As per Japanese physicist (Masahiro Hotta), energy teleporation is possible

[DevilsAvocado]

1) whether this QET phenomenon can be used as substitute to classical channel communication

ANS. The amount of 'teleported' energy becomes quite small, as the distance becomes macroscopically large. Thus, QET is not suitalble for macroscopic energy transfer like classical channel communication. QET is a small-world phenomenon, like processes in quantum devices.

2) whether the classical channel is an integral part of the process or not.
ANS. The classical channel for announcement of the measurement result is one of key ingredients of QET. This ensures that QET satisfies causality and prohibits superluminal (faster-than-light) energy transfer. What Dr.Chinese said about that is precisely correct.

Thanks a lot Hotta!

This explains a lot, and I guess "Mars Power Plants" is out of the question!

Explanation: We have "one guy" here who says dogs can fly, but not by themselves.

 

[pranj5]

1) whether this QET phenomenon can be used as substitute to classical channel communication

ANS. The amount of 'teleported' energy becomes quite small, as the distance becomes macroscopically large. Thus, QET is not suitalble for macroscopic energy transfer like classical channel communication. QET is a small-world phenomenon, like processes in quantum devices.

Well, from your answers, it seems that this phenomenon is useless beyond the volume of a hydrogen atom. In your papers, you have said about the damping factors, can you say something about that? I mean what are those damping factors that prevent QET to transfer large amount of energy to macroscopic distances.

2) whether the classical channel is an integral part of the process or not.
ANS. The classical channel for announcement of the measurement result is one of key ingredients of QET. This ensures that QET satisfies causality and prohibits superluminal (faster-than-light) energy transfer. What Dr.Chinese said about that is precisely correct.

Well, as per the paper you have mentioned in your first post, how big can the amount of energy that Alice can sent to Bob by thins method.

 

[DevilsAvocado]

Obviously not big enough for a power plant on Mars!

 

[yoron]

Nice, and thanks a lot for taking a interest Mr. Hotta. How do you view the interaction taken in measuring a entanglement? Do it impart a momentum as it measures? Will the momentum imparted, if existing, exist over the whole of the entanglement?

As for describing it as existing in a 'time symmetry', I don't know? Macroscopically there always should be someone initialising it, at least under our arrow of time. And when it comes to a controlled entanglement it is easy to define who's 'involved'. It all seems to fall back to what 'time' should be seen as, though? But as all theories it has to fit what we observe, and I do not know of any experiments made in 'reversed time'? To me they all have a causality chain following our macroscopic arrow of time, whether it is observing positrons or electrons?

To say that nothing happens to 'B' after me measuring 'A' gets me confused. It may be semantics, but as I understands it we define a entanglement as something being 'together', where an action taken on 'A' having a instantaneous effect on 'B'? I don't see how you can expect that to be true, at the same time as you define it as noting can have happened at 'B', until you measure it?

This one you need to explain MRChinese :)

"It is true that when A collapses first, it sets the wave state for B. However, and this is the point that is hard to grasp, it is equally true that when B is measured AFTER A, B sets the wave state for A."

Is that from the idea of a symmetric 'time'? If I use a beam splitter and split a 'photon' in two A and B. Then proceed to measure A after that go on to measure B, are they reversible? In 'time' that is?

What I mean here is that the action is taken on 'A' before the action taken on 'B'. That they are identical, and would give identical relations, no matter on which 'side' I started to measure don't invalidate the arrow I measured them under, well, as I see it?
=

And yes Mr Hotta

"The first is the fact that any energy has no tag which shows where it was stored, just like pure water. (Anyone cannot make distinction between pure water on Earth and pure water on moon.)"

That's how I think of it too. And then it to me become a question of what we mean by 'information' in this case?

 

[yoron]

To me it would have to be a very 'still' universe, if I define particles and anti particles this way, Almost like a lightcone of 'relations' stretching both forward and backward in 'time', not 'moving' in themselves as they exist simultaneously, using the eye of God. Which then should become a question about why we have a macroscopic arrow. If I get it right here.

