Re QM: Why Not Knowledge

[vanesch]

That's to say, with a density matrix approach to the QM of any brain, the drivers and processes will largely operated in the large-sample, classical domain. And then, classical? Quantum? it's all the same.

Density matrix... in what basis ? Because depending on the answer, the density matrix will describe something that 1) looks like a statistical distribution in classical phase space (what you imply), or 2) will look completely different !

Write the density matrix in the basis (|dead cat> + |live cat>) and (|dead cat> - |live cat>) for instance... Now, you can say that one OBVIOUSLY has to use the basis {|dead cat>, |live cat>} but I hope that you see the circularity of that argument...

Again, you seem to think that I fight the potentially probabilistic aspect of quantum theory. I'm not.

I'm pointing out that, along the chain, you need to say WHAT it is that you consider classical, because it is in THAT basis that you have to write your density matrix and to put the non-diagonal elements to 0, and that is a matter of convention (except in decoherence schemes, but these are inherently MWI). How do you get out your "classical" basis of your brain, when you have your Schroedinger equation ? And if you use projection, in what basis do you project, in order to get out probabilities (or for that matter, the density matrix) ?

The density matrix is the singly most abused quantity to "solve" the measurement problem (because it always leads to a circular reasoning), because of the easy sneaking in of the "classical basis".

I went to the observer's brain, because for all other apparatus, it is "obvious" that a measurement instrument is going to measure in the basis it is designed for (which is in fact absolutely not obvious... except, again, if you go to a decoherence approach, which is part of an MWI view). Tell me, what "basis" is our brain supposed to measure ? The "classical" states ? Why ?

 

[Sherlock]

I only replied to part of your last reply to me. I'll do the rest tomorrow. Anyway, the discussion you and Reilly are having seems more interesting. The sense of smell, for example, seems to operate in some sort of vibrational basis ... matching of resonant frequencies. More support for the notion that nature is fundamentally wavelike?

Metaphysics tries to describe what is "real". What is "existing out there". It is not a matter of convention, but of hypothesis.

If we use the word real to refer to anything that we can imagine, then it becomes absurdly ambiguous. The criterion that we use to separate fact from fiction is our collective sensory perception of the world outside our skins. We include as real, those objects and events reported to us by people we trust even though we haven't actually sensed the objects and events themselves. But, clearly there is a difference between saying that reality is composed of an infinite number of non-interacting brain-state branches and that a voltmeter reads 7V. Physical science is concerned with the latter sort of statement (the meaning of which is quite clear), while metaphysics is concerned with the former sort of statement (whatever it might mean).

I agree that metaphysics describes what MIGHT be out there. Physics describes what IS out there.

The following passage is from one of the places you linked to:
A more nuanced view is that metaphysical statements are not meaningless statements, but rather that they are generally not fallible, testable or provable statements. That is to say, there is no valid set of empirical observations nor a valid set of logical arguments which could definitively prove metaphysical statements to be true or false. Hence, a metaphysical statement usually implies a belief about the world or about the universe which may seem reasonable but is ultimately not provable. That belief could be changed in a non-arbitrary way, based on experience or argument, yet there exists no evidence or argument so compelling that it could rationally force a change in that belief, in the sense of definitely proving it false. Yet this does not mean that science can be altogether freed from metaphysical assumptions or beliefs, since scientific thought is based on axiomatic systems, which by definition operate with unprovable assumptions. One reason for that is that, typically, there are always more theories, than valid data that could corroborate or falsify those theories (Cf. also Stefan Amsterdamski's reflections on this topic). But whereas the metaphysician is likely to say, "this is how it is", the physician (i.e. natural scientist) is likely to say "this is how it is, though I could be proven wrong".

The existence of an objective world is definitional not hypothetical.
The physical existence of an object or an event is defined by our sensory experience of it.

Sorry, but you are now re-defining the concept of ontological existence, and in fact your definition coincides with what is usually called "subjective experience".

All experience is subjective. When we can communicate our subjective experience unambiguously, then we call it objective. We can communicate unambiguously when we are talking about sensory perceptions of objects and events that are defined as existing outside ourselves. Objects and events in the external world. The external world of our collective sensory perceptions isn't a hypothetical world. This world, as well as the internal world of our thoughts, dreams, and emotions is what we say exists. I see a computer screen in front of me. This isn't a hypothetical statement. It's simply what I call the thing that I'm seeing. To ascertain whether what I'm seeing is actually part of the external, objective world, I corroborate my perception with what others say they see when they're looking at my computer screen. This is reality, because we call it reality. This perception I'm experiencing is called a computer screen. On this computer screen are symbols and collections of symbols which either refer to objects and events that are either amenable in some way or other to our collective sensory perceptions, or they aren't --- and if they aren't, then we call them metaphysical. The BRANCHING world or brain states of MWI which, by definition, aren't amenable to our collective sensory perceptions are metaphysical. Voltmeters and voltmeter readings are not metaphysical.

The existence of an objective world isn't a question or a conundrum or a hypothesis in the physical sciences --- it's simply the way that things are talked about. It's what our collective behavior means. Whether we're all in some sort of dreamworld, or hallucinating in the same way, or whatever --- by definition, these are nonsensical considerations and aren't considerations of the physical sciences.

Well, they are exactly the subject of metaphysics.

I agree. But metaphysics isn't physics. That's why they tacked that META onto the beginning of it.

And metaphysics is also the defining frame of physical science: the theoretical description of an ontology. In other words, the starting hypothesis of physical science is that we are going to model reality (well knowing that this will always be on the level of a working hypothesis), and our guiding principle is empirical observation: empirical observation and its confrontation with what is deduced from our model of reality as a prediction for that observation is the judge by which we establish - or not - the quality of our model of reality. As such, agreement with observation is of course not a proof for the validity of our model. It is only a necessary condition. But the interpretation of our formal model is always that it describes objective reality. This is the defining frame of physics.

The defining frame of physics is our collective sensory perceptions. The guiding principles might be metaphysical, but they don't necessarily have to be.

Now, positivism tries to get rid of that part which is "model of reality" and sees the theory just as a relationship between observations. I think that as such, it misses the essence of physical science, because it reduces physics as a "curve fitting activity" that "fits curves" upon our subjective experiences. Any "curve fitting algorithm" works, in that case ; and there is no room for "general physical principles". THIS is what I think is the loss in the positivist attitude.

Positivism is about the meaning of statements, and the criterion of meaningfulness is, as you stated above, empirical observation. Is a statement that purports to describe reality but which is by definition not amenable to empirical observation really of any use if the goal is to describe physical reality?

Now, it wouldn't occur to you to do the same with classical physics, would it ? I mean, in Newtonian physics, matter points are supposed to be "really there" where the mathematical model says they are, and gravity is "really pulling" on planets.

I've learned to NOT think of 'point particles' and gravitational 'forces' that way. They are simplifications ... convenient mathematical conventions.

It wouldn't occur to you to say that the moon is a coherent set of descriptions which make visual observations of the sky agree with ocean tides, through a symbolic model of a matter ball and gravitational interactions which is needed in the formalism to explain the light we see from the moon and the water that rises at the shore, right ? You associate to the concept of a matter ball which we call Moon, an ontological reality even though we can't touch it, and so on.

We can SEE the moon. Men have walked on and taken samples of the moon.

In the same way, I'm simply proposing that we do the same with quantum theory: that the wave function is describing something that is "really there".

I agree. But it is an unfounded stretch to say that whatever the wave function is describing in the underlying reality is in 1-1 correspondence with the wave function. The success of the Schroedinger formulation is one good reason in support of the idea that the underlying quantum reality is essentially wavelike in its composition and behavior. But that's all that can be said for now.

And that's sufficient to arrive at MWI, at least if you do not think that "your observation" is going to change what "is really there" (what is NOT the case with the definition you gave of "objective reality" in the positivist viewpoint - and which corresponds to (collective) subjective experience: for instance, the neutrino was only "really there" since it has been detected and observed ; before it "was not really there").

The assumption that the wave function is in 1-1 correspondence with an underlying quantum world might be sufficient to arrive at MWI, but it doesn't NECESSARILY lead to MWI. And anyway, as I said, the assumption itself is an unnecessary stretch.

The neutrino, like all the particles of the standard model, is a creation of the experimental procedures which define and produce it. We have to talk about it this way because, unlike the moon, we have no other sensory apprehension of neutrinos. We have no way of knowing if they exist in nature in the absence of the structures that we've imposed to produce them.

If you think that observation is NOT going to change the entire ontology of the world, then there is NO basis for the projection postulate as a physical action which somehow happens during "measurement" and which is different from a physical interaction.

Even though it's an apparently underivable assertion, the projection postulate is an extension of the wave model of reality. If it didn't work, then we wouldn't be considering that model as a reasonable approximation of what is happening in the underlying quantum world, and quantum theory would have to be rethought and reformulated. But it does work (at least to a reasonably good approximation).

As such, only the unitary evolution of the state of the universe is a possibility, and as such, "parallel worlds" arrize unavoidably.

Parallel worlds arise if you deny the unique reality of irreversible data. And when you do that then all sorts of silly problems ensue ... the solving of which will not in any way either enhance the applicability or the efficacy of QM calculations.

Putting labels on our sensory perceptions isn't metaphysics. Putting labels on abstractions of our sensory perceptions isn't metaphysics.

Except if that label is "objective reality" because that is the subject matter of metaphysics.

No, that's exactly the problem with metaphysical statements. There's no way to objectify them. The subject matter of physics is objective reality. The subject matter of metaphysics is whatever subjective vision you or I might have wrt the way we think reality ought to be on presumed scales of interaction that are not amenable to our collective sensory perceptions.

MWI is constructing a metaphysical ontology (the existence of worlds that can't be verified) based on an assumption that can't be verified. This is why MWI isn't physics in any sense of the word. Or even natural philosophy.

Well, I claim that it is the core of physics, as defined by the frame set by natural philosophy, in the sense that every physical theory is supposed to describe, by its mathematical formalism, the ontology of the physical world.
(note that "a metaphysical ontology" is a tautology).

It's the behavior of the world of our collective sensory perceptions that we seek to explain. With the advent of quantum experimental phenomena (which are part of the world of our collective sensory perceptions, not the underlying reality), the classical metaphysical underlying reality was put to explanatory tests that it couldn't pass. So, a new theory emerged which was a combination of two, apparently mutually exclusive, apprehensions of the reality underlying what was observed at the instrumental level.

The core of quantum theory is the mathematical formalism and the algorithmic steps that one goes through to apply the formalism in order to correctly predict experimental results. MWI is something that got associated with it much after the fact of its basic development. To be sure, the developers of the theory, in using the mathematical formulations that they did, had some ideas about the composition and behavior of an underlying quantum world and how it might be related to the phenomena of our ordinary experience, and how the formulas that correctly describe behavior at the level of our sensory perceptions might be related to behavior at levels fundemental to and encompassing our sensory perceptions.

Then of course there's Heisenberg. I haven't learned his formulation yet.

There is, by definition, an objectively existing world. It's the world of our collective sensory experience.

Which is usually called the world of our subjective experience...

All sensory experience is, first, subjective. But all subjective experience isn't the apprehension of objects and events outside ourselves, and all subjective experience isn't objective. Objective experience (the objectively existing world) is the proper subset of all subjective experience that corresponds with objects and events that can be unambiguously communicated (ie., fapp, the stuff that we perceive as be external to us, the stuff that is not just thoughts, or dreams, or emotions, etc.). If I taste something sweet (say, a doughnut) and you try it and say that it tastes sweet to you also, then we've communicated a more or less objective qualitative property of doughnuts. Still somewhat ambiguous though. If I look at a group of doughnuts and count 10 of them, and you count the same number, then we've communicated an unambiguous fact about the objective world.

 

[vanesch]

The criterion that we use to separate fact from fiction is our collective sensory perception of the world outside our skins. We include as real, those objects and events reported to us by people we trust even though we haven't actually sensed the objects and events themselves.

Well, that viewpoint is, in itself, a metaphysical assumption, and goes under the name of "naive realism". It assigns reality to what "is perceived to be real". http://en.wikipedia.org/wiki/Naive_realism

But, clearly there is a difference between saying that reality is composed of an infinite number of non-interacting brain-state branches and that a voltmeter reads 7V.

I don't know. It depends upon your metaphysical assumptions, no ? In a naive realism view, you are right. In a positivist view, we don't talk metaphysics ("perceptions happen" and are supposed to be all we have to care about).

Physical science is concerned with the latter sort of statement (the meaning of which is quite clear), while metaphysics is concerned with the former sort of statement (whatever it might mean).

I agree that metaphysics describes what MIGHT be out there. Physics describes what IS out there.

Hehe, rather the opposite, no ? The fundamental assumption behind the idea of physics, is that there is a mathematical description of reality (metaphysical) from which it is possible to DEDUCE our perceptions. As such, in physics we make suppositions of what MIGHT be out there (in the form of a mathematical formalism representing nature) and we try to deduce from that, what we might perceive (what we call: experimental observation). If there is agreement, we say that our physical theory MIGHT be true (in the sense that its mathematical structure MIGHT correctly describe reality). But we know that we will never know for sure. Now, metaphysics is the reflection on all these concepts, and thus talks about what IS out there, because that is its very subject.

So the statement "this physical theory describes nature" is a metaphysical statement. IMO, it doesn't even make sense to talk about a certain physical theory without having made this previous, metaphysical statement about it. So when we talk about a physical theory (and its interpretation), we ALREADY are supposed to have made the metaphysical statement "this theory describes nature".

The following passage is from one of the places you linked to:
A more nuanced view is that metaphysical statements are not meaningless statements, but rather that they are generally not fallible, testable or provable statements. That is to say, there is no valid set of empirical observations nor a valid set of logical arguments which could definitively prove metaphysical statements to be true or false. Hence, a metaphysical statement usually implies a belief about the world or about the universe which may seem reasonable but is ultimately not provable. That belief could be changed in a non-arbitrary way, based on experience or argument, yet there exists no evidence or argument so compelling that it could rationally force a change in that belief, in the sense of definitely proving it false. Yet this does not mean that science can be altogether freed from metaphysical assumptions or beliefs, since scientific thought is based on axiomatic systems, which by definition operate with unprovable assumptions. One reason for that is that, typically, there are always more theories, than valid data that could corroborate or falsify those theories (Cf. also Stefan Amsterdamski's reflections on this topic). But whereas the metaphysician is likely to say, "this is how it is", the physician (i.e. natural scientist) is likely to say "this is how it is, though I could be proven wrong".

See... metaphysics says "how it is" and the physicist says "this is (according to theory X) how things are, but of course theory X could be wrong (although empirically correct)".

All experience is subjective. When we can communicate our subjective experience unambiguously, then we call it objective. We can communicate unambiguously when we are talking about sensory perceptions of objects and events that are defined as existing outside ourselves. Objects and events in the external world. The external world of our collective sensory perceptions isn't a hypothetical world.

Sorry, but it is. The proof of that is the unfalsifiability of solipsism. Now, I think that the HYPOTHESIS of an objective world (which is a metaphysical hypothesis, which can hence never be proved - hence the unfalsifiability of solipsism which is its negation) is a very useful one, and a FUNDAMENTAL metaphysical assumption to even start to do physics.

This world, as well as the internal world of our thoughts, dreams, and emotions is what we say exists. I see a computer screen in front of me. This isn't a hypothetical statement.

That is correct, you SEE a computer screen in front of you is a correct assesment of your subjective experience "seeing a computer screen". However, DEDUCING that there is such a thing as a computer screen, out there, is BASED UPON THE ASSUMPTION of the existence of an external world. The IDENTIFICATION of subjective experience with an external world (namely the assumption that all our perceptions correspond 1-1 with "things out there") is the metaphysical assumption of naive realism.

It's simply what I call the thing that I'm seeing. To ascertain whether what I'm seeing is actually part of the external, objective world, I corroborate my perception with what others say they see when they're looking at my computer screen.

Yes, but the fallacy in this reasoning is of course, that you don't KNOW FOR SURE that there are OTHERS confirming their perception of a computer screen. All YOU know, it that _you perceive them to do so_, and as such, you are using ONE subjective experience (perceiving others to confirm your computer screen) which you take tacitly to be real (hypothesis !!), to deduce that your other subjective experience (seeing a computer screen) is to be taken as real. So you USE the conclusion of your reasoning (my perceptions correspond to reality) in the argumentation of your conclusion. That's circular reasoning.

The BRANCHING world or brain states of MWI which, by definition, aren't amenable to our collective sensory perceptions are metaphysical. Voltmeters and voltmeter readings are not metaphysical.

That's a metaphysical statement as any other. You just decided what is real, and what is not.

I agree. But metaphysics isn't physics. That's why they tacked that META onto the beginning of it.

That is because metaphysics is the philosophical DEFINING FRAME of physics.

