Question on observer created reality

[Apak]

Before I begin I feel that I should state that I have only a passing amount of knowledge on the subject so if I've got something wrong let me know. My current understanding of QM is that certain atomic attributes are created through observation of these attributes. This seems to suggest that there are two values present in an observation, the observer and the reality created. So my question is what special properties does the observer possesses that allows an observation to be made. Here's what I mean, when a reality is present an observer is necessarily present. However, if an observer is present it does not neccesitate the presence of a reality. Looked at from this perspective the observer can be considered real, in that regardless of observations being made the observer always exist's and that reality only exists in relation to the observer. This would mean that the constituent parts of the observer in no way find their primary causes in the reality which the observer creates. This means that the system the observer creates finds all its values in the observer. The observer on the other hand finds none of its initial values in the system it creates. This is what troubles me the most about QM, if there is no separation between observer and observed, and the observer finds its initial values bound up within a system it creates through observation how is anything ever observed? Please help.

 

[seratend]

The first sentence of your post is promising, but in the rest you are introducing too many not well defined concepts (at list for a concrete physical and mathematical application).

(e.g. reality creation, etc ...).

In my opinion I will say: try to reformulate your post in a formal way with a reduced set of mathematical objects, it helps a lot to clarify the logical content.
For example, you may start to define mathematically (i.e. the logic) the consistent meaning of "certain atomic attributes" and "the observation of these attributes". If you do that, I think the following of your post is almost answered.

I hope this personal view may help.

Seratend.

 

[Apak]

Lets take the position attribute. To my understanding this attribute does not exist until it is measured. Now I don't know how its measured but it does not hold any particular value until it is measured unlike static attributes such as charge. So I guess you can define the reality created as those attributes that are not present until measured. Here is a measurement example, I think? Let's say you have a box with points A, B, C, D. At any of these points a particle may be present. So you put the particle in the box and make no observations. Since no observations are being made the particle has no definate position or, I'm not sure on this, no position. Now let's say detectors are placed at your points within the box and the particle is detected at position A. So what you have is the reality created, which is its position at the end of the measurement. So, from the standpoint of observation, the reality of the situation is that the particle is located at point A. However until that position was observed there was no reality to the situation, it may be there it may not. It is also my understanding that position does not exist unto the particle itself, but rather comes about as the result of the observer creating the value position and then measuring it. In other words the particles have no position until the observer decides to measure position at which time the particles then acquire position. So my question still is what gives the observer the ability to create its reality.

 

[vanesch]

In other words the particles have no position until the observer decides to measure position at which time the particles then acquire position. So my question still is what gives the observer the ability to create its reality.

This is the Copenhagen view of things, and its obvious problems. One of the reasons NOT to adhere to Copenhagen

But there are other ways of viewing quantum theory. First one has to make a big choice: is there an existing, real world out there or not ? This can sound like a completely crazy question from a physicist, but its answer is not so obvious.

A) there is a real world out there.

B) there's no real world.

Let's deal with B. What can it possibly mean ? It means that all there is, is "observation", and "knowledge". In that respect, quantum theory just tells us about relationships between observations (of nothing :-) and your knowledge (of nothing :-). I'd say that here we are in Alice in Wonderland: anything goes.
There's a variant: there is a real world out there all right, but it is not described by any laws ; all we are allowed to know and observe is given by quantum theory which doesn't describe it, but just gives us relationships between our observations and knowledge.


So let's go for A: there is some real world of some kind or other out there. What are the possibilities ?

1) there is only partly a real world, and some Alice in Wonderland. The real world is ruled by classical mechanics, and the microworld doesn't exist, and is ruled by quantum theory (that's Copenhagen, essentially). When certain aspects of that quantum world "go classical" they become real. I find that a very disturbing view, just as disturbing as B.

2) there is a real, classical world out there, and quantum theory is just a kind of statistical mechanics dealing with it. That was Einstein's view. Although it is not excluded, this classical world violates very, very fundamental properties in that case, like causality. Choices you will make tomorrow influence things today.

3) there is a real world out there, ruled by (unitary) quantum mechanics, and observers only observe part of it (one term of the wavefunction). It is this partial observation which introduces the apparent randomness. That's many worlds (comes in many subtle flavors). It's my favorite.

4) quantum theory + collapse are real phenomena ; certain processes do cause collapse, we simply haven't figured out the details yet. This is the von Neuman view. It suffers a bit from the same problems as 2), in that whatever causes collapse, is also non-causal.


My personal view is 3) with some hope for a subtle 4).

cheers,
Patrick.

 

[selfAdjoint]

How about (4) There is a real world out there but quantum theory doesn't describe it; quantum theory describes our relationship to it. This is why there is a "boundary" in interpreting QM, somewhere between the world and us. The world behaves non-classically on the other side of the boundary and we behave, "sort of classically" on our side, and the only thing that can cross the boundary is a probability. Any quantum setup we make is just constructing a window to look at the world through quantum theory glass.

 

[vanesch]

How about (4) There is a real world out there but quantum theory doesn't describe it; quantum theory describes our relationship to it. This is why there is a "boundary" in interpreting QM, somewhere between the world and us. The world behaves non-classically on the other side of the boundary and we behave, "sort of classically" on our side, and the only thing that can cross the boundary is a probability. Any quantum setup we make is just constructing a window to look at the world through quantum theory glass.

What's the difference with (my favorite) 3) ??

cheers,
Patrick

(BTW, I'm looking at that relational paper, but I still have to wrap my mind around it...)

 

[selfAdjoint]

What's the difference with (my favorite) 3) ??

cheers,
Patrick

(BTW, I'm looking at that relational paper, but I still have to wrap my mind around it...)

Umm, there's no difference, I guess. Just that it's important to stress that we can't be confident quantum theory shows us all the behavior of nature. It shows us what it is adapted to showing us. And that the reason we always come around to mind in interpreting QM is that QM is specifically designed to do that. To put a boundary between the world and "us".

Of course this all sounds Kantian, but I think any way we might interpret is going to sound like some philosopher - they seem to have covered all the bases between them!

But I'm eager to hear what you think about the relational paper.

 

[seratend]

How about (4) There is a real world out there but quantum theory doesn't describe it; quantum theory describes our relationship to it. This is why there is a "boundary" in interpreting QM, somewhere between the world and us. The world behaves non-classically on the other side of the boundary and we behave, "sort of classically" on our side, and the only thing that can cross the boundary is a probability. Any quantum setup we make is just constructing a window to look at the world through quantum theory glass.

This is almost equivalent to define a case C): we do not care (if there is a real world or not): out of the scope of physics (the epistemic view).

I think one should accept that the existence of a real world or not does not change the results of a physical theory: it is first a logical description (and prediction) of some phenomena with a domain of validity. Any extrapolation from this point is, in my opinion, somewhat the domain of philosophy or metaphysics.

Accepting this point may help in simplifying the interpretation scope of a physical theory such as QM.

Seratend.

 

[seratend]

Lets take the position attribute. To my understanding this attribute does not exist until it is measured.

For one moment forget about reality and try to focus on the properties needed to describe logically the reality (what we normally do when we describe an experiment and its results).

As with mathematics an object does not exist until it is defined. However, interpreting that the object exists because I have written it on a piece of paper (i.e. it does not exist before) is of the scope of mathematics (in this context).

Now, why do you need to say that the position attribute (I prefer to call it a property or proposition) does not exist until it is measured?
You just need to say that a given "experiment" has a given property, that's all. The logical definition of a given experiment defines the context (the domain of validity) of the property => different properties mean different experiments.
A "dynamical property" is a property (e.g. position x at time t) and an experiment may have a collection of properties (that defines a single property): this is the reformulation of the consistent histories formalism (i.e. stochastic processes).