 

[DevilsAvocado]

To say that nothing happens to 'B' after me measuring 'A' gets me confused. It may be semantics, but as I understands it we define a entanglement as something being 'together', where an action taken on 'A' having a instantaneous effect on 'B'? I don't see how you can expect that to be true, at the same time as you define it as noting can have happened at 'B', until you measure it?

Nothing final happens to B until you measure it. [In most cases] there is always a large amount of 'randomness' involved in EPR-Bell experiments when getting the final outcome. For instance, the angle is random and should be set in the very last moment (outside A’s light-cone) to do it properly. And depending on the relative angle a-b, you get very different probabilities for the final outcome. Malus' law: cos^2(a-b) gives you the probabilities. Hence, you cannot claim that A has an instant effect on B, what happens is that the shared wavefunction decohere/collapse and this sets the 'prerequisites' for the final outcome, but B isn’t 'materialized' until the measurement is performed.

This one you need to explain MRChinese :)

"It is true that when A collapses first, it sets the wave state for B. However, and this is the point that is hard to grasp, it is equally true that when B is measured AFTER A, B sets the wave state for A."

I think this falls back on our previous discussion on SR and RoS...

There’s absolutely no doubt that the entangled pair of photons share the one and only wavefunction, period.

Could one wavefunction decohere/collapse/branch twice?? Answer: NO

Now, suppose you want to decide which one of Alice & Bob do actually decohere the wavefunction and sets the state, given they have equal opportunities; it will be impossible to tell according to RoS.

(And this time it is 'bulletproof', no "timer" in the world could save you. )

However, if you arrange so that you first measure A, to let say spin up, and then take this result to Bob and do the B measurement – this will of course not have any possibility to change the A measurement (in retrospect) to spin down... that’s impossible.

 

[DrChinese]

Well, from your answers, it seems that this phenomenon is useless beyond the volume of a hydrogen atom. ...
Well, as per the paper you have mentioned in your first post, how big can the amount of energy that Alice can sent to Bob by thins method.

First, thanks to M. Hotta for the time to help us better understand QET!

pranj5, thanks for bring Hotta into the discussion, but you are still missing the big picture here. Hotta's work is theoretical, it doesn't really matter how much energy is teleported by the process. That there is a possibility that ANY could be shifted is a good result in itself (in my opinion).

I think most would understand that it's not likely this would be a net positive teleportation in the end (although I can't be sure). As mentioned previously, we already have practical devices that can do the same thing.

What I have been trying to tell you is that the speculative ideas you advanced early on are not appropriate for this forum. While yours is not science, Hotta's is. If you follow the following link, you will see that there were over 1000 papers written this year alone on theoretical AND experimental developments in entanglement. Many of the results presented are amazing papers, I think if you scan a few you will see all kinds of exotic terms and ideas mentioned that shed important new light on the quantum world. Every one is a step forward. This is how science works, it takes time and a bit of luck every now and then.

http://arxiv.org/find/quant-ph/1/abs:+OR+entanglement+OR+bell+epr/0/1/0/2011/0/1?per_page=100

Skip the sci fi speculation, it doesn't really do anyone any good.

 

[M.Hotta]

Dear all, thank you so much for your responces. I have no time to reply them in detail. I think DrChinese has ability of explanation about that. (He is one of the best persons who understand physics quite well among this thread participants, I think. ) Please ask him to discuss about that.

If you want to know about the effect of quantum measurement, please read my review:http://www.tuhep.phys.tohoku.ac.jp/~hotta/extended-version-qet-review.pdf
In particular, p29 and p36-38. Time dependence of switch on-off of measurement devices always excites quantum fields in the vacuum state locally.


Description about the distance and energy scale of QET exp using quantum Hall systems can be found in our recent paper publsihed in Physical Review A. (You can see it via
http://xxx.yukawa.kyoto-u.ac.jp/abs/1109.2203 .) The typical length scale of QET systems is 10μm and the order of teleported energy is estimated as 100μeV.

