I won't debate on the wavefunction collapse

[strangerep]

[...] I read about a proposal to look for [non-unitary evolution] effects in observatons of neutrinos from astrophysical sources. Neutrino oscillations lead to neutrinos of one flavor evolving into a superposition of the three flavors. But if a pure neutrino state evolves into a mixed state then that can be detected as it affects the relative probabilities for detecting the three flavors.

That's accounted for by flavor eigenstates not coinciding with mass eigenstates.
Where is the non-unitarity?

- strangerep.

 

[Count Iblis]

That's accounted for by flavor eigenstates not coinciding with mass eigenstates.
Where is the non-unitarity?

- strangerep.

That's right. However, decoherence would yield an extra measurable effect. See e.g. this article

 

[vanesch]

Why such pessimism? We do know something don't we?

That's not pessimism. It is realising up to what point we don't have any absolute knowledge, but only relative mental constructs which are useful. That's good enough reason to keep them, but we mustn't over-estimate the absolute character of any form of knowledge. There's no problem in living with the knowledge that our "knowledge" is up to a point arbitrary, conventional and probably even wrong. In fact, it frees oneself of dogmatic "holdons" which generate difficulties in thinking freely. But, as I said, there's no reason to *discard* our "shaky" knowledge, as it is still the best we can do.

The place to stop is determined by the concrete experimental situation. Ask the experimentalist conducting the experiment where is the boundary physical system/measuring device and you'll get a pretty accurate answer.

As I said, for the instrumentalist, this is not obvious!
For instance, in a photomultiplier, when is the "measurement" done ? By the freeing of an electron from the photocathode ? But if we study that in more detail, we do it with a quantum-mechanical description, and the photo-electric effect becomes a "system-under-study". Is it during the electron multiplication ? But then, the electron-metal interaction can also be accounted for quantum-mechanically...

Is it when the amplifier amplifies the signal on the anode ? But then, this amplifier has a fist stage with a FET transistor which can have a quantum-mechanical description...

Of course, at a certain point, the instrumentalist knows that a classical approximation will be good enough for the specific purpose, and places his "cut" there. But that's a matter of approximation, not something fundamental.

 

[vanesch]

That's accounted for by flavor eigenstates not coinciding with mass eigenstates.
Where is the non-unitarity?

The point is that it would probably be a lack of quantum interference there where it is expected and no decoherence effect can explain away the non-observation of the interference. In other words, it would be an attempt to falsify the applicability of quantum mechanics proper.

 

[vanesch]

Hmmm, is there always something "naive" about a system allowing for a paradox? What about the Banach-Tarski Paradox

Isn't this a bit like the counter-intuitive fact that an absolutely divergent series can always be re-arranged to yield any finite sum ?

 

[Count Iblis]

Isn't this a bit like the counter-intuitive fact that an absolutely divergent series can always be re-arranged to yield any finite sum ?

Yes, but the Banach-Tarski is much more counterintuitive (you only need to cut the ball into a finite number of pieces and reassemble them to make the new ball of twice the volume). I think that Banach and Tarski argued that the Axiom of Choice should be be dropped because of their theorem.

 

[Hans de Vries]

Personally, I don't find solipsism "unworthy of discussion" ; I only find it not a very useful ontology hypothesis, because we stop immediately.

If the solipsist physicist assumes that the universe is in some way the product of his own
mind, and this universe includes all the physics textbooks he owns, why does he have
to study these books year after year after year, when he himself is, in fact, the author?



Regards, Hans

 

[lightarrow]

If the solipsist physicist assumes that the universe is in some way the product of his own
mind, and this universe includes all the physics textbooks he owns, why does he have
to study these books year after year after year, when he himself is, in fact, the author?



Regards, Hans

Because he forgot his creation...

 

[Fra]

Please elaborate: propose an experiment that distinguishes between a real banana and the solipsist hypothesis.

You cannot be serious ! Solipsism is a ridiculous idea and not worth discussing.

I'm sorry for jumping into the late discussion and I'm not sure what you guys mean with solipsism in the context of physics, but I associate it closely to subjective reality in the sense that the local perception of reality needs a representation which I think is a relation to the environment, a sort of mirror. This I think is related to the subjective and relational interpretations of QM. The only reality for an observer is IMO represented by his relations to the environment. And a real observer or particle can most probably (I think) not keep infinite amounts of relations, the information capacity is bound to limit the relational complexity.

I personally don't think this is ridicilous. I rather think the opposite idea that there is an objective absolute reality is unfounded and overly speculative, whose purpose is to simplify the matter. But I think this simplification really produces inconsistencies.

