Is Everything in the Universe Entangled According to Physics?

[pallidin]

Given the hypothesis that everything that exists came from an original singularity, would it not follow, in physics, that everything is "entangled"?

I don't know, maybe I'm way-off here, but somehow it seems plausible.

 

[ZapperZ]

Given the hypothesis that everything that exists came from an original singularity, would it not follow, in physics, that everything is "entangled"?

I don't know, maybe I'm way-off here, but somehow it seems plausible.

If this is true, then entanglement phenomena would be so obvious that they would no longer be 'exotic' and that hard to show. But they ARE exotic and they ARE hard to show. So what does that mean?

It means that entangled properties are difficult to maintain coherently. Just because something started out being entangled doesn't mean that such a thing can be easily maintained. Long-distance entanglement right now can only be maintained by photons. Using particles are more restricted, both in time and distance, because such coherence are destroyed way too easily.

Zz.

 

[pallidin]

I appreciate your comment, Zapper; how you explained it makes this more clear to me.

 

[ueit]

If this is true, then entanglement phenomena would be so obvious that they would no longer be 'exotic' and that hard to show. But they ARE exotic and they ARE hard to show. So what does that mean?

I don't agree with this argument. First, entanglement appears pretty much in every chemical reaction, ionization, breaking of molecular bonds, etc. so it's not at all rare or "exotic". The fact that experiments showing correlations of entangled particles are difficult to do is irrelevant. Demonstrating gravitational interaction between two iron balls is also hard to do but this doesn't mean that such interaction is "exotic" or rare. It's also hard to "see" quarks but they are no less common than electrons.

It means that entangled properties are difficult to maintain coherently. Just because something started out being entangled doesn't mean that such a thing can be easily maintained. Long-distance entanglement right now can only be maintained by photons. Using particles are more restricted, both in time and distance, because such coherence are destroyed way too easily.

Those particles that interact with other particles from the environment become entangled with those. As the system becomes more and more complex, the experimental results cannot be interpreted in any meaningful way because of our lack of knowledge regarding the new, complex, system and computation limitation. However, this does not mean that entanglement disappears.

 

[ZapperZ]

I don't agree with this argument. First, entanglement appears pretty much in every chemical reaction, ionization, breaking of molecular bonds, etc. so it's not at all rare or "exotic". The fact that experiments showing correlations of entangled particles are difficult to do is irrelevant. Demonstrating gravitational interaction between two iron balls is also hard to do but this doesn't mean that such interaction is "exotic" or rare. It's also hard to "see" quarks but they are no less common than electrons.

But our "realization" of it is, i.e. we don't normally see such chemical reaction on the human scale that we identify as "entanglement". If it is, then we would see it easily and identify with it. Yet, we STILL consider quantum behavior as the behavior at the small scale, not the classical scale.

Those particles that interact with other particles from the environment become entangled with those. As the system becomes more and more complex, the experimental results cannot be interpreted in any meaningful way because of our lack of knowledge regarding the new, complex, system and computation limitation. However, this does not mean that entanglement disappears.

It has been shown that even ONE single interaction can destroy the coherence of a single-particle state. While that interaction results in a 2-particle state, it still has change the original state whereby the original single-particle coherent state has been destroyed.

The fact that we do not see, at the classical scale, all the quantum phenomena (and I deal with superconductivity, which Carver Mead claims is the clearest manifestation of quantum effects at the macroscopic scale), clearly shows that you can't simply carry those across from one scale to the next. You and I still do not know if the differences between the classical and quantum realms are simply separated by a crossover, or a "phase transition".

Zz.

 

[Naty1]

I,too, don't entirely agree with zapper. But entanglement does appear to be subtle.

While tehnically, correct, you don't EVER (no never) want to simply set aside a "thought nugget" because conventional physics hasn't gotten there yet. Zapper points out shortcomings based on current understanding...And those are legitimate insofar as they go.

The real issue is whether you believe your idea enough to find alternative explanations and experimental ways of verifying your idea...then you can claim Zapper and I were "shortsighted and myopic" in our thinking! The problem is focusing on those key thought experiments that lead to new solutions, not easy to do.

Roger Penrose has been working alrgely alone for many YEARS on twister theory and still can't get it completed... If Einstein, also largely on his own theoretically, had not cast aside fixed space and fixed time which "everybody" knows was 'correct", special relativity would have been delayed.

