How can we test the holographic principle and nonlocality in quantum mechanics?

[vanesch]

You're making my point for me. A is a possible state; B is a possible state; (A+B)/sqrt(2) is a possible state. (and lots more) But the crucial point is that the third is not the same as the first or the second. There are just these three distinct states. And so if the real state is the third, and someone believes it's the first, they're wrong. That's my whole point.

Ok, strictly talking you're right. So how do you describe the state where your body is in a superposition of being in the grocery store and riding a horse with some coefficients ? Although you're strictly right that these are different states than being "fully" in the grocery store, or "fully" riding a horse, you can understand the verbal description as being partly in the grocery store and partly on the horse, no ?

See, this is a bit like talking about "which slit did the lightpulse go through ?"
Answer: both. So is it wrong to say that the lightpulse went through the first slit ? Strictly speaking, yes. But it went "partly" through the first slit.
So all this is semantics.

 

[ttn]

Ok, strictly talking you're right. So how do you describe the state where your body is in a superposition of being in the grocery store and riding a horse with some coefficients ? Although you're strictly right that these are different states than being "fully" in the grocery store, or "fully" riding a horse, you can understand the verbal description as being partly in the grocery store and partly on the horse, no ?

See, this is a bit like talking about "which slit did the lightpulse go through ?"
Answer: both. So is it wrong to say that the lightpulse went through the first slit ? Strictly speaking, yes. But it went "partly" through the first slit.
So all this is semantics.

It's only "semantics" in the sense that I insist on using words with their precise meanings, and you want to be sloppy. Two states like A and (A+B)/sqrt(2) are just irreducibly different in QM -- as different as any two things could ever be classically (like the cat is dead and the cat is alive). If you say the cat is dead and really it's alive, that's just plain false. Likewise if you say A and the reality is (A+B)/sqrt(2). It's not "partly true", it's just false -- false as a statement of what the *real state is*. Same for your 2-slit example. I don't agree with your characterization that it went through "both" (for reasons I explained before). That's OK if we both know you mean, by "both", that it's a superposition, but the real state (according to OQM) is not "both" (which is vague) but (A+B)/sqrt(2). And then it's just the same as before. If someone thinks it's A, they're not "part correct", they're not stating "part" of the truth, their statement is not "partly true". It's just wrong. They think the state is one thing, when really it's something else.

Which is why I keep insisting that, according to MWI, we're deluded about such things as whether experiments have outcomes, whether cats are alive or dead, whether the dinosaurs still exist, etc. And which is, in turn, why I don't think any reasonable person can accept MWI. If I might be wrong about whether there's a cat sleeping on my lap (there is :!) then there's no bleeping way in hell I might be right about something so high-level as the deep structure of the universe.

 

[Rade]

... So how do you describe the state where your body is in a superposition of being in the grocery store and riding a horse with some coefficients ? ...

I would describe this state as being "impossible" unless I was riding the horse inside the grocery store.

 

[Hurkyl]

When you say "R is is unmeasurable" do you mean simply that the word 'area' is not applicable to R? Are you defining 'measure zero' as the end of an unending process such as ' as R tends to zero'?

I mean it in the technical sense that you would see in a real analysis class. One way to describe them is that "R is unmeasurable" means that:

$$\int_R 1$$

is undefined¹

and that "R has measure zero" means that:

$$\int_R 1 = 0$$

According to the theory put forward in that paper, two people can both look in Ernies drawer (not drawers!) and one of them can see the book there and one of them can fail to see the book there -- and they're both right, because the book *is* there "relative to the first observer" and the book *isn't* there "relative to the second observer".

Have I misunderstood you, or you actually trying to talk about the relational interpretation of QM? This doesn't look anything at all like what I've read about it.

The relational interpretation says that it's equally valid to say that Bert looks in the drawer and sees the book, while when Oscar considers the situation, that the drawer is in a superposition of containing and not containing a book. But it certainly does not say that it can be equally valid for Bert to say he sees a book, and Elmo to say he doesn't see a book.


1: note that if $\int_R 1 = +\infty$, I consider that integral to be defined.

 

[vanesch]

Which is why I keep insisting that, according to MWI, we're deluded about such things as whether experiments have outcomes, whether cats are alive or dead, whether the dinosaurs still exist, etc. And which is, in turn, why I don't think any reasonable person can accept MWI. If I might be wrong about whether there's a cat sleeping on my lap (there is :!) then there's no bleeping way in hell I might be right about something so high-level as the deep structure of the universe.

In absolute terms, you're right of course. But that doesn't shock me: why should you know anything directly about the "real universe out there"?
But in relative terms, you do have "understanding" of the organization of your observations. So there's some connection between the different observations you (thought you) made. And this relative description is a *part* of a potential overall description about "the real universe out there".

That's why I wanted to make a compromise: we're not FULLY deluded, but only HALF deluded

 

[Farsight]

If you thought it was interesting, you probably didn't understand it...

OK. I'll look at it again, but see hurkyl's note above.

Ernies: yes, "does not compute" was patois for "it doesn't make sense". When we're talking about the location of a photon and considering it to be a particle, consider the photons involved in long range radio communication.

All: (edited) I have a hundred bucks. It's a quantity, not a thing. I only think it's a thing because that's what I'm used to. I might be looking at it on the table in front of me, but a hundred dollar bill would be merely a scrap of paper, and in fact what really looking at is my bank statement. I think I spent it, but it still exists, kind of, although in a way it never really existed in the first place because money is a just a relative "capacity to do work" concept like energy. Anyhow. Right now half of it is with the grocery store where I used my debit card to pay for whiskey. And following a phone call, the other half in on a horse. Where is my hundred bucks? What's its length? Its location? Its area? In what point in space are the quanta that make up that hundred bucks? Where are the cent particles?

