Is the cat alive, dead, both or unknown

[BiGyElLoWhAt]

The big bang is indeed in the causal past of everything, but any residual entanglement between two particles that have not interacted since then is near as no never mind zero. That is, the wave function of the two-particle system is for all practical purposes completely factorizable and the two particles can be treated separately.

(This might, however, be a good time to suggest googling for "quantum superdeterminism", as long as everyone promises not to prolong this thread based on what they find).

I wasn't saying it was realistic to be able to extract any useful information nowadays, just that it didn't "make no sense" to view them as entangled from the beginning, as I think this was a confusing and unnecessary complication to the argument. Thanks for chiming in.

 

[atyy]

So I wouldn't exactly call that entanglement, although I concede there is a subtle point there. I would instead say that it is a rather interesting statement about the form certain types of entanglement can take. Also, the anti-symmetrization of the wavefunction is really a consequence of the spin-statistics theorem, which crucially relies on the existence of local relativistic field theory.

Now I want to emphasize that this is not merely intuition, but rather the history of a long line of failed attempts. So, if someone thinks that they can write down a local theory that can 'create' entanglement at spacelike separation out of thin air, without using a local, and causal third party (like a messenger particle in the case of entanglement swapping), then write down that theory. The problem will become obvious the second you attempt to do that, as you will find that you need to write down an interaction Hamiltonian that will either involve fields that are evaluated at different spacetime points, or that will require higher derivatives. I think this is where the Bohmians run into issues. They have to be able to allow ftl communication between say EPR pairs, but not for anything else, which then requires imposition of extra rules that adds theoretical baggage. As I said, I don't really know how successful they are with that.

The big bang is indeed in the causal past of everything, but any residual entanglement between two particles that have not interacted since then is near as no never mind zero. That is, the wave function of the two-particle system is for all practical purposes completely factorizable and the two particles can be treated separately.

(This might, however, be a good time to suggest googling for "quantum superdeterminism", as long as everyone promises not to prolong this thread based on what they find).

@Haelfix, my intuition is closer to what Nugatory is saying - it can be present, but in general it should be very diluted (because of monogamy of entanglement). Also, originally, you mentioned it as analogous to the horizon problem. So would it be right to understand it not so much as "impossible", but more a question of fine tuning - ie. "dman odd" as you put it?

 

[BiGyElLoWhAt]

Monogomy of entanglement? haven't they entangled as many as 5 particles intentionally? That's what I thought until google turned up th world record being 3000, but all the articles seemed to be pop-sci. Here's one on multiple entanglement.
http://m.phys.org/_news63037231.html

 

[atyy]

Monogomy of entanglement? haven't they entangled as many as 5 particles intentionally? That's what I thought until google turned up th world record being 3000, but all the articles seemed to be pop-sci. Here's one on multiple entanglement.
http://m.phys.org/_news63037231.html

It refers to maximal entanglement.

 

[BiGyElLoWhAt]

Hmmm... I'll have to look into that, would you care to elaborate a little bit?

 

[Haelfix]

Entanglement has nothing to do with anything like that - its simply applying the principle of superposition to systems. I gave a very careful explanation before - its really all there is to it. Nothing weird in the sense of being mystical etc etc is going on - it simply leads to a different type of correlation than occurs classically. The difference is classically you know it has properties all the time ie the green and red slips of paper are always green and red. In QM its more subtle as Bells theorem shows - but it's still just a correlation - its not some phenomena that needs further explanation. We know its explanation - systems can be in superposition and hence are correlated in a way different to classical correlations.

Thanks
Bill

Indeed, and that is the point. People get very tripped up about spooky action at a distance, or how quantum mechanics can seemingly feel measurements that are very far apart and adjust accordingly etc. But at the end of the day, as long as you give up realism (counterfactual definitiveness to use the philosophical lingo) and simply accept that we don't have bits, but instead we have qubits, there is absolutely nothing bizarre about Bells inequalities being violated. We don't have to give up locality, relativity or anything like that. The correlations found in quantum mechanics are different than classical mechanics, but we already knew this 40 years before Bell formulated his thought experiment.

 

[Haelfix]

Sorry, I don't think my point has come across. I am not saying anything controversial here. The point is you can only create entanglement locally. Forget about the horizon problem, or anything like that, I regret bringing that up b/c it seems like it has caused confusion.