I did some research on my own with 50 or 60 widely accepted conventional theories: ultimately all proved short sighted and most incorrect: the Earth is flat, the Earth is the center of the universe, orbits are circular, the universe is our galaxy, the universe is static, black holes are fictituous (these last two wrong ideas even sucked in Einstein) alchemy, atoms don't exist, there is an aether, there is man made global warming,etc,etc,etc

Let me offer an interesting alternative hypothesis: telepathy is due to entanglement! Unproven of course, but tantalizing! (not my idea, by the way)

And take your idea one step further: if our universe came from a random singularity then so did an infinite number of others...so not only is entangelment possible in our universe, maybe there is "entanglement" among all universes! Crazy, maybe, but if you consider a related hypothesis that gravity leaks to other dimensions...why not other universes...maybe via nearby branes that we are unable to detect (yet another hypothesis)...

 

[Fredrik]

I did some research on my own with 50 or 60 widely accepted conventional theories: ultimately all proved short sighted and most incorrect: the Earth is flat, the Earth is the center of the universe, orbits are circular, the universe is our galaxy, the universe is static, black holes are fictituous (these last two wrong ideas even sucked in Einstein) alchemy, atoms don't exist, there is an aether, there is man made global warming,etc,etc,etc

I was hoping that you were joking at first, but you seem to be serious. Anthropogenic global warming has definitely not been proved to be either of those things (shortsighted or incorrect), so you shouldn't be claiming that it has in a science forum.

 

[Doc Al]

Let me offer an interesting alternative hypothesis: telepathy is due to entanglement! Unproven of course, but tantalizing! (not my idea, by the way)

Alternative to what? Before you worry about "explaining" telepathy (using entanglement, no less), first you must demonstrate that it even exists.

 

[Naty1]

Telepathy is a stretch, in my book, but the discussion that went with it was interesting...
don't recall where I read it...

Entanglement, I thought, was generally accepted today, but is it rigorously verified...I don't know. ..but I don't plan on doing experiments anytime soon .

Brian Greene, for example, in Fabric of the Cosmos cites work by EPR, Bohm, Bell and Aspect and concludes:

Although the majority view holds there is a harmonious coexistence, some physicsts and philosophers consider the exact relationship between quantum mechanics, entangled particles and special relativity an open question.

It is amazing that these (quantum) connections exist and that in carefully arranged laboratory conditions they can be directly observed over significant distances. They show us fundamentally that space is not what we thought it was.

 

[Naty1]

Anthropogenic global warming has definitely not been proved to be either of those things (shortsighted or incorrect), so you shouldn't be claiming that it has in a science forum.

Perhaps, hadn't thought of it that way... yet, you make it sound as if it's a proven scientific reality: Should you be claiming such in a science forum...??

 

[ZapperZ]

Telepathy is a stretch, in my book, but the discussion that went with it was interesting...
don't recall where I read it...

Then you shouldn't even have brought it up. Explaining telepathy using quantum entanglement is a bastardization of QM. It is also crackpottery, which will NOT get you very far here in this forum if you've read the Guidelines.

I strongly suggest you halt this line of discussion.

Zz.

 

[Fredrik]

Perhaps, hadn't thought of it that way... yet, you make it sound as if it's a proven scientific reality: Should you be claiming such in a science forum...??

I didn't make that claim. It was you who claimed the opposite. I don't have the expertise to vouch for it personally, but it's clear that the evidence has convinced a vast majority of those who actually do research in that area. In my opinion that means that it's not inappropriate to say that AGW is real in a science forum. (It is however inappropriate to discuss this in a thread about entanglement in the quantum physics forum, so this will be my last post about this).

 

[ueit]

But our "realization" of it is, i.e. we don't normally see such chemical reaction on the human scale that we identify as "entanglement". If it is, then we would see it easily and identify with it. Yet, we STILL consider quantum behavior as the behavior at the small scale, not the classical scale.

Sure, quantum effects are not obvious at macro scale and I didn't say they are. What I want to point out is that this is not a valid argument against all particles in the universe being entangled.

It has been shown that even ONE single interaction can destroy the coherence of a single-particle state. While that interaction results in a 2-particle state, it still has change the original state whereby the original single-particle coherent state has been destroyed.