Now if you take into account this logical description of experiments, the things should be simplified and most of yours problems should disappear.

For example, rewrite your box example taking into account this logical approach. To do that, you must understand, logically, that the box without the detectors is neither the box with detectors nor a box without detectors before time to and with detectors after time to etc ... (implicitly different logical contexts). In other words, the observer is also part of the context of the experiment for the given property (the "measurement result").


Seratend.

 

[Nacho]

In other words, the observer is also part of the context of the experiment for the given property (the "measurement result").

Yeah, but take this setup .. Take a beam of electrons through a Stern-Gerlach magnet setup. Observer (A) sees 1/2 of them deflect up and 1/2 will deflect down. Take the "down" electrons and send it through the exact same setup and that same Observer (A) will see all of those electrons will deflect down.

You are Observer (B), and you take those "down" electrons and funnel over to Observer (C) who is doing the same thing as Observer (A), but Observer (C) is not aware of Observer (A) or what you are doing (also Observer (A) is not aware of you or Observer (C)).

Now let Observer (C) view those "down" electrons through his exact same Stern-Gerlach magnet setup as Observer (A). And then later you bring all three people together and discuss what yall observed.

Question: What does observer (C) see the electrons doing?

I don't know the answer. I suppose there is an outside chance 1/2 would defect up and 1/2 would deflect down. I doubt it.

I'd suppose he'd see them deflecting down. If so, he couldn't have created any reality in that experiment. Maybe either Observer (A) or you created the reality when you made the observation? I doubt it, because that would mean reality (in the context of "observer creating reality") is transferable from one person to another.

Or maybe it means that once reality is created by Observer (A), it is reality for all 3 Observers. If so, that begs the question: What "resets reality" so that Observer (A) is able to see of an initial beam of electrons, 1/2 deflect up and 1/2 deflect down? It can't be that he just got a sample of electrons that already were 1/2 "up" and 1/2 "down" electrons. We've come full circle in this "reality/observer part of the experiment" thing.

 

[vanesch]

This is almost equivalent to define a case C): we do not care (if there is a real world or not): out of the scope of physics (the epistemic view).

That was my case B): if you do not care whether there is some real world, you can just as well assume it doesn't exist, because all you're talking about then, are relationships between knowledge and observations (of nothing :-). This is what I referred to as Alice in Wonderland. I have some difficulties with this view, even if purely from a mathematical point of view. It seems to be equivalent, say, to having an atlas with coordinate patches, but "not to care" whether it describes an underlying manifold or not. I think that that does not make much sense: you'd have a geometrical description of a non-existent geometry! It is going to be difficult to do any meaningful work there, no ?

cheers,
Patrick.

 

[seratend]

That was my case B): if you do not care whether there is some real world, you can just as well assume it doesn't exist, because all you're talking about then, are relationships between knowledge and observations (of nothing :-).

Ok, so your case B) is "case A) is not true".
Beware, "nothing" is meaningless in case B).

This is what I referred to as Alice in Wonderland. I have some difficulties with this view, even if purely from a mathematical point of view. It seems to be equivalent, say, to having an atlas with coordinate patches, but "not to care" whether it describes an underlying manifold or not. I think that that does not make much sense: you'd have a geometrical description of a non-existent geometry! It is going to be difficult to do any meaningful work there, no ?

cheers,
Patrick.

Think on your logical meaning of meaningful as I think what you call meaningful is different from what I call meaningful (~ mainly the ability to do logical deductions/assertions).

Do you care if I say a natural number is for example peculiar subset of real numbers or a collection of potatoes or an inductive construction based the empty set, if the properties of natural numbers are preserved?

Think on the logical way to describe the reality: we have mainly a collection of properties (cat, black, eyes, speed ...) and a choice in the association of these properties with the properties of a mathematical theory in order to verify the consistency of the properties (e.g. mainly by a logical comparison with reference objects).

You can add your own reality property to the cat example above as long as it does not change the consistency of the other properties. Does it make the cat more meaningful than a simple collection of consistent properties?

What is the most important (anthropomorphic view)?: the consistency of the properties we attach to reality or their ontology?

Seratend.

 

[vanesch]

Do you care if I say a natural number is for example peculiar subset of real numbers or a collection of potatoes or an inductive construction based the empty set, if the properties of natural numbers are preserved?

This is slightly different, because the natural numbers are a mathematical concept, not yet part of any physical theory as such. Now, if you want to know my view on THAT issue (which is not the one in physics), I do associate a kind of ontology (Platonic existence) to the natural numbers, irrespective of whether I use representations of that concept based upon structures in set theory, or potatoes, or drops of dried ink on a sheet of paper.

Think on the logical way to describe the reality: we have mainly a collection of properties (cat, black, eyes, speed ...) and a choice in the association of these properties with the properties of a mathematical theory in order to verify the consistency of the properties (e.g. mainly by a logical comparison with reference objects).

You can add your own reality property to the cat example above as long as it does not change the consistency of the other properties. Does it make the cat more meaningful than a simple collection of consistent properties?

The ontology of "cat" is then the underlying Platonic existence of the mathematical structure (worked out in a specific representation) that we associate to "cat". Call it your collection of properties: we have to associate an underlying mathematical structure with them, or better, a REPRESENTATION of such an underlying structure (this representation can take on different forms, and only represent partly the whole structure: whether it is just a point in 3-dim Euclidean space "my cat is on the roof of that building" ; or something more sophisticated, up to "|psi> is the wavefunction of my cat"). All these things are representations of a mathematical object that is supposed to be my cat (in the same way as we have representations of abstract groups with matrices in n-dimensional vector spaces).
What I'm claiming is that there needs to be such an underlying mathematical object, and that there is a real (Platonic) ontology to be associated to this object. You seem to accept the existence of the different "properties" without them to be a representation of an underlying mathematical object.

It is what I tried to depict with "having an atlas without a manifold".

What is the most important (anthropomorphic view)?: the consistency of the properties we attach to reality or their ontology?

I'd say that from the latter follows the former !
(and probably from the former follows the latter)

cheers,
Patrick.

 

[seratend]

Yeah, but take this setup .. Take a beam of electrons through a Stern-Gerlach magnet setup. Observer (A) sees 1/2 of them deflect up and 1/2 will deflect down. Take the "down" electrons and send it through the exact same setup and that same Observer (A) will see all of those electrons will deflect down.

You are Observer (B), and you take those "down" electrons and funnel over to Observer (C) who is doing the same thing as Observer (A), but Observer (C) is not aware of Observer (A) or what you are doing (also Observer (A) is not aware of you or Observer (C)).

Now let Observer (C) view those "down" electrons through his exact same Stern-Gerlach magnet setup as Observer (A). And then later you bring all three people together and discuss what yall observed.

Question: What does observer (C) see the electrons doing?

I am not sure to understand your experiment. Can you make a small illustration?

e.g. this is the beginning of your description, after I am lost (i.e. I am not sure to understand what you mean)

        +---|+>--------------
        |           |
        |           V
-->-[SG]+       [obs A]   
     ^  |           ^
     |  |           |
     |  +---|->--------------+
     |                       |
     +----<------------------+

Seratend.

 

[Igor_S]

2) there is a real, classical world out there, and quantum theory is just a kind of statistical mechanics dealing with it. That was Einstein's view. Although it is not excluded, this classical world violates very, very fundamental properties in that case, like causality. Choices you will make tomorrow influence things today.

