Is Everything in the Universe Entangled According to Physics?

[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.

 

[ueit]

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".

Non-locality is not a general feature of Newtonian mechanics, only of his theory of gravity. We know this theory to be incorrect so I wouldn't use it as evidence for anything.

As to why our brains interpret things this way and not that way, that's entirely open to speculation I'd say.

If we accept the 3d space +particle view there is no room for speculation because we simply define "reality" as what we observe. There is no need to interpret anything, just use the experimental data, directly into the theory.

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 ?

The Hamiltonian formalism is not against Ockham's razor but the necessary translation between the proposed reality and what we observe is. As you said, it's only a speculation. If what we observe is what we put into equations there is no need to explain the observation. But if we observe a thing and the theory says it's an illusion, then you need to explain how such an illusion appears, assuming that the theory is true. If you cannot provide this explanation then you have to make an additional postulate and this is against Ockham.

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".

Exactly what I've said above. Isn't it better to deal away with the assumption that our brains are deluded and with the necessary "conversion work" and simply say that what we observe is what it really is?

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.

It makes sense to make additional postulates if you gain some explanatory power. I'll take a look to that link

 

[WaveJumper]

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".

I couldn't agree more. We don't see the whole picture, that's how/why the Newtonian world arises from space phase in our brains. It's our peculiar, limited and "coarse" sensory apparatus that brings about the notion of 3D vision.

 

[WaveJumper]

Exactly what I've said above. Isn't it better to deal away with the assumption that our brains are deluded and with the necessary "conversion work" and simply say that what we observe is what it really is?

For the experiment - yes, but there would be no Newtonian world if there were no living forms.

 

[vanesch]

Non-locality is not a general feature of Newtonian mechanics, only of his theory of gravity. We know this theory to be incorrect so I wouldn't use it as evidence for anything.

It was an analogy. Nor Newtonian mechanics, nor Hamiltonian dynamics is "ultimately correct". I was using it as an example, an analogy which might make the essence of what I want to say clearer.

What I wanted to say was that there can be different points of view, different theoretical approaches, which are observationally entirely equivalent, and in that case, one cannot ask for experimental discrimination between those different viewpoints (as they are equivalent: exactly, or "FAPP"). There are reasons to prefer one over the other viewpoint, but these reasons are based upon aesthetic, theoretical and philosophical preferences themselves. So at the end of the day, it is a matter of taste.

If we accept the 3d space +particle view there is no room for speculation because we simply define "reality" as what we observe. There is no need to interpret anything, just use the experimental data, directly into the theory.

Sure. But then one might be seduced by the Hamiltonian viewpoint too, for more theoretical grounds. So it is a matter of priority in your tastes. One might be marvelled by the mathematical structure of Hamiltonian dynamics and simplectic structures, and prefer to look upon things that way. Or one might prefer to remain as closely as possible to one's "senses".

The Hamiltonian formalism is not against Ockham's razor but the necessary translation between the proposed reality and what we observe is. As you said, it's only a speculation. If what we observe is what we put into equations there is no need to explain the observation. But if we observe a thing and the theory says it's an illusion, then you need to explain how such an illusion appears, assuming that the theory is true. If you cannot provide this explanation then you have to make an additional postulate and this is against Ockham.

Again, it depends. You might prefer the unifying view and the mathematical coherence of the Hamiltonian approach, and consider that what you win in "postulatedness" there, compensates for the extra price of introducing an interpretation of experienced observation. Again, that depends on the value you give to each, and we're back to square one: it is a matter of taste.

Exactly what I've said above. Isn't it better to deal away with the assumption that our brains are deluded and with the necessary "conversion work" and simply say that what we observe is what it really is?

That depends what is the price to pay on the theoretical side. If you have to give up a great mathematical structure for that, it is open to discussion. It's a matter of what you consider "better".