OTOH if solipsism means physicists human MIND then it is a statement of insufficient scope, unless the concept of mind is also attributed to an arbitrary system, like particles "minds". But that terminology gets awkward and a bit silly I agree.

We have to accept that we can believe our senses and that there is an objective reality or physics has no meaning or purpose.

I disagree with this. It still has meaning. The fact that reality is relational and subjective is not the same as to say it's totally arbitrary. Also I think that one can find that communicating/interacting observers will mutually favour understanding, and this will render an effective objective reality as emergent, but I think it is not _fundamentally objective_ which I personally think is an extremely important distinction.

/Fredrik

 

[vanesch]

If the solipsist physicist assumes that the universe is in some way the product of his own mind, and this universe includes all the physics textbooks he owns, why does he have to study these books year after year after year, when he himself is, in fact, the author?

In the same way as you may not understand your dreams, I guess... If you dream that you are a detective who's working on a case and cannot find the murderer, then you could say the same thing: how can it be that you, as creator of your own dream, wouldn't know who's the guilty one.
The idea of solipsism is not somehow that you are fully knowledgeably your own "god and creator" or something, but rather that the only thing you can be sure of, is that you undergo subjective impressions and that those impressions do not necessarily have to come from an evident "outside reality".

 

[vanesch]

I'm sorry for jumping into the late discussion and I'm not sure what you guys mean with solipsism in the context of physics, but I associate it closely to subjective reality in the sense that the local perception of reality needs a representation which I think is a relation to the environment, a sort of mirror. This I think is related to the subjective and relational interpretations of QM. The only reality for an observer is IMO represented by his relations to the environment. And a real observer or particle can most probably (I think) not keep infinite amounts of relations, the information capacity is bound to limit the relational complexity.

I personally don't think this is ridicilous. I rather think the opposite idea that there is an objective absolute reality is unfounded and overly speculative, whose purpose is to simplify the matter. But I think this simplification really produces inconsistencies.

This is to me a very good representation of what "solipsism" in quantum interpretations means, and what is the scope of "a reality hypothesis".

 

[Mentz114]

Hello Fredrik, I would like to restate my personal view that solipsism is ridiculous. How can any rational being contemplate for a moment the absurdity that they ( him, her, it) is 'dreaming' the universe. There is no reason whatever to think this.

I rather think the opposite idea that there is an objective absolute reality is unfounded and overly speculative, whose purpose is to simplify the matter. But I think this simplification really produces inconsistencies.

In my view, utter rubbish. I hope that isn't considered too strong, but this is a physics forum, and someone is telling me that assuming an objective reality is a 'simplification' !
What inconsistencies are found from this assumption ?


If you continue to disagree with me - I'll undream you !

 

[friend]

Hello Fredrik, I would like to restate my personal view that solipsism is ridiculous. How can any rational being contemplate for a moment the absurdity that they ( him, her, it) is 'dreaming' the universe. There is no reason whatever to think this.

Reason is a manifestation of imagination just as dreaming is. The weird things would be to consider dreaming inside this dream.

 

[Hurkyl]

Hello Fredrik, I would like to restate my personal view that solipsism is ridiculous. How can any rational being contemplate for a moment the absurdity that they ( him, her, it) is 'dreaming' the universe.

A rational being wouldn't reject the possibility simply because they find it aesthetically displeasing.

There is no reason whatever to think this.

What reason is there to think otherwise?



As I understand it, solipsism's main practical use is as a counterexample, and for proof-by-contradiction-like arguments.


For example, as a being who instinctively rejects solipsism, you should therefore tend to reject any philosophical position that reduces to solipsism. For example, the position that all knowledge of the universe comes entirely from sensory experience.

(If our only knowledge comes from sensory experience, that means we cannot trust our theories and conceptions about what happens "beyond" our sensory apparatuses -- and thus all our knowledge of the 'external universe' is a mental fiction we've cooked up to organize our sensory experience)

 

[Mentz114]

If our only knowledge comes from sensory experience, that means we cannot trust our theories and conceptions about what happens "beyond" our sensory apparatuses -- and thus all our knowledge of the 'external universe' is a mental fiction we've cooked up to organize our sensory experience.

Hi Hurkyl, nothing important is happening beyond your sensory experiences. If important parts of actuality were not perceptable by us, we'd have unexplained, ie magic phenomena all the time. I have not seen convincing evidence that my senses are not telling me everything I need to know to do physics, and make machines that work.

For example, as a being who instinctively rejects solipsism, you should therefore tend to reject any philosophical position that reduces to solipsism. For example, the position that all knowledge of the universe comes entirely from sensory experience.

Not logical in view of what I said above. Why is it so wrong to assume my senses are correct and not deceiving me (by Occam) ?