How can classical world violate causality?

 

[vanesch]

How can classical world violate causality?

Ok, that was a shortcut. If you insist on a classical existence of observation results, and EPR situations, you obviously have faster-than-light influences. Now, if you accept SR on an everyday scale (where it is amply tested), this means that you have some "back in time" influence.
Mind you, I didn't say "signalling". But clearly the classical process that determines what's going to happen to your photon in the polarizer right now at 12 AM, depends upon what Alice will do on Jupiter on 12:05, in certain reference frames. If you insist upon a classical mechanism, that is.

 

[Igor_S]

Yeah, this is the tricky part. There are 2 kinds of influences: one of them is real or I would say "causal", but in the sense of deliberate, real (not sure what word to use, sorry), influence - they produce observable effects, the other is "ethereal"[1]. "Ethereal" influences would be the kind you talked about. I don't see real problem with them, since you cannot really tell did Alice at 12:05 measure something or not (nor can she). In that sense casuality is not a problem. It's not the usual effect preceeded cause, but more subtle, non-detectable one, so for some people, not really fundamental a problem.


[1] (that's the word Griffiths used in his book)

 

[seratend]

This is slightly different, because the natural numbers are a mathematical concept, not yet part of any physical theory as such. Now, if you want to know my view on THAT issue (which is not the one in physics),

Yes, I do.

I do associate a kind of ontology (Platonic existence) to the natural numbers, irrespective of whether I use representations of that concept based upon structures in set theory, or potatoes, or drops of dried ink on a sheet of paper.

So you like complications and the risk of inconsistencies they carry. You have two jobs: using the properties of natural numbers and defining another externally consistent property on them (whatever it could be).

Logically I will say, ok fine. What kind of additionnal usefull information do you get from this additionnal property?

The ontology of "cat" is then the underlying Platonic existence of the mathematical structure (worked out in a specific representation) that we associate to "cat".

Note: "that we *choose* to associate to the cat".

Do you require a one to one mapping (between the mathematical structure and the cat "real" properties)?

Do you think that these properties define a single object or simply a class of different objects that cannot be distiguished from this collection of properties?

What I'm claiming is that there needs to be such an underlying mathematical object, and that there is a real (Platonic) ontology to be associated to this object.

Why do you say "there is a need". Personnally I do not requrie such a need, whatever it could be: I accept it if it is logically compatible with a choosen description.

You seem to accept the existence of the different "properties" without them to be a representation of an underlying mathematical object.

I am not assuming the a priori existence of properties (in the mathematical sense), just a formal choice of a collection of properties for a given object that is itself defined by a property.

What is the most important (anthropomorphic view)?: the consistency of the properties we attach to reality or their ontology?

I'd say that from the latter follows the former !
(and probably from the former follows the latter)

If you say that, you have to verify the logical consitency between the two concepts, i.e. you like the difficulties : ).
I prefer to say, I choose (formal choice) the former and I do not care of the later as, for me, it is not well defined mathematically.

Seratend.

 

[vanesch]

Using the properties of natural numbers and defining another externally consistent property on them (whatever it could be).
Logically I will say, ok fine. What kind of additionnal usefull information do you get from this additionnal property?

You have of course much more formal liberty in mathematics than in physics, so what I'm going to say about the natural numbers will sound a bit artificial. But it is my belief that the "natural numbers" somehow have a platonic existence, irrespective of whether we define them or not. We can define certain mathematical constructs, and they can, or cannot, be a representation for that intangible concept of natural number. If they are, well, then they are, and if they aren't well, eh, they aren't and we are doing something else.
But the concept of, say, the number "5" seems to exist, irrespective of whether we have the right definition for it. If we don't have it, we're simply talking about something else but the number 5. And if we have it, we simply have A FORMAL REPRESENTATION of the concept "5". There can be different formal representations of that same concept (with symbols on a sheet of paper, like with the set-theoretic construction, or with potatoes, or whatever), but if they are correct representations of that same concept, they are equivalent (that's somehow tautological).

Now, it seems that people like you DO NOT believe in that underlying concept, and ONLY see the formal game. It is my not so humble opinion that you're then missing something

I can (by definition !) of course not give you a formal argument of why this is so, but I'm firmly convinced that the concept "5" exists, even if we don't have a nice formal definition for it. It existed in the time of the Romans, if you want to. We only DISCOVERED a formal representation of it in the relatively recent history.

There's a nice argument for this in Penrose (I admit being greatly influenced by the man). It goes as follows: take Fermat's last theorem. Does that theorem "exist" ? Now, someone who only looks at the formalism, like you, will probably say that it exists if the proof is written down. But that's something funny then. Let's say that Wiles' proof is correct. So the theorem exists. But did it exist back at the time of Fermat ? And did it exist in the time of Diophantine ? Now, let us assume that we are now all convinced that it exists, and 100 years from now, someone discovers an error in Wiles' proof. Does suddenly the theorem not exist anymore ? After a life of about 100 years ?
No, you probably take the view that the theorem EXISTS (whether we have a proof for it or not), or DOESN'T (can be undecidable or false), and this is a "timeless" and "inspiration less" thing.
So, somehow, mathematical concepts have a kind of existence of their own, independent of whether we have discovered them or not, and written down a formal representation of it.

But as I said, the *mathematical* existence of concepts (in the Platonic world) is of course less "tangible" than the *physical* existence of concepts. So let's switch to physics instead.

Note: "that we *choose* to associate to the cat".

Do you require a one to one mapping (between the mathematical structure and the cat "real" properties)?

No, not a 1-1 mapping of course. Just a representation. A group representation doesn't have to be faithful.

Do you think that these properties define a single object or simply a class of different objects that cannot be distiguished from this collection of properties?

A class of course, UNTIL we finally hit upon a faithful representation: in that case we hit upon a mathematical structure which can serve as an ontology.
That's what I tried to illustrate: a cat corresponds to a complicated thing, but it center of gravity is a point in 3-dim euclidean space (unless you really do nasty things with your cat). So there's a (non-faithful) representation from the complicated mathematical object "cat" onto E^3. And that can be sufficient for my purpose (like when I say that my cat sits on the roof), or not. If I want to describe a bit more my cat, there's another (non-faithful) representation into the simply connected subspaces of E^3, and now I can talk about the form of my cat, etc...
But I do assume that there's an underlying concept, "my cat", which has an ontological existence irrespective of what representation I CHOOSE to use of it.

I am not assuming the a priori existence of properties (in the mathematical sense), just a formal choice of a collection of properties for a given object that is itself defined by a property.

Yes, you can define "my cat" as just the collection of all thinkable properties that you could possibly attribute to it. But my claim is that this collection of properties is like all possible atlases in differential geometry: in the end it describes an underlying mathematical concept, namely a differentiable manifold, which has, in my view, a platonic existence *INDEPENDENT* of how we chose to represent (define) it formally. In the same way, that collection of possible cat properties describes finally nothing else but an underlying physical (mathematical) concept, which is nothing else but "my cat" and has an ontological (platonic) existence, independent of exactly how I decided to define its properties etc...

If you say that, you have to verify the logical consitency between the two concepts, i.e. you like the difficulties : ).
I prefer to say, I choose (formal choice) the former and I do not care of the later as, for me, it is not well defined mathematically.