 

[ueit]

I couldn't agree more. We don't see the whole picture, that's how/why the Newtonian world arises from space phase in our brains. It's our peculiar, limited and "coarse" sensory apparatus that brings about the notion of 3D vision.

Do you have any evidence for this assertion? How exactly does the 3D world "arise" in a brain? What is the reason you feel the need to assume this?

there would be no Newtonian world if there were no living forms

Why?

 

[ueit]

It was an analogy. Nor Newtonian mechanics, nor Hamiltonian dynamics is "ultimately correct". I was using it as an example, an analogy which might make the essence of what I want to say clearer.

OK.

What I wanted to say was that there can be different points of view, different theoretical approaches, which are observationally entirely equivalent, and in that case, one cannot ask for experimental discrimination between those different viewpoints (as they are equivalent: exactly, or "FAPP"). There are reasons to prefer one over the other viewpoint, but these reasons are based upon aesthetic, theoretical and philosophical preferences themselves. So at the end of the day, it is a matter of taste.

When I look at a billiard ball I see, guess what, a billiard ball. I don't see a phase space. I would call this a great observational difference.

Sure. But then one might be seduced by the Hamiltonian viewpoint too, for more theoretical grounds. So it is a matter of priority in your tastes. One might be marvelled by the mathematical structure of Hamiltonian dynamics and simplectic structures, and prefer to look upon things that way. Or one might prefer to remain as closely as possible to one's "senses".

Nobody stops you to use the formalism that is more appropriate to the problem you have. As long as you cannot deal away with the "senses" (because otherwise you cannot relate the theory with observation) the beautiful Hamiltonian formalism must necessarily supplement them, not replace them. Therefore, it goes against Ockham.

Again, it depends. You might prefer the unifying view and the mathematical coherence of the Hamiltonian approach, and consider that what you win in "postulatedness" there, compensates for the extra price of introducing an interpretation of experienced observation. Again, that depends on the value you give to each, and we're back to square one: it is a matter of taste.

No it's not a matter of taste. You cannot replace anything from the "old stuff". To calculate the Hamiltonian of a hydrogen atom you need the assumption of a 3d space, point particles, coulomb force and so on. You cannot remove this stuff completely because you cannot calculate anything. So, above all Newtonian physics you ADD the Hamiltonian calculation.

That depends what is the price to pay on the theoretical side. If you have to give up a great mathematical structure for that, it is open to discussion. It's a matter of what you consider "better".

Why do you feel the need to assume that a mathematical structure, even if nice, must be real? You can use it anyway.

I think that you don't fully realize how big an assumption this "brain translation" is. This is not a simple postulate, like say the particle distribution in Bohm's interpretation. That is a simple and mathematically clear assumption about how 1D particles are placed in a 3d space. Only geometric primitives involved. You are making a claim about how a huge, complex system (the brain) works. Not only this is open to inconsistencies (may be your assumption contradicts energy conservation or some other physical constraint) but is a way to bring other assumptions throug the back door (a kind of cheating). I've read for example some so-called deductions of Born postulate from decision theory. But all this assumes already that a reasonable brain exist and that such a brain functions according to Born postulate. Circullar reasoning in the end, but well hidden.

 

[Count Iblis]

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?

I think that people who advocate Copenhagen should explain where the non-unitary effects that would lead to collapse which are not present in the dynamical laws are coming from and how it can be detected.

With only unitary time evolution, you can explain how a mass of, say, one gram in a superposition of two Gausian wavepackets that are separated by, say, 1 cm rapidly evolves into a mixed state of Gausian wavepackets (of the width of the thermal de-Broglie wavelength) if you take the interactions with the environment into account.

Then if this picture that does not have a fundamental collapse leads to objections because it leads to a Many Worlds scenario and people don't like that, then it is up to these people to explain how the theory should be modified and support that with experimental evidence.