So how about this. Take the usual EPR setup with system A and B prepared in a maximally entangled pure state and allow another system C to be nearby. Take B off to Alpha Centauri and after some time make a measurement on every box and write down the results. We have now broken the entanglement between A and B, and can allow those systems to develop new entanglements, by say allowing them to interact with the environment.

Now at some fixed and agreed upon later time after those initial measurements but before the light travel time between Earth and Alpha Centauri, make a measurement on box B and C. Write the results down, and have your partner fly back to compare notes.

Here is the important thing. There will never be a correlation between the results in box B and C. Repeat the experiment however many times you want, you will always find the same result. The conclusion is obvious. B/c A and B were in a maximally entangled state, by monogamy of entanglement they could not be entangled with C. Further, once C was spacelike seperated, it could never create entanglement with B, even after the original entanglement was broken. This is a physical statement about the locality of the laws of physics and is not just about the transfer of information.

 

[atyy]

Sorry, I don't think my point has come across. I am not saying anything controversial here. The point is you can only create entanglement locally. Forget about the horizon problem, or anything like that, I regret bringing that up b/c it seems like it has caused confusion.

So how about this. Take the usual EPR setup with system A and B prepared in a maximally entangled pure state and allow another system C to be nearby. Take B off to Alpha Centauri and after some time make a measurement on every box and write down the results. We have now broken the entanglement between A and B, and can allow those systems to develop new entanglements, by say allowing them to interact with the environment.

Now at some fixed and agreed upon later time after those initial measurements but before the light travel time between Earth and Alpha Centauri, make a measurement on box B and C. Write the results down, and have your partner fly back to compare notes.

Here is the important thing. There will never be a correlation between the results in box B and C. Repeat the experiment however many times you want, you will always find the same result. The conclusion is obvious. B/c A and B were in a maximally entangled state, by monogamy of entanglement they could not be entangled with C. Further, once C was spacelike seperated, it could never create entanglement with B, even after the original entanglement was broken. This is a physical statement about the locality of the laws of physics and is not just about the transfer of information.

Is that the same thing as eg. a limitation on the states that say LOCC can prepare? Or more than that?

Edit: Or is it the same as eg. if B and C are in a product state, then local unitaries can never cause B and C to be entangled?

 

[atyy]

Hmmm... I'll have to look into that, would you care to elaborate a little bit?

Monogamy of entanglement is misleading but standard jargon. It certainly doesn't mean that one particle can only be entangled with another - that's considered so "obvious" that the misleading jargon is considered not that misleading. http://quantiki.org/wiki/Monogamy_of_entanglement

 

[rootone]

Excuse my naivety please. I want to understand entanglement.
Two objects exist, one is red, the other is blue.
These objects are then separated. they can be a few meters separated or maybe light years;
When we look at either object we instantaniously know what the state of the other object must be,
and information does not have to travel any distance at all for this to be so.
It is not spooky at all..

 

[bhobba]

give me a dumbed down version of what entanglement actually means in a modern context? Because I was apparently unable to grasp it from what you've said...

See post 115. I will repeat it in summery - entanglement is the principle of superposition applied not just to the same system but composite systems.

If this is, in fact, how it works, then why are not ALL particles from the time of the big bang entangled, as nick666 has said?

Thats assuming they were all entangled to begin with - something those that know more cosmology than I do question:
http://physics.stackexchange.com/questions/55026/particles-entangled-after-the-big-bang

Thanks
Bill

 

[bhobba]

and information does not have to travel any distance at all for this to be so. It is not spooky at all..

No it inst.

Its only spooky if you want to hold to counter-factual definiteness. That's the root cause of all this angst. And even if you still want to hold to it then pick an interpretation like Bohmian Mechanics and see what happens there. In that interpretation you can see exactly why you have locality broken:
http://arxiv.org/pdf/quant-ph/0611032v1.pdf

Also let's look at the definition of locality in the paper on Bell I linked to before:
'Let us define a “local” theory as a one where the outcomes of an experiment on a system are independent of the actions performed on a different system which has no causal connection with the first. For example, the temperature of this room is independent on whether I choose to wear purple socks today. Einstein’s relativity provides a stringent condition for causal connections: if two events are outside their respective light cones, there cannot be any causal connection among them.'