I would say that it is somehow much more reassuring on the consistency side to HAVE an underlying concept from which we deduce properties (have representations), than just randomly have a set of properties. After all, if your set of properties is to be a consistent thing, I do not see what it can be else but a mathematical object !
As a simple example: let us take fractions. I claim that "fractions have a mathematical existence". You just say that fractions are "pairs of integers over which we defined an equivalence relation, because that's how they are formally defined". But if you define stuff like the sum of two fractions, and so on, more and more you get away from that "pair of integers ..." and you work more and more with Q, the set of rational numbers.
And you can begin to start to see that this "pair of integers with an equivalence relation" is not really the DEFINITION of rational numbers, but a REPRESENTATION (a faithful representation). We can think of other faithful representations, like decimal expansions with repeating sequences, or continued fractions, or whatever. So we see that we were simply DISCOVERING a mathematical concept, namely the rational numbers, in ONE OF ITS POSSIBLE FORMAL REPRESENTATIONS.
In the same way, we were discovering just different properties of our cat, but it was there all right, even before we started to write down its list of properties.

cheers,
Patrick.

 

[selfAdjoint]

But it is my belief that the "natural numbers" somehow have a platonic existence, irrespective of whether we define them or not. We can define certain mathematical constructs, and they can, or cannot, be a representation for that intangible concept of natural number. If they are, well, then they are, and if they aren't well, eh, they aren't and we are doing something else.

"Der liebe Gott hat die ganzen Zahlen gemacht. Alle anderes ist menschenwerk." Or that's how I remember itl; Was it Kummer who said that?

 

[George Jones]

"Der liebe Gott hat die ganzen Zahlen gemacht. Alle anderes ist menschenwerk." Or that's how I remember itl; Was it Kummer who said that?

Or was it the guy who helped drive Cantor bonkers?

Personally, I'm a whole-hearted enough Platonist that I like:

"... and there is no sort of agreement about the nature of mathematical reality among either mathematicians or philosophers. Some hold that it is 'mental' and that in some sense we construct it, others that it is outside and independent of us ... I believe that mathematical reality lies outside of us, that our function is to discover or observe it, and that the theorems which we prove, and which we describe grandiloquently as our 'creations', are simply our notes of our observations."

G. H. Hardy

Regards,
George

 

[vanesch]

"Der liebe Gott hat die ganzen Zahlen gemacht. Alle anderes ist menschenwerk."

I'd go further, and claim some platonic existence for just any well-defined mathematical concept. But I was driven into this point without me wanting so, because we were not arguing about an ontology about *mathematical* objects, but about *physical* objects.
My point was simply that physical ontology is (at least) the platonic existence of the mathematical concept that corresponds to our physical world, whether it is a manifold, a Hilbert space or whatever, but that something is out there and corresponds to a mathematical concept, of which our physical theories and our observations are (meager ?) representations. I have difficulties with just a bunch of observations and knowledge if it is not somehow related to an underlying concept.

cheers,
Patrick.

 

[Nacho]

Seratin:

I'm not going to be too good at this .. but here goes:

             --- (+) ------
             |
---->(SG)--->|
             |
             --- (-) ----->(SG)--->|
                                   |
                                   ------ (-) --- ( input to (C) )

That is what Observer (A) sees .. the electrons going into the first SG magnet. 1/2 are deflected UP (+), 1/2 are deflected down (-). The "down" electrons are sent through another SG magnet, same setup as the 1st SG magnet. All of them will deflect down (-), as they are "already measured".

Now, Observer (B), unbeknownest to (A) or (C), takes those down (-) electrons and shoves those through a SG magnet that (C) is watching. The SG magnet is oriented exactly the same as the 2 SG magnets that (A) is observing.

That's it .. but remember:

A is not aware of B or C.
C is not aware of B or A.
B is aware of what A and B is doing .. but I don't think it matters to the setup.

 

[ShalomShlomo]

Originally Posted by Igor_S
How can classical world violate causality?

If you insist on a classical existence of observation results, and EPR situations, you obviously have faster-than-light influences.

It's important, so let's get this clear (for some reason, this hasn't been grasped properly yet across our community)...

Bell showed that QM itself formally breaks causality.
ie whether QM is Classical, Copenhagen, Many Worlds, Bohmiam, etc all describe a QM that violates causality because QM itself violates causality.


HowSo ?

In the famous EPR thought experiment, two entangled photons are sent in
opposite directions, say, to two planets distant from each other, with the
photon generator somewhere between them.
At each of the two planets, the photon travels through a polarised filter
held at a certain angle before being measured.

If the two polarisation filters on the two planets are held at the same
angle, then since the photons are entangled the same measurement will be
recorded at the two planets.
EPR (Einstein, Podolsky & Rosen) derived that since the photon can't know
what angle the polarisation filter will be held at on each planet, and since
the results have to match if the filters are held at the same angle,
therefore the photon must leave the photon generator knowing what result to give for each angle that the filter will be held at.

Then in the 1964 John Bell came and disproved this incorrect derivation, and
showed that the result at each planet depended upon the angle that the
filter on the other planet was held at, and that the angle of the filter on
the other planet was always known to the photon instantaneously even though the planets was separated by large spatial distances.

But the implications of Bell's discovery to time and causality haven't been
fully spelled out. We know from Special Relativity that neither filter is
positioned first. To one observer traveling in a spaceship, the filter on
planet A is positioned first. To another observer traveling in a different
spaceship in a different direction, the filter on planet B is positioned
first. And yet each filter causes a change in the measurement at the other
planet. It is clearly evident that measurments do affect the past, and we are forced to narrow our definition of causality significantly. Indeed, only because no information capable of being interpreted is passed between the filters does any form of causality remain at all.

Consequences of the above:

1) We remain with a macro-causality but have to abandon causality on a Quantum level
2) Everything depends on what we understand 'Time' to be. We don't really understand what Time is, and since everything hinges on 'Time', our understanding of physics is ignorant
3) Given the fact that QM itself is proven causality-breaking, many of the objections to the classical view of QM have been removed, and this view ought to get a lot more attention than it does.

Shalom Shlomo

 

[Igor_S]

Bell showed that QM itself formally breaks causality.
ie whether QM is Classical, Copenhagen, Many Worlds, Bohmiam, etc all describe a QM that violates causality because QM itself violates causality.

I would againt not use that word (but I think the rest of your post shows that we're talking about the same thing, eg.:

It is clearly evident that measurments do affect the past, and we are forced to narrow our definition of causality significantly

), because observer in the past cannot really tell if he is being influenced. Bell showed that QM breaks locality (and "soft" breaks causality). Nonlocality is connected with unseparability of the wave function which has deep physical meaning and that leads us to a statement you wrote later:

2) Everything depends on what we understand 'Time' to be. We don't really understand what Time is, and since everything hinges on 'Time', our understanding of physics is ignorant

I think this is really important problem to be solved.

 

[vanesch]

Bell showed that QM itself formally breaks causality.
ie whether QM is Classical, Copenhagen, Many Worlds, Bohmiam, etc all describe a QM that violates causality because QM itself violates causality.

This is not true, and it is one of the merits of Many Worlds to allow QM to respect locality and causality. If you want to know the details, I put it in my journal, but the point is essentially this:
when Alice performs her "measurement", with respect to Bob, she's just in a superposition, and got entangled with her photon, BUT ACCORDING TO BOB, THERE WASN'T ANY RESULT AT ALICE'S. It is only when Bob LEARNS about Alice's result that he in fact chooses in which branch he lives, but this happens of course when he's in local (causal) contact with Alice, or with a messenger of Alice.
So that's the way how many worlds gets around Bell's theorem: there simply WASN'T A RESULT at Alice's and at Bob's, so you cannot talk about the probability of Alice to have observed something, from Bob's point of view.