 

[ttn]

Have I misunderstood you, or you actually trying to talk about the relational interpretation of QM? This doesn't look anything at all like what I've read about it.

The relational interpretation says that it's equally valid to say that Bert looks in the drawer and sees the book, while when Oscar considers the situation, that the drawer is in a superposition of containing and not containing a book. But it certainly does not say that it can be equally valid for Bert to say he sees a book, and Elmo to say he doesn't see a book.

See the section from the Smerlak/Rovelli paper where they finally apply their ideas to the EPR situation. You have to read between the lines a bit -- they don't come right out and say what their ideas imply (which is what I described above), and for obvious reasons. (If they did describe the implications clearly, nobody could possibly take it seriously.) But pay attention to the part about "everybody seeing the same elephant" or whatever. This is actually an attempt to answer the kind of objection I made before. But the answer isn't that the two people actually see the same thing -- it's that the first guy sees the book *and sees the second guy agreeing with him that the book is there*, while the second guy sees no book *and sees the first guy agreeing with him that there's no book*. That's the sense in which "everybody sees the same elephant".

 

[Ernies]

Ernies: yes, "does not compute" was patois for "it doesn't make sense". When we're talking about the location of a photon and considering it to be a particle, consider the photons involved in long range radio communication.

All: (edited) I have a hundred bucks. It's a quantity, not a thing. I only think it's a thing because that's what I'm used to.

Photons: An astronomer says that some photons he has just detected were emitted from a star 100million light-years away. Does this mean anything in your terms? Does it make sense to ask what they were doing in the intervening time? Does it make sense to ask where they were? If not, why not.

All: your hundred bucks is a mere token, as is the bank statement etc. You may exchange these for things of 'value', or even other tokens you deem of 'value' such as company shares. But all of the tokens, including the bet on horses you mention. are wholly dependent on opinion, good faith, or trust. When this fails the things become valueless, as in a scam, a stock-market crash, or re-estimation of the provenance of a painting.
I hope you managed to drink the beer before it went off.

I'm afraid I cannot see where this is relevant to any of the discussions.

Ernies

 

[vanesch]

See the section from the Smerlak/Rovelli paper where they finally apply their ideas to the EPR situation. You have to read between the lines a bit -- they don't come right out and say what their ideas imply (which is what I described above), and for obvious reasons. (If they did describe the implications clearly, nobody could possibly take it seriously.) But pay attention to the part about "everybody seeing the same elephant" or whatever. This is actually an attempt to answer the kind of objection I made before. But the answer isn't that the two people actually see the same thing -- it's that the first guy sees the book *and sees the second guy agreeing with him that the book is there*, while the second guy sees no book *and sees the first guy agreeing with him that there's no book*. That's the sense in which "everybody sees the same elephant".

YES !

You've got it !

I'm trying to say this already for ages on the "beyond the standard model" subforum (in the thread "everybody sees the same elephant").
My point there is EXACTLY what you write above: that the everybody sees the same elephant, actually means:
everybody SEES everybody else agree on the same elephant (and nevertheless, everybody sees something different than everybody else).

That's why I'm claiming already since quite a while that the Rovelli and Smerlak PoV the "single observer" PoV is from MWI.

And not to get this thread off topic, I'd invite all further comments specifically about RQM in the relevant thread over there.

That said, there's nothing WRONG with it. If a theory tells you that Jack sees a book and Joe doesn't, but Jack sees "a" Joe seeing a book, while Joe sees "a" Jack not seeing a book, then everybody, in his own little world, sees an entirely consistent picture ; nevertheless, each picture can be different, but the whole point is: we can never verify this.
I know that it feels wrong, because we are so convinced that what we see, and only what we see, must be "out there", that we have a hard time thinking that what we see is only our own private vision on the universe, only shared with versions of the others, and that there might be other such worlds where there are other versions of "you" who live in the private visions of others.

I agree that it would be nicer to be able to say that what we see is what is there, and that's it. But things don't NEED to be that way.

 

[nrqed]

YES !

You've got it !

I'm trying to say this already for ages on the "beyond the standard model" subforum (in the thread "everybody sees the same elephant").
My point there is EXACTLY what you write above: that the everybody sees the same elephant, actually means:
everybody SEES everybody else agree on the same elephant (and nevertheless, everybody sees something different than everybody else).

That's why I'm claiming already since quite a while that the Rovelli and Smerlak PoV the "single observer" PoV is from MWI.

And not to get this thread off topic, I'd invite all further comments specifically about RQM in the relevant thread over there.

That said, there's nothing WRONG with it. If a theory tells you that Jack sees a book and Joe doesn't, but Jack sees "a" Joe seeing a book, while Joe sees "a" Jack not seeing a book, then everybody, in his own little world, sees an entirely consistent picture ; nevertheless, each picture can be different, but the whole point is: we can never verify this.
I know that it feels wrong, because we are so convinced that what we see, and only what we see, must be "out there", that we have a hard time thinking that what we see is only our own private vision on the universe, only shared with versions of the others, and that there might be other such worlds where there are other versions of "you" who live in the private visions of others.

I agree that it would be nicer to be able to say that what we see is what is there, and that's it. But things don't NEED to be that way.

But then, this feels like solipsism to me. I mean, I m talking to all those people and asking them what they are feeling, what they are experiencing and so on...Are these people "zombies"? I can never "really" access what they are really experiencing ?? So maybe when my girlfriend is saying that she loves me, maybe the "true" her is really experiencing a world where she hates me?
Or am I missing the point completely?

 

[vanesch]

I would describe this state as being "impossible" unless I was riding the horse inside the grocery store.

I know. But it is THE FOUNDING PRINCIPLE of quantum theory.
It is from this principle (the superposition principle) and the principle of complementarity that the entire machinery of quantum theory is build up.