That is a slightly less clearly stated version of the cluster decomposition property - it doesn't state a necessary caveat - namely - it can't apply to correlated systems. Entangled systems are correlated so - it isn't even an applicable definition. Only if you want counter-factual definiteness is it even a worry. If you do then you have to allow locality to apply to correlated systems.

Thanks
Bill

 

[atyy]

Also let's look at the definition of locality in the paper on Bell I linked to before:
'Let us define a “local” theory as a one where the outcomes of an experiment on a system are independent of the actions performed on a different system which has no causal connection with the first. For example, the temperature of this room is independent on whether I choose to wear purple socks today. Einstein’s relativity provides a stringent condition for causal connections: if two events are outside their respective light cones, there cannot be any causal connection among them.'

That is a slightly less clearly stated version of the cluster decomposition property - it doesn't state a necessary caveat - namely - it can't apply to correlated systems. Entangled systems are correlated so - it isn't even an applicable definition. Only if you want counter-factual definiteness is it even a worry. If you do then you have to allow locality to apply to correlated systems.

But aren't Bertlmann's socks correlated systems?

 

[bhobba]

But aren't Bertlmann's socks correlated systems?

Of course. But its a classically correlated system and obeys Bell's inequalities. Quantum correlated systems do not and there is the rub. But if you remove correlated systems from the definition of locality, and you are pretty well forced to in the cluster decomposition property for it to be reasonable, then its of no concern as far as locality goes. If however you want counter-factual definiteness then it must be included and you get something like: 'experiments that are sufficiently separated in space have unrelated results'. It immediately jumps out - what if they are correlated to begin with. So you say - of course - that needs to be removed and you get 'Uncorrelated experiments that are sufficiently separated in space have unrelated results'. But if you do that you can't have counter-factual definiteness because in order for Bells inequality to be broken correlated systems need to break locality. In a sense you are led to something quite unnatural.

Thanks
Bill

 

[Nick666]

There are some who think entanglement is something that could exist at macroscopic scale, cause of a topological property of spacetime . They proposed some sort of macroscopic experiment based on an arvix paper, and that arvix paper was apparently reviewed by these guys . If anyone's interested I can post the paper.

 

[bhobba]

There are some who think entanglement is something that could exist at macroscopic scale,

Everything is quantum. Of course it exists at the macroscopic scale. The very reason for classical properties is classical objects are all the time being observed by its environment and entangled with it.

I am unaware of any relation to the topology of space-time. But it sounds highly speculative and probably best in its own thread.

Thanks
Bill

 

[Nick666]

Yeah the proposer of the experiment says the macroscopic things will also be corelated just like the entangled photons, so there would be nothing special about the quantum realm when it comes to entanglement, the correlations being consequences of the topological properties of space. And the experiment being macroscopic it would manifestly be local and realistic.

 

[atyy]

Of course. But its a classically correlated system and obeys Bell's inequalities. Quantum correlated systems do not and there is the rub. But if you remove correlated systems from the definition of locality, and you are pretty well forced to in the cluster decomposition property for it to be reasonable, then its of no concern as far as locality goes. If however you want counter-factual definiteness then it must be included and you get something like: 'experiments that are sufficiently separated in space have unrelated results'. It immediately jumps out - what if they are correlated to begin with. So you say - of course - that needs to be removed and you get 'Uncorrelated experiments that are sufficiently separated in space have unrelated results'. But if you do that you can't have counter-factual definiteness because in order for Bells inequality to be broken correlated systems need to break locality. In a sense you are led to something quite unnatural.

I don't know if your definition of cluster decomposition is the same as Wikipedia's https://en.wikipedia.org/wiki/Cluster_decomposition_theorem, which makes use of the vacuum state. I also don't think that Wikipedia's definition of cluster decomposition is the same as that used in Bell's theorem, because Bell's theorem is independent of QM, whereas cluster decomposition is defined with respect to QM, since it uses the concept of a vacuum state.

 

[StevieTNZ]

There are some who think entanglement is something that could exist at macroscopic scale

I am reminded of this experiment - two macroscopic diamonds entangled: http://www.nature.com/news/entangled-diamonds-vibrate-together-1.9532

I would also be interested in reading the paper.