The defining frame of physics is our collective sensory perceptions. The guiding principles might be metaphysical, but they don't necessarily have to be.

I think I've shown that, while you think you can do away with it, you are making your own metaphysical assumptions (but as hidden hypotheses).

Positivism is about the meaning of statements, and the criterion of meaningfulness is, as you stated above, empirical observation. Is a statement that purports to describe reality but which is by definition not amenable to empirical observation really of any use if the goal is to describe physical reality?

Of course it is useful, because it is an organizing principle from which our observations can be deduced. What is probably less useful, is to have TWO different statements which lead to the same empirical observations. (that is: two different physical theories with different formalism, but which are empirically equivalent). Then, you take your pick and all discussion about which one to take is a matter of taste.
But it is always better to have ONE such statement than ZERO, because (as do positivists) with ZERO metaphysical statements, you've LOST your organizing principle. You've lost the logical structure from which empirical observation can be deduced.

I've learned to NOT think of 'point particles' and gravitational 'forces' that way. They are simplifications ... convenient mathematical conventions.

Then, how do you think of it ? (without of course saying, curved spacetime! We now "know" that Newtonian gravity is an approximation to general relativity, but that has simply displaced the interpretational issue to GR - let's assume for the sake of simplicity that you don't know of GR, and you don't know that Newtonian gravity is not ultimately the correct description of gravity).
Is repeating in your head "everything in the formalism LOOKS AS IF the sun is pulling on the earth, but that's NOT what I should think of it" the best way to devellop an intuition for doing Newtonian gravity ?

We can SEE the moon. Men have walked on and taken samples of the moon.

Well, you've heard stories and saw movies about men who walked on the moon (= subjective perception).

I agree. But it is an unfounded stretch to say that whatever the wave function is describing in the underlying reality is in 1-1 correspondence with the wave function. The success of the Schroedinger formulation is one good reason in support of the idea that the underlying quantum reality is essentially wavelike in its composition and behavior. But that's all that can be said for now.

Well, it is not an unfounded stretch, in the following way. Contrary to the case of Newtonian gravity, were you can now easily say "hey, look, we KNOW that the sun is not pulling on the earth, it is only deforming the spacetime continuum, look at GR", we DO NOT HAVE SUCH AN UNDERLYING theory for QM. So *we do not know* if the quantum mechanical structure is there to stay or not. Making the assumption that it is NOT is a less founded assumption, than making the assumption that it IS going to stay. This assumption can be wrong, but we have less indications for it being wrong than for it being right. So, given the metaphysical frame of every physical theory, we START by stating that quantum theory DOES DESCRIBE REALITY WITH ITS FORMALISM. As a metaphysical starting assumption, well knowing that this is ALWAYS going to be hypothetical.
You can take on another metaphysical starting assumption, which is naive realism. But it is JUST AS WELL AN ASSUMPTION. So take your pick. I'm only saying that *if we are going to do an interpretation of a physical theory, we are supposed to make the metaphysical assumption that its formalism is going to describe nature*.

And ONCE you do that, you arrive at MWI. You can avoid arriving at MWI by introducing 2 possible things:
1) you can introduce "unknown measurement interactions" which only happen in physical constructions called "measurement instruments", and which collapse the wavefunction - which moreover introduce non-locality as a physical process, and as such screw up Lorentz invariance, or:

2) you can say that there IS no physical reality, take on the strictly solipsist viewpoint, and as such say that the wavefunction is what guides your subjective experience. The "collapse" is then simply "you perceiving". The wavefunction describes your dream.

The assumption that the wave function is in 1-1 correspondence with an underlying quantum world might be sufficient to arrive at MWI, but it doesn't NECESSARILY lead to MWI.

Let's look at the logic of this statement:
proposition (1) : "the wavefunction is in 1-1 correspondence with quantum world"
proposition (2): "MWI"

statement 1: (1) is sufficient to arrive at (2)
statement 2: (1) does not necessary lead to (2)

Hummm....

The neutrino, like all the particles of the standard model, is a creation of the experimental procedures which define and produce it. We have to talk about it this way because, unlike the moon, we have no other sensory apprehension of neutrinos. We have no way of knowing if they exist in nature in the absence of the structures that we've imposed to produce them.

Well, I don't know if the president of the united states is a guy called Bush. In fact, I think that the world is a flat disk, and that there is no such thing as the united states, as I've never been there. So the US, to me, is a "creation of the experimental procedure of taking an airplane and go and see" ? Come on... :rofl:

Even though it's an apparently underivable assertion, the projection postulate is an extension of the wave model of reality.

The projection postulate, as presented in the Copenhagen view, is simply an INCONSISTENT operation, because the theory presents TWO CONTRADICTORY WAYS of arriving at the state of the measurement apparatus: one is the unitary way, which is build up by all elementary interactions of the constituents of the apparatus, which gives you RESULT A, and the OTHER is the projection postulate, which gives you result B.
A and B are NOT equal. So you have now to decide - in a totally arbitrary way - what things are suddenly NOT to be described by the interactions of their constituents, and are to be labelled "measurement apparatus", and what things are NOT a measurement apparatus, and hence are to be described by the normal unitary laws followed by their constituents.

If it didn't work, then we wouldn't be considering that model as a reasonable approximation of what is happening in the underlying quantum world, and quantum theory would have to be rethought and reformulated. But it does work (at least to a reasonably good approximation).

It works only because we happen to have an intuitive "list of measurement apparatus" in our head, and we switch to the 'right rule' when it suits us. But quantum theory, by itself CANNOT TELL US WHEN A SYSTEM IS A MEASUREMENT APPARATUS OR NOT. We have to do so, intuitively, in order not to be inconsistent. We have to split the world into two different kinds of systems: those that are build up of elementary constituents and follow unitary evolution, and those OF WHICH WE'RE NOT SUPPOSED TO SAY THAT THEY ARE BUILD UP OF ELEMENTARY CONSTITUENTS, and which we call "measurement apparatus". In order to be consistent, there should be a general rule for when a system is build up from constituents, and when it is a holistic measurement apparatus. And then try to find a physical explication of why systems behave differently if they are, or not, a measurement system.

Parallel worlds arise if you deny the unique reality of irreversible data.

No, parallel worlds arise when we deny certain systems to NOT FOLLOW the laws of physics of their constituents.

And when you do that then all sorts of silly problems ensue ... the solving of which will not in any way either enhance the applicability or the efficacy of QM calculations.

No, that's exactly the problem with metaphysical statements. There's no way to objectify them. The subject matter of physics is objective reality.

No, that's the subject matter of metaphysics. There is a metaphysical assumption, called "physics" which says that objective reality is describable by a mathematical theory, and that subjective experiences (experimental observation) is to be deducible from that theory.

The subject matter of metaphysics is whatever subjective vision you or I might have wrt the way we think reality ought to be on presumed scales of interaction that are not amenable to our collective sensory perceptions.

Of course, and one of those visions is that there ought to be a mathematical theory describing objective reality. That vision is called "physics".

It's the behavior of the world of our collective sensory perceptions that we seek to explain. With the advent of quantum experimental phenomena (which are part of the world of our collective sensory perceptions, not the underlying reality), the classical metaphysical underlying reality was put to explanatory tests that it couldn't pass. So, a new theory emerged which was a combination of two, apparently mutually exclusive, apprehensions of the reality underlying what was observed at the instrumental level.

That was the crazy assumption of Bohr, but we're not obliged to follow him. The classical metaphysical underlying reality was simply that there was that naive realism helt, up to a point, in that objective reality corresponded more or less to our perception of it (like you try to push here). Indeed, this could not be brought in accordance with quantum theory (but also not with general relativity, which has no special treatment of "now", contrary to Newtonian physics).
So IN ORDER TO CLING TO NAIVE REALISM, Bohr kicked out the fundamental metaphysical frame that physical theories describe objective nature, and as such, introduced a lot of inconsistency.

However, if you take the opposite step, which is, to consider that physical theory DOES describe objective nature, and you let go naive realism, you can do fine (that's MWI). You have 1) a mathematical description of objective nature and 2) a rule how to deduce your perceptions (given that they now do not correspond anymore 1-1).

To be sure, the developers of the theory, in using the mathematical formulations that they did, had some ideas about the composition and behavior of an underlying quantum world and how it might be related to the phenomena of our ordinary experience, and how the formulas that correctly describe behavior at the level of our sensory perceptions might be related to behavior at levels fundemental to and encompassing our sensory perceptions.

Of course they did, and they did so by playing a schizophrenic game. When they were reasoning about the physics, they were in fact taking the wavefunction for more or less real, and when they switched to interpretational problems, they said we didn't have to take it for real.
You cannot require, for instance, that interaction terms written as operators on wavefunctions, should obey certain principles such as locality, or charge conservation or momentum conservation, and then claim that the items on which they work are not really describing the physics that is going on "for real".

Still somewhat ambiguous though. If I look at a group of doughnuts and count 10 of them, and you count the same number, then we've communicated an unambiguous fact about the objective world.

Except of course, that you will never know if *I* counted them or whether you only perceived me counting them...

 

[vanesch]

An interesting read about the viewpoint I'm defending (called scientific realism, as opposed to Logical positivism) can be found here:

http://en.wikipedia.org/wiki/Scientific_realism


http://en.wikipedia.org/wiki/Logical_positivism

 

[selfAdjoint]

An interesting read about the viewpoint I'm defending (called scientific realism, as opposed to Logical positivism) can be found here:

http://en.wikipedia.org/wiki/Scientific_realism

http://en.wikipedia.org/wiki/Logical_positivism

I think from the descriptions in the article I would describe myself as a pessimistic inductionist. Not that I assert that physical theories of the past have failed; they have succeeded in sometimes quite spectacular ways, but at the cost of employing unobservable entities (epicycles, elastic ether) that were later shown not to exist. Young's elastic ether theory accurately and quantitatively predicted the two slit interference of light, for example, and Young actually developed his modulus, still in use, to describe the mechanical elasticity of his supposed ether.

And I don't assert either that multiple worlds don't or can't exist; just that they seem very unlikely to me and that the success of quantum mechanics in predicting experimental behavior is not really an argument in favor of them.

 

[Sherlock]

... it doesn't even make sense to talk about a certain physical theory without having made this previous, metaphysical statement about it. So when we talk about a physical theory (and its interpretation), we ALREADY are supposed to have made the metaphysical statement "this theory describes nature".

What doesn't make sense is to talk about the constructs of a theory as being in 1-1 correspondence with an underlying reality that we have no sensory apprehension of.

The external world of our collective sensory perceptions isn't a hypothetical world.

Sorry, but it is. The proof of that is the unfalsifiability of solipsism.

Objective reality is just a term that refers to collective sensory perceptions meeting certain criteria. It's definitional. It's a convention.

We just DEFINE terms like knowing and knowledge, objective reality, etc. and then proceed.

... you SEE a computer screen in front of you is a correct assesment of your subjective experience "seeing a computer screen". However, DEDUCING that there is such a thing as a computer screen, out there, is BASED UPON THE ASSUMPTION of the existence of an external world.

If I can't know that what I AM seeing is part of the objective physical world, then why should I assume that something that I CAN'T see is part of the objective physical world? What do terms like objective reality, and really out there MEAN then?

It's simply what I call the thing that I'm seeing. To ascertain whether what I'm seeing is actually part of the external, objective world, I corroborate my perception with what others say they see when they're looking at my computer screen.

Yes, but the fallacy in this reasoning is of course, that you don't KNOW FOR SURE that there are OTHERS confirming their perception of a computer screen. All YOU know, is that _you perceive them to do so_, and as such, you are using ONE subjective experience (perceiving others to confirm your computer screen) which you take tacitly to be real (hypothesis !!) ...

... So you USE the conclusion of your reasoning (my perceptions correspond to reality) in the argumentation of your conclusion. That's circular reasoning.

It's not reasoning, per se. It's how we DEFINE reality. Our collective (communicated) perceptions ARE reality. This is the basis that the physical sciences use to evaluate statements about the world.

Now, if you have some other idea about what reality IS, then what is it?

The BRANCHING world or brain states of MWI which, by definition, aren't amenable to our collective sensory perceptions are metaphysical. Voltmeters and voltmeter readings are not metaphysical.

That's a metaphysical statement as any other. You just decided what is real, and what is not.

Real is a four-letter word. If you don't assign some meaning to it (ie., if you have no criterion for discerning what is real from what isn't) then the word has no utility.

So yes, we DECIDE what is real and what is not based on some definition or other of the term, real.

I agree. But metaphysics isn't physics. That's why they tacked that META onto the beginning of it.

That is because metaphysics is the philosophical DEFINING FRAME of physics.

I agree (to the extent that the formulation of physical theories does involve a certain amount of metaphysical speculation), but metaphysics isn't the physical defining frame of physics. The physical defining frame is our collective sensory perceptions. Metaphysical HYPOTHESES aren't physical hypotheses, and are therefore excluded from the actual SCIENCE of physics. That is, the metaphysical part or interpretation of a physical theory isn't amenable to scientific investigation. So, for example, nothing definitive can be said about the veracity of the claim of MWI world-branching. It just seems like a silly way to think about things. But how can one possibly KNOW whether MWI actually is silly or if it actually is the way things are? So, the MWI interpretation does have that going for it.

The defining frame of physics is our collective sensory perceptions. The guiding principles might be metaphysical, but they don't necessarily have to be.

I think I've shown that, while you think you can do away with it, you are making your own metaphysical assumptions (but as hidden hypotheses).

So, in your view, everything is metaphysical? Or what? I would suppose not, but I'm not even sure what we're talking about any more. It seems like you're taking an unnecessarily circuitous route to get to a place where physics already was. This is the same thing that the MWI interpretation itself does. You're trying to recover the Born rule in MWI, but quantum theory already includes that. Ok, so nobody understands exactly why it works as well as it does. Then that's what the problem is, and that's what is to be investigated --- rather than trying to find how it can be derived from an interpretation of quantum theory that really doesn't seem to fit with what is known about our universe. I do, by the way, believe that the idea of other universes makes sense, but not in the MWI sense. It follows from contemplating the (yes, metaphysical) implications of the Big Bang theory.

The MWI and it's associated problems come back to the assumption that the constructs of quantum theory are in 1-1 correspondence with an underlying quantum world. But, with or without that assumption quantum theory will be making the same predictions --- and with that assumption (and all the fussing over the MWI) you might be overlooking some very important clues.

The general problem, as I see it, is that physics hasn't come up with a definitive formulation of the first principles of nature yet. I believe that the Schroedinger approach of quantum theory is on the right track, in that it hints that nature is fundamentally waves and wave complexes in various media. But quantum theory, just as special relativity (and ordinary experience for that matter) tells me that what you see depends on how you look at something. We don't SEE the evolutions and interactions on the quantum scale. But if they are actually evolutions and interactions of wave structures of varying complexity, then the Born rule makes sense. It applies to macroscopic and irreversible measurement results because this is the context in which we're observing the underlying quantum world.

Have you ever contemplated the movements of a drum head after you hit it? Standing waves, harmonic resonances. You can't actually see them. Put some powder or sand on the drum head and you get more or less static geometric patterns corresponding to these wave motions and interactions. This is one way to think about the difference between the underlying quantum world and our macroscopic apprehension of it.

Or is this not a good analogy. I don't know. Remember I'm still just a novice at this stuff.

 

[Sherlock]

But it is always better to have ONE such (metaphysical) statement than ZERO, because (as do positivists) with ZERO metaphysical statements, you've LOST your organizing principle. You've lost the logical structure from which empirical observation can be deduced.

Positivism (physical science) is just a way to sort out which statements make more sense, or any sense. There's lots of metaphysical speculation going on, both conceptual and mathematical. Some speculations make more sense than others. MWI makes very little sense, imo.

I've learned to NOT think of 'point particles' and gravitational 'forces' that way. They are simplifications ... convenient mathematical conventions.

Then, how do you think of it ? (without of course saying, curved spacetime! We now "know" that Newtonian gravity is an approximation to general relativity, but that has simply displaced the interpretational issue to GR - let's assume for the sake of simplicity that you don't know of GR, and you don't know that Newtonian gravity is not ultimately the correct description of gravity).
Is repeating in your head "everything in the formalism LOOKS AS IF the sun is pulling on the earth, but that's NOT what I should think of it" the best way to devellop an intuition for doing Newtonian gravity ?

My intuition, such that it is, tells me that everything is a matter of wave mechanics. GR and Newtonian gravity are simplifications of the underlying wave mechanics that actually determines gravitational behavior. The standard model, with it's particles and forces and exchange particles, is a simplification of the underlying wave mechanics.

... it is an unfounded stretch to say that whatever the wave function is describing in the underlying reality is in 1-1 correspondence with the wave function. The success of the Schroedinger formulation is one good reason in support of the idea that the underlying quantum reality is essentially wavelike in its composition and behavior. But that's all that can be said for now.