So it would be totally crazy to deny the principle *to interpret quantum theory*. You might reject the principle, or limit its applicability (as did Bohr: only to the microscopic world). But doing so means also that you kill off the entire formalism of quantum theory that was build upon this. Fine. Go ahead. But come back with something to replace it that explains its empirical success then.

It is a bit as having the principle of relativity (nature is the same for all inertial observers) - take it from Galileo or from Einstein - and clinging on the existence of an absolute space (such as in ether theory).
If you do so - which you can, of course - then the principle is dead. You can try to build something that is empirically equivalent, like introducing AD HOC rules for "length contraction" and "time dilatation", but these are things introduced BY HAND. There's not one single reason for things to be so. For instance, length contraction and time dilatation could work for matter made out of the even elements, while it could not work for stuff made out of uneven elements in the periodic table. Nothing requires it.

The power of physical theories has always been that some fundamental principles are taken as their foundation, and from there, everything is build up. For special relativity, these are the principle of relativity and the fact that lightspeed is the same for all observers. For general relativity, these are the equivalence principle and general covariance. And for quantum theory, this is the superposition principle (and the principle of complementarity).

The naturalness by which the formalism is deduced from these fundamental principles is much greater, than when one has to start from an opposite paradigm, and introduce a lot of tricks BY HAND to obtain the empirically verified formal results. This is, for instance, what happens in ether theory, or what happens in Bohmian mechanics when dealing with 1) relativity and 2) the very existence of the quantum formalism.
The entire machinery of the wavefunction is incorporated in BM *by hand*. It is not required by any fundamental principle, but things are put in this way so that it comes out the same *as if* the superposition principle were true (which it isn't, of course), and so that things come out *as if* the principle of relativity were true (which it isn't, of course).
Of course, all this is just an esthetical judgement. Nature doesn't have to follow anything we desire. Solipsism is not falsifiable, and there's no obligation for causality either. Things can happen and if we cannot make sense of it, because there is no deeper sense or no underlying principle, then so be it.

So whether or not we should require there to be a causal ontology, or even an ontology in the first place or whether or not we should require there to be some fundamental principles from which we can derive an ultimate theory of nature describing such an ontology, is an open question. After all, the only thing we can really do is to find some regularities in our observations. All the rest is hypothesis. Nevertheless, the tradition of taking some basic principles, and stick to it, has given us very impressive results in the past. Have we exhausted that line ? Who can tell ?

So, if we stick to the idea that founding principles of a theory are somehow universal and strict, then the superposition principle, on which all of quantum theory is constructed, tells us that we can be in a state made up of us being in the grocery store, and us riding a horse in the woods.

One doesn't realize from the start what is the totally crazy, mindboggling implication of this statement, when formally announced in quantum theory.

It is from this statement that follows that quantum states span a hilbert space, and that we should use linear operators over the space, for instance.

Then one learns about hermitean operators, eigenvalues, harmonic oscillators, unitary time evolution, etc... and after a long time, one starts to think again about the "measurment problem" and this funny formalism that doesn't allow you to describe a measurement as a physical interaction described by a hamiltonian, and those remaining superpositions and all that. And one blames the formalism of quantum theory, and "to reify the mathematics" and all that.
But it was put in from day 1 ! It was put in that the voltmeter could be in a state which is a superposition of "reading 5V" and "reading -2V" at the same time. That's simply the superposition principle, applied to a voltmeter. It isn't surprising, then, that this comes out of the formalism.
This has nothing to do with "taking the maths too seriously" (like using unphysical solutions to an equation or so).

 

[vanesch]

But then, this feels like solipsism to me. I mean, I m talking to all those people and asking them what they are feeling, what they are experiencing and so on...Are these people "zombies"? I can never "really" access what they are really experiencing ?? So maybe when my girlfriend is saying that she loves me, maybe the "true" her is really experiencing a world where she hates me?
Or am I missing the point completely?

First of all, we're talking about the interpretation of quantum theory. I don't know if quantum theory is ultimately correct, so before using these ideas to beat up your girlfriend (she knows why, you don't ), one should first be sure that quantum theory is ultimately true - which we don't.
All I say is from the viewpoint: 'let's take a toy universe where quantum theory is strictly true and see what that toy universe looks like" and it turns out that there are indications that this looks quite a lot like ours - but that's no proof of course that both are the same. There's still a lot we don't know (and I think we will ALWAYS be in such a situation).
As you know, we might all just be characters in a big computer simulation program a la Matrix, or any other "reality". So let's simply assume we talk now about a toy universe where quantum theory holds strictly (the superposition principle holds strictly).

Second, there is no "true" her. There are TWO "hers". You better be nice to the one in YOUR subjective world, because it is with THAT one (or her later spin-off copies which will have her memories) that you will have to deal from now on (while the other "hers" will have to deal with the spinoffs from you - let them have their life!). The question is: from this PoV, does it make any sense to try to be a hero and take "risks for the sake of the others" ?

But again, be careful about drawing any moral implications from this. They'd turn you into a politician or a business man ; and after all, we don't know if quantum theory is ultimately correct !

 

[ttn]

YES !

You've got it !

Nice to finally agree with you about something!

I'm trying to say this already for ages on the "beyond the standard model" subforum (in the thread "everybody sees the same elephant").
My point there is EXACTLY what you write above: that the everybody sees the same elephant, actually means:
everybody SEES everybody else agree on the same elephant (and nevertheless, everybody sees something different than everybody else).

That's why I'm claiming already since quite a while that the Rovelli and Smerlak PoV the "single observer" PoV is from MWI.