 

[bhobba]

I don't know if your definition of cluster decomposition is the same as Wikipedia's

I gave a link earlier that addressed that:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

Even Weinberg is a bit loose in his bible textbook. The key point is it doesn't apply to correlated systems in QFT.

The definition of locality I gave from my linked paper on Bell is very similar to the cluster decomposition property.

Thanks
Bill

 

[zonde]

But if you remove correlated systems from the definition of locality, and you are pretty well forced to in the cluster decomposition property for it to be reasonable, then its of no concern as far as locality goes. If however you want counter-factual definiteness then it must be included and you get something like: 'experiments that are sufficiently separated in space have unrelated results'. It immediately jumps out - what if they are correlated to begin with. So you say - of course - that needs to be removed and you get 'Uncorrelated experiments that are sufficiently separated in space have unrelated results'. But if you do that you can't have counter-factual definiteness because in order for Bells inequality to be broken correlated systems need to break locality. In a sense you are led to something quite unnatural.

You are fooling with definitions. You are bringing in irrelevant definition of "locality" while there is common and widely used relevant definition of "locality".
Your irrelevant definition - Uncorrelated experiments that are sufficiently separated in space have unrelated results
Relevant definition - There can't be any influence between spacelike separated events.

 

[atyy]

@bhobba, here is a different explanation of cluster decomposition - the underlying principle would then be no superluminal signalling of classical information.

http://relativity.livingreviews.org/Articles/lrr-2005-5/ (section 2.7.1)

Yes, I do think Weinberg's explanation is wrong.

 

[Nick666]

I am reminded of this experiment - two macroscopic diamonds entangled: http://www.nature.com/news/entangled-diamonds-vibrate-together-1.9532

I would also be interested in reading the paper.

http://arxiv.org/pdf/1211.0784v4.pdf

 

[bhobba]

You are fooling with definitions. You are bringing in irrelevant definition of "locality" while there is common and widely used relevant definition of "locality".

I gave the common and widely used one as found in my linked paper on Bell.

Thanks
Bill

 

[atyy]

Also let's look at the definition of locality in the paper on Bell I linked to before:
'Let us define a “local” theory as a one where the outcomes of an experiment on a system are independent of the actions performed on a different system which has no causal connection with the first. For example, the temperature of this room is independent on whether I choose to wear purple socks today. Einstein’s relativity provides a stringent condition for causal connections: if two events are outside their respective light cones, there cannot be any causal connection among them.'

That is a slightly less clearly stated version of the cluster decomposition property - it doesn't state a necessary caveat - namely - it can't apply to correlated systems. Entangled systems are correlated so - it isn't even an applicable definition. Only if you want counter-factual definiteness is it even a worry. If you do then you have to allow locality to apply to correlated systems.

I think the definition of "local" is ok without the caveat that about correlated systems. It means that if two systems are spacelike separated, then an action on one cannot affect the probabilities of local observables on the other. This prevents superluminal signalling, and that is the basis of the cluster decomposition.

Weinberg's informal statement is just so wrong, I don't think it is worth rescuing by adding caveats. If we use "no superluminal signalling", we get cluster decomposition, and an acceptable definition of locality used in some derivations of Bell's theorem.

 

[atyy]

http://www.scholarpedia.org/article/Wightman_quantum_field_theory

If I understand correctly, the cluster decomposition does mean spacelike experiments have uncorrelated results - BUT the caveat is that it refers to ground state expectation values, and is derived from (1) no superluminal signalling (2) Poincare invariance of the ground state (3) uniqueness of the ground state.

The ground state is a property of the Hamiltonian, so this puts a constraint on the Hamiltonian, which provides some notion of "interactions". However, the "no superluminal signalling" assumption does enter, so cluster decomposition doesn't seem to provide a notion of "local interactions" that is distinct from "no superluminal signalling"?

 

[bhobba]

However, the "no superluminal signalling" assumption does enter, so cluster decomposition doesn't seem to provide a notion of "local interactions" that is distinct from "no superluminal signalling"?

Wienberg's definition is rather naive - yes even wrong - but regardless of how you look at it removing correlated systems is quite natural- if you don't you are asking for problems:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

As Bill_K said:
'But what he's talking about is a situation in which all of the in states (α1, α2,...), (αj,αj+1,...) are known and independent. In your pion example the in states α1 and αj are correlated and dependent.'