... *we do not know* if the quantum mechanical structure is there to stay or not.

Isn't that what I said?

Making the assumption that it is NOT is a less founded assumption, than making the assumption that it IS going to stay.

I'm not making either assumption. I'm saying it's too early to make either assumption about the qm structure , but that its success indicates that the wave APPROACH is the right one, conceptually.

This assumption can be wrong, but we have less indications for it being wrong than for it being right. So, given the metaphysical frame of every physical theory, we START by stating that quantum theory DOES DESCRIBE REALITY WITH ITS FORMALISM. As a metaphysical starting assumption, well knowing that this is ALWAYS going to be hypothetical.
You can take on another metaphysical starting assumption, which is naive realism. But it is JUST AS WELL AN ASSUMPTION. So take your pick. I'm only saying that *if we are going to do an interpretation of a physical theory, we are supposed to make the metaphysical assumption that its formalism is going to describe nature*.

This is where I think you're making a mistake. The history of physics theories indicates that we should regard current quantum theory as a simplification of what is actually happening in the underlying quantum world.

Your starting metaphysical hypothesis should be that nature is fundamentally waves and wave interactions.

And ONCE you do that, you arrive at MWI. You can avoid arriving at MWI by introducing 2 possible things:
1) you can introduce "unknown measurement interactions" which only happen in physical constructions called "measurement instruments", and which collapse the wavefunction - which moreover introduce non-locality as a physical process, and as such screw up Lorentz invariance, or:

2) you can say that there IS no physical reality, take on the strictly solipsist viewpoint, and as such say that the wavefunction is what guides your subjective experience. The "collapse" is then simply "you perceiving". The wavefunction describes your dream.

It's reasonable to assume that there are some unknown interactions going on, and it's reasonable to assume that nature is fundamentally waves and wave interactions. And from this it's reasonable to assume that quantum theory is a simplification of what is happening, fundamentally, in nature. And this doesn't lead to MWI.

The assumption that the wave function is in 1-1 correspondence with an underlying quantum world might be sufficient to arrive at MWI, but it doesn't NECESSARILY lead to MWI.

Let's look at the logic of this statement:
proposition (1) : "the wavefunction is in 1-1 correspondence with quantum world"
proposition (2): "MWI"

statement 1: (1) is sufficient to arrive at (2)
statement 2: (1) does not necessary lead to (2)

Hummm....

You forgot the part about interpreting what the wavefunction means. You say that it means that two or more mutually exclusive measurement possibilities exist simultaneously in nature. I say it doesn't mean that at all. What I think it means is that the principle of linear superposition in wave mechanics seems to apply in the underlying quantum world as well as it does in the macroscopic world. Thinking of it this way does not lead to the world-branching of MWI.

The neutrino, like all the particles of the standard model, is a creation of the experimental procedures which define and produce it. We have to talk about it this way because, unlike the moon, we have no other sensory apprehension of neutrinos. We have no way of knowing if they exist in nature in the absence of the structures that we've imposed to produce them.

Well, I don't know if the president of the united states is a guy called Bush. In fact, I think that the world is a flat disk, and that there is no such thing as the united states, as I've never been there. So the US, to me, is a "creation of the experimental procedure of taking an airplane and go and see" ? Come on...

Bush is undoubtedly a pinhead, but to equate him with a neutrino is going too far. Anyway, neutrinos and photons and electrons, etc. are creations of experimental procedures. If they exist in nature independent of these experiments, then show me just one.

It would be nice if Bush didn't actually exist in nature independent of our observations of him.

But I see your point. If I don't actually do a certain set of operations that allows me to see Bush, then I won't see him.

The difference of course is that the composition and behavior of the macroscopic world in which I might see Bush is the world that I actually SEE, whereas the composition and behavior of the underlying quantum world can ONLY be inferred from macroscopic instrumental behavior.

The projection postulate, as presented in the Copenhagen view, is simply an INCONSISTENT operation, because the theory presents TWO CONTRADICTORY WAYS of arriving at the state of the measurement apparatus: one is the unitary way, which is build up by all elementary interactions of the constituents of the apparatus, which gives you RESULT A, and the OTHER is the projection postulate, which gives you result B.
A and B are NOT equal. So you have now to decide - in a totally arbitrary way - what things are suddenly NOT to be described by the interactions of their constituents, and are to be labelled "measurement apparatus", and what things are NOT a measurement apparatus, and hence are to be described by the normal unitary laws followed by their constituents.

I don't think it's a totally arbitrary decision. If it was, then physicists would be getting about as many wrong predictions as correct ones by using quantum theory. Obviously, once you get a sufficient detector output, then the unitary evolution(s) involved in predicting that output no longer applies.

In his Quantum Theory (the chapter on the quantum theory of the measurement process, page 622), Bohm says:
Finally, it is perhaps interesting to consider in a new light the fact that the mathematical description provided by the wave function is not in a one-to-one correspondence with the actual behavior of matter. From this fact, we are led to conclude that, contrary to general opinion, quantum theory is less mathematical in its philosophical basis than is classical theory, for, as we have seen, it does not assume that the world is constructed according to a precisely defined mathematical plan. Instead, we have come to the point of view that the wave function is an abstraction, providing a mathematical reflection of certain aspects of reality, but not a one-to-one mapping. To obtain a description of all aspects of the world, one must, in fact, supplement the mathematical description with a physical interpretation in terms of incompletely defined potentialities. Moreover, the present form of quantum theory implies that the world cannot be put into a one-to-one correspondence with any conceivable kind of precisely defined mathematical quantities, and that a complete theory will always require concepts that are more general than that of analysis into precisely defined elements. We may probably expect that even the more general types of concepts provided by the present quantum theory will also ultimately be found to provide only a partial reflection of the infinitely complex and subtle structure of the world. As science develops, we may therefore look forward to the appearance of still newer concepts, which are only faintly foreshadowed at present, but there is no strong reason to suppose that these new concepts are likely to lead to a return to the comparatively simple idea of a one-to-one correspondence between the real world and precisely defined mathematical abstractions.

It works only because we happen to have an intuitive "list of measurement apparatus" in our head, and we switch to the 'right rule' when it suits us. But quantum theory, by itself CANNOT TELL US WHEN A SYSTEM IS A MEASUREMENT APPARATUS OR NOT. We have to do so, intuitively, in order not to be inconsistent. We have to split the world into two different kinds of systems: those that are build up of elementary constituents and follow unitary evolution, and those OF WHICH WE'RE NOT SUPPOSED TO SAY THAT THEY ARE BUILD UP OF ELEMENTARY CONSTITUENTS, and which we call "measurement apparatus". In order to be consistent, there should be a general rule for when a system is build up from constituents, and when it is a holistic measurement apparatus. And then try to find a physical explication of why systems behave differently if they are, or not, a measurement system.

This is what Bohm's chapter on the quantum theory of the measurement process is about..
I've only scanned it so far.

It's the behavior of the world of our collective sensory perceptions that we seek to explain. With the advent of quantum experimental phenomena (which are part of the world of our collective sensory perceptions, not the underlying reality), the classical metaphysical underlying reality was put to explanatory tests that it couldn't pass. So, a new theory emerged which was a combination of two, apparently mutually exclusive, apprehensions of the reality underlying what was observed at the instrumental level.

That was the crazy assumption of Bohr, but we're not obliged to follow him. The classical metaphysical underlying reality was simply that there was that naive realism held, up to a point, in that objective reality corresponded more or less to our perception of it (like you try to push here). Indeed, this could not be brought in accordance with quantum theory (but also not with general relativity, which has no special treatment of "now", contrary to Newtonian physics).
So IN ORDER TO CLING TO NAIVE REALISM, Bohr kicked out the fundamental metaphysical frame that physical theories describe objective nature, and as such, introduced a lot of inconsistency.

However, if you take the opposite step, which is, to consider that physical theory DOES describe objective nature, and you let go naive realism, you can do fine (that's MWI). You have 1) a mathematical description of objective nature and 2) a rule how to deduce your perceptions (given that they now do not correspond anymore 1-1).

At this point in my education I can only say that, so far, Bohr's ideas make sense to me (and they are the ideas pushed by Bohm in his textbook), and that your's don't.

I think that Bohr might say that your MWI is giving you consistency at the expense of truth.

To be sure, the developers of the theory, in using the mathematical formulations that they did, had some ideas about the composition and behavior of an underlying quantum world and how it might be related to the phenomena of our ordinary experience, and how the formulas that correctly describe behavior at the level of our sensory perceptions might be related to behavior at levels fundamental to and encompassing our sensory perceptions.

Of course they did, and they did so by playing a schizophrenic game. When they were reasoning about the physics, they were in fact taking the wavefunction for more or less real, and when they switched to interpretational problems, they said we didn't have to take it for real.
You cannot require, for instance, that interaction terms written as operators on wavefunctions, should obey certain principles such as locality, or charge conservation or momentum conservation, and then claim that the items on which they work are not really describing the physics that is going on "for real".

The idea that the "... wave function is an abstraction, providing a mathematical reflection of certain aspects of reality, but not a one-to-one mapping" seems to me like a much better way to consider it --- wrt both calculation and interpretation.

 

[vanesch]

I think from the descriptions in the article I would describe myself as a pessimistic inductionist.

I'm aware of that (likely) possibility. That's why I ALWAYS put as a *working hypothesis* that we take it that the theory we are going to interpret, is correct. I find it not helpful to start with the opposite working hypothesis, namely that the theory we're going to interpret, is wrong. The reason for that is simply that you tend to sweep many nagging little problems in your theory under the rug of "well, anyway there will be an underlying theory which can change all of this, so don't worry". I mean, imagine you write software, and you start from the principle that anyway, the real firmware of your computer does not correspond to the documentation and your understanding of it. Are you going to write great software that way ? I guess every silly bug you encounter (which is your fault) will be put on the shoulders of the "bad documentation" or even of the bad functioning of the computer. So EVEN if you take the viewpoint that there might be a much better documentation coming along, one day, explaining the functioning of your hardware and firmware using totally different concepts, *in order to use it with your current set of documentation* you better assume that it is correct, no ? Because, hey, it MIGHT even be correct!

As to these "parallel worlds", I really have not so much difficulty with it. For most of what's happening, it doesn't really matter. You really get used to the weirdness. What, finally, can it matter to you whether, or not, there are invisible copies of you that run around in "other worlds" you'll never hear about ? Does that change your "view of the world" ? No, I wouldn't think so, because for YOU, it doesn't make any difference.
Do you have difficulties, in relativity, to consider that "yesterday" and "tomorrow" are just as well "statically there" as "today", while you only experience "today" ?

Look at all the people trying to "look for what is propagating faster than light" in EPR situations, while a many-worlds view on it solves the issue without invoking non-locality or something propagating. It is an amazing and simple solution to the riddle. No need to invoke *inconsistencies*, or "unknown interactions" or concepts such as the "inpossibility to say what really happens on micro scale", or "inexploitable non-localities" or whatever. It all fits together nicely: Bob's in a superposition wrt to Alice, and when she meets him, she will be in one of the branches, and hence find the right correlations. I find this, by itself, the most interesting application of the MWI view. It gives you a clear physical picture of what's going on, and why there is NOTHING propagating from Alice to Bob, and why there is NOTHING special happening during a measurement process.

Look at to what extend people are ready to sacrifice such fundamental things as CONSISTENCY in order to have to avoid an MWI picture. Do they have such a difficulty too with the existance, or not, of "yesterday" and "tomorrow" ? Nevertheless, if you ask them about "spacetime" do they think it "exists" ?

That's again, why I think that, *when interpreting a quantum mechanical situation*, taking on an MWI viewpoint is often the cleanest, most logical viewpoint. In the same way as taking on the viewpoint that the sun pulls on Jupiter is the cleanest, most logical viewpoint when doing Newtonian physics, and supposing that there is a 4-dim spacetime manifold is the most logical viewpoint when doing relativity, and assuming that dinosaurs really ran around on earth are the most logical viewpoint when doing paleontology. I find it always as the most productive viewpoint that one takes the theory one is working with, seriously.

If you ask me now: ARE THERE REALLY parallel worlds, according to me ? My answer is simply: I don't know. Quantum theory suggests it. But then, quantum theory might be wrong on that (but then, tell me what is right...). It might be right on it. *the best information I have* is that they are there, but I know that that information is still rather uncertain (mainly given the problems with unification with GR). I'm even more pessimistic than you are: I think I'll never get an update on the information in my lifetime. So this is the viewpoint I'll have to deal with, until I'm dead (unless a good surprise comes along).

Again, I'm fully aware that another theory might come along which will put the entire quantum framework down, just to replace it with some other framework. A world vision is tied to the knowledge one has, in one's time. But even with all its imperfections, I think it is still better to HAVE a consistent world vision (knowing it might be wrong) than REFUSING to have one, or to accept an INCONSISTENT world vision.

 

[vanesch]

You say:

What doesn't make sense is to talk about the constructs of a theory as being in 1-1 correspondence with an underlying reality that we have no sensory apprehension of.

Objective reality is just a term that refers to collective sensory perceptions meeting certain criteria. It's definitional. It's a convention.

Ok, then, I told you that that is not the standard view, and that it is a branch of philosophy, called metaphysics, which is supposed to ponder on these issues. But let's accept your point of view, namely that "objective reality" is a matter of convention. Well, I'm proposing the convention that "objective reality" is nothing else but the mathematical structure of the best physical theory that is around at a certain moment. There :tongue2:

If I can't know that what I AM seeing is part of the objective physical world, then why should I assume that something that I CAN'T see is part of the objective physical world? What do terms like objective reality, and really out there MEAN then?

Right, you're now doing a metaphysical reflection. Good

It's not reasoning, per se. It's how we DEFINE reality. Our collective (communicated) perceptions ARE reality. This is the basis that the physical sciences use to evaluate statements about the world.

Not really. Did dinosaurs really exist, or are they just "bones in the ground" ?

Now, if you have some other idea about what reality IS, then what is it?

The mathematical structure of our best physical theory.

So yes, we DECIDE what is real and what is not based on some definition or other of the term, real.

Ok, then I have the same liberty

I agree (to the extent that the formulation of physical theories does involve a certain amount of metaphysical speculation), but metaphysics isn't the physical defining frame of physics. The physical defining frame is our collective sensory perceptions. Metaphysical HYPOTHESES aren't physical hypotheses, and are therefore excluded from the actual SCIENCE of physics. That is, the metaphysical part or interpretation of a physical theory isn't amenable to scientific investigation. So, for example, nothing definitive can be said about the veracity of the claim of MWI world-branching. It just seems like a silly way to think about things. But how can one possibly KNOW whether MWI actually is silly or if it actually is the way things are? So, the MWI interpretation does have that going for it.

The problem with your view is the circularity of it: this is the main critique of positivism. WITHOUT a metaphysical frame, there is NO LINK between any formalism and any empirical observation. You *always* sneak in some metaphysical hypothesis when doing so. At a certain point, you ALWAYS identify certain aspects of the formalism with a reality. But you do so intuitively, in order to make things come out right, without any logics behind it.

See, you first say that "reality" is a matter of convention. And then you wonder how you can KNOW whether or not the other branches in MWI are real. If it is a matter of convention, we can decide about it by, say, voting ! You cannot IGNORE a convention you decided upon!
But if you decide, by convention, to call only your collective experiences as real, then I can decide to call the theoretical elements of quantum theory and the parallel worlds "hyporeal".
And if we now REDEFINE the words "real" into "subjectively experienced" and "hyporeal" into "objectively real", we arrive at MWI.
If we keep the words as we have them, then, the wavefunction has a hyporeal meaning, and locality is a hyporeal concept about hyporeal worlds. Ok. So in this hyporeal meaning, dynamics is given by unitary time evolution. And now that I have hyporeal operators, corresponding to hyporeal interactions, how can I link them to "real" apparatus ?
At what point does a hyporeal structure of particles that looks like a hyporeal voltmeter, become a real voltmeter ?

You're trying to recover the Born rule in MWI, but quantum theory already includes that. Ok, so nobody understands exactly why it works as well as it does.

No, I'm not. I think it is the error many MWI proponents make. One shouldn't try to derive the Born rule, it is the rule that gives the relationship between the MWI ontology (the hyporeal world) and the subjective experience (the conventional "real" world). As such, it is an axiom of the theory, related to perception.

But, with or without that assumption quantum theory will be making the same predictions --- and with that assumption (and all the fussing over the MWI) you might be overlooking some very important clues.

Quantum theory (without MWI) does not make predictions, without you sneaking in some extra hypothesis. You cannot say that the wavefunction is NOT in correspondence with physical reality and then 2 minutes later, find it obvious how we can extract measurement results from it, because in order to do so, you have to find a link between the physical operation of your measurement apparatus, and your non-physical quantum state. That's where most people say the most schizophrenic things.