Yeah, but if the system is the whole universe there is nothing that could alter its state, right?

The fact that we do not see, at the classical scale, all the quantum phenomena (and I deal with superconductivity, which Carver Mead claims is the clearest manifestation of quantum effects at the macroscopic scale), clearly shows that you can't simply carry those across from one scale to the next. You and I still do not know if the differences between the classical and quantum realms are simply separated by a crossover, or a "phase transition".

I think that the classical world is a quantum world. We do not realize this because a macroscopic object is too complex to be described in terms of its constituent particles. So, we use statistics, and by doing so, we loose the interesting stuff.

 

[ZapperZ]

Sure, quantum effects are not obvious at macro scale and I didn't say they are. What I want to point out is that this is not a valid argument against all particles in the universe being entangled.

A "valid argument" is one that is supported by experimental evidence. You have none.

Simply claiming that the whole universe is entangled says nothing when you cannot show that. I'm sticking my left leg out. Show me the effect of that via entanglement. And no, I'm not being silly, because this IS the type of effects that we are asking for at the classical scale.

Yeah, but if the system is the whole universe there is nothing that could alter its state, right?

What state of the universe? You can actually write the quantum state of the whole universe? I'd like to see it please.

And why wouldn't it change? The entropy state can certainly very well change!

I think that the classical world is a quantum world. We do not realize this because a macroscopic object is too complex to be described in terms of its constituent particles. So, we use statistics, and by doing so, we loose the interesting stuff.

You don't know that, and at this stage, that is pure speculation. If we are speculating, then my speculation is as valid as yours. So what are we left with? Arguing about our favorite color?

Zz.

 

[gendou2]

If the system is the whole universe there is nothing that could alter its state, right?

There is nothing "outside" the universe.
If we decide that the universe started in one state, it must have spontaneously de-cohered and/or interacted with its self.
Because quantum states don't act like this (that I know of), I don't suppose the universe could have started out as a quantum state.

 

[gendou2]

The entropy state can certainly very well change!

Can you refer me to a text that explains this?

 

[ZapperZ]

Can you refer me to a text that explains this?

Er.. any text on Thermodynamics?

Zz.

 

[gendou2]

Er.. any text on Thermodynamics?

Zz.

I feel like a retard.

 

[schroder]

I wonder if gravity might be a form of entanglement. For all the trying, no one has detected the gravity wave or gravity particle, and if it was instantaneous, instead of propagating at velocity 'c' that could explain orbital mechanics more accurately.

 

[Hurkyl]

I wonder if gravity might be a form of entanglement...

Please don't clutter up thread with rampant speculation.

 

[Hurkyl]

I've seen you argue this before ZZ, but I've never really felt enlightened by your arguments. Maybe a historical analogy would help -- at what point in its development would you have considered the kinetic theory of gas to be credible? At what point would you have considered it favored above the alternatives? (Did it really have any credible alternatives?)

Now back to this one. What would have to happen before you consider "classical mechanics as an emergent property of unitary evolution, via decoherence" to be a credible theory of classical systems? What has to happen to consider it favored above the credible alternatives? Does it even have credible alternatives? If not, what about favoring it above its (noncredible) alternatives?

 

[schroder]

Please don't clutter up thread with rampant speculation.

Are you talking about This thread? The one which starts with the question “Is everything entangled”? And then it goes on to develop the idea of telepathy as a form of entanglement. And I am “cluttering” it up by mentioning gravity? A bit pompous on your part, don’t you think?

 

[Hurkyl]

Are you talking about This thread? The one which starts with the question “Is everything entangled”? And then it goes on to develop the idea of telepathy as a form of entanglement. And I am “cluttering” it up by mentioning gravity? A bit pompous on your part, don’t you think?

The presense of other clutter in this thread does not excuse your crackpottery. That post on telepathy was also inappropriate. (And, if you look, has already been decried)

However, "is everything entangled?" is actually mainstream science, being a question prompted by the behavior of unitary evolution (which, of course, is backed by oodles of experimental evidence).

 

[vanesch]

Should I stay or should I go ?

If I stay it will be trouble ...

If I go it will be double...



