# 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 possess 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.

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#### 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 lets 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 aquire position. So my question still is what gives the observer the ability to create its reality.

#### vanesch

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Apak said:
In other words the particles have no position until the observer decides to measure position at which time the particles then aquire 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 :yuck:

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.

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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

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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...)

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vanesch said:
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.

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#### 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

Apak said:
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

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seratend said:
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

vanesch said:
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).

vanesch said:
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

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seratend said:
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

Nacho said:
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)

Code:
        +---|+>--------------
|           |
|           V
-->-[SG]+       [obs A]
^  |           ^
|  |           |
|  +---|->--------------+
|                       |
+----<------------------+
Seratend.

#### Igor_S

vanesch said:
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

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Igor_S said:
How can classical world violate causality?
Ok, that was a shortcut. If you insist on a classical existance 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

vanesch said:
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.

vanesch said:
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?

vanesch said:
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?

vanesch said:
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.

vanesch said:
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.

vanesch said:
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

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seratend said:
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 :tongue:

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.

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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

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"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

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"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:

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.

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#### ShalomShlomo

vanesch said:
Originally Posted by Igor_S
How can classical world violate causality?

If you insist on a classical existance 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 travelling in a spaceship, the filter on
planet A is positioned first. To another observer travelling 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

ShalomShlomo said:
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.:

ShalomShlomo said:
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:

ShalomShlomo said:
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.

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