The amount of teleported energy per one QET channel is quite small. However, if you consider huge numbers of QET channels paralley laid, the total amount of energy becomes large, in principle. Therefore it is valid to apply the QET argument to various gedanken experiments with cosmological distance scales or black hole physics, by taking a large N limit in terms of the number of quantum matter fields. The total amount of teleported energy can be N-times enhanced. About this, please see the above review (p51) and my recent paper published in Physical Review D.(You can see it via http://xxx.yukawa.kyoto-u.ac.jp/abs/0907.1378 .)

About the case with many people who extract energy using Alice's information, please see p49-50 of the above review.

 

[yoron]

DA :)

It's about definitions I think. To me causality exist in SpaceTime. Although you might want to define it as times arrow can take on different values, when comparing 'frames of reference', to me it have only one direction, into the future. Locally your clock always will be the same (relative your heartbeats, as a weak example), and that is enough to prove a casualty chain at the local plane.

On the conceptual plane, comparing frames of reference, you can find some other clock to, possibly, become unmeasurable, not ticking at all as you observe it. But you will nowhere find a 'clock' that, relative your local 'clock' ticks backward.

And that's where you make your experiments, inside SpaceTime.

"In relativistic QFT, all particles (and antiparticles) travel forward
in time, corresponding to timelike or lightlike momenta.
(Only 'virtual' particles may have unrestricted momenta; but these are
unobservable artifacts of perturbation theory.)

The need for antiparticles is in QFT instead revealed by the fact that
they are necessary to construct operators with causal (anti)commutation
relations, in connection with the spin-statistic theorem. See, e.g.,
Volume 1 of Weinberg's quantum field theory book."

So it is a question of 'definitions' to me. The same will be true with how you define that 'wave function' collapsing. As I understand it we can talk of a entanglement as existing as one wave function only, same as you described it. Assuming a arrow of time pointing one way, and with causality chains defined as above I expect us to be able to define who measured first, ignoring simultaneous measurements. Although there always will exist a doubt from a third observer, not involved in the process, we can, assuming that Lorentz transformations hold for defining a 'same universe' use those to prove who did what relative their own frames of reference.

Failing that, assuming that there is no coherent background, even though Lorentz transformations exist and work, we will have to look at the persons involved here, 'A' and 'B' and then define it as the measuring they do relative each other, as well as the message received, will define who did what, relative the relation created in their measuring, and messaging. Assuming no message but still a measurement we will have to define whom is observing them both, and then also 'measuring' their respective measurements ( in time :)

Why I discussed a 'timer' was just the remarkable definitions 'energy' has, which I'm still not sure of how to see. But I'm pretty sure that a measurement should impart a momentum, and as I expect, be present in all of it, not only one side. Whether you choose to measure that or something else, and no matter whether HUP treats it one way or another, I still would expect a addition by that measurments momentum.

As for it falling out, when it does it should to me be defined by one who did it first, even though there is a 'time symmetry' assumed in physics. And 'first' will easiest be defined relative a 'relation' as in a communication by message. Without it we fall back on defining a observer and his relation to those doing the experiment, or possibly assume that they was watching each other, and then use Lorentz transformations for defining who did it 'first'.

What I mean is that from the entanglements side there can be no two interactions on it, only one, if we define it as a 'wave collapse'.

 

[bohm2]

Thanks to everyone. This was a very useful thread and also a lesson to me to read the original papers more carefully and not through secondary sources. Because M. Hotta did suggest possible uses of QET on p. 50:

Much after the transportation, dynamical evolution of the system begins and then heat is generated. Thus, the time scale for effective energy transportation by QET is much shorter than that of heat generation. This property is one of the remarkable advantages of QET. Due to this property, QET in expected to find use use as an energy distribution scheme inside quantum devices that avoids thermal decoherence and would thus assist in the development of quantum computers.

 

[DevilsAvocado]

Dear all, thank you so much for your responces.

Thanks again, for taking your time explaining QET!

 

[DevilsAvocado]

... and also a lesson to me to read the original papers more carefully and not through secondary sources

extremely good point, thanks...

 

[DevilsAvocado]

It's about definitions I think.

It’s all about definitions!