Here we go again. Entanglement is a theoretical concept in quantum theory. Now, according to your favorite interpretation, and hence to your favorite "resolution" of the measurement problem, a measurement results in "irreversible entanglement" if you are of the unitary evolution crowd (the MWIers and so on), or results in "breaking up of entanglement" if you are of the projection crowd (Copenhagen etc...).

But both have the same observable consequences: quantum interference (the difference between the pure state and the mixture descriptions) disappear.

 

[ZapperZ]

I've seen you argue this before ZZ, but I've never really felt enlightened by your arguments. Maybe a historical analogy would help -- at what point in its development would you have considered the kinetic theory of gas to be credible? At what point would you have considered it favored above the alternatives? (Did it really have any credible alternatives?)

I don't know what "historical analogy" would have anything to do with this.

I'm a simple-minded experimentalist, not a historian. Maybe that's why the only thing I can "understand" is an experimental demonstration of what people are trying to sell. So if one is trying to sell that "entanglement is everywhere", then demonstrate to me that that entanglement is everywhere. It is THAT simple.

So far, I've shown why entanglement is NOT everywhere. I'll stand on my head, and see if someone else who's "entangle" with me would have the urge to want to assume the appropriate position.

Now back to this one. What would have to happen before you consider "classical mechanics as an emergent property of unitary evolution, via decoherence" to be a credible theory of classical systems? What has to happen to consider it favored above the credible alternatives? Does it even have credible alternatives? If not, what about favoring it above its (noncredible) alternatives?

That makes it even more of MY point. If classical mechanics is an "emergent property of unitary evolution, via decoherence", then by the definition of emergent property (per Laughlin and Anderson), then one CANNOT, in principle, derive classical behavior out of quantum theory. Period! More Is Different!

Zz.

 

[Hurkyl]

So far, I've shown why entanglement is NOT everywhere. I'll stand on my head, and see if someone else who's "entangle" with me would have the urge to want to assume the appropriate position.

You would make a mockery of the topic?

 

[ZapperZ]

You would make a mockery of the topic?

Don't change the subject and lump this on me. I said earlier that I was NOT trying to be silly in asking for such a thing.

I still want to see the empirical evidence (which no one has provided) to back up the claim that entanglement is everywhere. What has been made a "mockery" of is my request to support such a claim.

Zz.

 

[atyy]

I still want to see the empirical evidence (which no one has provided) to back up the claim that entanglement is everywhere. What has been made a "mockery" of is my request to support such a claim.

This isn't experimental evidence, but I'm curious what you make of their claim that the generic ground state of eg. their Eq 23 is entangled.

Entanglement in Many-Body Systems
Luigi Amico, Rosario Fazio, Andreas Osterloh, Vlatko Vedral
http://arxiv.org/abs/quant-ph/0703044

 

[Hurkyl]

Don't change the subject and lump this on me. I said earlier that I was NOT trying to be silly in asking for such a thing.

In response to the hypothesis that classical behavior is a by-product of unitary evolution, you demand evidence of non-classical behavior. In what way is that not being silly?

 

[ZapperZ]

This isn't experimental evidence, but I'm curious what you make of their claim that the generic ground state of eg. their Eq 23 is entangled.

Entanglement in Many-Body Systems
Luigi Amico, Rosario Fazio, Andreas Osterloh, Vlatko Vedral
http://arxiv.org/abs/quant-ph/0703044

That isn't a surprised. Note that in a superconductor, not only are the electrons making up a Copper pair entangled with each other, but ALL of the Cooper pairs that have condensed to form the long-range coherence are also technically entangled to each other. This is a very obvious example of a many-body system. Again, this isn't a surprised, nor is it anything new. As I've said earlier, Carver Mead used superconductivity as the clearest manifestation of quantum phenomena at the macroscopic level.

But note to what extent we have to do to preserve such coherence to be able to show quantum phenomena, i.e. it is NOT easy. Once you lose coherence, all traces of the obvious quantum effect are gone and we are left with our familiar classical world. So if a superconductor had to undergo a phase transition to get from the quantum to classical behavior, I'd say there's more than ample suggestion that the transition from classical to quantum realm isn't as trivial as everyone makes it out to be.

Zz.

 

[ZapperZ]

In response to the hypothesis that classical behavior is a by-product of unitary evolution, you demand evidence of non-classical behavior. In what way is that not being silly?