It is described in much more detail in my journal (collection of old posts on the subject).

cheers,
Patrick.

 

[ShalomShlomo]

...one of the merits of Many Worlds to allow QM to respect locality and causality.

Sorry, Vanesch. You are right. I blithely included the wacky Many Worlds interpretation of QM amongst the rest, and forgot that of course it does not suffer from the normal problems, and it answers all normal questions and doubts.

I'm sorry.

It's just such a wacky theory, I find it difficult to be professional and take it seriously as we all need to. I am at fault in this.

So it's either throw out causality (keeping only soft-causality) or Many Worlds.

Shalom Shlomo

 

[vanesch]

So it's either throw out causality (keeping only soft-causality) or Many Worlds.

I'll pretend not having noticed a certain sarcasm in your post , but what you write above is essentially the choice we have, at least if we stick to special relativity. Everything which induces a real collapse, and which considers that there is an ontology to the measurement results of Bob and Alice, and which accepts SR cannot escape the throwing out of causality, thanks to Bell's theorem.
In fact it is worse: your theory is even not lorentz invariant !
So if I have to choose between a "wacky theory" but which is lorentz invariant, local, causal, and explains all my *subjective* observations, or a theory which is not "wacky", but violates locality, lorentz invariance and causality, but allows me to associate my subjective observations to objective facts in a 1-1 relationship (I think that that is what "wacky" means, no ?), I opt for causality, and if unwackyness has to go, then so be it

There might be an intermediate way out, in that *some* violations of unwackyness are allowed on "small enough scales", and that on "larger scales", unwackyness is restored, and there are deviations from unitary QM. My hope is that gravity does such a thing, but it might very well not, and then I don't see how to save unwackyness

But the message of all this is simply that jumping to the conclusion that Bell's theorem NECESSARILY implies non-causality is wrong: there's a counter example and that's Many Worlds (even if you don't like it). In the same way as saying that Bell's theorem doesn't allow for a hidden variable model of QM: Bohm's mechanics is an example (even if you don't like it).

cheers,
Patrick.

 

[Miserable]

Seratin:

I'm not going to be too good at this .. but here goes:

Code:

--- (+) ------ | ---->(SG)--->| | --- (-) ----->(SG)--->| | ------ (-) --- ( input to (C) )



That is what Observer (A) sees .. the electrons going into the first SG magnet. 1/2 are deflected UP (+), 1/2 are deflected down (-). The "down" electrons are sent through another SG magnet, same setup as the 1st SG magnet. All of them will deflect down (-), as they are "already measured".

Now, Observer (B), unbeknownest to (A) or (C), takes those down (-) electrons and shoves those through a SG magnet that (C) is watching. The SG magnet is oriented exactly the same as the 2 SG magnets that (A) is observing.

That's it .. but remember:

A is not aware of B or C.
C is not aware of B or A.
B is aware of what A and B is doing .. but I don't think it matters to the setup.

There is no problem with this- C will conclude that he was observing a bunch of electrons which had already been prepared in the down eigenstate in the direction of his SG. C's observation doesn't affect the electrons because they were not in an uncertain state (no superposition of up and down) before his measurement.

 

[seratend]

But the concept of, say, the number "5" seems to exist, irrespective of whether we have the right definition for it. If we don't have it, we're simply talking about something else but the number 5. And if we have it, we simply have A FORMAL REPRESENTATION of the concept "5". There can be different formal representations of that same concept (with symbols on a sheet of paper, like with the set-theoretic construction, or with potatoes, or whatever), but if they are correct representations of that same concept, they are equivalent (that's somehow tautological).

You have implicitly choosen a context: the numbers.

Now, it seems that people like you DO NOT believe in that underlying concept, and ONLY see the formal game. It is my not so humble opinion that you're then missing something

I think you are missing the point, I have no belief, I am just using logic to make statements (with sometimes some logical errors : ) and up to now, I think both maths and physics have also made this choice.

I know I may always construct an underlying property assuming a set of all properties (E), I may call the [contextual] ontological property (e.g. belongs to P(E)). This is a formal logical construction and the equivalence between these 2 views through what can be viewed as a context (i.e. the set E). But this not a true ontological property (it depends on the choosen context). In addition, it requires some care to extend the equivalence to other mathematical objects larger than sets: it may leads to logical inconsistencies and in fine these new mathematical objects define a new context.

I just say that currently physics chooses to describe the “reality” objects by a set of logical propositions (a choice and not an obligation). The description by a reduced set of properties of a “real” object includes [i.e. is compatible with] the case where the object may have an “ontological reality” (it does not require the existence of such an ontological property). However, assuming an *ab initio* ontological status of the “reality” object may lead to logical inconsistencies as long as we are not able to prove logically the validity of the “ontology” property – whatever, it could be (hence my remark: you like the difficulties): QM is full of such examples (e.g. the improvements in the bohmian mechanics in order to keep the compatibility with QM result, etc ...).

I can (by definition !) of course not give you a formal argument of why this is so, but I'm firmly convinced that the concept "5" exists, even if we don't have a nice formal definition for it.

If you look at the axiomatic set theory (e.g. ZF theory), you will see that the mathematical existence is one of the most difficult properties to obtain/understand (e.g. axiom of choice in set theory). It usually requires the formal statement of the existence of wider objects (usually the theory itself). What we can obtain more easily is the consistency of a logical construction: I do not know (logic) if a set exists (without a larger theory containing the set objects), I just know (logic) that the ZF, ZF+C and ZF not C is logically consistent, hence my claim: I do not care that “5” exists, I just want that the logical constructions I make with 5 are consistent (i.e. I usually choose the inductive construction of naturals numbers based on the ZF set theory).

It existed in the time of the Romans, if you want to. We only DISCOVERED a formal representation of it in the relatively recent history.
There's a nice argument for this in Penrose (I admit being greatly influenced by the man). It goes as follows: take Fermat's last theorem. Does that theorem "exist" ?

One of the main problems of physicists: the mixture between the logical content of physics and the philosophical external extension (that should remain consistent with the logical content otherwise we have no more the same theory).
The following of this section of your post tries to give another meaning to the “existence” we have in the mathematical language => Once again, I say ok. You are free to choose your own definition. Everyone has this formal right (logical choice). However, as long as you are not able to give a formal logical meaning to this new definition, it is almost impossible to see the logical consistency of such affirmations.

In mathematics, we have theorems and proofs about these theorems. A proof may be wrong. Depending on the assumptions (formal choices), we have different conclusions, and these conclusions may be also false or inconsistent . That’s all we can say in general when we *choose* to use logic.

A class of course, UNTIL we finally hit upon a faithful representation: in that case we hit upon a mathematical structure which can serve as an ontology.
That's what I tried to illustrate: a cat corresponds to a complicated thing, but it center of gravity is a point in 3-dim euclidean space (unless you really do nasty things with your cat). So there's a (non-faithful) representation from the complicated mathematical object "cat" onto E^3. And that can be sufficient for my purpose (like when I say that my cat sits on the roof), or not. If I want to describe a bit more my cat, there's another (non-faithful) representation into the simply connected subspaces of E^3, and now I can talk about the form of my cat, etc...
But I do assume that there's an underlying concept, "my cat", which has an ontological existence irrespective of what representation I CHOOSE to use of it. ?

So as long as you are not able to prove the existence of an “underlying concept” irrespective of what interpretation you choose, you follow the epistemic view : )).
Does that mean you choose (logical choice) to reduce the collection of possible representations to the ones compatible with the existence of such an underlying concept?