 

[Hurkyl]

Hi Hurkyl, nothing important is happening beyond your sensory experiences. If important parts of actuality were not perceptable by us, we'd have unexplained, ie magic phenomena all the time.

I could take this statement several ways, depending on just what you mean by "perceptable". Choose the response that best fits your intent.

. If something was causing magic phenomena, then it wouldn't be imperceptable.

. Lots of important things aren't perceptable, and once really were unexplained. But that hasn't prevented us from postulating theories about them.

I have not seen convincing evidence that my senses are not telling me everything I need to know to do physics, and make machines that work.

But the question is whether there is really a machine out there, or if the existence of the machine is a concept you invented to organize your sensory experience.


The modern age has given us wonderful examples of the latter -- there is no 'real' object called an icon, but it is certainly a good descriptor of my visual experiences with my computer. Similarly my television set doesn't contain people or the land of Hyrule, nor does my stereo contain a symphony orchestra.

And yet, my mind still organizes this data as it would anything 'real'. I can see and manipulate the icon, I can recognize 'people' in my television, and can learn the physics of Hyrule, I can pick out the different instruments in my 'stereo', and so forth.

And it also gives examples of the inverse hypothesis too -- it gives examples where we infer existence in a decidedly intellectual way, rather than directly with our senses. We have all sorts of wonderful tools for measuring things we couldn't otherwise see. And I assume you believe that I exist; how did you infer that?

Why is it so wrong to assume my senses are correct and not deceiving me by Occam.

Nobody said your senses are deceiving you. If you take the position that your senses are all that you can trust, then the conclusion is that your mind is deceiving you. Raw sensory data doesn't tell you that apple exists. You simply see an image. It is your mind that processes that image and declares that there is a real apple out there.

So, if you take the position that you can only trust your senses, that means you cannot trust your mental constructs. You can trust that you saw an image, but you cannot trust the inference that there is an apple out there.



Of course, most people when they say "sensory experience", they usually mean "sensory experience and all of the mental constructs that I like to use". And that's an incredibly important philosophical distinction.

 

[friend]

...If important parts of actuality were not perceptable by us, we'd have unexplained, ie magic phenomena all the time. I have not seen convincing evidence that my senses are not telling me everything I need to know to do physics...

Actually, the path integral formulation of QM requires us to account for an infinity of other possibilities that we do not observe/preceive. We seem to have to make an assumption about things we do not preceive in order to account for things we do see/observe. This is very interesting. Is reality (things we observe) really the result of presuming without evidence/observation an infinite number of other possiblities? Does reality consist of just our musings about other possibilities we will never observe? I'm not sure what to make of all this.

 

[Mentz114]

But the question is whether there is really a machine out there, or if the existence of the machine is a concept you invented to organize your sensory experience.

Suppose there is no machine out there, then where am I and why do I have senses ?
Am I the machine ? This looks like a conspiracy-theory philosophy.

If there's no objective reality, then surely I cannot exist either.

That clinches it for me.

The modern age has given us wonderful examples of the latter -- there is no 'real' object called an icon, but it is certainly a good descriptor of my visual experiences with my computer. Similarly my television set doesn't contain people or the land of Hyrule, nor does my stereo contain a symphony orchestra.

I disagree. The icon does exist, as a collection of coloured pixels on the screen. The music exists as ordered information stored on disc or whatever even when you're not playing it, and when it is playing the air vibrates as well, and your eardrums.

So, if you take the position that you can only trust your senses, that means you cannot trust your mental constructs. You can trust that you saw an image, but you cannot trust the inference that there is an apple out there.

I don't take that position. Yes I can and do trust my mental constructs. I can test the inference by eating the apple. It's never failed, it was an apple every time.

Hurkyl, respectfully, you do a good argument but it's tiring and I have better things to do. I don't want to be a last worder - so, I wonder if there's anything we can agree on?

Regards,
M

Friend:

Actually, the path integral formulation of QM requires us to account for an infinity of other possibilities that we do not observe/preceive. We seem to have to make an assumption about things we do not preceive in order to account for things we do see/observe.

There's nothing strange going here - it's because probability is involved.
Whenever we work out a probability we do so over a range of possible outcomes, only one of which we will see per throw ( so to speak). But things which won't happen must be included in the calculation.

 

[Hurkyl]

Hurkyl, respectfully, you do a good argument but it's tiring and I have better things to do. I don't want to be a last worder - so, I wonder if there's anything we can agree on?

Well, let's recall how this tangent even started! meopemuk, vanesch, and I were debating over what really exists -- meopemuk was taking the position that labelling some things (like spots on a scintillating screen) as being "directly observable", and thus real, whereas he labelled other things (like superposition) as not being "directly observable", and thus unreal.