It is not silly when applied to the topic, something that you tried to point out.

So do you think EVERYTHING (capitalized in the topic) is entangled? If you do, forget unitary evolution or not (as if this is a done deal already in QM). Show me such evidence.

Zz.

 

[atyy]

But note to what extent we have to do to preserve such coherence to be able to show quantum phenomena, i.e. it is NOT easy. Once you lose coherence, all traces of the obvious quantum effect are gone and we are left with our familiar classical world. So if a superconductor had to undergo a phase transition to get from the quantum to classical behavior, I'd say there's more than ample suggestion that the transition from classical to quantum realm isn't as trivial as everyone makes it out to be.

That seems reasonable, but I don't understand whether that meshes with vanesch's characterization of decoherence as irreversible entanglement?

 

[ZapperZ]

That seems reasonable, but I don't understand whether that meshes with vanesch's characterization of decoherence as irreversible entanglement?

I don't know either, mainly because I've yet to be presented with compelling evidence of such "irreversible entanglement".

Remember that until Bell proposed his theory, most of the discussion on entanglement were nothing more than what most people are doing here - a discussion based on a matter of tastes. After Bell, at the very least, we have a way to empirically test one consequence of quantum entanglement (there are other "tests" that exploit other aspects of entanglement, such as beating the diffraction limit, etc). This now makes it into the realm of accepted physics.

I think by now, people should know me well enough that the only way to convince me of anything is via such experimental evidence. Till then, we are arguing about our favorite colors.

Zz.

 

[atyy]

I don't know either, mainly because I've yet to be presented with compelling evidence of such "irreversible entanglement".

But you would go with decoherence rather than say Copenhagen?

Edit: Well, I guess they're not mutually exclusive ...

 

[Hurkyl]

It is not silly when applied to the topic, something that you tried to point out.

I don't recall giving the tiniest suggestion of something so obviously contradictory.

 

[ZapperZ]

I don't recall giving the tiniest suggestion of something so obviously contradictory.

Fine, but you still ignore (and continue to ignore) the rest of what I had asked for. I can't believe that you care more about THAT than backing up your assertion with valid evidence.

Zz.

 

[Hurkyl]

Fine, but you still ignore (and continue to ignore) the rest of what I had asked for.

Yes, and intentionally. Originally, it was because I thought it pointless to have a discussion if you were going to caricaturize the topic. Now, I do so because I realize it's irrelevant -- I really don't understand how my desire to better understand why you are so vehemently opposed to the idea that classical systems might be described by quantum states turned into you demanding me to provide proof of said idea.

I can't believe that you care more about THAT than backing up your assertion with valid evidence.

Frankly, I'm appalled that you would think that I wouldn't care about being misrepresented like that. And just what assertion have I made, pray tell, that you would dispute? The most controversial that I can find is that things like MWI / Bohm are 'mainstream science'... but that doesn't seem at all controversial, and is incongruous with the demands you have been making.

 

[schroder]

The presense of other clutter in this thread does not excuse your crackpottery. That post on telepathy was also inappropriate. (And, if you look, has already been decried)

However, "is everything entangled?" is actually mainstream science, being a question prompted by the behavior of unitary evolution (which, of course, is backed by oodles of experimental evidence).

Frankly, I am appalled that you are appalled at being misrepresented, while accusing me of “crack pottery” for suggesting some connection between gravity and entanglement. For your information, investigation of such a connection is mainstream science, and has been for some years. I do not appreciate your charge of cluttering up this thread, and trying to link my comment with the earlier one on telepathy.
There are many papers in mainstream science concerning a possible linkage between gravity and entanglement, as well as quantum gravity.
Here is a brief excerpt from one:

If Bob falls into a black hole, he feels no acceleration and observes perfect entanglement with Alice. But if Alice fires a powerful rocket to accelerate away from the black hole and stay outside its "event horizon," she sees no entanglement at all.
Acceleration is linked to gravity through Einstein's general theory of relativity, so the result hints at a connection between gravity and entanglement, says Christoph Adami of the California Institute of Technology in Pasadena and the Keck Graduate Institute in Claremont. However, the tie between the two remains to be unraveled.