Don’t you think the above question defines an implicit context of the underlying concept and hence is not strictly compatible with the ontology.

Yes, you can define "my cat" as just the collection of all thinkable properties that you could possibly attribute to it. But my claim is that this collection of properties is like all possible atlases in differential geometry: in the end it describes an underlying mathematical concept, namely a differentiable manifold, which has, in my view, a platonic existence *INDEPENDENT* of how we chose to represent (define) it formally.

For a given context (e.g. choice of a given set of properties), you may have a common denominator, that you may call a representation. However, for another context, you may have another representation. These representations may be logically incompatible (e.g. the incompatible observables in QM, or if you prefer one proposition true in one context may be false in another context) => to get a common representation compatible with these 2 incompatible representations you will need to define an ad-hoc external mathematical object (e.g. Boolean lattices vs non Boolean lattices in QM).

I do not know if this inductive construction is always possible (i.e. consistency) and I do not see what additional information it brings (my remark: you like complications ; ).

I would say that it is somehow much more reassuring on the consistency side to HAVE an underlying concept from which we deduce properties (have representations), than just randomly have a set of properties.
After all, if your set of properties is to be a consistent thing, I do not see what it can be else but a mathematical object !

You have a context: the set of properties hence an underlying concept valid for this context. For me an ontological property that depends on the context is not really ontological (once again, it depends on the logical content of the ontological concept).
If you accept a context (e.g. a given mathematical theory) to define the consistency of your properties, you are implicitly rejecting the ontology (in the sense: independent of the context).

As a simple example: let us take fractions. I claim that "fractions have a mathematical existence". You just say that fractions are "pairs of integers over which we defined an equivalence relation, because that's how they are formally defined". But if you define stuff like the sum of two fractions, and so on, more and more you get away from that "pair of integers ..." and you work more and more with Q, the set of rational numbers.
And you can begin to start to see that this "pair of integers with an equivalence relation" is not really the DEFINITION of rational numbers, but a REPRESENTATION (a faithful representation).

Yes an implicitly contextual representation: the numbers.

Seratend.

 

[seratend]

Seratin:

I'm not going to be too good at this .. but here goes:

             --- (+) ------
             |
---->(SG)--->|
             |
             --- (-) ----->(SG)--->|
                                   |
                                   ------ (-) --- ( input to (C) )

That is what Observer (A) sees .. the electrons going into the first SG magnet. 1/2 are deflected UP (+), 1/2 are deflected down (-). The "down" electrons are sent through another SG magnet, same setup as the 1st SG magnet. All of them will deflect down (-), as they are "already measured".

Now, Observer (B), unbeknownest to (A) or (C), takes those down (-) electrons and shoves those through a SG magnet that (C) is watching. The SG magnet is oriented exactly the same as the 2 SG magnets that (A) is observing.

That's it .. but remember:

A is not aware of B or C.
C is not aware of B or A.
B is aware of what A and B is doing .. but I don't think it matters to the setup.

Ok (sorry for the late answer). What is for you the logical content of an observer?
For me, you are implicitly choosing an observer with 2 properties:
a) an observer may interact with the experiment: with QM I describe it through an hamiltonian interaction (property: the hamiltonian)
b) the result of a given experiment (the eigenvalue of an observable or more precisely the property for a given experiment, i.e. an electron with spin down at time t within a given finite area).

In this case what does mean "not aware"? Do you see that this decomposition of the "observer" allows to split the problem into the time evolution of the state defining the probability law of a collection of compatible properties (the results)?
Do you understand that these results are not predictive ones but just reflect (acknowledge) what a peculiar experiment gives? (i.e. they do not exist outside the experiment that has - and not will have- these properties).

If you choose a collection of properties that have a zero probability (for a given context), you will have a zero probabiltiy to *find* an experiment with such results. That's all you can say.

Seratend.

P.S. Answer to your post, if I asume the good interactions, spin down for (C).

 

[Nacho]

Miserable,

There is no problem with this- C will conclude that he was observing a bunch of electrons which had already been prepared in the down eigenstate in the direction of his SG. C's observation doesn't affect the electrons because they were not in an uncertain state (no superposition of up and down) before his measurement.

I agree, but that was just the setting up of the experiment to show some subtilies of how a person tries to explain away the measurement/reality problem.

As you answered, C's participation in the experiment couldn't have introduced/made any reality into the outcome of the experiment. So, I think that on least some measurements you (anybody) have to conclude that the observer doesn't create any reality.

Maybe you could come back and say reality is transferable to other observers, or once reality is made, all other persons would see that same reality. But, then if you still hold onto observer-creating-reality, look back to that very initial observation that "A" made .. where the electron beam split in two and examine that a bit.

The beam couldn't have split in two just because of randomness of a predetermined orientation of the electrons (I'm told that is not possible, and agree). And you (anybody) adhere to the thought that the observer creates the reality. How then did those electrons get "reset" from a previous observation on them to a state that your reality of observation can set them? Another person making an observation couldn't have done it. I think you (anybody) must conclude that "nature" resets them so that your observation can make the reality.

And if you conclude that, then "nature" itself can make a change in a state of reality .. an observer is not needed for at least some changes in reality. Then why is an observer needed to create any reality? Leave it all to be "nature" (particle interactions).

 

[Nacho]

Seratend,

My diagram was just a problem setup to explore some subtilies of the "reality" problem. It went further in my last post to "Miserable".

Of your response .. well, it appears to me that that is a QM/mathmatical description of what is happening. I'm not disagreeing with it, but I want to bear this out. QM/mathmatical interpretations don't really make any predictions about the reality aspects of an experiment. I think that is added on solely as a study in philosophy.

 

[seratend]

Seratend,

My diagram was just a problem setup to explore some subtilies of the "reality" problem. It went further in my last post to "Miserable".

Of your response .. well, it appears to me that that is a QM/mathmatical description of what is happening. I'm not disagreeing with it, but I want to bear this out.

Sorry, If you leave the light of mathematics and physics, I have nothing to say. I think this forum section and this thread are not the good ones to continue in this direction.

Seratend.

 

[Nacho]

Seratend,

Sorry, If you leave the light of mathematics and physics, I have nothing to say. I think this forum section and this thread are not the good ones to continue in this direction.

Maybe I misunderstood when you posted this:

In other words, the observer is also part of the context of the experiment for the given property (the "measurement result").

I took that to mean that you believed actions of the observer took part in the reality of measurements. Where did I go wrong there? I'm not necessarily wanting a discussion of the philosophy .. maybe just to show that how a person thinks about/interprets observer created reality is really a discussion in philosophy.

 

[vanesch]

For a given context (e.g. choice of a given set of properties), you may have a common denominator, that you may call a representation. However, for another context, you may have another representation. These representations may be logically incompatible (e.g. the incompatible observables in QM, or if you prefer one proposition true in one context may be false in another context) => to get a common representation compatible with these 2 incompatible representations you will need to define an ad-hoc external mathematical object (e.g. Boolean lattices vs non Boolean lattices in QM).

I do not know if this inductive construction is always possible (i.e. consistency) and I do not see what additional information it brings (my remark: you like complications ; ).

Well, I'd say: that's the point exactly. I think it would be seen by most physicists as a problem if we have 2 sets of properties (2 representations) of "nature" which are logically incompatible, if it is not in the context that at least one of them is known to be only "an approximation". This is exactly what "unification" is all about, no ?