And I admit being a bit 'sloppy'... this is no easy matters. Fact: We know that Local Realism is a dead parrot (99%), what’s left is the Grand Funeral. Then we have 3 options left on how the world works at the fundamental level:

• non-local + realism
• local + non-realism
• non-local + non-realism

It’s only in solutions containing non-locality you get this tension between SR and QM. However, if you accept the Many-worlds interpretation (MWI), this tension is gone immediately.

If you are still left, we can start the 'fight'!

Although there always will exist a doubt from a third observer, not involved in the process, we can, assuming that Lorentz transformations hold for defining a 'same universe' use those to prove who did what relative their own frames of reference.

I don’t agree that you need a third observer to get problems with RoS, and I think Einstein is on my side...

Einstein's old train thought experiment from 1917:

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I don’t want to make a big fuss over this; although I find it very interesting, with the tension between SR and QM (in case of confirmed non-locality), because here we have an experiment, alive and kicking, that could be performed in the undergraduate laboratory, which is much easier than travel back to Big Bang and t0!

But I can promise you – this is not my 'idea'.

A few months before John Stewart Bell died he held a lecture where he expressed his thoughts around the incompatibility between SR and QM, when it comes to non-locality. You can also find it the literature:

http://books.google.com/books?id=BaOoqbLrXK8C&dq=ladyman+every+thing+ross&hl=en

Every Thing Must Go - Metaphysics Naturalized (2007)
James Ladyman, Don Ross, David Spurrett, John Gordon Collier

(Page 165)

The upshot seems to be that the status of the arrow of time in QM is open. The tension between SR and QM is made into a definite contradiction if collapse of the wave function is regarded as an objective physical process, as in the dynamical collapse theories along the lines developed by Ghiradi et al. (1986), or if non-local hidden variables are introduced as in Bohm theory, since both imply action at a distance and pick out a preferred foliation of spacetime (Timpson and Brown forthcoming, Maudlin 1994). The real questions concern what happens to time if quantum theory is married with GR, and we return to that issue below. (Since relativistic quantum field theory is based on the background of Minkowski spacetime the status of time in the former is the same as in SR.)

But I'm pretty sure that a measurement should impart a momentum, and as I expect, be present in all of it, not only one side.

I’m not sure what you mean... did you get my explanation of a standard EPR-Bell experiment with entangled photons measuring a superposition of spin, in https://www.physicsforums.com/showpost.php?p=3612060&postcount=96"?

I can’t tell to you what to do, but my 'recommendation' is to leave momentum out of it for the moment, and make sure you got the "EPRB standard experiment" right... (it’s complex as it is)

What I mean is that from the entanglements side there can be no two interactions on it, only one, if we define it as a 'wave collapse'.

Yep! That’s my point also:

There’s absolutely no doubt that the entangled pair of photons share the one and only wavefunction, period.

Could one wavefunction decohere/collapse/branch twice?? Answer: NO

 

[bohm2]

It’s all about definitions!

And I admit being a bit 'sloppy'... this is no easy matters. Fact: We know that Local Realism is a dead parrot (99%), what’s left is the Grand Funeral. Then we have 3 options left on how the world works at the fundamental level:

• non-local + realism
• local + non-realism
• non-local + non-realism

I never understood non-local or local non-realism. If there's no reality/realism (non-realism) what does the local or non-local part refer to?

 

[DevilsAvocado]

I never understood non-local or local non-realism. If there's no reality/realism (non-realism) what does the local or non-local part refer to?

Very good question (but I was hoping no one should ask... ).

Seriously, I can’t give a straight answer (maybe DrC can?), but according to RUTA (PhD) you could exchange non-realism for http://plato.stanford.edu/entries/physics-holism/" .

That’s all help I can give you at the moment, sorry...

 

[Maui]

I never understood non-local or local non-realism. If there's no reality/realism (non-realism) what does the local or non-local part refer to?