Yes, I think that's right. This RQM stuff is just MWI in disguise, except that it's an especially subjectivist, anti-realist version of MWI. I'm not sure it's "the single observer" version that you sometimes advocate (where there's just the one "consciousness token" -- yours -- flowing down the branches in some random way, everybody else being mindless hulks) since they go so far out of their way to talk about how all different people all get to have some "consistent" sort of experience. So it's more like a "many observer" version (lots of "consciousness tokens" flowing down the river, but all likely to be in different branches and hence to experience only mindless hulks in their own branch -- as nrqed also pointed out). But whatever; it doesn't speak too highly of this theory that it leaves all these questions vague. And I think the fundamental thing to say about it doesn't have much to do with consciousness anyway: RQM is like MWI except that instead of saying "there's a real world out there which is described completely by some big universal wf" they deny that the wf is a (complete) description of something -- they regard it as merely "information" (in somebody's head?). So it's like MWI but anti-realist (in the sense that *even* MWI is realist). Indeed, as far as I know, RQM is the only version of quantum theory ever proposed which is thoroughly, fundamentally anti-realist. According to it, there simply is no external reality at all (not classical level stuff as in Copenhagen, not particle positions as in Bohm, not a big crazy wf as in MWI, not a wf obeying a modified Sch eq as in GRW, etc.). There's just: some person's (or maybe some peoples') ideas/information. This is *idealism* in the hard-core philosophical sense (Berkeley, etc.). There is literally no physical reality according to this theory -- just ideas (and not even any heads, which are physical objects, for those ideas to be in!).

And not to get this thread off topic, I'd invite all further comments specifically about RQM in the relevant thread over there.

I don't really think it's off topic (at least no more than the stuff about whether MWI requires everything to be a delusion). What we're exploring here are the possible ways of *avoiding* Bell's conclusion that violation of the inequalities signals real nonlocality in nature. MWI and RQM are indeed two such options, but look at the price you pay. According to MWI you can't trust your senses to give you correct information about the real world, which pretty much undermines whatever (empirical!) reason you thought you might have had for believing MWI (or the Sch equation, or relativity, or the Copernican theory of the solar system, or ...) in the first place. And RQM manages to elude the claim that nature is nonlocal by saying: there's no such thing as nature!

That said, there's nothing WRONG with it.

Well, other than the false advertising. If RQM's advocates explained what it really meant, though, they'd get laughed off the stage. They (I think) deliberately trade on obfuscation to make the theory sound less crazy than it really is. And that is wrong. But yeah, if they explained it honestly and clearly, there'd be nothing wrong with the theory as such -- except that it's so crazy no scientist should believe it.

If a theory tells you that Jack sees a book and Joe doesn't, but Jack sees "a" Joe seeing a book, while Joe sees "a" Jack not seeing a book, then everybody, in his own little world, sees an entirely consistent picture ; nevertheless, each picture can be different, but the whole point is: we can never verify this.

Mmmmm, science (said in Homer Simpson voice with drool running out of the mouth).

 

[ttn]

But again, be careful about drawing any moral implications from this. They'd turn you into a politician or a business man ; and after all, we don't know if quantum theory is ultimately correct !

That's an interesting comment. You said, though, that it's nice to imagine a universe which *is* the way (say) MWI says it is (in order to better understand how the theory works). Well can't we imagine too that, in that universe, we scientists *knew* the truth of MWI? And then, wouldn't the "moral implications" you're worrying about here come very much into play? If I can be certain that everyone around me is really in fact only a mindless hulk, then why shouldn't I beat them up (or whatever)? I'm not really hurting anyone, right?

This is probably starting to be sufficiently far off topic that we shouldln't pursue it. But I thought it was interesting that you said, basically, that it is only the fact that *we aren't sure* if MWI is true, that prevents us from justifiably taking horrible actions (which would be completely OK if MWI were true). It makes me hope that nobody ever proves that MWI is true (not that I'm worried about that anyway)... or if they do, I hope I don't live near you!

 

[Farsight]

Vanesch: I beg to differ. The founding principle of quantum theory is Quanta. Increments. But somewhere along the line these got turned into particles.

All: I came across this paper by Simon Saunders called "Complementary and Scientific Rationality. I haven't read it yet, but it looks interesting:

http://users.ox.ac.uk/~lina0174/cushing.pdf

Ernies: An astronomer says that some photons he has just detected were emitted from a star 100million light-years away... Does it make sense to ask what they were doing in the intervening time/where they were? Sure it does. But an axiom that says quanta are particles does not. Your hundred bucks is a mere token... I know. It's relevant because money has no tangible existence or location, but people can't stop thinking of it as being in a place.

 

[vanesch]

Vanesch: I beg to differ. The founding principle of quantum theory is Quanta. Increments. But somewhere along the line these got turned into particles.

That's an often considered mistake, induced by the name "quantum" physics.

The "quanta" in quantum physics are not put in as a principle, they come out as spectra of operators, which often have a discrete part.

Particles are only put in literally in non-relativistic quantum theory of, eh, a finite set of classical particles.
But in quantum field theory, for instance, the fundamental entities are FIELDS (you can't get more "continuous"). It turns out, by APPLYING the principles of quantum theory, that come out of it, "steps" or "particles". But these principles don't go IN the theory.

There's no axiom, somewhere in the formalism of quantum theory, that is supposed to be the mathematical translation of the "principle of the quanta" or something. It comes OUT of the theory, you don't put it IN.

However, what goes into the axiomatic structure, is: "states of a system are described by a vector in hilbert space" and:
"there is a complete set of observables, whose eigenstates span the hilbertspace" (ok, shortcut to the construction with the spectral projectors and so on).

For the quantum system associated to a classical system, this "complete set of observables" is taken to have a spectrum that is equivalent to the configuration space. That's why, for a single particle, whose configuration space is given by (x,y,z), there is a complete set of observables X, Y and Z, whose spectrum covers (x,y,z), the configuration space.
And from that, plus the idea of the hilbert space, is that to each point in configuration space (classical position) (x1,y1,z1), corresponds one basis vector |x1,y1,z1> of the Hilbert space, and the Hilbert space being a complex vector space, all superpositions of the kind A |x1,y1,z1> + B |x2,y2,z2> are also states of our quantum system.
The hilbert space is now spanned.
The principle of complementary now requires that the associated conjugate momenta p correspond to operators P that satisfy the canonical commutation relations: [Q, P] = i hbar

The entire quantum machinery is set up for a single particle here.
The only thing that's still missing is the dynamics, which can be inspired by the classical analogon, or entirely empirical, or by other principles.