However, I do not have any problem with "incompatible observables" in QM as logically incompatible: I do not assign something like a position property and a momentum property to a quantum particle ; if quantum theory is correct, its existence is given by a wavefunction in hilbert space, and I'm able to observe a component of that wavefunction, which can be in the position basis or the momentum basis, according to the experiment I try to perform.
Of course, this can all be wrong - after all physics is about DISCOVERING the laws of nature, not about formally setting them up. So it can be that QM is not correct.

cheers,
Patrick.

 

[seratend]

Well, I'd say: that's the point exactly. I think it would be seen by most physicists as a problem if we have 2 sets of properties (2 representations) of "nature" which are logically incompatible, if it is not in the context that at least one of them is known to be only "an approximation".

This is the heart of the QM formalism and the interpretation problems it rises. QM postulates say that you can describe the "reality" properties through, e.g. the position or momentum filter => We obtain 2 incompatible descriptions and there is no approximation in these descriptions (we have, formally, "a particle at position x" or "a particle with momentum p" properties).

However, I do not have any problem with "incompatible observables" in QM as logically incompatible: I do not assign something like a position property and a momentum property to a quantum particle ;

Yes you do. When you describe the results of an experiment, you implicitly have these properties. You can't avoid it (otherwise you cannot describe your experiment).

if quantum theory is correct, its existence is given by a wavefunction in hilbert space, and I'm able to observe a component of that wavefunction, which can be in the position basis or the momentum basis, according to the experiment I try to perform.

You are not able to observe a component of that wavefunction. All you can say is that you may deduce a component of a peculiar wavefunction from the [observed] properties of a set of experiments. That's all what the formalism allow you to do (i.e. it is a choice of description). The rest is outside the theory content (i.e. interpretation) and may lead to some inconsistencies.

Of course, this can all be wrong - after all physics is about DISCOVERING the laws of nature, not about formally setting them up. So it can be that QM is not correct.

Yes discovering (or may be describing the nature in a large sense), but with the use of logic : )).

Seratend.

 

[seratend]

I took that to mean that you believed actions of the observer took part in the reality of measurements. Where did I go wrong there?

I think you attach to the observer more properties than I do (hence it lacks a minimum of mathematical rigor).

I'm not necessarily wanting a discussion of the philosophy .. maybe just to show that how a person thinks about/interprets observer created reality is really a discussion in philosophy.

Ok. I think the main problem you have is that you do not seem to see that physics in general is a description of reality and not a creation of reality (whatever it could mean : )).
A description (e.g. a set of properties), may include the past the present and future (you need to think in space time and not in space or in time).

A description applies or not to a physical system but not "will apply" nor "will not apply". All QM formalism is based on this distinction and many paradoxes rise from this misunderstanding. (e.g. collapse postulate does not say how the things will be but how the things are).

The "observer" (when we remove the interaction part cf previous post reply) is formally a property (or a collection of= another property). A property is not a person (cloud, a stone, etc ...). However a person is a property or the property applies to this person.

Now you can add a creation of reality concept, but it is an additionnal object to the QM formalism description and hence may have a lot of inconsistencies until you proove it is formally consistent.

Seratend.

 

[vanesch]

Yes you do. When you describe the results of an experiment, you implicitly have these properties. You can't avoid it (otherwise you cannot describe your experiment).

What's wrong with the view that the meaning of "and the result of the position measurement of particle A is x" comes down to: "I'm an observer which is now entangled with the particle A's part of the wavefunction which is an eigenstate of the position operator I've assigned to particle A", which says in the end more about my state as an observer, than about particle A. So particle A has absolutely not "a position x" or whatever, but I can pretend it to be in such a state.

This is somehow a bit analoguous to: "and the x-coordinate of the astronaut is", and then saying a lot about incompatible results about x-coordinates from different possible observations (coordinate systems).
The x-coordinate is simply an observer-dependent property which is not "a property of the astronaute" but describes the relationship between the astronaute and the observer.

cheers,
Patrick.

 

[ShalomShlomo]

...a certain sarcasm in your post...

I wasn't being sarcastic.
Honest - I made a mistake and I was apologising.
I'm Sorry.
Shalom Shlomo

 

[seratend]

What's wrong with the view that the meaning of "and the result of the position measurement of particle A is x" comes down to: "I'm an observer which is now entangled with the particle A's part of the wavefunction which is an eigenstate of the position operator I've assigned to particle A", which says in the end more about my state as an observer, than about particle A. So particle A has absolutely not "a position x" or whatever, but I can pretend it to be in such a state.

Basically nothing (wrong with the view). You have 2 different propositions that may be incompatible depending on the context where they are used.

The second proposition is equivalent to the state of the (observer, particle A) is "entangled state". Where we may attach a real value to "entangled state" to define a projector and hence we have a proposition "and the result of the position measurement of (observer, particle A) is the real value "entangled state" (we just recover a first proposition concerning a system "observer +particle A").
=> I do not see why you can say this proposition "says in the end more about my state as an observer, than about particle A". (May be I have not understood your example).

So particle A has absolutely not "a position x" or whatever, but I can pretend it to be in such a state" without external data.

You are free to assign the propositions you want to a "real" system (in this case observer+particleA), this is a logical choice. However, if you do not compare the consistency of this proposition with deduced propositions from "real" systems (i.e. the "measurement results"), you have no more physics, just a mathematical theory (i.e. "disconnected from reality").

I think I am missing what you want to mean.

This is somehow a bit analoguous to: "and the x-coordinate of the astronaut is", and then saying a lot about incompatible results about x-coordinates from different possible observations (coordinate systems).
The x-coordinate is simply an observer-dependent property which is not "a property of the astronaute" but describes the relationship between the astronaute and the observer.

It's funny. I am not sure I have understood at all this post (in a non pejorative way). In the previous posts, I understand you try to introduce an ontological view of reality and in this final post you just reintroduce, implicitly, an epistemic view through the observer. All what I say is that I have properties and these properties are defined (sometimes implicitly) within a context (that may be "an observer").

Seratend.

P.S. (astronaute vs astronaut => Parlez vous français et aimez vous le bon vin et le fromage qui sent pas bon?

 

[selfAdjoint]

You are free to assign the propositions you want to a "real" system (in this case observer+particleA), this is a logical choice. However, if you do not compare the consistency of this proposition with deduced propositions from "real" systems (i.e. the "measurement results"), you have no more physics, just a mathematical theory (i.e. "disconnected from reality").

I think you have put your finger on the nub of the whole measurement problem. There is no physics associated with the observation/measurement. The "consciousness of the observer" is not a controlled or objectively observable system.

 

[gptejms]

collapse of the wavefunction

The following is what I wrote in one of the 'meataphysics and epistemology' threads('no observer no existence').Surprisingly it has received no comments,good or bad,there.So I am putting it up here with the hope that it generates at least a few replies:-

I think 'collapse of the wavefunction' is not such a mysterious thing as it is made out to be.What do you do when you do a measurement----you just reduce the \Delta x or the position uncertainty of the particle(so that you know the position of the particle (reasonably well)),whereas the momentum uncertainty becomes high.So what you do when you make a measurement is simply this-------you reduce the particle's position uncertainty whereas you increase its momentum uncertainty(given any initial wavefunction)--it's 'as if ' you have a gamma ray microscope in your hands and you 'observe' the particle---in doing so you inevitably disturb the particle,so whatever interference/diffraction pattern you would have expected in absence of the measurement is disturbed.The 'collapse' is a literal collapse in the position sense---the problem is to show that this can come out of a unitary process.'If ' we can do that(may be we could take the measurement to be introduction of some sort of a potential which changes the wavefunction and localizes the particle in the position sense) then the need for mysterious things like consciousness,MWI etc. goes away--note the 'if' in the statement.