Look at a photomultiplier, with a single atom as a photocathode. The EM quantum field is in an excited state, described by a wavefunction in Fock space (but that's not real of course). We know how to calculate the interaction of an atom in the ground state with the EM field state, through unitary evolution. So now the atom's wavefunction becomes partly in a state that corresponds to an ionized atom, and partly in its ground state, entangled with the EM wavefunction (which did the opposite thing). But all this is not real of course. In the state with the ionized atom, the electron will accelerate towards the dynodes (in the other state, not, of course) through a unitary evolution. On the dynodes, it will interact (unitarily) with the metal and entangle with other electronstates, until we get an appreciable amount of electrons coming down on the anode. In the other state, no such thing will happen. But remember, that all this is just hyporeal mathematical manoeuvring on a wavefunction which has no physical meaning. So now we end with a wavefunction which is a superposition of the state where no charge arrives on the anode, and where a lot of charge arrives on the anode. We could continue that way, and we'd find that the amplifier and the light bulb attached to it, in their wavefunction are written as a superposition of a lightbulb that doesn't light up, and one that does light up. But all this is hyporeal of course (and the two branches are hyporeal). At what point did they become "real" ? At what point can I say that THIS corresponds to a genuine real effect, predicted by quantum theory ? BTW, have you noticed that we could reason in each branch, as if it were a world of its own, and that, in doing so, we took the implicit assumption that there was "something real" to them ? While nevertheless each individual operation was described by a UNITARY operator ? If I don't do that, how am I going to link the above wavefunction to my lightbulb lighting up or not ? How am I going to describe the unitary operator that describes the physics of the electrons within the apparatus ?

The general problem, as I see it, is that physics hasn't come up with a definitive formulation of the first principles of nature yet.

But you will be able to make that statement along the entire history and future of humankind. What do we do in the mean time ?

I believe that the Schroedinger approach of quantum theory is on the right track, in that it hints that nature is fundamentally waves and wave complexes in various media.

There's a theorem against that statement, which is Bell's theorem. No local realist field theory can have the same empirical predictions as quantum theory. Now, as I said, experimentally there are strong indications, but no proof, that quantum theory is right. There is still room to wiggle in such a theory. Only, I don't know of any. And it will make in any case different predictions than quantum theory. So, in order to "interpret" quantum theory this way, you must make the assumption that quantum theory will make empirically WRONG predictions in certain respects, and you'll need to invent a realistic wave theory that DOES give you all the right other predictions. Some people (local realists) do try to do so. But you see that you are also TRYING to find a physical theory that is in 1-1 correspondence with a physical reality behind the scenes. You have 3 possibilities (if you accept a physical reality that can be mathematically described, and on which your mind has no physical influence on cosmic scales):

1) let go certain empirical predictions of QM and try to find a correct field theory that does all that, and that wins from QM (local realist approach, good luck). It's main prediction is that the EPR effect doesn't exist.

2) let go locality (and hence relativity, both SR and GR). Bohm's theory does exactly that (and still has some conceptual problems). Good luck with quantum field theory! And back to ether theory.

3) accept the reality of the wavefunction, and hence MWI.

These are the directions that people have explored since 80 years. The other possibilities are to DENY a possibility of mathematical description of nature (like Bohr proposes) - hence accepting an inconsistent behaviour of nature, to deny reality all together, or to speculate other things, like backwards causation (although I have yet to see a working model that works as well as current theory).

But quantum theory, just as special relativity (and ordinary experience for that matter) tells me that what you see depends on how you look at something.

Yes. Or even classical physics.

 

[reilly]

leandros_p Small world. Some years ago I wrote a paper, for a neural network conference, about using Shannon's Information Theory as a framework for describing mental and perceptual processing. We agree quite substantially on our basic models. The differences lie in our words and meanings.

Dear Sir,

Let me present a schema of information and knowledge; doing that I will try to use your "language".

The process of "knowing" is the following:

Source -- Transmitter -------- Receiver -- Destination

Between source and destination travels a Message – this message is called knowledge.

Leandros

More often than not, the message is just called a message. Not that it means that much, but,the earnest folks in the Knowledge Mangement field, have been greatly hampered by the fact that they can't fully agree on a definition of knowledge. Although there is a often used heirarchy, which goes: data -> information -> knowledge ( and, yes, some say -> wisdom). It is true, I've checked, that, all three, data, information, knowledge, are used interchangeably in many but not all circumstances.
For many of us, knowledge is what you know -- if you think about the limitations of language and human logic, your estimation of the worth of that seemingly trivial statement might strengthen.

And note, that Shannon and Weaver and Weiner didn't touch the issue of meaning. So, in my opinion, your definition of knowledge is unusual. What does it buy you?

Between the Transmitter and Receiver there is “noise”, always.

The reception of message and the possession of the message thereafter are called knowledge status, at the destination.

This is a general logical schema. The absolute “knowledge”, in the way that you understand the term, is when in the above procedure the destination accepts the message in the original, unchanged and complete form, which had at the source.

Unfortunately, the intermediate stages of transmitter and of receiver, in being imperfect, combined with the noise that exists through the propagation media introduce alteration to the message, either by addition, or by subtraction. Therefore, the original message arrives at the destination modified, that is, the message at the destination is true but has a degree of uncertainty, while the original message at the source had no degree of uncertainty. The message at the destination is not the same as the message at the source. There is an uncertainty factor introduced in the message at the destination, during the process, which was not present at the source.

This uncertain knowledge is called “information”.


Leandros

Not quite. Information refers to the message as a whole, and is, in a crude sense, a measure of surprises -- improbable messages, submessages, etc carry high information content.

Information, in communication theory, is a purely technical, probability based, property of messages -- often measured in bits. This is not quite the same as the more colloquial notions of information.As in any computer seup, you need to know how to translate "binary' to human -- so, with action, there's a whole new set of comunication channels to transmit orders from the brain to the hand, foot, .....

There was a time, when Science also used such conventions. Today, Science of physics can not accept these conventions. It has to use literal terms in defining the “message” that physical objects transmit to our “receivers” as information, because the physical sources that are being examined, such as the atomic and subatomic particles and phenomena, send inconsistent messages.

The objects of classic physics are sending messages to our scientific receivers that during the above process are altered by the imperfection of the stages of the system and by the noise. Scientists have learned how to overcome these problems, which are called measurement problems. BUT, the objects of quantum physics are sending messages to our scientific receivers that are inconsistent, not just altered or modified. So scientists felt obligated to treat these messages in their “true” form, that is, as information. This is the “truth” of physical reality that we refused to face in classic physics, in the past: We can not know physical reality; we can only be informed about physical reality.

Leandros

I do not at all understand the so-called quantum message inconsistencies -- what are they? (I hope you are not thinking waves and particles and interference,..... These clearly happen. The inconsistencies come from our inability to describe quantum phenomena in ordinary language.) I'm curious.

Yes, messages can be distorted, But, as Shannon and followers showed, virtually any noise from most any system can be filtered out, so that the probability of extracting the sent message is very high -- the cost might be high also. For pracical purposes, I suspect that the major human communication problems aren't so much noise based, but rather tranaslation based -- like we have some badly coded, biased receivers for certain messages, or message types.



That we can, in your language, only be informed about physical reality has been around for a while -- at least since Plato -- and, in fact, makes very good practical sense -- circumstantial evidence and all that.
Interesting.

Regards,
Reilly Atkinson

 

[Sherlock]

... let's accept your point of view, namely that "objective reality" is a matter of convention. Well, I'm proposing the convention that "objective reality" is nothing else but the mathematical structure of the best physical theory that is around at a certain moment.

You can have the words, objective reality, refer to anything you want. We define these terms differently, that's all --- and there's no point in arguing about which definition is better. The history of the development of modern science has already decided that for us.

You say that we MUST assume that the mathematical structure of quantum theory is in 1-1 correspondence with an underlying reality --- that, in other words, the theory is defining an underlying reality. I say, no, that idea is not a necessary part of the interpretation and development of the theory.

The development of quantum theory is almost a purely mathematical enterprise with the aim of accounting for, and hopefully predicting new, experimental phenomena. The theory's relationship to an underlying reality depends on one's speculative vision of an underlying reality. You say that the mathematical structure of the theory implies that there are an infinite number of simultaneously existing subjective worlds. I don't know what that might mean. I say that at least one mathematical formulation of the theory indicates that nature is fundamentally interacting waves. But of course neither one of us has any way of knowing the truth of either of these interpretations. The upside is that the science of physics doesn't depend on these sorts of speculations.

The validity of the MWI, just as with my current metaphysical view, can neither be verified nor falsified. The difference is that the current predictive state and the development of quantum theory doesn't depend on the existence or development of the MWI at all, whereas wave mechanics is an important part of the most widely used formulation of the theory --- and the Born rule is part of the wave mechanical picture.

The problem with your view is the circularity of it: this is the main critique of positivism. WITHOUT a metaphysical frame, there is NO LINK between any formalism and any empirical observation. You *always* sneak in some metaphysical hypothesis when doing so. At a certain point, you ALWAYS identify certain aspects of the formalism with a reality. But you do so intuitively, in order to make things come out right, without any logics behind it.

There is some logic behind it.

... you first say that "reality" is a matter of convention.

Yes, defining agile terms is a matter of convention. Witness the fact that you have lots of ordinary language terms associated with various aspects of quantum theory and quantum experimental phenomena which, in that context, don't mean what they mean in ordinary discourse.

And then you wonder how you can KNOW whether or not the other branches in MWI are real. If it is a matter of convention, we can decide about it by, say, voting! You cannot IGNORE a convention you decided upon!
But if you decide, by convention, to call only your collective experiences as real, then I can decide to call the theoretical elements of quantum theory and the parallel worlds "hyporeal".
And if we now REDEFINE the words "real" into "subjectively experienced" and "hyporeal" into "objectively real", we arrive at MWI.

Yes, I agree that it's all a matter of semantics. We decide whether something is real or not by, in effect, voting on it --- and MWI isn't getting too many votes.

If we keep the words as we have them, then, the wavefunction has a hyporeal meaning, and locality is a hyporeal concept about hyporeal worlds. Ok. So in this hyporeal meaning, dynamics is given by unitary time evolution. And now that I have hyporeal operators, corresponding to hyporeal interactions, how can I link them to "real" apparatus ?
At what point does a hyporeal structure of particles that looks like a hyporeal voltmeter, become a real voltmeter ?

I have no idea. It sounds like a very hard question.

Presumably, one would already have included the voltmeter in one's instrumental/material preparation, so one wouldn't have to worry about when it became real.

But I suppose that would depend on one's definition of real.

One shouldn't try to derive the Born rule, it is the rule that gives the relationship between the MWI ontology (the hyporeal world) and the subjective experience (the conventional "real" world). As such, it is an axiom of the theory, related to perception.

I thought that there is, presumed by MWIers, an inconsistency between the Born rule and the unitary evolution that is the problem that MWI is trying to fix? So, you now refer to this axiom (which was formerly about the objective world) as an axiom about subjective perceptions? That doesn't seem like much of a fix. But then, it does introduce a sort of creation mechanism where you get as many perceptual worlds from an experimental trial (or is it an entire run) as there are possible results ... and they're all undetectable except the one that we say we're percieving, and the unitary evolution marches on, apparently unimpeded. So, there's that.

Or is the supposed inconsistency between the unitary evolution (the wavelike behavior in the underlying quantum world), and the appearance of measurement results on data tapes or monitors, etc., in the perceptual world? But that's just an apparent inconsistency. (Refer to the vibrating drumhead with powder on it example from my previous message.)

Or is it just that quantum theory doesn't detail precisely how and when measurement results occur. So, with MWI, you can do that?

Quantum theory (without MWI) does not make predictions, without you sneaking in some extra hypothesis.

This will be news to most professional users of quantum theory I think.

You cannot say that the wavefunction is NOT in correspondence with physical reality and then 2 minutes later, find it obvious how we can extract measurement results from it, because in order to do so, you have to find a link between the physical operation of your measurement apparatus, and your non-physical quantum state. That's where most people say the most schizophrenic things.

I think that most working physicists don't actually bother to interpret the theory. Of those that do, a minority are fascinated by MWI.

If you're referring to the collapse of the wave function as part of the schizo (in your opinion) standard interpretation, then it's good to remember that the wave function is not taken to be in 1-1 correspondence with an underlying quantum reality in that interpretation.

Of course, I'm not a professional, but I did say that I think that the mathematical structure of the Schroedinger formulation seems like it might be very insightful wrt what is happening in an underlying quantum world. And, I think that proponents of the standard probabilistic interpretation would tend to think that way. That is, while the wave function might be an insight into an eventual conceptual (as well as mathematical) understanding, it is nevertheless most likely the case that the wave function isn't a 1-1 mapping of the underlying quantum world. Collapse, used in that interpretational context, doesn't mean what collapse does in ordinary discourse. It just means that when a sufficient number of detections are recorded, or by time-limiting, a run is over and the wave function that predicted the result(s) from a range of possibilities no longer applies to that particular run. Although, if it is in good approximation to the results, then you can have some confidence that not only does the theory work but that you used it correctly --- and so retain that formulation for that particular preparation.

Look at a photomultiplier, with a single atom as a photocathode. The EM quantum field is in an excited state, described by a wavefunction in Fock space (but that's not real of course). We know how to calculate the interaction of an atom in the ground state with the EM field state, through unitary evolution. So now the atom's wavefunction becomes partly in a state that corresponds to an ionized atom, and partly in its ground state, entangled with the EM wavefunction (which did the opposite thing). But all this is not real of course. In the state with the ionized atom, the electron will accelerate towards the dynodes (in the other state, not, of course) through a unitary evolution. On the dynodes, it will interact (unitarily) with the metal and entangle with other electronstates, until we get an appreciable amount of electrons coming down on the anode. In the other state, no such thing will happen. But remember, that all this is just hyporeal mathematical manoeuvring on a wavefunction which has no physical meaning. So now we end with a wavefunction which is a superposition of the state where no charge arrives on the anode, and where a lot of charge arrives on the anode. We could continue that way, and we'd find that the amplifier and the light bulb attached to it, in their wavefunction are written as a superposition of a lightbulb that doesn't light up, and one that does light up. But all this is hyporeal of course (and the two branches are hyporeal). At what point did they become "real" ? At what point can I say that THIS corresponds to a genuine real effect, predicted by quantum theory ?

You know the difference between a detector clicking or a light bulb lighting and a mathematical model. If you want to know when the click or the lighting-up did occur, then correlate a clock-time with the event. If you want to flesh-out quantum theory so that it tells you exactly when a certain possible result at a certain location WILL occur, then do that. And good luck. If MWI has any practical utility at all, it's that it AMPLIFIES the measurement problem.

BTW, have you noticed that we could reason in each branch, as if it were a world of its own, and that, in doing so, we took the implicit assumption that there was "something real" to them ? While nevertheless each individual operation was described by a UNITARY operator ? If I don't do that, how am I going to link the above wavefunction to my lightbulb lighting up or not ? How am I going to describe the unitary operator that describes the physics of the electrons within the apparatus ?

Your linkage is as problematic as the linkage you're trying to fix.

There's a theorem against that statement, which is Bell's theorem. No local realist field theory can have the same empirical predictions as quantum theory.

Bell's Theorem has nothing to do with the possibly insightful idea that the Schroedinger formulation of quantum theory hints that reality's deep nature might be understood in terms of wave mechanics.

Now, as I said, experimentally there are strong indications, but no proof, that quantum theory is right.

Especially since we have no underlying reality criteria for evaluating the rightness of the theory wrt an underlying reality --- only instrumental results. Yet, you've stated that we MUST assume that quantum theory is RIGHT wrt the behavior of the underlying reality --- and that assumption is what the convoluted ontology of MWI is based on.

Did you ever consider the possibility that maybe YOUR argument is circular?

There is still room to wiggle in such a theory. Only, I don't know of any. And it will make in any case different predictions than quantum theory.

There's a difference between noting the possible heuristic value of quantum theory, and saying that a deterministic wave theory employing precisely defined values and making precise predictions is possible. If anything, the wave heuristic gotten from quantum theory indicates that there are limits to what can be experimentally determined. So, even without Bell, it would seem to be a mistake to pursue a 1-1 mapping of some conception of the underworld.

So, in order to "interpret" quantum theory this way, you must make the assumption that quantum theory will make empirically WRONG predictions in certain respects, and you'll need to invent a realistic wave theory that DOES give you all the right other predictions. Some people (local realists) do try to do so. But you see that you are also TRYING to find a physical theory that is in 1-1 correspondence with a physical reality behind the scenes. You have 3 possibilities (if you accept a physical reality that can be mathematically described, and on which your mind has no physical influence on cosmic scales):

Quantum theory itself tells us that there can't be a 1-1 mapping between physical reality and precisely defined mathematical abstractions. It imposes limits. So, if you take the theory as right in this respect, then it can't ever be right in the respect that you assume it to be.