If you want the full text, here is the link:

http://http://www.sciencemag.org/cgi/content/full/sci;309/5742/1801a?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=gravity+%2B+entanglement&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT"


But, be advised, you will need to log in first as a member of that crack pot organization, AAAS!

 

[ZapperZ]

If you want the full text, here is the link:

http://http://www.sciencemag.org/cgi/content/full/sci;309/5742/1801a?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=gravity+%2B+entanglement&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT"

Please note that you should give a proper citation (rather than just a link like this). This means author, journal, volume number, page number, and year.

Furthermore, the paper was actually published in PRL[1]. Adian Cho is simply writing a commentary in Science of the PRL paper.

Zz.

[1] I. Fuentes-Schuller and R. B. Mann, Phys. Rev. Lett. 95, 120404 (2005).

 

[schroder]

Please note that you should give a proper citation (rather than just a link like this). This means author, journal, volume number, page number, and year.

Furthermore, the paper was actually published in PRL[1]. Adian Cho is simply writing a commentary in Science of the PRL paper.

Zz.

[1] I. Fuentes-Schuller and R. B. Mann, Phys. Rev. Lett. 95, 120404 (2005).

Thank you for the correct reference

 

[vanesch]

I don't know either, mainly because I've yet to be presented with compelling evidence of such "irreversible entanglement".

The point is that there are TWO ways to explain *conceptually* the *same* observational phenomena. One way is to say that "entanglement stops", which can be interpreted as saying that we switch to a statistical mixture of product state description, which can then in a second step be re-interpreted as a classical description (there's still a distinction between both, in that individual subsystems can still be in non-classical states, but the entanglement between subsystems seems to be gone: we have a product state). The observable consequence of this is that one cannot obtain any quantum interference effects in the CORRELATIONS between observations on the different subsystems.

But the other way is to say that the "entanglement is now irreversibly enlarged with the environment". Well, the observable consequence of this is ALSO that one will not obtain any quantum interference effects anymore in the CORRELATIONS between observations of ONLY the two subsystems (and not of the miriads of "subsystems" of the environment).

In other words "everything entangled" and "end of entanglemetn" are observationally equivalent. They are just two conceptually different ways of thinking about how things behave. They are FAPP observationally indistinguishable. So asking for *experimental proof* for one or the other is an impossible request.

One shouldn't confuse "entanglement" with "quantum interference effects". In fact, entanglement SUPPRESSES low-order interference effects, to show them in higher-order correlations. And with irreversible entanglement with the environment, that means then that the ONLY potentially observable quantum interference effects will happen in the n-point correlation functions with n very large, meaning: impossible to observe. We can't observe 10^20-point correlation functions.

How does this come about ?

Let's look at a toy example:

We have 5 quantum systems in our toy world: S1, S2, S3, S4, and S5.

Let us assume that we prepared system S1 in a non-classical state (a superposition of "classical" states |S1A> and |S1B>).

Our "universe state" is now:

{ |S1A> - |S1B> } |S2X> |S3Y> |S4Z> |S5U>

It is a product state, in which we can consider the 5 systems independently. But, by JUST doing a measurement on system S1, we can find quantum interference, if somehow we find a measurement setup that measures |S1A> + |S1B> versus |S1A> - |S1B>.
Indeed, "classically" we would expect this to be 50% 50% (if we assumed that the system was a 50% / 50% mixture of S1A and S1B). And we will find 0% and 100%. That DEVIATION from the statistical mixture is a quantum interference phenomenon. It is the fingerprint of quantum effects.

Assume now that system S1 interacts with system S2.

We now have the universe state:

{ |S1A> |S2A> - |S1B>|S2B> } |S3Y> |S4Z> |S5U>

Well, if we NOW do the mesurement on S1 with the |S1A> + |S1B> versus |S1A> - |S1B> measurement device, we will find: 50% and 50%. The quantum signature 100% - 0% is gone. The system S1, BY ITSELF, doesn't seem to show ahy quantum behaviour anymore.