That reality is completely local but happens/takes place as you go(i.e. not pre-existing). This is thought by some to be at least theoretically plausible as it allows doing local physics without magical influences. But this is philosophy, as is much of QM(actually anything out of the formalism). The difficulty seems to reside not in terms like local, non-local, real or non-real and their combinations but in what we mean by "to understand" and what it is that understands and how it understands. The other difficulty resides in constructing an incomprehensible model of the world and calling it "The World". It's likely not the world but a limited and crippled model of the world. You won't experience these problems if you regard matter as that which you observe(if you observe it, it must be real in a certain sense) and the formalism as that which makes predictions.

 

[yoron]

I reckon I already defined my position :)

To me the question is about indeterminism and superposition's, on a quantum level. Macroscopically we have no difficulties defining what is 'real' and 'imaginary' locally, well as I see it. In my view one can use locality as a 'golden rule', measuring all other frames of reference macroscopically. And assuming that we all can do so, even if getting to different results relative each others definitions of time and distance we have to find what join those definitions. And that would to me be radiation, describing what we see, and 'gravity' defining a metric for space.

Can you expand on how you define that 'Local realism' a little DA? As expressions of 'conceptually made' comparisons of different 'frames of reference', or as doubting what radiation tells you locally? Or maybe you are thinking of something entirely different there.
=

Eh, I'm presuming a arrow of time too, the 'exact same' locally, measured as a 'clock', as 'c' is to us locally. And the really interesting part of assuming it to be this way, is that we then find a 'invariant local time' for all, joining us through the radiation communicating between 'frames of reference'. That makes 'c' my 'clock of choice', not only its 'speed'.

 

[yoron]

Nothing final happens to B until you measure it. [In most cases] there is always a large amount of 'randomness' involved in EPR-Bell experiments when getting the final outcome. For instance, the angle is random and should be set in the very last moment (outside A’s light-cone) to do it properly. And depending on the relative angle a-b, you get very different probabilities for the final outcome. Malus' law: cos^2(a-b) gives you the probabilities. Hence, you cannot claim that A has an instant effect on B, what happens is that the shared wavefunction decohere/collapse and this sets the 'prerequisites' for the final outcome, but B isn’t 'materialized' until the measurement is performed.



I think this falls back on our previous discussion on SR and RoS...

There’s absolutely no doubt that the entangled pair of photons share the one and only wavefunction, period.

Yep but it is there we don't agree, unless you can give me a experiment on entanglements showing that they fall out differently, if measuring a 'spin' for example. And if you can then I would start to wonder how a 'entanglement' can describe two things/spins in this case. What you can say about different measurements is that they are dependent on the one measuring and that they seem to share a connection to how you define the circumstances for your measuring. But that is no different than saying the exact same about lights duality.

 

[DrChinese]

Yep but it is there we don't agree, unless you can give me a experiment on entanglements showing that they fall out differently, if measuring a 'spin' for example. And if you can then I would start to wonder how a 'entanglement' can describe two things/spins in this case. What you can say about different measurements is that they are dependent on the one measuring and that they seem to share a connection to how you define the circumstances for your measuring. But that is no different than saying the exact same about lights duality.

Not true! Bell's Theorem shows us differently.

The ONLY variable known to be relevant to outcomes of any two spin (polarization) measurements on entangled photons is the RELATIVE different of their measurement angle. The reality of one is dependent on the nature of a measurement of the other, and vice versa, in accordance with the predictions of QM - and completely in opposition to LR (local realism).

 

[yoron]

What I was thinking of was the Quantum eraser experiment, when I spoke of the experimenter as part of the entanglement DRc. As for "The reality of one is dependent on the nature of a measurement of the other, and vice versa, in accordance with the predictions of QM - and completely in opposition to LR (local realism)"

I don't know what 'local realism' should be seen as? Even macroscopically, in relativity, you have Lorentz contractions. If you define them as real, which I do, then there is no such thing as a 'defined distance' globally, Lorentz transformations non-withstanding, I differ between 'conceptual comparisons', and what you see locally. I also define it such as 'what you see is what you got', meaning that if you're 'speeding away' like a muon the Lorentz contraction I expect you to see will be as 'real' as it can be in this 'reality', for you.

If you mean that I state that we can know the spin before measuring? Or that I think that "all objects must objectively have a pre-existing value for any possible measurement before the measurement is made." then I sincerely doubt that one.