... other possibilities are to DENY a possibility of mathematical description of nature (like Bohr proposes) - hence accepting an inconsistent behaviour of nature ...

Well, we're presumably part of nature (whatever nature might BE), and we're somewhat inconsistent, so insofar as we're the creators of theories ABOUT nature, then the Bohr approach seems like the best one to me. But that's not to say that the behavior of nature is inconsistent. After all, we don't know what nature IS, do we?

If you want to reify physical theories, then physicists are in the process of inventing nature via theory. And MWI seems like a silly invention to me.

 

[vanesch]

You say that we MUST assume that the mathematical structure of quantum theory is in 1-1 correspondence with an underlying reality --- that, in other words, the theory is defining an underlying reality. I say, no, that idea is not a necessary part of the interpretation and development of the theory.

Well, if the aim of an interpretation is to say "what nature is like", then this looks like me like a necessary condition, that it makes a statement about "what nature is like" in a 1-1 way, no ?

The development of quantum theory is almost a purely mathematical enterprise with the aim of accounting for, and hopefully predicting new, experimental phenomena. The theory's relationship to an underlying reality depends on one's speculative vision of an underlying reality. You say that the mathematical structure of the theory implies that there are an infinite number of simultaneously existing subjective worlds. I don't know what that might mean.

Well, formally, it is quite simple. How would you interpret the situation, where you found the final state of a system which includes your body, as:

|psi> = 0.3|red_lamp>|yourbodyseesredlamp>|stuff1> + 0.91|green_lamp>|yourbodyseesgreenlamp>|stuff2>

This is somewhat symbolic, but each of these ket vectors correspond to specific subhilbert spaces and is the result of taking into account ALL microphysical interactions of the system. In practice we cannot do that, because it's way too complicated, but it is easy to show that the wavefunction of the system will have to take on the above form.
It is important that this *follows* from applying, systematically, the Schroedinger equation to the entire system. I didn't INTRODUCE any of this. It follows, if we allow each proton, electron etc... in the room to be described by its quantum-mechanical state, and if we can identify gross conglomerates as "your body" and so on.

If we apply the Born rule and the projection postulate, we just 'pick out one term' with a certain probability. I accept this. But it has to be known that the moment we do this, and the basis we do this in, is totally arbitrary. IF YOU PICK THE BASIS RIGHT, this is what you will observe. However, what is almost inacceptable, is that now, we just "throw away" the rest of the wavefunction. If that wavefunction represents something physical out there, however, it is hard to see how an ARBITRARY decision on your part to "apply the Born rule" would suddenly CHANGE THE STATE OF NATURE. Isn't it more sensible to say that you just OBSERVE, with the given probability, ONE term ? But that the others are "still out there" ?
At what point does it become essential to "choose" ? The essential point is when you would, otherwise, be aware of TWO DISTINCT BODY STATES. This doesn't happen. So we interpret this Born rule simply as THE PROBABILITY FOR US TO BE AWARE OF A BODYSTATE. Not about something that happened to the entire universe because we happened to look at it.
Ok, then so now you are "aware" of, say, the body state in the term:
|green_lamp>|yourbodyseesgreenlamp>|stuff2>
That bodystate will only evolve further with its "partners" (the green lamp, and stuff2). It will almost never interact anymore with stuff in the other states. So everything will appear as if we projected out this state.

Why don't we project it out then ? Well, because we take it that the state describes the physical state of the system, overall, and that _nothing in particular_ happened to the system when we decided to go and calculate probabilities with the Born rule. It is not because I became aware of the second term, that the first suddenly must disappear. There's no physical (unitary) interaction doing so (and it would need to be non-local).

I say that at least one mathematical formulation of the theory indicates that nature is fundamentally interacting waves.

Uh ? What's that supposed to mean ? The Schrodinger equation gives you how the vector |psi> evolves in hilbert space...

The validity of the MWI, just as with my current metaphysical view, can neither be verified nor falsified. The difference is that the current predictive state and the development of quantum theory doesn't depend on the existence or development of the MWI at all

The experiment I would suggest to "prove" MWI would be an EPR experiment. It would indicate that, if Bob were not in a superposition of states after his measurement, that Alice would find correlations which would lead to very strange results, leading one to believe that Alice's action somehow had a "spooky action at a distance" on the Bob measurements ; while if Bob WAS in two worlds, that this would be seen as "quantum interference" between the Alice state and the two Bob states.

whereas wave mechanics is an important part of the most widely used formulation of the theory --- and the Born rule is part of the wave mechanical picture.

Eh, it isn't, really. The Born rule is not really part of the wave mechanical picture. You STOP the wave equation, and suddenly chop off a piece of it. You send a plane wave on a detector, and suddenly, it becomes a localized lump (WITHOUT ANY EQUATION SAYING SO).
You need the Born rule to go from the "end" of your wave equation evolution to say: here we stop with the physics, and we are now going to look at measurements.

I thought that there is, presumed by MWIers, an inconsistency between the Born rule and the unitary evolution that is the problem that MWI is trying to fix? So, you now refer to this axiom (which was formerly about the objective world) as an axiom about subjective perceptions? That doesn't seem like much of a fix.

First of all, let's clear up terminology. The Born rule is the rule that gives probabilities to the components of the state vector in a certain basis, by saying that it is their length, squared. Clearly, one needs to say in which basis this is. But then there is the projection postulate, which says that we PICK one of the components in the basis, randomly, according to the probabilities of the Born rule, and that this component, renormalized to 1, becomes the new state.
This is an instantaneous, non-dynamic, and global change of the state, and is something that only happens in "measurement devices". This is only introduced to accept the observation that, after a measurement, if it is applied again, we shouldn't find another result than the one we already had. BUT THERE IS NO PHYSICAL JUSTIFICATION for such a projection (and it is clearly non-local). It is not clear *when* it happens, and *in what basis* it happens. YOU HAVE TO GUESS CORRECTLY in what basis you apply it.
So it is *not* something that is clearly objective. It is just _stopping the wave equation_ and then projecting out. What magical action in nature can do such a thing: instantaneously, and everywhere (non-locally!) stopping the equations of nature, and make the state of the system JUMP? In a basis that is related to the "observed data" ? Doesn't this sound VERY MUCH like something related to perception ?

It's the only thing MWI does. It says: no, you do not CHANGE the state of nature, you just PERCEIVE one term of it (yeah, in the right basis, and yeah, instantaneously, when you "learn" the result ; different brain states correspond to different subjective perceptions, and you just perceive ONE of those states - while eventually, other "yous" perceive other states). But the state of nature doesn't care about what you perceive, it doesn't STOP its equation (the Schroedinger equation) and doesn't change its entire, global state, it just marches on, always following its wave equation.

But then, it does introduce a sort of creation mechanism where you get as many perceptual worlds from an experimental trial (or is it an entire run) as there are possible results ... and they're all undetectable except the one that we say we're percieving, and the unitary evolution marches on, apparently unimpeded. So, there's that.

Yes, but you do not need any "creation mechanism". The very appearance of the different states in the wave equation are its "creation". Do you object to the "creation mechanism" of Fourier components when a signal gets non-linearly deformed ? They just appear in the equation, that's all...

Or is it just that quantum theory doesn't detail precisely how and when measurement results occur. So, with MWI, you can do that?

Yes, of course. The "measurement result" appears when the observer's body gets entangled with the system under observation, because at that point, the single term splits in two or more terms, each corresponding to one of the different outcomes.

This will be news to most professional users of quantum theory I think.

Probably, because they've been relying on their intuition. For instance, if you have a photodetector, you usually TAKE FOR GRANTED that it measures the photon at the position of the photocathode. You systematically write the photon state in a position basis here. It wouldn't occur to you to write it in a momentum basis. Nevertheless, there is NO REASON not to do so. But photodetectors "measure position", right ? Right. So that's then the correct basis.

I think that most working physicists don't actually bother to interpret the theory. Of those that do, a minority are fascinated by MWI.

I agree with the first statement. I'm less sure about the second.

If you're referring to the collapse of the wave function as part of the schizo (in your opinion) standard interpretation, then it's good to remember that the wave function is not taken to be in 1-1 correspondence with an underlying quantum reality in that interpretation.

Except when it relates to the measurement to be performed. Suddenly, it DOES become "real". Suddenly the photon's wavefunction DID have something to do with photodectectors.

Of course, I'm not a professional, but I did say that I think that the mathematical structure of the Schroedinger formulation seems like it might be very insightful wrt what is happening in an underlying quantum world.

And the Schroedinger equation = unitary evolution with NO possibility of having a collapse. You have to STOP the Schroedinger equation to do so.

it is nevertheless most likely the case that the wave function isn't a 1-1 mapping of the underlying quantum world. Collapse, used in that interpretational context, doesn't mean what collapse does in ordinary discourse. It just means that when a sufficient number of detections are recorded, or by time-limiting, a run is over and the wave function that predicted the result(s) from a range of possibilities no longer applies to that particular run. Although, if it is in good approximation to the results, then you can have some confidence that not only does the theory work but that you used it correctly --- and so retain that formulation for that particular preparation.

Don't you find this an extremely poor physical theory ? And now I ask you, if the wavefunction is not in a 1-1 mapping with the underlying quantum world, then *what is in a 1-1 mapping* ? There must be *something* that is in a 1-1 mapping, right ?

And all that, while it is *possible* to consider the wavefunction to be in a 1-1 mapping with "nature", to restore locality, not to have this arbitrary projection and stopping of the wave equation. Is this picture not much more compelling ? We HAVE a 1-1 mapping, we KNOW the unique law of the evolution (Schroedinger equation) and we CAN explain the random aspect of it, and the apparent non-locality as one of its side effects ?

Your linkage is as problematic as the linkage you're trying to fix.

I don't think so. I have less problems to say that when my brain state changes, my perception changes (in this case, randomly, I pick one of the daughter states), than to say that when I look at nature, it's global state changes.

Especially since we have no underlying reality criteria for evaluating the rightness of the theory wrt an underlying reality --- only instrumental results. Yet, you've stated that we MUST assume that quantum theory is RIGHT wrt the behavior of the underlying reality --- and that assumption is what the convoluted ontology of MWI is based on.

Did you ever consider the possibility that maybe YOUR argument is circular?

I don't think it is circular. I say: you have a theory, which gives good empirical results. Now, look at its underlying formalism. It has a nice mathematical structure, but it goes wry in two points: 1) you STOP the physical evolution equation, to do something you've introduced ad hoc when you "observe", and 2) you then do something to the entire state of the system (which implies non-locality...)
Clearly, the last part makes it impossible to be considered as a true physical action, and it is from THIS, and THIS thing alone, that people concluded that the wave function cannot describe nature 1-1.

But it could, if we kept running the wave equation. We're used to that: the state of nature evolves through an equation, describing the interactions. Great. We have that: the wavefunction, and Schroedinger's equation.
Then what with the stopping and projecting ? Well, let's put that in the "perception" part: we only perceive part of the wavefunction, in a probabilistic way.
As such, we've now eliminated the thing that blocks us from taking the theory seriously as a description of what really happens. Why a priori assume that this cannot be right ? Of course that is no proof.

Quantum theory itself tells us that there can't be a 1-1 mapping between physical reality and precisely defined mathematical abstractions. It imposes limits. So, if you take the theory as right in this respect, then it can't ever be right in the respect that you assume it to be.

That's a misunderstanding. The wave function evolves deterministically, and very precisely, following a wave equation (the Schroedinger equation). There's nothing random to the state evolution. It doesn't say that "there are limits to its precision". What it does say, is that our PERCEPTION of the state will involve probabilistic aspects if we do measurements.
If you are referring to the HUP, it only tells you something about those probabilistic aspects of perception (= measurement). The HUP DOES NOT tell you that the state of a particle is somehow "unknown". It only tells you that there is a relationship between the probability distribution of the measurement of quantity A and the probability distribution of quantity B (and in MWI, the probability is a consequence of perception, not of indeterminism in nature).

After all, we don't know what nature IS, do we?

Why starting with that hypothesis ? Why not start with the hypothesis that we DO know nature (up to a point) ? Isn't this the most sensible starting point ?
"I'm going to repair my car ; let's assume I don't know how a car works"
Not the most fruitful approach, no ?

 

[reilly]

It would be greatly helpful, if someone could clearly define "physical reality" and how this 1-1 mapping is to be determined -- and judged to be or not to be. Why is such a mapping important, and are we talking unique


(Don't really have to worry 'bout such things with the knowledge interpretation.)/
Regards,
Reilly Atkinson

 

[vanesch]

It would be greatly helpful, if someone could clearly define "physical reality" and how this 1-1 mapping is to be determined -- and judged to be or not to be. Why is such a mapping important.

To me, "Reality" is a metaphysical hypothesis, and can never be absolutely demonstrated (cfr the unfalsifiability of solipsism). We should take up the one that is most useful in visualising and in develloping an intuition for how our physical theories work, and to have a consistent view on what's going on. It is in this context that I find statements such as "the theory only describes our knowledge about something, but has nothing to say about the something itself" rather bad viewpoints: what GOOD does it do to say that you REFUSE to take up a hypothesis of reality ? What do you WIN by doing that ? Avoiding to be confronted one day with having to change ? I have no problems CHANGING my hypothesis of reality, the day that we find out more. But _in the mean time_, what good is it to keep telling to yourself that the theory is _not_ a description of reality ? What can one win, conceptually, that way ? Of course our view on reality is not "correct" in an absolute way (or at least, we will never be able to find out until it is falsified). So what ? Should we then just _refuse_ to have one ?

(Don't really have to worry 'bout such things with the knowledge interpretation.)

The "knowledge interpretation" is a _refusal of interpretation_, and it is an illusion to think that it has no problems: the main problem it has is the arbitrariness of the hermitean operator to be associated to a measurement apparatus. It has to be chosen intuitively, and cannot be derived from the physics of the apparatus. So there is total arbitrariness in the assignment of the formalism to the results: the formalism does NOT give you, in any unique way, a description of your knowledge. You PICK OUT the one that intuitively (from assigning a kind of reality to what was not supposed to have any reality) seems to correspond to what the apparatus *would do if it were a classical apparatus*, and if the quantum system were a classical system - but as such, you have to pick, intuitively, a basis.
You picture, in doing so, a classical device and a classical system (in a certain basis).

That said, I can understand the attitude of people taking on the knowledge view, but it is a messy view of things. It is just that we have to use our intuition (there are no rules) to say WHAT a certain apparatus is measuring, and that if we do that, quantum theory seems to give us certain mathematical rules to find statistical results of measurements, which seem to work out when we do it right. A kind of happy hokus-pokus which works, although we don't know why. But I find it a depressing view, to deny oneself a picture of reality. Sure, that way you are sure NOT to make a wrong statement: you're not making any!

 

[Paul Martin]

QM probabilities represent states of knowledge

To define 'state of knowledge' don't we need a 'knower' and a set of 'known' information? This would complete Shannon's definition of information in specifying to whom or what the difference makes a difference. Information would be a difference that makes a difference to the knower. I propose assuming a knower as primordial. In its most primitive form, this knower would be simply the ability to know, similar to the classical definition of energy being the ability to do work.

When I do a measurement, indeed the wave function collapses to provide the knowledge of the particular outcome. The collapse is a physical phenomena, as the brain goes from knowledge of probabilities to knowledge of the outcome.

If the brain is the only seat of knowledge, then this means that in the billions of years prior to the development of brains there were no wave function collapses. This seems to imply that the entire universe remained in a superposed state up until the emergence of the first proto-brain at which time the wave function collapsed to produce the first actualization of the universe. Wouldn't the existence of a primordial knower make the scenario more plausible by allowing earlier wave function collapses?

I'm fairly convinced that all of physics, at the minimum. can be fully described as a communication system

Can a communication system be completely described without at least one knower? It seems to me that the sender must at least know the contents, if not the meaning, of the message. And it seems to me that you couldn't consider any communication to be successful or complete unless the receiver ended up knowing the contents, if not the meaning, of the message. So, if we are both right in our guesses here, it would seem that the existence of a knower is a necessary condition for physics. (Incidentally, a single knower is sufficient for communication, as shown by the example of memory and recall functions which involve only a single knower.

If there is any magic here, it has to do with physics itself. Physics tells Mr. A about things outside his immediate environment, by inference rather than by direct observation. It is our cumulative knowledge that allows Mr. A to transcend space and time with his knowledge.

By acknowledging the existence of "cumulative knowledge" you introduce yet another type of knower. I think Occam would suggest considering all knowers -- the primordial knower, the individual knowers associated with individual brains, and the cumulative knower associated with collections of brains -- to be one and the same. This would indeed transcend the 4D space and time of physics and it would seem to suggest at least one additional temporal dimension. I think that in this way, sense could be made of everything. For example, it would clear up the following question from vanesch.