However, if we do a quantum CORRELATION experiment between system S1 and S2, and we check for "AA" versus "BB" results, we will find 50% AA, 50% BB, 0% AB and 0% BA. That still corresponds to a mixture, but if we start doing Bell-type experiments on the double system S1 and S2, we WILL find quantum interference effects, which show up here as violations of Bell's inequalities for instance. Or simpler: a measurement on the state:
{ ( |S1A> - |S1B> ) (|S2A> - |S2B> ) - ( |S1A> + |S1B> ) (|S2A> + |S2B> ) }
= - 2 |S1A> |S2B> - 2 |S1B> |S2A>

would yield 0 while we would expect, if we would have a statistical mixture: 25% (one should normalize the states).

This deviation from the statistical mixture prediction indicates a quantum effect, but notice that now, it only appears in 2-point correlation functions (between S1 and S2). It doesn't appear anymore in any measurement that you can do on S1 alone, or on S2 alone.

Now, let us suppose that we have the 5 systems entangled:

|S1A>|S2A>|S3A>|S4A>|S5A> - |S1A>|S2A>|S3A>|S4A>|S5A>

It takes more algebra, but you can find out that you will not find any deviation from any measurement that only takes into account 1, 2, 3 or 4 of these 5 systems. Each of these individual measurements, or 2-point correlations, or 3-point correlations (say, between S1, S2 and S3), or 4-point correlations (say, between S1,S2,S3 and S4) will be indistinguishable from the "mixture" case. BUT there will now be an observable interference effect in the 5-point correlation function (the measurement on |S1A>|S2A>|S3A>|S4A>|S5A> + |S1A>|S2A>|S3A>|S4A>|S5A> will yield zero, while we expect it to be 50%)

As our toy universe doesn't have more than 5 subsystems, 5-point correlation functions describe every thinkable experimental outcome. So "entanglement forever" will be equivalent to "no entanglement anymore" for 1, 2, 3 and 4-point correlation functions, but for 5-point correlation functions, we WILL see the difference.

In our universe however, there are many many more subsystems.

 

[Count Iblis]

So, ZapperZ's position is similar to only believing that the interior of a star is really millions of degrees of Kelvin if someone can measure it using a thermometer.

 

[atyy]

I wonder whether ZapperZ's demand for "experimentally verifiable entanglement" and "collapse entanglement" can be found in one of these different definitions, eg.
On experimental procedures for entanglement verification
S.J. van Enk, N. Lutkenhaus, H.J. Kimble
http://arxiv.org/abs/quant-ph/0611219

 

[ZapperZ]

So, ZapperZ's position is similar to only believing that the interior of a star is really millions of degrees of Kelvin if someone can measure it using a thermometer.

A thermometer is so 1950's already! I haven't used a thermometer at work to measure a temperature since I was in grad school!

One can make a very good estimate of something, even indirectly. But at least, there's SOME experimental justification for it, rather than just hand-waving argument. One can make a very good argument for the existence of the Higgs, but yet, we STILL want to make as direct of a verification as we can. This is because even if it is there, its true properties still need to be pin down. Look at what happens with the top quark. I accept that it exists, but do you think its presence was "directly" measured as directly as using a thermometer?

So what's the difference between that, and this one here? Why would I accept the evidence for the top quark, but not for everything being entangled? Are there any compelling evidence to point to the latter, which is what I've been asking for all long (and with zero response)? I'm not even asking for a "direct" evidence.

I also want to point out how difficult it is to demonstrate the Schrodinger Cat-type states at a "macroscopic" level. The Delft/Stony Brook experiments were not trivial, and they had to use superconducting device to enable them to preserve the coherence of the system.

So if superpostion, which is an essential "ingredient" in entanglement, is already THAT difficult to demonstrate as a system becomes larger, how easy do you think we can get quantum entanglement, which is even harder? Is my demand for evidence unjustified?

Zz.

 

[Count Iblis]

The fact that it is so difficult to perform these experiments involving macroscopic superpositions is precisely because of fast decoherence. The theoretical predictions on decoherence rates have been confirmed in these experiments.

Then because there are no well motivated alternative theories out there that propose some form of non unitary corrections to time evolution that becomes large on the macro or meso scale, I don't see where the extreme scepticism about applicability of quantum mechanics to the macro scale comes from.

 

[atyy]

But doesn't decoherence still need collapse? I understand decoherence as irreversible entanglement gives the preferred states into which collapse occurs, but doesn't actually predict any collapse. Or we could have MWI, but isn't MWI versus Copenhagen a matter of taste?