A very similar procedure is used in QFT, but we do not start from the "configuration space" of a particle, but rather of a (classical) field, and we take inspiration from the classical field theory to define the dynamics.
From the dynamics follows the Hamiltonian (or energy), and we look for states with definite energy. Guess what ? It comes in steps, and each step is called "a quantum" of the field.

Nowhere we used a "basic concept of quanta" here as a principle. It comes out of the machinery. It's not put in. What is put in, is the linear machinery, which is the mathematical translation of the superposition principle.

 

[ttn]

I'm trying to say this already for ages on the "beyond the standard model" subforum (in the thread "everybody sees the same elephant").
My point there is EXACTLY what you write above: that the everybody sees the same elephant, actually means:
everybody SEES everybody else agree on the same elephant (and nevertheless, everybody sees something different than everybody else).

I just went and skimmed through some of the recent posts on that other thread. Patrick, you're completely right about everything (there). And the imaginary real FTL telephone is a nice pedagogical idea. I'm not sure what all your opponents there (not to mention Rovelli) are thinking. Or maybe it's as simple as: they aren't.

 

[vanesch]

That's an interesting comment. You said, though, that it's nice to imagine a universe which *is* the way (say) MWI says it is (in order to better understand how the theory works). Well can't we imagine too that, in that universe, we scientists *knew* the truth of MWI? And then, wouldn't the "moral implications" you're worrying about here come very much into play? If I can be certain that everyone around me is really in fact only a mindless hulk, then why shouldn't I beat them up (or whatever)? I'm not really hurting anyone, right?

You keep insisting about the "mindless hulks" ; that's not true ! EVERY copy of an observer is as mindfull or as mindless as any other, and the point you touch upon has in fact nothing to do with MWI - it is a perfectly sensible position to posit that you are the only conscious being around, classically, or in MWI or whatever, which would lead to immoral behaviour towards others. MWI has nothing special about that, on the contrary.
Nowhere, the claim is made that the "copies" are "mindless" (although you keep insisting on that). The copies are copies, just as TWINS are.
So the moral implications are NOT that the others are mindless or not. They are, or they aren't, according to your belief whether in a classical world, the others are, or aren't, mindless.

The moral implications specifically related to MWI are on another ground: because all possibilities are realized somewhere, one could ask whether it has any use to take risk which doesn't bring *yourself* any profit (in other words, altruistic risk), because in as much as it might bring profit to the copies in YOUR world, the failure will bring harm to the copies in some other world.

Imagine, for instance, that there's some gangsters (now, the politically correct word is "terrorist" I guess ) hijacking a plane. You have a gun, and you might shoot them, but then, this might work, or this might fail, in which case the others are in a worse situation than if you do nothing. In a "single world" this is a "chance to take", with a happy or unhappy outcome. In MWI, both will happen. Does this influence the decision ?

Now, if you are going to "weight" the happiness or harm of all the others, in your and in other worlds, with their hilbert norm, then you will actually take a decision which will optimise your own chances of being in a "happy world", and, by doing so, also for the copies now in your world. So in fact, (I'm with Deutsch here), the most rational "morality" is to optimise your own chances for "observing happiness". And that coincides with exactly the rational behaviour of any being. Depends then, on what it means for you, to be happy.
So any rational decision will not be altered by an MWI or no MWI view. It's only the "emotional" part that's different and you might, for instance, think twice about "sacrificing yourself for the sake of humanity"
(which, according to MWI, is most of the time a silly idea - and honestly, probably for most people too).

This is probably starting to be sufficiently far off topic that we shouldln't pursue it. But I thought it was interesting that you said, basically, that it is only the fact that *we aren't sure* if MWI is true, that prevents us from justifiably taking horrible actions (which would be completely OK if MWI were true). It makes me hope that nobody ever proves that MWI is true (not that I'm worried about that anyway)... or if they do, I hope I don't live near you!

No, again, you think that MWI is locked up with mindless hulks, but it isn't (or it is, but then you already consider that others are mindless right now, without MWI-like considerations).

And it isn't the first time that one hesitates to draw fully the potential moral conclusions from a physical theory. What to think about full determinism for instance ? Should we let murderers go, because after all, it was a law of nature that they had to kill the other, and they didn't really have a choice ? And then, do WE have a choice ? And should we care what we do, given that we don't have a choice ?
And given that we slaughter cows for dinner, and that these are mammals like us, shouldn't we slaughter people too ? Etc...

I think that in general, considerations of morality are so remote from the basic principles of a physical theory that one shouldn't base oneself on it to do so, and MWI is no exception.

 

[vanesch]

Just to add a point (although we're getting far off topic), to this insistance upon "mindless hulks" which are in no way implied by MWI.

If the state is in 0.95 |bob+> + 0.31 |bob-> after evolving out of |bob0>, and we put the "original bob0 token" in bob+, this doesn't mean that bob- is not any "more" bob than bob+, or is a mindless hulk.
It just means that it is a NEW COPY of the original bob, and hence with a new mind, which just got "created".

This is one way of viewing this, from a single-observer perspective, which evolved from |bob0> to |bob+>.

There's another way to view things: that is: if you are A BOB MIND, then your chances to "live" bob+ are 90% and your chances to live bob- are 10%.

Consider that there are in fact 10 billion "bob minds", then 9 billion will have the same bob+ experience and 1 billion will have the bob- experience.