This is the positivist viewpoint. It takes that there is only a "state of knowledge". But the problem I have with it, is:
knowledge about WHAT ? If there is no state of nature, what does it mean for me to have "the knowledge that the electron is in position x" ?

Let's separate two cases here. In your second question, you refer to "me" as the knower of the state of an electron. This is clearly a reference to a knower associated with a brain. I'll call this one Case 2. Case 1 is the primordial case in which the primordial knower initially knows absolutely nothing. Since the primordial knower has the ability to know, it seems reasonable that it could know the fact that nothing is known. As soon as this happened, the difference between knowing nothing and knowing that nothing was known would qualify as one bit of information in Shannon's sense. From this rudimentary "data base" of one bit, it is trivial to see how additional bits of information could be developed. Moving on to Case 2, by the time brains emerged in the universe, the number of bits in that data base had become quite large (although still finite).

The picture here ends up being Berkeley's: all of reality is simply a knower along with the knowledge accumulated so far. Part of that knowledge makes up the physical universe. Contrary to Berkeley, however, the knower is not perfect, infinite, omnipotent, omniscient, complete, immutable, etc.

And from the moment you DO introduce a (classically-like) state of nature of which we learn stuff, you run into troubles, no ?

I don't think so. What troubles do you see? The state of nature is the state of the known information. "We" learn stuff by the process of the one-and-only knower learning from information accumulated in the brain, and transmitted to the one knower.

The only phrase that is not metaphysical is "I perceive a voltmeter reading 7V". But we are so very used to making this identification that we don't even bother.

I respectfully suggest that we do bother. By tacitly assuming that the entity "I" is a conscious agent seated in a brain, we close off possible explanations of reality which "I", for "one", expect might be closer to the truth.

Assuming the existence of only a single knower, as I suggest, leads to the obvious implication that a version of solipsism is true. It is not the commonly discussed solipsism in which nothing exists but the mind associated with a particular brain. Instead, it says that nothing exists but the single primordial knower along with all the knowledge accumulated so far. No problem.

Paul

 

[vanesch]

If the brain is the only seat of knowledge, then this means that in the billions of years prior to the development of brains there were no wave function collapses. This seems to imply that the entire universe remained in a superposed state up until the emergence of the first proto-brain at which time the wave function collapsed to produce the first actualization of the universe.

Indeed. And in fact, it wouldn't matter, because collapse is "transitive" in the sense that you can always choose NOT to collapse now, but only later. The result (after that final collapse) is the same, whether or not the decohered branches remained still a while in superposition, or got projected out long ago.

That's why, in the MWI view, we just let the universe *continue* to be in a superposed state, even AFTER there has been an observation.

Wouldn't the existence of a primordial knower make the scenario more plausible by allowing earlier wave function collapses?

Your analysis is correct, in that, as long as there is no "knower" that there is no collapse ; I'd even say that in this view, there is even no wavefunction, because, if the wavefunction is somehow to represent any knowledge, and there was nobody to "know", then there is no knowledge to be represented in the first place.
This is one of the reasons why I prefer (by far) to take the wavefunction to represent the physical state of the universe, and not just "the knowledge".

Can a communication system be completely described without at least one knower? It seems to me that the sender must at least know the contents, if not the meaning, of the message. And it seems to me that you couldn't consider any communication to be successful or complete unless the receiver ended up knowing the contents, if not the meaning, of the message. So, if we are both right in our guesses here, it would seem that the existence of a knower is a necessary condition for physics.

I agree with your analysis, except for the last statement: the existence of a knower is necessary *if the wavefunction is to represent knowledge*. But of course, if it is to represent the actual physical STATE of the universe, then it doesn't care whether it is known or not. So I see your argument more as an argument against the view that the wavefunction is knowledge.

Since the primordial knower has the ability to know, it seems reasonable that it could know the fact that nothing is known. As soon as this happened, the difference between knowing nothing and knowing that nothing was known would qualify as one bit of information in Shannon's sense. From this rudimentary "data base" of one bit, it is trivial to see how additional bits of information could be developed.

I fail to see how ?

Assuming the existence of only a single knower, as I suggest, leads to the obvious implication that a version of solipsism is true. It is not the commonly discussed solipsism in which nothing exists but the mind associated with a particular brain. Instead, it says that nothing exists but the single primordial knower along with all the knowledge accumulated so far. No problem.

This is indeed a possible view, and it is indeed about the only view I see that can really make sense of the "wavefunction = knowledge" POV. But the view that quantum theory must be interpreted as solipsism is, IMO, rather more far-reaching than the MWI view, no ?

So if people already say "naaah, too crazy" against MWI, I don't see how they can embrace *this* view without any problem !

 

[Paul Martin]

From this rudimentary "data base" of one bit, it is trivial to see how additional bits of information could be developed.

I fail to see how ?

It could be done in a manner similar to the way in which Frege (I think it was) defined the natural numbers set theoretically. For example, the difference between knowing nothing and knowing that one new bit is a difference which could be taken as the second bit. Then knowing the difference between those two bits could be taken as the third bit. (Or, knowing the difference between knowing nothing and knowing the second bit could be taken as the third bit.) Whatever sequence is chosen, it is logically possible to construct a set of bits in this way.


In "Universe has a mind of its own", post #136, I outlined how the entire physical universe might have been constructed with this as its starting point. There I said:

"By hypothesis, we start with the existence of [PC, meaning primordial] consciousness (thus obviating the Hard Problem that all the theories accepting competing hypotheses haven't yet solved). Since the consciousness we each are familiar with has the capability of imagination, memory, recollection, and judgment, it is reasonable to assume that the primordial consciousness also has these capabilities.

"These capabilities are sufficient to imagine differences, which can be remembered and recalled, so that patterns in collections of them can be noticed, using the capability of judgment. These patterns can be judged by PC to represent numbers and elements of symbolic logic with which all the familiar mathematical structures can be constructed.

"Among these structures are algorithms, which, by a pure exercise of PC's thought, can transform sets of numbers into other sets of numbers. The "before" and "after" sets of numbers after such a transformation represent a causal relationship between the two sets. Many such relationships can be built up with second order causal relationships established among them. Likewise, third order, and higher, relationships can be constructed by a combination of applying certain algorithms to certain sets of numbers, and by the direct intervention by PC of setting certain of these numbers to any values PC chooses to set them for whatever "reason" occurs to PC.

"As Renate Loll has recently shown, dynamically evolving networks of triples of these causal relationships when aggregated in huge numbers, form a sort of fractal foam which takes on a 4D geometry at the largest scales. Influences on this aggregate network due either to the outcome of the processing of some algorithm, or by the direct intervention of PC by changing some numbers, propagate through the network as PC grinds out the results of the change. This has the effect of waves through the network which, if taken as the standard of speed or as the standard of time, will provide a definition and a calibration for the other.

"This structure is what our physical universe is made of. Whether some of those triangles form strings, or loops, or some other structure that will appear in the real TOE remains to be discovered."

I guess I was wrong to characterize it as "trivial", but it does seem to logically hang together to me. And, it does seem to provide a reasonable basis for an explanation for everything including consciousness.

I agree with your analysis, except for the last statement: the existence of a knower is necessary *if the wavefunction is to represent knowledge*. But of course, if it is to represent the actual physical STATE of the universe, then it doesn't care whether it is known or not. So I see your argument more as an argument against the view that the wavefunction is knowledge.

In this view, the wavefunction is an algorithm which causes, in the sense described above, the generation of evolving sets of numbers. The sets of numbers are the actual physical state. They contain, among other things, the numbers populating the Hilbert space matrices.

As for what exactly is known by the knower, I think there are some shades of gray we need to talk about. As an example, what can we say that we know about the Mandelbrot set? We know it at several levels. Prior to Mandelbrot's (and possibly others') insight, it was not known at all. It would be merely a semantic question to ask whether the Mandelbrot set existed during that time. It is even a semantic question to ask whether it really exists now. Could we say that the algorithm that generates the set is known? I would think we would all agree that it is known. Could we say that some of the features of the pattern the boundary of the set makes are known? Yes, we know about the "Seahorse Valley". What about detailed features that have never been observed by any human? Could we say that those are known? I would think not. Could we come to know those features merely by looking? I would say, yes, we could.

So in similar fashion, it seems reasonable to suppose that in the construction of the physical universe, the one knower would not necessarily know the outcomes of the operations of algorithms whose operation produces the ontological fabric of the physical universe. It also seems reasonable that via biological sense organs, central nervous systems, and some means of communication between brains and the knower, the knower could come to know macro-level features of the physical universe, giving the illusion that independently conscious scientists were discovering those features and knowing about them strictly in their brains.

So it wouldn't be quite correct to say that the wavefunction represents knowledge. The wavefunction is a known algorithm, and the evolving results of the algorithm are the physical universe, but those results need not be known by the knower. But, as Reilly has suggested, when the knower pays attention to the outcome and comes to know it, this is the wavefunction collapse and the state of the universe takes on one set of values.

This scenario opens up a couple possibilities for wavefunction collapse. One possibility would be that when the knower, however this might happen, chooses to observe the state of the sets of numbers, a separate algorithm using a probability distribution would pick out a "random" outcome from the possible outcomes. A second possibility would be that the knower could exercise what we experience as free will and deliberately and consciously choose a particular outcome for whatever reason. This kind of direct intervention would be indistinguishable from a truly random outcome to observers like us. (I.e. it would appear random to PC when viewed via the sense organs and brains of humans.)

But the view that quantum theory must be interpreted as solipsism is, IMO, rather more far-reaching than the MWI view, no ?

I see it as much simpler. Since, in my scenario, reality started out with a single entity, viz. the ability to know, and, starting with one bit of knowledge, evolved to at least what we see today, the entire thing is always finite and in principle measurable and knowable. It seems to me that MWI is much wilder than this.

So if people already say "naaah, too crazy" against MWI, I don't see how they can embrace *this* view without any problem !

I don't really expect them to. I think any significant move towards truth in scientific theory is always greeted with "naaah, too crazy".

Thanks for your thoughts, vanesch.

Paul

 

[vanesch]

Sorry, couldn't resist: in the following post I'm just poking some fun. Don't be offended, it was just to have a good laugh :-)

It could be done in a manner similar to the way in which Frege (I think it was) defined the natural numbers set theoretically.

Ok, it seems to me that you are constructing a kind of Platonic world of Ideas this way.

I like your naming, PC Highly appropriate

So you essentially say: the PC has constructed an entire logical language, and has been pondering about about all possible mathematical structures that can be deduced from it, and you now happen to "experience" one of these structures - in fact you ARE one of these structures, and you think it has anything to do with a real universe out there. Great. That's the most universal fit I've ever seen
You are a mathematical structure, thought up by a primordial PC

In this view, the wavefunction is an algorithm which causes, in the sense described above, the generation of evolving sets of numbers. The sets of numbers are the actual physical state. They contain, among other things, the numbers populating the Hilbert space matrices.

Ok, so I'm a Hilbert space and my neighbour is a Conway lifeform , while my best friend is in fact Fermat's last theorem. He's a much nicer chap than all those Cayley tables, getting associative all the time. :rofl: :rofl:

So it wouldn't be quite correct to say that the wavefunction represents knowledge. The wavefunction is a known algorithm, and the evolving results of the algorithm are the physical universe, but those results need not be known by the knower. But, as Reilly has suggested, when the knower pays attention to the outcome and comes to know it, this is the wavefunction collapse and the state of the universe takes on one set of values.

Yes, but you're forgetting the miriad of OTHER logical structures that the knower has thought up, and are probably consciously experienced as well. I'm personally quite happy that I don't have to go through life as a low-dimensional Euclidean space. I prefer by far my happy Hilbert space life, given by my nice wave function algorithm...
But then, there's so much to choose from. Would life not be better as a topological space ? Or is it great to be Monstruous Moonshine ?

And you thought the universe was big, and the multiverse was huge. Plato's world is mindbogglingly larger ! A conscious life for every mathematical construction, thought up by PC !

the entire thing is always finite and in principle measurable and knowable. It seems to me that MWI is much wilder than this.

??? You're going to get the prime number set angry with your statements! He has a lot of powerful friends, you know...

 

[Paul Martin]

Sorry, couldn't resist: in the following post I'm just poking some fun. Don't be offended, it was just to have a good laugh :-)

No offense taken. Glad you could have some fun with this. I am extra glad you took the time to read it at all.

Ok, it seems to me that you are constructing a kind of Platonic world of Ideas this way.

Seriously, yes I am. It's not that I am constructing the Platonic world, but that I suppose that PC has constructed a Platonic world in addition to the physical world. As I have remarked other places in this forum, I agree with Penrose's suggestion that there are three separate and distinct "worlds" in reality, each with its own kind of existence: the Mental World (my "PC" but which I think should be called the Cartesian World), the Physical World (the "universe" of science, which I think should be called the Aristotelian World), and the Ideal world (which is usually called the Platonic world). As I see it, the Mental World consists of only that single consciousness. What we think of as individual human consciousnesses is an illusion experienced by PC during the time it is actively experiencing the world line of a particular person. And so on... I would be happy to go into more detail about the relationships among these three worlds if you are interested but I'll stop for now.

I like your naming, PC Highly appropriate

Thank you. That happened quite by accident. I'm not that clever.

So you essentially say: the PC has constructed an entire logical language, and has been pondering about about all possible mathematical structures that can be deduced from it,

Yes. Exactly.

and you now happen to "experience" one of these structures

No. Here you seem to have missed the crucial point of what I said. Since PC is the only consciousness in existence, PC is the only entity capable of "experiencing" anything. So to interpret what you said here, we need to know what you mean by "you". Of course we use pronouns like that virtually all the time. I did so in every sentence in this paragraph so far. To understand what I am saying, you need to think of a human being as an uncouscious biological vehicle being "driven" by PC, which is the only entity able to know or to will. So as my body sits here at the keyboard typing this response, it is PC, and PC alone who is having the experience of doing so, and it is PC who is deciding what to write and how to phrase it. I maintain that the same is true of "you" as you read this. It is not your biological body having the experience and knowing what I wrote; it is PC who is doing so. There must be some fantastic time-sharing or multiplexing mechanism to allow this to happen, but our modern technology can do something pretty similar so it's not such an outlandish idea after all.

in fact you ARE one of these structures,

Ummm....Yes. But in this case, the "you" refers strictly to the physical biological body.

and you think it has anything to do with a real universe out there.

Ummm....Now we have to switch back to the other connotation of 'you'. Since PC is the only entity in reality that can think, it has to be PC thinking it has anything to do with a real universe. "Out there" is a little misleading. If "in here" is the conscious experience of PC, then I guess the Physical World, and also the Platonic World are both "out there".

Great. That's the most universal fit I've ever seen

Thank you. I think so too.

You are a mathematical structure, thought up by a primordial PC

Yes, in a manner of speaking. I suspect you are waxing into whimsy here, as if you haven't been all along, but I'll try to seriously respond to it anyway. First, the use of 'you' here means my physical body. Yes, it is a mathematical structure thought up by PC. But not as a thing in itself. My body came to exist pretty much exactly as current scientific theory explains. It is a result of a complex series of physical interactions going back billions of years. The mathematical structure dreamed up by PC is the laws of physics and the big bang initial conditions that produced the evolutionary changes in huge sets of numbers representing the "things" (as defined by Bertrand Russell) on which the laws of physics acts. Of course we don't know yet just what these "things" are, whether they are fields, strings, loops, turtles, or what.

Yes, but you're forgetting the miriad of OTHER logical structures that the knower has thought up, and are probably consciously experienced as well.

Seriously, (again I hope you don't mind if I attempt a serious response to a whimsical expression) my guess is that PC did indeed try myriad other combinations of laws and initial conditions in order to arrive at this life-friendly physical universe. (Actually I don't think there was much option on the laws. I think they were either consistent, which are the laws we live under, or inconsistent, which I don't think can produce a stable universe.) As for what's in the Platonic World, I think there probably is a myriad of stuff in there which has not much to do with anything going on. But who knows? (Only PC knows for sure, or even at all. Maybe I should have named it The Shadow instead of PC.)

A conscious life for every mathematical construction, thought up by PC !

Whoops. Nothing in the Platonic World, or the Physical World for that matter, is conscious so if we are talking about life that is conscious, we are only talking about PC.

??? You're going to get the prime number set angry with your statements! He has a lot of powerful friends, you know...

Yes, but I'm not worried. And, I'm sure the religious guys will warn me that God is going to get angry with me for what I have said. When they do, I maintain that my finite, limited, evolving, bumbling, and baffled PC is still unimaginably greater, more powerful, and awesome than their infinite, immutable, omnipotent, omniscient, perfect, and eternal God. So there... No lightning bolts yet.