 

[vanesch]

But doesn't decoherence still need collapse? I understand decoherence as irreversible entanglement gives the preferred states into which collapse occurs, but doesn't actually predict any collapse. Or we could have MWI, but isn't MWI versus Copenhagen a matter of taste?

You got it. In the end it is a matter of theoretical, philosophical and esthetical taste.

I could think this to be somehow similar to the question whether classically, the universe is "Newtonian" with several particles in a single 3-dim space, or whether the universe is a Hamiltonian phase space in which we trace out a single world line.

Now, historically and intuitively, we would opt of course for the "Newtonian" view. Theoretically, we might be inclined to think more of a phase space thing. There's no way to distinguish between them experimentally.

The analogy is not perfect, because the Hamiltonian and Newtonian views are *strictly* equivalent, while the "everything entangled/MWI/..." versus the "collapse/no entanglement/..." are only equivalent for all practical purposes.

 

[ueit]

I could think this to be somehow similar to the question whether classically, the universe is "Newtonian" with several particles in a single 3-dim space, or whether the universe is a Hamiltonian phase space in which we trace out a single world line.

Now, historically and intuitively, we would opt of course for the "Newtonian" view. Theoretically, we might be inclined to think more of a phase space thing. There's no way to distinguish between them experimentally.

I think that the experimental evidence strongly favors the Newtonian view. We cannot observe phase spaces and world lines. We can observe, however, particles moving in a 3D world. In order to claim that what we observe is not real you need to redefine what "real" means, explain how is that that our brains are interpreting the phase space as particles, etc. I have yet to see such an explanation. Needless to say, this is also strongly against Occam's razor. Also, I don't see how can you find the Hamiltonian of a system without presupposing particles and forces, another reason to reject this view as a fundamental one.

I see no reason at all to not accept that "reality" is what we observe it to be.

The analogy is not perfect, because the Hamiltonian and Newtonian views are *strictly* equivalent, while the "everything entangled/MWI/..." versus the "collapse/no entanglement/..." are only equivalent for all practical purposes.

Same objections apply here.

 

[ZapperZ]

The fact that it is so difficult to perform these experiments involving macroscopic superpositions is precisely because of fast decoherence. The theoretical predictions on decoherence rates have been confirmed in these experiments.

Then because there are no well motivated alternative theories out there that propose some form of non unitary corrections to time evolution that becomes large on the macro or meso scale, I don't see where the extreme scepticism about applicability of quantum mechanics to the macro scale comes from.

What about from... observation!, or lack thereof?

Zz.

 

[vanesch]

I think that the experimental evidence strongly favors the Newtonian view. We cannot observe phase spaces and world lines. We can observe, however, particles moving in a 3D world. In order to claim that what we observe is not real you need to redefine what "real" means, explain how is that that our brains are interpreting the phase space as particles, etc.

In fact, you are correct, there is experimental evidence for the 3D view, but it doesn't come from the Newtonian side. It comes from the relativity side, where the concept of locality is introduced. The purely Newtonian view with "action-at-a-distance" would rather favor the Hamiltonian approach, in fact, although there would still remain the issue of why this more general Hamiltonian structure is nevertheless restricted to the special case of "several particles in 3D" instead of "one universe-particle in 3N-D".
As to why our brains interpret things this way and not that way, that's entirely open to speculation I'd say.

Needless to say, this is also strongly against Occam's razor. Also, I don't see how can you find the Hamiltonian of a system without presupposing particles and forces, another reason to reject this view as a fundamental one.

It is not necessarily against Occam's razor, after all a single phase space and a single world line seems to be conceptually simpler than a lot of stuff of different kinds interacting through a lot of different interactions. After all, a single world dynamics is conceptually simpler than many individual dynamics and interactions, no ?
As to how to "find" the Hamiltonian through presupposing particles and forces, that's because we have to start from our (maybe totally deluded) descriptions which our brains prefer to state in 3D visions. So we have to use that "interface" to go from an observed situation to the "deeper reality" behind it, if we take on that picture. The fact that we have to do that dirty conversion work in the setup description and in the interpretation of the results is then just using the "window through which we see the universe".

Now, if you think I'm nuts even proposing this, then think of the holographic principle http://en.wikipedia.org/wiki/Holographic_principle where space is actually an illusion resulting from a 2-dimensional universe.