away with quantum postulates.
For 2/
We agree this result..
QUOTE (me+)
As I understand it .. if I place a detector on one slit .. the photons going through the other slit seem to know the detector is there and give a diffraction pattern rather than an interference pattern .. they detect the detector without the detector detecting them ..
But we lack an explanation for 2/ .
This is all tied to just how large the fundamental photon can really be considered and exactly where you may find this "particle" in "configuration space". While its wavelength in the direction of propagation is fixed by the speed of light, in the transverse direction it spreads quite dramatically. This is the same for one photon or many. The same spreading for all photons so that the further they travel from the source the the more of the Universe each photon explores. Remember this is a non-local theory and the photon is traveling in quantum space "undetected". The geometry is non-local so when we "detect" the photon it is "projected" onto the state vector. Do not assume for even a second that the projected state vector is the entire story... It is stripped of some dimensions.
QUOTE (C2+)
QUOTE (Good_Elf's reply+)
You still appear to want to distinguish between photons in a bosonic state when you know they all occupy the same state when they can.
Sorry , I don't understand this answer. My 'superposition' would assume the use of the correct statistics but I feel the wave can be fully analyzed as 'photons' (which would give us a probability distribution in time and space) .. your answer remains unclear.
Any probability distribution would be "secondary" to the dynamics of the particle in "configuration space". In configuration space the particles assume a normal three dimensional dynamics as they have "here" in our "spacetime"... The projection by "detection" removes the non-local aspect of the particles and "localizes then" through
quantum demolition. When in configuration space the only indication of the particles is "indirect" through their waves and the way they interact with our local environment. Naturally we are unable to "see" this interaction unless we sacrifice a few of these photons to see where those waves are "pushing" those "eyes of the storm" around relative to the projection. The photon is more than just a point particle or even a little extended billiard ball, the "waves" fill the space and "penetrate" into ours in the evanescent region as de Broglie phenomena.
QUOTE (C2+)
I suspect your 'two speeds of light' are strangely similar to my 'not knowing where a photon is without detecting it'. Do either or both (potentially) give us a hand-waving way of getting information back from an apparently later event to an earlier event? This would seem to be the issue we need to examine in the delay part of the DCQE. Do you want to go into this?
We know that photons cannot "lag behind" on a wavefront or "zip ahead" so they are confined to the expanding wavefront. They can criss-cross and self-interfere given the chance... that is within the one "expanding" photon you understand. Interference with other "fermions" can also occur too and "defines" the dimensional space in which they are moving. What one photon does in a coherent beam is what all photons in that beam do as "interference". I have stated before that there is a self organizing influence, even between "adjacent" photons emitted from a condensed source, to become partially coherent. This is just the way these bosons behave. Pairs of electrons also exhibit such synchronization of phase (Cooper Pairs... bosons). Not that this has anything directly to do with entanglement, but entangled photons also partake in boson states.
Cheers
Confused2
6th October 2006 - 09:34 AM
Hi Good Elf, younghand et al,
Just a quickie..
yquantum posted this link on another thread .. just in case anyone missed it ..
http://www.fortunecity.com/emachines/e11/86/qphil.html-C2.
Good Elf
7th October 2006 - 02:51 AM
Hi Confused2, younghand, Yquantum et al,
The key point in the experiment DCQE is this statement...
QUOTE (Yquantum's Reference above... Quantum Philosophy: Psychic Photons+)
The comparison of arrival times need not actually be performed to destroy the interference pattern. The mere "threat" of obtaining information about which way the photon traveled, Mandel explains, forces it to travel only one route. "The quantum state reflects not only what we know about the system but what is in principle knowable," Mandel says.
Quantum Philosophy: Psychic Photons So the tree falls in the forest and nobody is there to see it... yet it falls (as it should). This flies in the face of certain Quantum Non-Deterministic Theories such as the Copenhagen Interpretation where the tree does not fall if it not observed, it remains in a "superposition of states". The page is a little "old" dated Jan 2002. I liked the bit about Bell when he commented just before his death...
QUOTE (Quantum Philosophy: Orthodoxy under Attack (from the same source)+)
To be sure, the Copenhagen interpretation has come under attack from theorists in recent years, most notably from John Bell, author of the brilliant proof of the divergence between "realistic" and quantum predictions for EPR experiments. In a television interview just before his sudden death from a stroke two years ago, the Irish physicist expressed his dissatisfaction with the Copenhagen interpretation, noting that it "says we must accept meaninglessness." Does that make you afraid? th
Perhaps what we term 'spirituality'
.
The way this question has been constructed is a dilemma in Law. To most this is a perfectly good question and the way a person answers it is a convincing and "damming" result. Either answer is proof of wife beating and you get several years in prison. It is not science but you get an instant but satisfying "result".