 

[vanesch]

B
It's funny. I am not sure I have understood at all this post (in a non pejorative way). In the previous posts, I understand you try to introduce an ontological view of reality and in this final post you just reintroduce, implicitly, an epistemic view through the observer. All what I say is that I have properties and these properties are defined (sometimes implicitly) within a context (that may be "an observer").

Seratend.

P.S. (astronaute vs astronaut => Parlez vous français et aimez vous le bon vin et le fromage qui sent pas bon?

First of all, yes, I like the good wine and the smelly cheese (and lots of other stuff around here :-) ; one of the reasons to stick to a certain ontology :-)

I have indeed the impression that we are talking next to each other, and I'm affraid I'm not clear on your viewpoint as well.

I'm *for the moment* a kind of MWI fan, with the hope that I'm wrong
I have difficulties with a purely epistemological view because *something* exists (a la Descartes, also from cheese and wine fame). Now, because we don't have anything better, the mathematical object that seems to be a representation of "what exists" (ontological view) is "the wavefunction". I'm fully aware that this can be wrong, but for the moment we don't have anything better. What I was trying to argue was that *some representation* of what is "really out there" must be part of a successfull physical theory. (why ? Because my bones (and Descartes) tell me so :-) Maybe QM is not such a theory and one day we will understand our confusion (that's my hope, in fact). But for the moment we don't have anything of the kind. So we'll have to do with it. Where does it lead us ?
If we take the wavefunction to be a representation of reality, clearly the collapse gives us a problem: how can a meager observation by a humble human change the state of the entire universe ?
So this "collapse" stuff must be something EPISTEMOLOGICAL.
And MWI shows you how:

System "before":
|ignorant me> (a |u> + b |v> )

System "after":

a |u> |the-me-i'm-aware-of> + b |v> |some-other-me-i-don't-know-about>

So through the "looking glasses of the observations I'm aware of" (call this epistemology if you want), the system is now in state |u> and I got there with probability |a|^2.

But when you look at the "ontology" (if that's what the wavefunction represents), this measurement did in fact more to me than to the system, which is still with amplitude a in |u> and with amplitud b in |v> except that it's now entangled with my bodystates ; that's what I meant.

cheers,
Patrick.

 

[vanesch]

you just reduce the \Delta x or the position uncertainty of the particle(so that you know the position of the particle (reasonably well)),whereas the momentum uncertainty becomes high.

The classical argument against saying that "the wavefunction is a representation of the information we have about a system" is that hydrogen molecules exist, independent of the information we have about them, for instance. The binding energy of a hydrogen molecule (calculated from its wavefunction in the ground state) doesn't "change" because we know, or don't know, things about it.
That's different in classical statistical mechanics: if for one reason or another, you KNOW the microscopic state of, say, a gas in a container, this changes drastically the density in phase space (from the canonical ensemble, it becomes a delta-function), but that doesn't change any physical property of the gas.

The 'collapse' is a literal collapse in the position sense---the problem is to show that this can come out of a unitary process.'If ' we can do that(may be we could take the measurement to be introduction of some sort of a potential which changes the wavefunction and localizes the particle in the position sense) then the need for mysterious things like consciousness,MWI etc. goes away--note the 'if' in the statement.

I think it is easy to show that collapse cannot come from a unitary process. I showed it here already (it takes 5 lines or so). Unitarity implies linearity and conservation of hilbert norm, so you CANNOT collapse the wavefunction with a unitary operator. Even the decoherence people acknowledge this (sometimes :-).

cheers,
Patrick.

 

[Nicky]

Unitarity implies linearity and conservation of hilbert norm, so you CANNOT collapse the wavefunction with a unitary operator. Even the decoherence people acknowledge this (sometimes :-).

Does that mean, therefore, that if wavefunction collapse is "real", there must be some nonlinearity in the time evolution operator?

 

[vanesch]

Does that mean, therefore, that if wavefunction collapse is "real", there must be some nonlinearity in the time evolution operator?

Yes. Some people try to add some tiny non-linearities and some noise to the Schroedinger equation, with the hope that it doesn't change most of what works in QM, and that it induces a genuine collapse.

The problem I have with that approach is that it is "fiddling" and that it destroys completely the mathematical structure of QM without replacing it with another fundamental principle. What we also know is that, given the EPR results, those terms will have to violate SR too.
In fact, if you allow for all that, there's no point in looking further, there IS already a theory which does that, correctly: Bohmian mechanics !

My uninformed gut-feeling is that if we are to do that, it should be by a modification of GR based upon some or other general principle, and not just by adding a fudge term in some equation.

cheers,
Patrick.

 

[gptejms]

I think it is easy to show that collapse cannot come from a unitary process. I showed it here already (it takes 5 lines or so). Unitarity implies linearity and conservation of hilbert norm, so you CANNOT collapse the wavefunction with a unitary operator. Even the decoherence people acknowledge this (sometimes :-).

I realize that but at the same time I am against a special role for consciousness in the measurement process.Say you have a double slit experiment(with electrons) and you look for photons with a gamma ray microscope at one of the slits.What I am saying is that this measurement process may be pictured as the introduction of 'some potential' which localizes the wavefunction--the potential would necessarily change the wavefunction and in this case localizes it to one of the slits.In other words,one could picture the measurement process here as the interaction between two fields, the electron field and the photon field and somehow this interaction forces the electrons to appear at one or the other slit.

 

[vanesch]

Say you have a double slit experiment(with electrons) and you look for photons with a gamma ray microscope at one of the slits.What I am saying is that this measurement process may be pictured as the introduction of 'some potential' which localizes the wavefunction--the potential would necessarily change the wavefunction and in this case localizes it to one of the slits.In other words,one could picture the measurement process here as the interaction between two fields, the electron field and the photon field and somehow this interaction forces the electrons to appear at one or the other slit.

In order to say so, you have to consider the measurement system "classical", in that you put a "classical" potential in the Schroedinger equation of the electron. In doing so, you've neglected the quantum nature of the microscope. Of course, in practice this works in many occasions (semi-classical models work very well in different fields) ; after all that is the correspondence principle.
But doing so puts you in a Copenhagen view (the "macroscopic, classical, ontological" world vs the "microscopic, quantum, epistemological" world) already, and you have again to explain what differentiates both.
If you insist on all the atoms and so on of the gamma ray microscope to be described quantum-mechanically, and the EM field of the gamma ray microscope also through QFT, then the gamma ray microscope doesn't introduce "a potential" in the electron schroedinger equation, but both systems (electron + microscope) are COUPLED through an interaction term in the overall product hilbertspace.
And if you do that, again, you do not obtain a projection, but an entanglement.

As with all resolutions of the projection postulate without modifying the unitary part of QM that I've come across: the projection postulate follows naturally if you have sneaked it in through the back door
That is the case in Copenhagen (you POSTULATE a classical macroscopic world, and its (fuzzy) transition from the quantum world by projection), that's true for those who think that decoherence solves the problem (they use the density matrix, which itself is based upon the Born rule and the projection postulate), it is even true for Deutsch (who introduces some "reasonable assumptions" for his rational deciders which comes down to the Born rule).

cheers,
Patrick.

 

[Nicky]

In fact, if you allow for all that, there's no point in looking further, there IS already a theory which does that, correctly: Bohmian mechanics !

I was under the impression that Bohmian mechanics does not explain well the collapse of wavefunctions, i.e. the sudden discontinuity in Bohm's "quantum potential" after measurement.