I do understand that the debate on this issue will be going on, but what I don't understand is the extreme scepticism against the idea that you only have unitary time evolution without a fundamental collapse. This is the minimal hypothesis that, as far as we can check, fits all experimental data, while the fundamental collapse idea requires new physics for which there isn't a shred of evidence.

 

[ueit]

I do understand that the debate on this issue will be going on, but what I don't understand is the extreme scepticism against the idea that you only have unitary time evolution without a fundamental collapse. This is the minimal hypothesis that, as far as we can check, fits all experimental data, while the fundamental collapse idea requires new physics for which there isn't a shred of evidence.

The unitary evolution, by itself, does not explain our observations. We never observe superpositions. Therefore you need an additional postulate that explains how is that we see point particles in a 3d space and not a smoothly evolving universal wavefunction. IMHO it is this postulate that is hard to accept, and for a good reason.

 

[Count Iblis]

The unitary evolution, by itself, does not explain our observations. We never observe superpositions. Therefore you need an additional postulate that explains how is that we see point particles in a 3d space and not a smoothly evolving universal wavefunction. IMHO it is this postulate that is hard to accept, and for a good reason.

The additional postulate you need is simply the definition of observer states. The fact that the fundamental Hamiltonian contains local interactions takes care of superpositions that are widely separated in position due to decoherence.

You cannot expect that a fundamental theory would tell you how to define an observer. The best you could do in theory is to use the theory to compute what an observer, put in by hand but defined in the language of the theory, would evolve as he interacts with the rest of the universe.

 

[WaveJumper]

I couldn't agree more. We don't see the whole picture, that's how/why the Newtonian world arises from space phase in our brains. It's our peculiar, limited and "coarse" sensory apparatus that brings about the notion of 3D vision.

Do you have any evidence for this assertion? How exactly does the 3D world "arise" in a brain? What is the reason you feel the need to assume this?

I am not assuming anything, quite simply the morphological structure of your sensory apparatus is painting a limited and somewhat distorted picture of reality. Have a look at it this way:

People think objects are at rest when every particle they are made of is in constant motion at immense speeds. People think objects are made of "stuff", when solid objects feel solid because of a force called electromagnetism. Switch off electromagnetism and the strong nuclear force and the otherwise "solid" looking objects will disappear. People think solid objects are solid and physical when even the biggest physical thing they have ever seen in their lives - the Sun will disappear into a zero dimensional "point" without a trace if it were to hit a black hole. This event would seem mind boggling only because people usually think of "solid" matter from the perspective of their everyday lives at the Newtonian level. But that's an abstraction created by the mind and the inputs of our "coarse" sensory apparatuses at our level of existence.
People think the universe is lit when in reality it's fundamentally dark. We've "picked" one wavelength of the EMR spectrum and "learned" to use it to find our way in the dark, but fundamentally there is no light and the universe is dark. It's lit only to us, who have this peculiar human sensory apparatus(and to the animals that have vision).
At the fundamental level, the universe is much different to what we think of it, due to the way we see it. Had we used neutrinos instead of photons for our vision, we'd see only extreme light and empty space. Neutrinos can pass through your body, then go on on their journey and pass right through the Earth and exit on other side and head for the sun and pass straigth through it like nothing ever happened and go on on their journey.
That's how our notion of the Newtonian world arises. It's based on what we are able to perceive through the body apparatus(somebody used the word "interface" earlier). A bat sees the Newtonian world differently as it's not limited by the availability of light, as it uses echolocation.

So if i were to use a summary, i'd pick my initial quote:
We don't see the whole picture, that's how/why the Newtonian world arises from space phase in our brains. It's our peculiar, limited and "coarse" sensory apparatus that brings about the notion of 3D vision.

there would be no Newtonian world if there were no living forms

Why?

Because it arises in the mind. If you didn't have the senses you have in your body, you wouldn't know where the atoms of an object end and where the atoms of air take over. At the very least, you need senses + a brain to infer the implied "meaning" in the phase space.