I think that the error many MWI people commit is trying to do "state counting" to do the "minds assignement". I don't see any problem in assigning a non-uniform weight.

Amen.

 

[ttn]

Just to add a point (although we're getting far off topic), to this insistance upon "mindless hulks" which are in no way implied by MWI.

If the state is in 0.95 |bob+> + 0.31 |bob-> after evolving out of |bob0>, and we put the "original bob0 token" in bob+, this doesn't mean that bob- is not any "more" bob than bob+, or is a mindless hulk.
It just means that it is a NEW COPY of the original bob, and hence with a new mind, which just got "created".

I also have no interest in pursuing this diversion, but just to clarify what I had in mind before: I was thinking of the version of MWI I thought you usually advocate, in which there is just a single "consciousness token" associated with any given physical observer, and we flip a Born-rule coin to decide which branch the token ends up in when branches split. Thus, whichever branches don't get the token contain mere mindless hulks. And then I had in mind an extension of this in which there is one "cs token" for each physical observer... in which case it becomes overwhelmingly probable that the copies of all other observers inhabiting the same branch as *my* "cs token", are mindless hulks. And same for your cs token, etc.

Now it's true that you can take the approach you suggested, namely not just having one "cs token" per observer, but have a million of them or just forget about "tokens" and say that consciousness exists wherever an observer with an appropriately-configured brain exists. The problem (as I know you already know) is then making some sense of Born rule probabilities. With this approach, it becomes absolutely certain that "bob+" and "bob-" both occur and get experienced. So what do the 91% and 9% then refer to? What are these probabilities probabilities *for*? It was precisely to answer this question that the first version (with a single cs token) was so nice.

But anyway. This is just subtly different versions of something that's crazy no matter what flavor you select. So I'll leave it for the crazy MWI supporters to work out.

 

[Hurkyl]

You have to read between the lines a bit -- they don't come right out and say what their ideas imply

I would prefer to discuss the theory overtly described in the papers I've read, and not the secret one hidden "between the lines".

This is actually an attempt to answer the kind of objection I made before. But the answer isn't that the two people actually see the same thing -- it's that the first guy sees the book *and sees the second guy agreeing with him that the book is there*

Of course. The question you ask is not a physical one. The question they answer is physical. I am quite pleased that they make this distinction.

This is a far cry from your accusation that:

two people can both look in Ernies drawer (not drawers!) and one of them can see the book there and one of them can fail to see the book there

(But, incidentally, I don't have any problem with a theory for which this accusation is true)

Yes, I think that's right. This RQM stuff is just MWI in disguise, except that it's an especially subjectivist, anti-realist version of MWI.

I disagree with this -- they do appear to have some similarities, but they have a very different viewpoint.

MWI says that ultimately, reality "is" in a superposition of states, and the collapse is a mathematical fiction, or what a consciousness sees, or something like that that I haven't followed much yet.

OTH, as I understand it, RQM says that collapse is a gauge freedom. Where and how you make the collapse is an entirely aphysical choice. Different choices are just studying the same physical system from a different viewpoint. (Much like how in SR you can analyze the same physical state in many different coordinate charts)

 

[Farsight]

Vanesh, thanks for the lengthy response. I was rather thinking about black-body radiation, and I meant particles as the axiom.

"Quantum field theory (QFT) is the application of quantum mechanics to fields. It provides a theoretical framework, widely used in particle physics and condensed matter physics, in which to formulate consistent quantum theories of many-particle systems, especially in situations where particles may be created and destroyed...

 

[Farsight]

I found this on Google. Any comments? Is it hogwash?

http://www.blazelabs.com/f-p-inst.asp

"Astronomical studies indicate that the Earth's acceleration is toward the gravitational centre of the sun even though it is moving around the sun, whereas light from the sun is observed to be aberated. If the gravitational force between the sun and the Earth were aberated, then gravitational forces tangential to the Earth's orbit would result, causing the Earth to spiral away from the sun, due to conservation of angular momentum...

Edit: Oh boy. I've just noticed the title.

 

[Hurkyl]

Odd. It sounds like Tom Van Flandern, but his name doesn't seem to be attached. Anyways, the whole thing is based on a simple mistake: it assumes that the gravitational field is simply a bunch of arrows that say "go that way". That picture doesn't even work for the electromagnetic field!

 

[Rade]

Originally Posted by vanesch
... So how do you describe the state where your body is in a superposition of being in the grocery store and riding a horse with some coefficients ? ...

First Question. According to HUP, it is impossible to visualize any thing simultaneously that has both definite position (e.g., body being in a grocery store) and definite momentum (e.g., body moving on a horse in the woods). So your argument that superposition principle allows human body to have a "state" of definite position in one place (in store) and momentum in another (on horse) appears to be false, HUP does not allow it--but perhaps I am missing something that you need to clarify.

Second question. Can you supply some publications where a superposition of a macroscopic entity (e.g., such as what you call a human body having a state) has been experimentally documented to simultaneously have position in one place (e.g., your store) with momentum in a second place (e.g., your woods).

 

[vanesch]

I also have no interest in pursuing this diversion, but just to clarify what I had in mind before: I was thinking of the version of MWI I thought you usually advocate, in which there is just a single "consciousness token" associated with any given physical observer

Yes. And the others are OTHER observers (living in the same body).
One is not excluding the other, right ? The "single token" is a voyage of ONE SINGLE conscious observation. Nothing stops you from having others of these, but that doesn't matter for a single observer.

Now it's true that you can take the approach you suggested, namely not just having one "cs token" per observer, but have a million of them or just forget about "tokens" and say that consciousness exists wherever an observer with an appropriately-configured brain exists. The problem (as I know you already know) is then making some sense of Born rule probabilities. With this approach, it becomes absolutely certain that "bob+" and "bob-" both occur and get experienced. So what do the 91% and 9% then refer to?