Paul

 

[vanesch]

As I have remarked other places in this forum, I agree with Penrose's suggestion that there are three separate and distinct "worlds" in reality, each with its own kind of existence: the Mental World (my "PC" but which I think should be called the Cartesian World), the Physical World (the "universe" of science, which I think should be called the Aristotelian World), and the Ideal world (which is usually called the Platonic world).

I like his presentation too, but as a kind of metaphysical poetry (there are different faces to the word "real" - that's how I understand it - and each face incorporates another one).

Yes, in a manner of speaking. I suspect you are waxing into whimsy here, as if you haven't been all along, but I'll try to seriously respond to it anyway. First, the use of 'you' here means my physical body. Yes, it is a mathematical structure thought up by PC. But not as a thing in itself. My body came to exist pretty much exactly as current scientific theory explains. It is a result of a complex series of physical interactions going back billions of years. The mathematical structure dreamed up by PC is the laws of physics and the big bang initial conditions that produced the evolutionary changes in huge sets of numbers representing the "things" (as defined by Bertrand Russell) on which the laws of physics acts. Of course we don't know yet just what these "things" are, whether they are fields, strings, loops, turtles, or what.

Except of course, that they are all simply "thought up" by a non-physical PC - which is hence "outside of time" and "outside of the universe". It starts to sound like the Confessions of Saint-Augustin - especially the last few books in it!
But, if we assign "physical reality" to the thoughts of the PC (which, remember, has no notion of time, which is a physical concept) - that is, to the logical structures, and hence, to the mathematical constructions, then there's no reason to just _pick out the single one of our universe_. For instance, all worlds in the different terms of the wavefunction in MWI are ALSO constructions of this PC - so this view already _encompasses_ MWI, but much, much, much more.

Seriously, (again I hope you don't mind if I attempt a serious response to a whimsical expression) my guess is that PC did indeed try myriad other combinations of laws and initial conditions in order to arrive at this life-friendly physical universe. (Actually I don't think there was much option on the laws. I think they were either consistent, which are the laws we live under, or inconsistent, which I don't think can produce a stable universe.)

Note that at least, the "possible" worlds in MWI are just as good constructions as the one we're in !

But, as Weinberg said about the no-options thing: "I don't see what's wrong with a Newtonian universe with elastic balls"

As for what's in the Platonic World, I think there probably is a myriad of stuff in there which has not much to do with anything going on. But who knows? (Only PC knows for sure, or even at all. Maybe I should have named it The Shadow instead of PC.)

Ok, and you think that MWI is taking liberty with postulating an excessive amount of un-needed ontology ?

Note that it is enjoyable to envision these possibilities you are proposing ; they are mind-opening on a metaphysical level. However, my only reason for making ontological hypotheses (and it can never be more than hypotheses, as we know) is to help me picture the world, as seen by a certain physical theory, in order for me to devellop an intuition for the workings of the theory and its relationship to empirical evidence. As such, your scheme is a bit "too rich". Everything goes, in your scheme.

Ontological hypotheses are a TOOL in our toolbox for reasoning, and draw a mental synthesis of what we think we know, in my viewpoint. Your metaphysical gymnastics goes, from my POV, way too far to be helpful as a mental synthesis for using contemporary physical theories.
However, there ARE people looking into such things (the name that comes to mind is Wolfram, of course, but there are others). But then, these are no interpretational schemes for current physics ; they are frames for speculative theories.

 

[reilly]

To me, "Reality" is a metaphysical hypothesis
, and can never be absolutely demonstrated (cfr the unfalsifiability of solipsism). We should take up the one that is most useful in visualising and in develloping an intuition for how our physical theories work, and to have a consistent view on what's going on/

/
What is your hypothesis?

And what do you mean by "useful" -- in what fashion, and to whom?. Don't forget Godel -- the poet Louis MacNeice put it elegantly, "There ain't no universals in this man's town" (Autumn Journal, 1939). And, anyway, arguably, most physicists will say that standard QM fits the bill quite nicely -- sophisiticated intuitions and intuitive arguments abound in physics, particularly in solid state and nuclear physics.

. It is in this context that I find statements such as "the theory only describes our knowledge about something, but has nothing to say about the something itself" rather bad viewpoints: what GOOD does it do to say that you REFUSE to take up a hypothesis of reality ? What do you WIN by doing that ? Avoiding to be confronted one day with having to change ? I have no problems CHANGING my hypothesis of reality, the day that we find out more. But _in the mean time_, what good is it to keep telling to yourself that the theory is _not_ a description of reality ? What can one win, conceptually, that way ? Of course our view on reality is not "correct" in an absolute way (or at least, we will never be able to find out until it is falsified). So what ? Should we then just _refuse_ to have one ?

I'll ask but one question: given your categories of "knowledge of something" VS. the "Knowledge(?) of the thing iteself?, in which category do you fit the statement," the hydrogen atom is composed of an electron and a proton"? What's with "refuse'? (I use units in which 1 = 2)

The "knowledge interpretation" is a _refusal of interpretation_, and it is an illusion to think that it has no problems: the main problem it has is the arbitrariness of the hermitean operator to be associated to a measurement apparatus. It has to be chosen intuitively, and cannot be derived from the physics of the apparatus. So there is total arbitrariness in the assignment of the formalism to the results: the formalism does NOT give you, in any unique way, a description of your knowledge. You PICK OUT the one that intuitively (from assigning a kind of reality to what was not supposed to have any reality) seems to correspond to what the apparatus *would do if it were a classical apparatus*, and if the quantum system were a classical system - but as such, you have to pick, intuitively, a basis. You picture, in doing so, a classical device and a classical system (in a certain basis). /

Quite the contrary. The structure of key operators is strongly suggested by their role in transformation (semi)groups, ones not unknown in classical physics. Lagrangians, Hamiltonians are no more arbitrary in QM than in Classical Physis(CP). It's no surprise that many of the interactions of QFT. those dealing with emission/absorbtion/transformation of particles take the formal form of a classical Poisson process. /

By the way, I sort of remember times in CP in which intuition played a huge role -- Maxwell, Boltzman, Einstein, Bohr's push into Quantum land, Fermat, J.J. Thomsen, Rutherford, .... Most, but not all, physics is indeed intuited from empirical evidence. What's the problem with intuition?
/
I simply do not understand your claim of arbitrariness in QM. Perhaps you could explain where the arbitrariness is in a scattering experiment -- once I've picked the z axis -- along the beam -- the x axis -- say in a horizontal plane so x is perpendicular to z, etc.... If I want to count electrons at a particular X,Y,Z, then I put a counter there, and say that I expect to find electrons with prob of detection The INTEGRAL OF THE ABSOLUTE SQUARE OF THE ELECTRON WAVE FUNCTION OVER THE APERATURE OF THE COUNTER.


/
What's so arbitrary about my description? What am I missing? /
/
/

That said, I can understand the attitude of people taking on the knowledge view, but it is a messy view of things. It is just that we have to use our intuition (there are no rules) to say WHAT a certain apparatus is measuring, and that if we do that, quantum theory seems to give us certain mathematical rules to find statistical results of measurements, which seem to work out when we do it right. A kind of happy hokus-pokus which works, although we don't know why. But I find it a depressing view, to deny oneself a picture of reality. Sure, that way you are sure NOT to make a wrong statement: you're not making any!

/
/
/
If you have not, peruse in Mandel and Wolff's Optical Coherence and Qunatum Optics, Chapters 9,14 , 100 pages or so of a very detailed account of measurements by means of the photoelectric process. You tell me where the "hokus-pocus" is in their book, or even another one. The level of our comprehension of QM is much higher than many think./

By the way, why are linear electrical circuits governed by a 2nd order differential equation? Why do we have electric charge, mass?Why does CP work so well? Plenty of unresolved mysteries in CP. /
/
Models of reality? Cheer up, I go for Plato's notion. It's the metaphysical hypothesis that works for me.

Regards,
Reilly Atkinson

 

[Paul Martin]

But, if we assign "physical reality" to the thoughts of the PC (which, remember, has no notion of time, which is a physical concept)

PC must have a notion of time since the thoughts of PC change. You are right, though, that this time is completely separate and distinct from the time of our physical spacetime. This would obviously allow PC to peruse and edit the evolving spacetime in the same way that a film editor can choose and change the sequence of frames on a movie.

- that is, to the logical structures, and hence, to the mathematical constructions, then there's no reason to just _pick out the single one of our universe_.

Of course there could be reasons to pick out specific universes. PC, being the thoughtful entity that it is, might choose stable and complex universes. In particular, those which are capable of supporting life. This answers the anthropic question.

For instance, all worlds in the different terms of the wavefunction in MWI are ALSO constructions of this PC - so this view already _encompasses_ MWI, but much, much, much more.

True. But nothing compells PC to retain any but the chosen ones. MWI on the other hand, must retain the results of all the mindless bifurcations. In my view, this encompasses much, much, much, much more than the select few actually chosen by PC.

Note that at least, the "possible" worlds in MWI are just as good constructions as the one we're in !

Not all of them if being life-friendly is a criterion.

But, as Weinberg said about the no-options thing: "I don't see what's wrong with a Newtonian universe with elastic balls"

Ok, and you think that MWI is taking liberty with postulating an excessive amount of un-needed ontology ?

That depends on what you mean by 'ontology'. Not being a philosopher, I am not exactly sure what the term means. So I'll give you two answers depending on what you might mean.

If, by 'ontology' you mean whatever exists, then, as I explained above, I think MWI implies (not postulates...) an excessive amount of un-needed ontology.

But, if by 'ontology' you mean the fundamental constituent of which everything real is made, then I don't recall you ever declaring what that constituent is. I don't think it is elastic balls.

In my PC view, the fundamental constituent is an ability to know together with the knowledge accumulated so far.

What do you think the fundamental constituent is if not concepts? And if concepts, in what mind?

Note that it is enjoyable to envision these possibilities you are proposing ; they are mind-opening on a metaphysical level.

As you can no doubt tell, I have a lot of fun thinking about these things.

However, my only reason for making ontological hypotheses (and it can never be more than hypotheses, as we know) is to help me picture the world, as seen by a certain physical theory, in order for me to devellop an intuition for the workings of the theory and its relationship to empirical evidence. As such, your scheme is a bit "too rich".

In my view, your scheme is not quite rich enough: it doesn't provide a satisfactory explanation for consciousness. Mine does.

Everything goes, in your scheme.

Yes. I think it provides a way to arrive at an explanation for everything.

However, there ARE people looking into such things (the name that comes to mind is Wolfram, of course, but there are others). But then, these are no interpretational schemes for current physics ; they are frames for speculative theories.

Yes. I think Wolfram is on to something. But, instead of viewing the world as a cellular automaton grinding away, I see it more as an implementation of a cellular automaton as provided on some web sites. That is, the automaton proceeds algorithmically unless and until some conscious operator stops the action, changes the contents of a few cells, and then restarts the action. That conscious operator, of course, is PC.

Thanks again for your thoughts,

Paul

 

[vanesch]

What is your hypothesis?

That the "thing" in my theory that is supposed to represent reality, does exactly that.

And, anyway, arguably, most physicists will say that standard QM fits the bill quite nicely -- sophisiticated intuitions and intuitive arguments abound in physics, particularly in solid state and nuclear physics.

Yes, and that is because at a certain point, people DO take the theory seriously as a description of reality. They DO think of the wavefunctions they are handling, as something "real". I have a hard time imagining how people could handle a certain concept intuitively and at the same time deny it any ontological status. Now maybe that's just me...

I'll ask but one question: given your categories of "knowledge of something" VS. the "Knowledge(?) of the thing iteself?, in which category do you fit the statement," the hydrogen atom is composed of an electron and a proton"? What's with "refuse'? (I use units in which 1 = 2)

In the "knowledge" view, it depends on what you take as a priori, no ? In non-relativistic QM, you take it to be real because these are the degrees of freedom you put in yourself (there IS a proton, and there IS an electron). What you take as not being real, is that the wavefunction tells you that the electron is ABOVE the proton, and is (simultaneously) beneath the proton. In other words, you take the degrees of freedom of the Hilbert space for real (you put it in), but you don't take the wavefunction for real. That results then in saying that "it doesn't make sense to talk about the position of the electron if I didn't measure it".

However, when you are working *intuitively* with wavefunctions, you nevertheless do exactly that! For instance, when you do a double slit experiment, you intuitively say: the electron went through slit 1 AND went, simultaneously, through slit 2. Afterwards, it met itself going through the two slits, and hence arrived simultaneously at several spots on the screen. At least, that's how I view these things. As in Feynman diagrams for instance.
So you DO assign reality to this description (as I'm trying to propose here), in order to reason intuitively about it, just to deny it a bit later, when you say: and I only observed the electron in one spot, so the fact that my previous description said that it was simultaneously at different spots must NOT have corresponded to something real. That's illogical to me.

But if you go further, and you go to a quantum field view, then now the electron and the proton are, themselves, specific states of the fields. So their reality now depends on how real you want those states to be. If you say that the only thing that counts is knowledge, then those states are NOT real, and hence the electron and proton are NOT real, but just a tool to link the emission of light of a UV lamp and the observations of lines on a spectrographical film. And certainly do not attach any reality to the "atoms" being in between, generating the spectrum. They are abstract quantum states of field excitations. Not very intuitive, is it ?

By the way, I sort of remember times in CP in which intuition played a huge role -- Maxwell, Boltzman, Einstein, Bohr's push into Quantum land, Fermat, J.J. Thomsen, Rutherford, .... Most, but not all, physics is indeed intuited from empirical evidence. What's the problem with intuition?

There is no problem with intuition, when you put yourself in the mindset that you're thinking about a certain reality. I have, however, difficulties having an intuition for something that is postulated NOT to correspond to any reality. Faraday thinking of his "force lines" as real, seeing the electric and magnetic fields as "real" helps you to think about it. Saying that these concepts are just tools to find the right relation between experimental preparation and observation are, IMO, stiffling intuition. I find it much more intuitive to say that a particle is really emitted, and then goes through the left slit, and through the right slit, simultaneously, than to say that I have something physical here that I call "particle source" (but it is NOT really emitting particles), I have on the other hand something that is called "particle detector" (but it is of course NOT detecting particles), and that I can now set up some abstract calculation scheme that *erroneously seems to suggest that some particle is travelling through the apparatus* but is just an abstract scheme to which we do not have to attach any reality, but that gives us, at the end, the correct statistics of the "particle detector" saying "click" - which is what the knowledge view is trying to tell us, no ?

I simply do not understand your claim of arbitrariness in QM. Perhaps you could explain where the arbitrariness is in a scattering experiment -- once I've picked the z axis -- along the beam -- the x axis -- say in a horizontal plane so x is perpendicular to z, etc.... If I want to count electrons at a particular X,Y,Z, then I put a counter there, and say that I expect to find electrons with prob of detection The INTEGRAL OF THE ABSOLUTE SQUARE OF THE ELECTRON WAVE FUNCTION OVER THE APERATURE OF THE COUNTER.

Well, that's exactly the intuitive input: you assume the detector to be in two possible states: CLICK and NO-CLICK. These are the pointer states. From that, you trace back to the interaction with the electron wave function, and you'll see that it splits the hilbert space of states in two orthogonal complements, which are the eigenspaces of the detection observable C (from "click") ; one which will correspond to all position eigenstates of the electron within the aperture of the counter (associated to the eigenvalue 1), and the other which will correspond to the eigenstates of teh electron OUTSIDE of the aperture (associated to the eigenvalue 0).

But the intuitive content has been that such a detector can only be in two possible (classical!) states, namely |click> and |no-click>.
If you would have worked in the basis |click>+|no-click> and |click>-|noclick> then you would have found a different observable L (lunatic observable ;-) ; it would have had totally different eigenspaces, and you would have had totally different outcomes.
What I mean, is: you have to DEFINE what are classical states of your aparatus, and this is only done using some intuition. You cannot PREDICT (apart from decoherence, and MWI) that such a device will "click" or "not click" and not, that it will click+no-click and click-no-click if you remain STRICTLY within a quantum-mechanical framework. There is an intuitive input (which seems so evident that it is often jumped over) of WHAT are the pointer states of an apparatus, that this is not often realized.

But the example I prefer is the one of a dial indicating "momentum" of a particle. A certain POSITION of the dial indicates a certain measured momentum. But on the other hand, a certain MOMENTUM of the dial, would indicate a certain POSITION of the particle. So what's this device measuring ?

If you have not, peruse in Mandel and Wolff's Optical Coherence and Qunatum Optics, Chapters 9,14 , 100 pages or so of a very detailed account of measurements by means of the photoelectric process.
You tell me where the "hokus-pocus" is in their book, or even another one. The level of our comprehension of QM is much higher than many think./

At a certain point, a transition to a classical description is made, and it is "arbitrarily" decided WHAT are the classical states - which is usually SO EVIDENT that it goes by unnoticed: OF COURSE there is a click or not a click, right ? It wouldn't cross your mind that there could be a state |click>+|no-click>..., simply because we have no _classical_ description for that. We are not used to write the electrical current in the wire leading from the anode to the amplifier as being |i1> + |i2>. So that's where we pick our intuitive preferred basis: when we calculate classical quantities.