In QFT superluminal is even trickier because you need to include all sorts of paths in the path integral formulation - even superluminal ones. Even I got confused about this and I well remember a thread where I was corrected. Best to avoid it in the definition of locality.

Thanks
Bill

 

[Feeble Wonk]

Take the usual EPR setup with system A and B prepared in a maximally entangled pure state and allow another system C to be nearby. Take B off to Alpha Centauri and after some time make a measurement on every box and write down the results. We have now broken the entanglement between A and B, and can allow those systems to develop new entanglements, by say allowing them to interact with the environment.

Now at some fixed and agreed upon later time after those initial measurements but before the light travel time between Earth and Alpha Centauri, make a measurement on box B and C. Write the results down, and have your partner fly back to compare notes.

Here is the important thing. There will never be a correlation between the results in box B and C. Repeat the experiment however many times you want, you will always find the same result. The conclusion is obvious. B/c A and B were in a maximally entangled state, by monogamy of entanglement they could not be entangled with C. Further, once C was spacelike seperated, it could never create entanglement with B, even after the original entanglement was broken. This is a physical statement about the locality of the laws of physics and is not just about the transfer of information.

This part is confusing to me. IF A and B were maximally entangled before B took its trip to Alpha Centauri, and C subsequently became entangled with A, wouldn't C also be entangled with B by proxy? Wouldn't you have to consider there to be an A/B/C system? If you measure B at its Alpha Centauri address, it yields information about A, which would then yield information about C. What am I missing?

 

[jerromyjon]

http://arxiv.org/pdf/1211.0784v4.pdf

Very interesting, reminds me of a mobius strip.

 

[Xertese]

The cat is alive since the measurement or observation of said cat before during and after being placed in the box is alive so at a quantum level that cannot change as the possibility has already been determined.

The only way the cat will die without interaction is through dehydration (unlikely) or starvation (more likely)

Also which a lot of people seem to neglect is that the cat itself is making observations and measurements itself.

 

[jerromyjon]

The only way the cat will die without interaction is through dehydration (unlikely) or starvation (more likely)

I don't know about the cat, per se, but I would die of thirst, first, waiting for science to explain this.

Also which a lot of people seem to neglect is that the cat itself is making observations and measurements itself.

So would a camera, if it just took a picture of the atom. Until you look at the classical picture, is it a picture yet?

 

[Xertese]

Yes the camera in it's measurement since being created thus predetermining an outcome would take and make the picture without someone looking at it.

 

[atyy]

In QFT superluminal is even trickier because you need to include all sorts of paths in the path integral formulation - even superluminal ones. Even I got confused about this and I well remember a thread where I was corrected. Best to avoid it in the definition of locality.

If you avoid it, it is unclear that the statement of Bell's theorem is correct, since it isn't obvious that your definition corresponds to "classical relativistic causality" or to "no superluminal signalling".

Although it may be technically hard to implement, no superluminal siganalling for pairs of observables is straightforward - observables at spacelike separation commute.

The easy way to think about it is that a measurement will collapse the wave function, and so will change the probabilities of outcomes, and can be used to send a message.

If observables commute, they can be measured in any order, and the wave function collapse will not change the probabilities of outcomes. So no superluminal signalling is implemented by observables at spacelike separation commuting.

 

[harrylin]

Excuse my naivety please. I want to understand entanglement.
Two objects exist, one is red, the other is blue.
These objects are then separated. they can be a few meters separated or maybe light years;
When we look at either object we instantaniously know what the state of the other object must be,
and information does not have to travel any distance at all for this to be so.
It is not spooky at all..

The "spooky" aspect of entanglement was discussed by Bell by means of an illustration with two socks of different colours, you can read it here (and if you want to understand that issue, you probably should read it): http://cds.cern.ch/record/142461?ln=en
His conclusion which is often called "Bell's theorem" has been the topic of many threads on this forum.

 

[rootone]

Thanks Bhobba and harrylin for pointing me in a useful direction (Bell's theorum.).

 

[Feeble Wonk]

This part is confusing to me. IF A and B were maximally entangled before B took its trip to Alpha Centauri, and C subsequently became entangled with A, wouldn't C also be entangled with B by proxy? Wouldn't you have to consider there to be an A/B/C system? If you measure B at its Alpha Centauri address, it yields information about A, which would then yield information about C. What am I missing?