That bob+ is the experience state of 91% of "the consciousnesses" and bob- is the experience of 9% of the "consciousnesses".
But I only need to introduce "many consciousnesses for the same state" because you seem to stick to some unwritten "law of conservation of consciousness" which doesn't allow you to create some along the way.

The single-observer version with token is the voyage of ONE consciousness if you want. It is a typical voyage.
The "single token" version is all you need to *explain observations*.
You only need to think of multiple or not, tokens, to have moral considerations. So it is cleanest to consider the single token version in all those aspects where you want to interpret the theory as a physical theory, in order to "understand" what is going on (like in, say, an EPR experiment, or a quantum eraser or so). Then you consider all others indeed as "mindless hulks", but that doesn't change any observation.
And this can just as well be applied to classical thinking.

What are these probabilities probabilities *for*? It was precisely to answer this question that the first version (with a single cs token) was so nice.

The point is: it is not strictly necessary (although admittedly natural), that, if there are twins, and you are one of them, that the probability to be either Joe or Jack (the two twins) be 50-50%.
There might be "more Joe-ness" than "Jack-ness" although both exist, and if you have to draw between them, be rather 90% of the time Joe, and 10% of the time, Jack.
See, there's a difference between: "Joe and Jack exist both", and "the probability for me to be Joe is 50%". The last doesn't have to follow from the first (which is, nevertheless, what world counters try to do).
The probabilities here are purely Bayesian, and are not frequentist, because there's only one draw for a consciousness of course.

Another way of formulating this is: the probabilities 91% / 9% are the typical probabilties of branching of a typical "consciousness worldline " represented by a token.

But anyway. This is just subtly different versions of something that's crazy no matter what flavor you select. So I'll leave it for the crazy MWI supporters to work out.

I completely understand the critique The exercise is: try to make sense of it. Again, I'm not claiming that the world we live in is like that for sure. I'm just claiming, that, GIVEN the basic principles of quantum mechanics, this is then, to me, how a toy universe strictly ruled by those principles looks like. It sounds indeed very crazy, I'll grant you that. But it doesn't sound totally illogical, and honestly, amongst the alternatives, it sounds, to me, still the LESS crazy of all. I prefer positing an at first sight crazy reality, than positing that there's no such thing in the first place (like Bohr, partly, or RQM or other variants).
Apart from views like Bohmian mechanics, but which give up on the basic principles of quantum theory, as founding principle.

So I consider MWI as the result of an interpretation process where you start from: take the fundamental principles rigorously true, where does this lead you ? If that leads you to something which is totally crazy, then this means that the fundamental principles are fundamentally crazy, that's all.

 

[vanesch]

First Question. According to HUP, it is impossible to visualize any thing simultaneously that has both definite position (e.g., body being in a grocery store) and definite momentum (e.g., body moving on a horse in the woods).

No, not necessarily. There's room enough to have two classically-looking states where there's a small uncertainty on your position and momentum for you to be in the grocery store (if the store is big enough, which I would presume it is) or to be on the horse, again, with some small uncertainty on your momentum and your position, but which corresponds still with "you riding a horse".
When I specified "you're in the grocery store" I didn't give your position to within 10^(-15) meter or so, did I ?

So your argument that superposition principle allows human body to have a "state" of definite position in one place (in store) and momentum in another (on horse) appears to be false, HUP does not allow it--but perhaps I am missing something that you need to clarify.

Yes, that I'm talking about "classically-looking" states, like coherent states, and not about entirely specified positions and entirely unspecified momenta. These states are like wave packets, and have a slight uncertainty on position and on momentum. For a human being, these uncertainties are entirely neglegible.
BTW, if that were the case, you could NEVER "be in the grocery store" by yourself for more than a microsecond, because after that microsecond, you'd be splattered all over the walls of the store.
So if you want to nitpick on that, it becomes even impossible to say "you're in the grocery store".

That said, the superposition of a pure position state, with a pure momentum state, is entirely possible (not confortable for a human, though).

You can write this as: |x0> + |p0>
and the waveform is then:

delta(x-x0) + exp(i p0 x)

(with appropriate normalisation factors, which are a bit tricky here).

That's an entirely possible wavefunction.

Second question. Can you supply some publications where a superposition of a macroscopic entity (e.g., such as what you call a human body having a state) has been experimentally documented to simultaneously have position in one place (e.g., your store) with momentum in a second place (e.g., your woods).

No

We are talking about *applying a principle* (= the superposition principle), not about empirical observations. As far as I know, no experiment has ever "established" the superposition of a human being. I personally consider an EPR experiment with human observers as coming close to that (but as you need other hypotheses too, it's of course no proof), but it has never been performed, and there are plenty of other explanations of the results too.

The point was: if you introduce a PRINCIPLE, and you SAY that it is universally valid, then it should apply to humans too.
I'm simply pointing out that the superposition principle, thus introduced, TELLS you that these strange superpositions of humans are POSTULATED to exist in that case (and that one shouldn't be surprised to find them coming out of the theory and scratch one's head).

Whether this is what really happens or not, is just a matter of whether the enounced principle has anything to do with reality, which is an entirely different question.

The entire thought process is simply an exercise in thinking about what the principles that are at the basis of a physical theory, really mean.

 

[Farsight]

Rade, here's superposition of a macroscopic entity:

I've got one cent. That's the quantum of US currency. Feeling flush I called my bookmaker and made a bet, putting my one cent on a horse. And then I went down to the grocery store and spent it on whiskey. My cent is now on the horse and in the grocery store.

A cent is not of course a coin. That's just a token. It's an action, or a potential action rather than something real and tangible. It is however the messenger "particle" for the human energy we call money.