I expect the observer to define his reality through his local observations, and as he compares that to other frames of reference, then use his local definitions. Just as any experimenter does, using his own 'clock' defining a time for example. But I don't expect a entanglement to be known before the measurement?

Also I expect a outcome to be defined by the relations circumstancing it, including the experimenter, and his choice of measuring, set-up etc.

As I understand it Aspect proved that there was no such thing, as pre-existing values? That doesn't mean that I'm wrong in defining it from locality. And it doesn't mean that I necessarily must be wrong in saying that that the experimenter defines the experiment, as in the delayed choice quantum eraser.

In it they say "Some have interpreted this result to mean that the delayed choice to observe or not observe the path of the idler photon will change the outcome of an event in the past. However, an interference pattern may only be observed after the idlers have been detected (i.e., at D1 or D2)." as the signal photon reach D0 before the idler, due to a shorter 'path'.

But it will still be the experimenters choice that defines what there is to see, "the choice of whether to preserve or erase the which-path information of the idler need not be made until after the position of the signal photon has already been measured by D0."

And it is a still a function of both photons in the entanglement, meaning that your choice defines the outcome for the whole entanglement.

 

[DevilsAvocado]

To me the question is about indeterminism and superposition's, on a quantum level. Macroscopically we have no difficulties defining what is 'real' and 'imaginary' locally, well as I see it. In my view one can use locality as a 'golden rule', measuring all other frames of reference macroscopically. And assuming that we all can do so, even if getting to different results relative each others definitions of time and distance we have to find what join those definitions. And that would to me be radiation, describing what we see, and 'gravity' defining a metric for space.

Yeah sure, but now we are talking about the fundamental properties at the fundamental level = QM. The macroscopic world 'behaves' different, to us, but in the end it’s the same thing, more or less 'screened off'. (Yep, elephants could probably be entangled too, but it’s very hard trick! )

Can you expand on how you define that 'Local realism' a little DA? As expressions of 'conceptually made' comparisons of different 'frames of reference', or as doubting what radiation tells you locally? Or maybe you are thinking of something entirely different there.

DrC is the real expert on this subject, but I’ll give it a try (and maybe he could fill in 'the blanks'):

Local Realism is the view of Einstein; there is a world of pre-existing particles (objects) in the microscopic world, having pre-existing values for any possible measurement before the measurement is made (=realism), and these 'real' particles is influenced directly only by its immediate surroundings, at speed ≤ c (=locality).

Eh, I'm presuming a arrow of time too, the 'exact same' locally, measured as a 'clock', as 'c' is to us locally.

Yup, that’s what we do in the macroscopic world, however if you build the same assumptions for QM you will run into difficulties...

 

[DevilsAvocado]

Yep but it is there we don't agree, unless you can give me a experiment on entanglements showing that they fall out differently, if measuring a 'spin' for example. And if you can then I would start to wonder how a 'entanglement' can describe two things/spins in this case.

DrC already explained it clearly; the 'magic thing' is the relative angle between the two detectors at Alice & Bob. If Alice’s detector is finally set to +30° and Bob’s detector is finally set to 0° and, you get sin^2(+30°) = 25% discordance (i.e. the number of measurements where we get a randomly mismatching outcome up/down).

If Alice’s detector is finally set to 0° and Bob’s detector is finally set to -30° and, you get sin^2(-30°) = 25% discordance, same as above.

And now comes "the genius move" of John Bell.

In a world of Local Realism you would expect that if Alice’s detector is finally set to +30° and Bob’s detector is finally set to -30° you could predict the outcome from the measurements above, right? All logic in the world says that if the relative angle between Alice & Bob is 60°, we could just double the values from the 30° and get 50%, right?

EDIT: The explanation above isn’t perfect... Maybe it’s better to think of it like "anything you do in the 'other end' shouldn’t make any difference to Alice or Bob". When they are set to 0° this should be 'obvious', and when they are not, you just take their "local" values and add them together.

Here’s the formula for this Bell Inequality:

N(+30°, -30°) ≤ N(+30°, 0°) + N(0°, -30°)

There’s only one 'little' problem... if you actually perform the experiment and do the math, you get:

sin^2(60°) = 75%

This is the 'magic'!