Never mind. Sorry for the stupid mistake. The entanglement between A and B was broken upon the initial measurement of B at Alpha Centauri, so B couldn't be entangled with with C by proxy.

 

[Derek Potter]

I do not understand why entanglement is such a mystery. Entanglement is not a magic connection between two particles. Neither is it (pace bhobba) merely a correlation. It is plain old superposition. It doesn't arise unless there is superposition - which is, of course, always the case in one basis or another. But given superposition, entanglement is a direct result. With superposition there is no spooky action at a distance. No non-locality.

So what is the problem?

The problem is that people don't like superposition and want to get rid of it. It is just about psychologically acceptable to allow that a small system is in a weird quantum state until we look at it, but, as soon as we have observed it, surely the wierdness disappears? They say. So we have collapse of the wavefunction - or some similar ad hoc hypothesis - introduced to make our interpretation feel more natural. But when does the wavefunction collapse? When is an observation complete? In the case of an EPR experiment, Alice and Bob make measurements on their own photons. But Charles, who compares their results, has not yet made a measurement. Thus we must regard Alice and Bob, be they real people or mere detectors and recording devices, as being in superpositions *as far as Charles is concerned*. (Technically in his measurement basis.) And that doesn't feel right. You mean Alice sees both outcomes but only one Alice state is actualized and then only when Charles observes her? I don't think so! They say.

And yet, if Alice and Bob do enter an unambiguous state (of having seen a particular outcome - which is 100% common-sense!) then spooky action at a distance is inevitable unless you really bend over backwards to concoct weird superdeterministic theories. Suppose Alice's measurement is a tiny bit ahead of Bob's - nowhere near enough to alter their spacelike separation but enough to be able to say that, at a certain time, Alice and Bob have set their detectors; Alice has made her measurement but Bob has not. During this time, Bob's detector must alter its detection sensitivity to reflect the angle between the two detectors. It's as simple as that. Bob's detector presumably knows its own angle so the information about Alice's setting must get to it superluminally. It is actually possible to get quite good correlations if Bob's detector is allowed to know everything about how Alice's photon interacts with her detector (edit - without the information about her setting). This covers all sorts of hidden variables, pre-arrangements and so on and certainly covers the red/green sock case. However Bell's Theorem (the CHSH part) proves that, regardless of quantum mechanics, there are limits to what it can do unless Bob has the additional information of Alice's setting. QM predicts, and experiment confirms, that the correlations are the strongest that would be possible if Bob did have that information. Remember, Bob's sensitivity must adjust itself according to this information even though it cannot have reached him yet. That's spooky.

So the choice is yours:
1 Shelter behind "it's only a correlation" and "you can't send signals with it". Edit - Shut up and calculate!
2 Accept spooky action at a distance (edit - as well as superposition).
3 Accept that Alice and Bob, like Schrodinger's Cat, remain in superposition at least until Charles observes them (edit - and no spooky stuff needed).
4 Come up with an alternative theory involving time-travelling fairies or brains in a vat (edit - not spooky at all, oh no! ).

 

[Nick666]

spooky action at a distance

Maybe there's something inside the distance ( inside the space, a property of space) that determines the spookyness ?

 

[Derek Potter]

Maybe there's something inside the distance ( inside the space, a property of space) that determines the spookyness ?

Like I said, there is no spookiness other than superposition.

 

[jerromyjon]

https://en.wikipedia.org/wiki/File:Quantum_superposition_of_states_and_decoherence.ogv
Very nice 3 minute video, I finally know what "Rabi oscillations" are. But what I was looking for was the "birdhouse?" thing about how 2 birds must go through 1 hole? I have a mental block and can vaguely remember the concept but I forget the analogy that described it, can anyone point me to it, I would be extremely grateful.

 

[TrickyDicky]

So what is the problem?

The problem is that people don't like superposition and want to get rid of it.

Surely there must be a reason for this, because superpositions are nice and simple.

3 Accept that Alice and Bob, like Schrodinger's Cat, remain in superposition at least until Charles observes them (edit - and no spooky stuff needed).

This seems like your option, which leads to the question:why only until Charles observe them?, but that's precisely the reason most people is not satisfied with superposition so you're back to spot one.