By the way, why are linear electrical circuits governed by a 2nd order differential equation? Why do we have electric charge, mass?Why does CP work so well? Plenty of unresolved mysteries in CP.

When you do classical physics, you ALWAYS attach a physical reality to your intermediate descriptions: in an electrical circuit, you really imagine that the currents and voltages you calculate are really there, even if you do not measure them. When you do quantum-mechanical ponderings, suddenly it should be forbidden to think of the wavefunction as something real. THAT's what I'm trying to argue, is unnecessarily severe. You CAN think of the wavefunction as being really there, as describing really what's going on, all the time. It doesn't contradict any observed phenomenon. It's the only point I'm trying to make: let us stop claiming that the wavefunction "is not describing reality". It can do it very well. And IF you allow it to do so, a lot of "paradoxes" in QM are seen to be not paradoxial at all.

Models of reality? Cheer up, I go for Plato's notion. It's the metaphysical hypothesis that works for me.

Well, if you're happy with quantum theory as such, all the better. I'm only trying to offer the MWI view, because of the illuminating aspects it had on my personal understanding of quantum theory, especially related to things such as EPR setups and delayed-choice quantum erasers, as well as ponderings about simpler things such as the double-slit experiment.

 

[Sherlock]

Well, if the aim of an interpretation is to say "what nature is like", then this looks like me like a necessary condition, that it makes a statement about "what nature is like" in a 1-1 way, no ?

The point is that an assumption wrt whether the mathematical structure of qm is or isn't in 1-1 correspondence with an underlying reality is not something that was necessary to the theory's development, and still isn't necessary to the theory's development --- since there's no way to know one way or the other.

If we apply the Born rule and the projection postulate, we just 'pick out one term' with a certain probability. I accept this. But it has to be known that the moment we do this, and the basis we do this in, is totally arbitrary.

The Born rule and the projection postulate are parts of the formalism that are not JUST about an underlying quantum world. The underlying reality is, presumably, the evolution-interaction of wavelike disturbances --- the precise qualitative characteristics and details of which are hidden from us. But, again presumably, it is the intensity of the incident quanta which interact with the quanta of detection instruments that determines the observable output. Hence, the Born rule.

I don't know what you mean by the choice of basis being totally arbitrary. It depends on the instrumental settings, doesn't it? You might say that the choice of settings, within some allowed range, is arbitrary --- but once those settings have been made and are in effect wrt incident quanta, then the expansion isn't arbitrary, is it?

IF YOU PICK THE BASIS RIGHT, this is what you will observe. However, what is almost inacceptable, is that now, we just "throw away" the rest of the wavefunction. If that wavefunction represents something physical out there, however, it is hard to see how an ARBITRARY decision on your part to "apply the Born rule" would suddenly CHANGE THE STATE OF NATURE. Isn't it more sensible to say that you just OBSERVE, with the given probability, ONE term ? But that the others are "still out there" ?

No. It's more sensible to try to determine what the formalism pertains to, rather than arbitrarily assign it a meaning that can't be verified and that it therefore might not have.

I say that at least one mathematical formulation of the theory indicates that nature is fundamentally interacting waves.

Uh ? What's that supposed to mean ? The Schrodinger equation gives you how the vector |psi> evolves in hilbert space...

The Schroedinger equation is a wave equation. Vectors in Hilbert Space are similar to vectors in the 3D space of our sensory perceptions. My estimation of the significance of these symbolic formulations wrt the qualitative characteristics of an underlying quantum world is at least as meaningful as your saying that the mathematical structure of quantum theory is in 1-1 correspondence with an underlying quantum world --- and I accept that that might mean that it isn't meaningful at all.

Don't you think that nature is fundamentally waves, or have you no ideas on that? The prohibition on local realist formulations just tells us that this (presumed) underlying wave activity (especially when it's manifested instrumentally as correlations between spatially separated, entangled events) won't be describable by us in terms of precisely defined mathematical abstractions. Rather, our apprehension of the underlying realm is limited to talking about it in terms of indefinite potentialities --- a range of probabilities existing simultaneously, prior to a detection event, in an imaginary space.

The experiment I would suggest to "prove" MWI would be an EPR experiment. It would indicate that, if Bob were not in a superposition of states after his measurement, that Alice would find correlations which would lead to very strange results, leading one to believe that Alice's action somehow had a "spooky action at a distance" on the Bob measurements ; while if Bob WAS in two worlds, that this would be seen as "quantum interference" between the Alice state and the two Bob states.

But all indications are that events at Alice's end have not affected events at Bob's end, and conversely. So, I don't see how an EPR or a Bell experiment could be used to support MWI.

The Born rule is not really part of the wave mechanical picture. You STOP the wave equation, and suddenly chop off a piece of it. You send a plane wave on a detector, and suddenly, it becomes a localized lump (WITHOUT ANY EQUATION SAYING SO).
You need the Born rule to go from the "end" of your wave equation evolution to say: here we stop with the physics, and we are now going to look at measurements.
...

The Born rule is the rule that gives probabilities to the components of the state vector in a certain basis, by saying that it is their length, squared. Clearly, one needs to say in which basis this is. But then there is the projection postulate, which says that we PICK one of the components in the basis, randomly, according to the probabilities of the Born rule, and that this component, renormalized to 1, becomes the new state.
This is an instantaneous, non-dynamic, and global change of the state, and is something that only happens in "measurement devices". This is only introduced to accept the observation that, after a measurement, if it is applied again, we shouldn't find another result than the one we already had. BUT THERE IS NO PHYSICAL JUSTIFICATION for such a projection (and it is clearly non-local). It is not clear *when* it happens, and *in what basis* it happens. YOU HAVE TO GUESS CORRECTLY in what basis you apply it.
So it is *not* something that is clearly objective. It is just _stopping the wave equation_ and then projecting out. What magical action in nature can do such a thing: instantaneously, and everywhere (non-locally!) stopping the equations of nature, and make the state of the system JUMP? In a basis that is related to the "observed data" ? Doesn't this sound VERY MUCH like something related to perception ?

Of course it's related to perception. Measurement results (data) are related to perception.

The expansion theorem-postulate and the Born rule are part of an overall wave mechanical mathematical apparatus for predicting instrumental results that we can perceive.

The probability interpretation is a physical (in terms of what we see) interpretation of this mathematical apparatus.

It's the only thing MWI does. It says: no, you do not CHANGE the state of nature, you just PERCEIVE one term of it ...

So you're not affecting the incident quantum disturbance by putting filters and detectors in its path? That doesn't make any sense at all.

The very appearance of the different states in the wave equation are its "creation". Do you object to the "creation mechanism" of Fourier components when a signal gets non-linearly deformed ? They just appear in the equation, that's all...

What I object to is the out of hand reification of all this stuff. It really isn't known just how closely it might be corresponding to an underlying reality.

... if the wavefunction is not in a 1-1 mapping with the underlying quantum world, then *what is in a 1-1 mapping* ? There must be *something* that is in a 1-1 mapping, right ?

*Something* ? Like what ? There's no particular reason to believe that any symbolic representation yet invented by physicists is a 1-1 mapping of an underlying quantum world. And anyway, there's no way to know. Is there ?

And all that, while it is *possible* to consider the wavefunction to be in a 1-1 mapping with "nature", to restore locality, not to have this arbitrary projection and stopping of the wave equation. Is this picture not much more compelling ?

It's not compelling at all. Locality didn't need to be restored in the first place (depending on how you interpret locality-nonlocality considerations), and you still have to deal with the same mathematical apparatus in order to predict results. What you've added is a metaphysical vision, which itself seems somewhat removed from, say, an underlying wave reality, that can neither be verified nor falsified.

We HAVE a 1-1 mapping, we KNOW the unique law of the evolution (Schroedinger equation) and we CAN explain the random aspect of it, and the apparent non-locality as one of its side effects ?

You don't have a 1-1 mapping. You have an unfounded assumption of a 1-1 mapping.

I have less problems to say that when my brain state changes, my perception changes (in this case, randomly, I pick one of the daughter states), than to say that when I look at nature, it's global state changes.

Your brain state and your perception are part of nature. Aren't they? (Quantum theory, as all of physical science, assumes that your brain and perceptual faculties function pretty much like mine and any other human being's. And, that assumption has yielded an ever-expanding body of knowledge of nature, and technological progress.)

When you PROBE a quantum system, assuming that quantum system refers to some underlying physical reality, you alter it. Like when you cut a cake you alter the cake, or when you put a glove or a bat in the path of a baseball you alter the path of the baseball (as well as the baseball itself). FAPP you don't change the state of a cake or a baseball's trajectory just by LOOKING at them. The thing is, the only way to LOOK AT most quantum systems alters them severely.

If you're, say, LOOKING AT quantum optical emissions with a PMT, then of course you're going to alter the emissions. Their unitary evolution is halted by the PMT.

In any case, strictly speaking, the act of navigating through (including just looking at) nature changes the global state of nature --- whether you use the MWI or some other interpretation.

I don't think it is circular. I say: you have a theory, which gives good empirical results. Now, look at its underlying formalism. It has a nice mathematical structure, but it goes wry in two points: 1) you STOP the physical evolution equation, to do something you've introduced ad hoc when you "observe" and 2) you then do something to the entire state of the system (which implies non-locality...)
Clearly, the last part makes it impossible to be considered as a true physical action, and it is from THIS, and THIS thing alone, that people concluded that the wave function cannot describe nature 1-1.

At some point you stop talking about the quantum system in terms of an evolution in an underlying quantum world (an imaginary space) and talk about it in terms of stuff that we can see. I think that qm, interpreted probabilistically, does this clearly enough --- and that MWI continues the unitary evolution in a way that doesn't make any physical sense in the first place and only introduces a new set of unnecessary semantic-philosophical problems to deal with.

The real, physical problem of course is that there's no way to KNOW what the underlying quantum world IS. Is the wave function live or is it memorex, so to speak, or is it just a gross simplification of what's really happening in an underlying reality?

But it could, if we kept running the wave equation. We're used to that: the state of nature evolves through an equation, describing the interactions. Great. We have that: the wavefunction, and Schroedinger's equation.
Then what with the stopping and projecting ? Well, let's put that in the "perception" part: we only perceive part of the wavefunction, in a probabilistic way.
As such, we've now eliminated the thing that blocks us from taking the theory seriously as a description of what really happens. Why a priori assume that this cannot be right ? Of course that is no proof.

The assumption that the theory is not a 1-1 mapping of the underworld is not an a priori assumption.

The theory functions quite well enough, apparently, without an assumption about its relationship to an underlying reality. What is of utmost importance, however, is some sort of statement about its relationship to our sensory experience of experimental preparations and results.

The probability interpretation already provides this. The MWI provides it also, but in a much more circuitous, much less, er, physical way.

Quantum theory itself tells us that there can't be a 1-1 mapping between physical reality and precisely defined mathematical abstractions. It imposes limits. So, if you take the theory as right in this respect, then it can't ever be right in the respect that you assume it to be.

That's a misunderstanding. The wave function evolves deterministically, and very precisely, following a wave equation (the Schroedinger equation). There's nothing random to the state evolution. It doesn't say that "there are limits to its precision". What it does say, is that our PERCEPTION of the state will involve probabilistic aspects if we do measurements.

If you are referring to the HUP, it only tells you something about those probabilistic aspects of perception (= measurement). The HUP DOES NOT tell you that the state of a particle is somehow "unknown". It only tells you that there is a relationship between the probability distribution of the measurement of quantity A and the probability distribution of quantity B (and in MWI, the probability is a consequence of perception, not of indeterminism in nature).

I agree that quantum theory doesn't necessarily allow one to say that an underlying quantum world is indeterministic ... or deterministic. The working assumption, however, is that nature is deterministic.

But quantum theory is concerned with what can be experimentally determined, isn't it? And there are limits, imposed by the theory itself, on what can be experimentally determined.

Quantum theory does very well predicting gross distributions, but not very well predicting individual events. For example, in the quantum two-slit experiment, qm depicts quite accurately the distribution after several tens of thousands of individual detection events --- but it does not accurately depict the actual evolution of this distribution. Likewise, in, eg. Bell experiments, the wavefunction doesn't depict the time evolution of the individual data sequences accumulated at A or B.

The probabilistic aspects go hand in hand with measurement. And, measurements (the data) are our only window to an underlying physical reality. The wavefunction is a probability distribution. The assumption that the wavefunction is a 1-1 mapping of the evolution of events at the level of an underlying reality doesn't follow from the observation of the relationship of the wavefunction to the evolution of events at the level of macroscopic detector output.

The quantum two-slit experiments, the Bell experiments, et al., are still mysteries, whether you look at them via the MWI or not.

After all, we don't know what nature IS, do we?

Why starting with that hypothesis ? Why not start with the hypothesis that we DO know nature (up to a point) ?

That we can, and do, know nature "up to a point" IS the hypothesis. The line is drawn by what can be experimentally determined.

"I'm going to repair my car ; let's assume I don't know how a car works"
Not the most fruitful approach, no ?

Either you know how your car works or you don't. The workings of nature are a bit more mysterious. The assumption that quantum theory is in 1-1 correspondence with nature, while at the same time not allowing us to predict individual data sequences, doesn't seem to me to make much sense.

I'm forced to conclude that the assumption that the mathematical structure of quantum theory is a 1-1 mapping of nature is an unfounded assumption. It seems more sensible to me to say that quantum theory is saying SOMETHING about an underlying quantum world --- and I think that that something entails the idea that the underlying reality of nature might be thought of purely in terms of waves, and that waves in the underlying quantum world behave very much like the waves that we observe in macroscopic media --- but that it's not a complete accounting.

Just WANTING qm to be a 1-1 mapping, or saying that our best theory SHOULD BE a 1-1 mapping, are NOT good enough reasons to assume that the mathematical structure of quantum theory IS a 1-1 mapping of an underlying quantum world.

 

[Sherlock]

To define 'state of knowledge' don't we need a 'knower' and a set of 'known' information?

Yes --- the knowers are human beings, and the sets of known info are (for the purpose of this thread) the quantum experimental preparations and the symbolic representations which are the theories of the quantum experimental preparations.

I propose assuming a knower as primordial. In its most primitive form, this knower would be simply the ability to know, similar to the classical definition of energy being the ability to do work.

We've already defined the set of knowers.

If the brain is the only seat of knowledge, then this means that in the billions of years prior to the development of brains there were no wave function collapses.

That's correct. Prior to the invention of wave functions, there were no wave functions ... hence, no wave function collapses.

This seems to imply that the entire universe remained in a superposed state up until the emergence of the first proto-brain at which time the wave function collapsed to produce the first actualization of the universe.

The principle of linear superposition is a wave mechanical phenomenon. Assuming that you model the entire universe as, fundamentally, a vast complex of wave structures in a hierarchy of media, then superposition of the universal constituents is an ongoing phenomenon. The computer screen you're looking at, the chair you're sitting on, the earth, the sun, you, me --- all ponderable objects are wave interference phenomena.

It might be said that the preceding statement resulted from a certain set of actualizations.

Wouldn't the existence of a primordial knower make the scenario more plausible by allowing earlier wave function collapses?

No. It would make it semantically more confusing.

By acknowledging the existence of "cumulative knowledge" you introduce yet another type of knower.

Not really. Just human beings.

I think Occam would suggest considering all knowers -- the primordial knower, the individual knowers associated with individual brains, and the cumulative knower associated with collections of brains -- to be one and the same.

I think Occam would have stopped you at (and disallowed) the primordial knower = ability to know thing.

This would indeed transcend the 4D space and time of physics and it would seem to suggest at least one additional temporal dimension.

This would also further annoy Occam.

By tacitly assuming that the entity "I" is a conscious agent seated in a brain, we close off possible explanations of reality which "I", for "one", expect might be closer to the truth.

Physical science doesn't tacitly assume that consciousness corresponds to brain activity, it overtly assumes it. Consciousness = brain activity.

Assuming the existence of only a single knower, as I suggest, leads to the obvious implication that a version of solipsism is true. It is not the commonly discussed solipsism in which nothing exists but the mind associated with a particular brain. Instead, it says that nothing exists but the single primordial knower along with all the knowledge accumulated so far. No problem.

No problem for who? Your construction is very ... anthropic. You've abstracted from too high a level of complexity. The vocabulary that you're applying is scale-specific. You want something more general. A way of talking about nature that transcends all scales and is therefore applicable to any scale. Then Occam will not be offended (unless of course you unnecessarily complicate things using the more fundamental terms.

In my PC view, the fundamental constituent is an ability to know together with the knowledge accumulated so far.

What do you think the fundamental constituent is if not concepts?

The fundamental constituent of the universe is waves in media of unknown structure.