 

[selfAdjoint]

Rade, here's superposition of a macroscopic entity:

I've got one cent. That's the quantum of US currency. Feeling flush I called my bookmaker and made a bet, putting my one cent on a horse. And then I went down to the grocery store and spent it on whiskey. My cent is now on the horse and in the grocery store.

A cent is not of course a coin. That's just a token. It's an action, or a potential action rather than something real and tangible. It is however the messenger "particle" for the human energy we call money.

Nah, the cent you spent is not the cent you bet; you didn't have to come up with a token to satisfy the bookie (the more fool he, and the more fool you when his boys break your kneecaps because you welshed).

 

[RandallB]

I agree with tnn that this thread has moved far from the original intent of “Is Non-locality a requirement”. Although I desire it not to be so, I think it has been answered that currently from both experiment and the requirements of viable popular theories that the answer for now is YES.
And any theory that supports a purely classic local (the local realist) view is not expected to be viable.

Non-Local viable theories discussed here competing to be THE solution include:
1) GR
2) MWI-QM (Strings included)
3) OQM
4) QFT
5) BM

All are non-local, and basically in competition with each other, with General Relativity having the widest differences with and all the others.

I’d like to draw out a particular comment and relate it to all 5 of these:

Bohmian mechanics being non-local, it rejects of course relativity.

With respect to Special Relativity I don’t think this is true for BM, GR or any of the other Non-local theories.
IMO They all embrace the embrace the principles within SR; Composition of speeds instead of addition, Time dilation, etc. They just deny that those SR elements by themselves can provide a complete solution and a non-local addition is required to complete the picture. Essentially not being able to do it with SR is what put Einstein on the path of GR.

GR is a non-local option (background independent) to complete that picture, so naturally in principle it competes with other non-local options to be the complete solution. But does anyone feel their preferred non-local theory needs to reject the basic principals in SR?

 

[CarlB]

IMO They all embrace the embrace the principles within SR; Composition of speeds instead of addition, Time dilation, etc. They just deny that those SR elements by themselves can provide a complete solution and a non-local addition is required to complete the picture. Essentially not being able to do it with SR is what put Einstein on the path of GR.

The problem with non local interactions and special relativity is that faster than light interactions in one frame imply backwards in time interactions in another.

Bohm himself wrote that special relativity is supported by "bohmian mechanics" only in that under the usual statistical assumptions, there is no way to pass information faster than light, and the results of any calculation do not depend on the frame of refernce chosen to make the calculation. There is a chapter in Bohm and Hiley "The Undivided Universe" devoted to this issue.

Admitting that I am not a scholar on this, the way I would put it is to say that Bohmian mechanics supports relativity as a "phenomenological" model, but not as a part of the "ontology". I believe that Bohm explicitly supports the concept of a preferred frame of reference, but as with Poincare and Lorentz, that frame of reference cannot be determined.

My belief is that special relativity is an "accidental symmetry". That is, if one understood the underlying theory one would see that there is, in fact, a preferred frame of reference, but that finding it experimentally in the obvious fashion might require energies on the order of the Plank mass.

Carl

 

[Hurkyl]

Non-Local viable theories discussed here competing to be THE solution include:
1) GR
2) MWI-QM (Strings included)
3) OQM
4) QFT
5) BM

How do you figure that??

GR is, essentially by definition, as local as a theory can get!

And while QFT does have non-locality to it, it is in a wildly different sense than is discussed here. States form a structure called a "presheaf" which essentially says that you cannot fully understand an entire object simply by looking at its individual parts.

The same goes, I think, for MWI.

 

[RandallB]

GR is, essentially by definition, as local as a theory can get!

What definition??
Not the incorrect assumption that GR is a simple extension of SR,
- it certainly is not that. See Smolin; The case for background independence; perimeter institute. Being local is going to require background dependence not independence.

And what does it mean to say “QFT does have non-locality to it” but here I want to get away with calling it local? Same goes for MWI, just because you can account for the probabilities OQM would use in the freedoms gained in (unproven) additional dimensions of reality doesn’t change the fact that it still non-local. That would be like saying OQM is local as long as I insist the only the HUP has “non-locality to it”.
Ridiculous.

The point with SR is that although it would like to solve reality within what we see as local reality in a local solution in cannot. And the debate comes down to what non-local theory can complete the picture.

 

[Careful]

**What definition??
Not the incorrect assumption that GR is a simple extension of SR,
- it certainly is not that. See Smolin; The case for background independence; perimeter institute. Being local is going to require background dependence not independence. **

That is (presumably) true in QUANTUM gravity, but not GR (GR is background independent and local) - btw that is exactly why I started investigating the superposition principle and (superpositions of different universes are terribly non local) think a deterministic local reformulation of QM is in place. You could return the question to Smolin and ask him why a non-local theory is going to reproduce local physics.

I do not see what in a unitary evolution of the universe would tell me that (a) something prohibits entanglement to spread out uncontrollably - hence the universe would behave as one entity very much in contrast to what we observe (b) what in QM tells me that I can apply the decoherence trick to a pair of entangled apples and not an EPR pair of electrons ? (btw tracing over the degrees of freedom in the environment gives a non-unitary evolution for subsystem - what should it have to do with the unitarity evolution of some wave function of the universe ?) (c) what would prohibit wave functions of subsystems to spread out - the quantum stability of matter is a very hard question ??

A nonperturbative detailed investigation of all interactions could bring more insight into the issue whether QM needs scales to impose macrorealism or not.

And why RandallB should the principles of QM apply at all on the shortest scales where people expect quantum gravity to be of any importance ?

Careful

 

[Hurkyl]

And what does it mean to say “QFT does have non-locality to it”

I don't really follow the phrasing of your paragraph, but I'll try to answer anyways.

I would have just said "QFT" is local, because it is local in the sense we have been discussing in this thread. But I can't bring myself to do it, because it is non-local in the sense that a quantum state cannot be fully understood merely by looking at its restrictions to different spatial regions.