In fact the problem with superposition in mathematical terms is sort of the opposite from the Schrodinger's cat kind of situation where one wonders why are not superpositions in the caricature sense that Schrodinger intended observed. Actually the problem with wave functions in the scattering case is that we only consider physical the superpositions of plane wave solutions, that are not normalizable and cannot be observed.

 

[Derek Potter]

Surely there must be a reason for this, because superpositions are nice and simple.
This seems like your option, which leads to the question:why only until Charles observe them?,

They can go on forever as far as I'm concerned. The point is, they must go on at least until Charles observes them. (There are loopholes like backward causality or superdeterminism but frankly they sound pretty contrived and, in any case the discussion, although it has veered off into EPR, is about Schrodinger's Cat and we should limit ourselves to the paradigm that Schrodinger used.) But as far as collapse is concerned it cannot occur before Charles makes his observation. Otherwise he would be observing a mixed state of Alice and Bob's independent observations (assuming no spooky action at a distance) and the correlations would not be seen.

but that's precisely the reason most people is not satisfied with superposition so you're back to spot one.

You mean they prefer spooky action at a distance plus a mysterious collapse of the wavefunction rather than plain wave mechanics which accounts for the appearence of both without needing either? You may be right. There's no accounting for taste.

 

[Buzz Bloom]

Hi JerromyJon:

https://en.wikipedia.org/wiki/File:Quantum_superposition_of_states_and_decoherence.ogv
Very nice 3 minute video

I found the video gave a good illustration of the physics of superpostion, but I have a problem with the language used to describe it:

a particle is in two energy states at the same time.​

That is not intended to be an exact quote. I would have to watch the video again to catch the exact quote, and I don't think it is important enough to do that.

To me the desciptive language is a philosophical interpretation about what is shown in the video.

QM is a collection of mathematical tools that can be used to make certain kinds of predictions that quite often and naively seem absurd. There is also a body of theory explaining what the ability to make such predictions means about the universe in which we live, and the theory can be helpful in developing new tools. But such a theory is not necessarily a complete and true description about how the universe really works. QM only predicts probabilities about possible measurement values.

With this in mind, the video particle having a superposition of two energy states simply means that if it's energy is measured the value will either be one specific value or the other. QM will predict the probability of which value it will be (with an error range depending on the measurement method). It does not mean it has both energy states at the same time.

I hope this is helpful,
Buzz

 

[jerromyjon]

It does not mean it has both energy states at the same time.

I agree to disagree... I certainly don't see it that way. I see it as "oscillatory interference" in a basic sense.

 

[bhobba]

I agree to disagree... I certainly don't see it that way. I see it as "oscillatory interference" in a basic sense.

You can view it any way you like, but I have to say I don't understand "oscillatory interference". The math however is quite clear - you can't say anything about what's going on without observing it - a superposition does NOT mean it has both properties at once.

Thanks
Bill

 

[jerromyjon]

I can't explain what is in my head any better than the term that just popped into my mind which was "oscillation interference", so I googled and found a similar biological term with pictures that kind of show what I mean but not quite.

I'll just solve any doubt by saying this. The cat is alive or dead. Period. That's obviously the point, you never get to see a cat die, or dying. Just the same as saying it is an atom in the ground state, or in the excited state. The "superimposed energy states" part specifically, I can't think of any way to depict it visually.

 

[atyy]

But what I was looking for was the "birdhouse?" thing about how 2 birds must go through 1 hole? I have a mental block and can vaguely remember the concept but I forget the analogy that described it, can anyone point me to it, I would be extremely grateful.

http://arxiv.org/abs/1407.3194

 

[jerromyjon]

Ahh pigeonhole! Thanks a million!

 

[atyy]

You can view it any way you like, but I have to say I don't understand "oscillatory interference".

Maybe:

Oscillatory: Φ(t) = e^iEtΦ

Interference: |Ψ(t)|² = |Σe^iEtΦ|²

 

[jerromyjon]

Yeah that's mostly greek to me. I just think the interference of the wave function needs to interfere exactly right to "bump it over the hump to flip the switch" so to speak. I already know the geometry of the universe so that part is simple. I'm just not quite good enough to piece it all together with the math. Actually it's even simpler than that now that I think deeper about it. You observe the nodes or the peaks of the interferences. Yeah, I think that pretty much sums it up right there.