There is no way for Alice or Bob to get this information about the other detector before the final measurement is carried out, since they are (should be) outside each other’s light cone.

 

[DrChinese]

If you mean that I state that we can know the spin before measuring? Or that I think that "all objects must objectively have a pre-existing value for any possible measurement before the measurement is made." then I sincerely doubt that one.

That's realism! Once you throw that out, you are good to go.

 

[bohm2]

That reality is completely local but happens/takes place as you go(i.e. not pre-existing).

What does that "reality" that is not pre-existing but becomes "actualized" then refer to?

 

[Maui]

What does that "reality" that is not pre-existing but becomes "actualized" then refer to?

Good question, but it belongs in the Philosophy forum. It's not an easier task to make sense of a pre-existing reality with instantaneous influences across it either. Perhaps it's true that mathematics and relationships underlie reality and are more fundamental than our crippled attempts to make sense of it(esp. with the clasicallity baggage and its preconceptions). I see it as a biological problem of how the brain was wired, its task has never been to make sense of the universe in its entirety, so maybe we should be more modest at this point.

 

[yoron]

Yes, DA I agree to both your definitions above. But I can't see where I go wrong in assuming that a wave function is set, no matter if you never look at the second entangled photon. As for the formalism defining different outcomes I have no argument, I think :) I better think some more there.

Look at it this way, Bell proved that there was no hidden causality as I understands it. That is okay with me. Either the wavefunction sets for 'both' and in that case the result is defined. Then it still will be a matter of how you choose to measure as I see it. But I can't see where Bells theorem demands that you must measure both particles before defining that collapse?

 

[DrChinese]

Look at it this way, Bell proved that there was no hidden causality as I understands it. That is okay with me. Either the wavefunction sets for 'both' and in that case the result is defined. Then it still will be a matter of how you choose to measure as I see it. But I can't see where Bells theorem demands that you must measure both particles before defining that collapse?

Bell doesn't demand such an interpretation. You could define the collapse as occurring when the first particle is measured. There is no difference in the predicted outcomes, per QM, as to the ordering. The relevant issue is that outcome stats are related to the two angle settings alone, exposing a relationship between them. Bell simply shows that this relationship cannot be one in which all possible angle settings were locally predetermined.

 

[DevilsAvocado]

hehe DrC is always *fast*... anyway... :)

Yes, DA I agree to both your definitions above. But I can't see where I go wrong in assuming that a wave function is set, no matter if you never look at the second entangled photon

The one and only shared wavefunction decohere/collapse at measurement.

Look at it this way, Bell proved that there was no hidden causality as I understands it.

Bell proved that Local Realism is not compatible with the predictions of QM.

That is okay with me. Either the wavefunction sets for 'both' and in that case the result is defined.

Nope! The final results of the measurements can never be pre-defined; they are always 100% random up/down. What the collapse of the wavefunction does is setting the probabilities for the final correlations (up/down).

But I can't see where Bells theorem demands that you must measure both particles before defining that collapse?

I don’t think it does...

 

[yoron]

"The final results of the measurements can never be pre-defined; they are always 100% random up/down. What the collapse of the wavefunction does is setting the probabilities for the final correlations (up/down)."

Maybe that is it?

Assume that I set up a entanglement by a beam splitter (A&B). Then I measure the spin for A to 'up'. Have I set the wave function then, or not?

According to how I think of it I now 'know' the spin of B, as it has to be the opposite. I see no probability for that spin to be anything else?

 

[DrChinese]

According to how I think of it I now 'know' the spin of B, as it has to be the opposite. I see no probability for that spin to be anything else?

You sure? Because that can be erased by bringing A's beamsplitter outputs back together again in a suitable manner. So that implies that you must wait and evaluate the final context as a whole. As I have said over and over again, you cannot say the first measurement causes collapse. It might be the last one that does that. No one really understands the mechanism. You're way of thinking of it works most of the time and is the easiest to use - it's what I do most of the time. But that is just a tool.