And so, vanesch presented the usual derivation of solipsism from meopemuk's hypothesis that only what is "directly observable" is real -- vanesch demonstrated that the notion of a banana is a mental construct. The implication is that if meopemuk really insists on his hypothesis, then he must consider the banana unreal.

This is where you chimed in with your remark that there is an easy test to see if the banana is real.


But you and I agree that the banana is a mental construct -- that is the important point. If everyone agrees the banana is a mental construct, and also that the banana is real, then we see that the quality of being a mental construct does not render something unreal, and so meopemuk's argument loses most of its force.

 

[friend]

Friend:
There's nothing strange going here - it's because probability is involved.
Whenever we work out a probability we do so over a range of possible outcomes, only one of which we will see per throw ( so to speak). But things which won't happen must be included in the calculation.

This gets into the question as to whether mere possibilities can be actually real that we have to account for them in our theoretical models. In QM mere possibilities actually have a real effect in interference patterns, etc. We know that possibilities are a real consideration in the mind of those who are trying to decide what to do because they are uncertain as to what is real. But that nature itself seems to consider the possibilities begs the question to whether there really is some objective reality or whether it's all in our heads.

 

[Hurkyl]

But that nature itself seems to consider the possibilities begs the question to whether there really is some objective reality or whether it's all in our heads.

I don't see why.

 

[friend]

I don't see why.

Well, typically I would think that possibilities are by definition things that could happen but do not necessarily happen. The only other place that mere possibilities do have an effect is in our minds as we consider how to prepare for the most likely alternatives. If reality also seems to be "considering" all the possibilities, then that makes one wonder if reality isn't the result of a mind.

 

[Mentz114]

Posted by Friend.

The only other place that mere possibilities do have an effect is in our minds as we consider how to prepare for the most likely alternatives.

If you strike out the word 'other' I would agree with that. That would describe what happens when a wave function is used to calculate a probability.

If reality also seems to be "considering" all the possibilities, then that makes one wonder if reality isn't the result of a mind.

Good point. But surely probability is a psychological construct without a correlate in the real world ? There is no probability meter, we have to count events in order to estimate the values.

You've made a crucial distinction - does the universe 'consider' anything, or just happen ?

 

[friend]

Good point. But surely probability is a psychological construct without a correlate in the real world ? There is no probability meter, we have to count events in order to estimate the values.

You've made a crucial distinction - does the universe 'consider' anything, or just happen ?

This correspondence between the probability considerations in our head and the inteference of possibilities in nature may indicate that nature really does operated by the same logic that we use in our minds.

 

[Fra]

Hello Fredrik, I would like to restate my personal view that solipsism is ridiculous. How can any rational being contemplate for a moment the absurdity that they ( him, her, it) is 'dreaming' the universe. There is no reason whatever to think this.

Mmm "dreaming" wouldn't be my choice of wording in the context of physics as it usually associates to human specific things. And I don't suggest the universe doesn't exists only in the _human_ mind.

I rather think the opposite idea that there is an objective absolute reality is unfounded and overly speculative, whose purpose is to simplify the matter. But I think this simplification really produces inconsistencies.

In my view, utter rubbish. I hope that isn't considered too strong, but this is a physics forum, and someone is telling me that assuming an objective reality is a 'simplification' !
What inconsistencies are found from this assumption ?

I see an inconsistencies in the line of reasoning and line of logic, but this admittedly overlaps with philosophical questions. But then, foundations of science in general have roots in philosophy.

IMO, the parts of modern physics and QM I like the most is that science deals with we can observe and measure. Which effectively means we are dealing with information. We make observations and measurements of "black boxes". What is really inside this black box we can only guess from the information we have about it. I consider the information to be first instance of reality. The information I have is my relations to the black box.

The best I can do is to make the best possible bet. Unless there is a way to ever define the best objective bet, it's a bit naive to think that the unknown has a definite shape until we know the shape.

My induced reality is an expectation, and in generally expectations are conditional on the prior information at hand.

For example. In normal QM, the probability space itself is assume to be objective and known with certainty - this alone does not quite IMO comply to the basic idea that we should deal with information at hand, and that information is always induced. How does the induction of the probability space itself look like? Some analysis of this will result in a relational interpretation of reality.

If the probability space in the one-particle QM is uncertain, QFT comes to the rescue, but that is just doing the same thing over again. The question remains but applied to the fock space. Do we observe the fock space itself? It's clearly a sort of idealisation, that is admittedly excellent in many cases. But I think "excellent" just isn't good enough when you try to make some deeper connections with the fundamentals.

If you like to think there exists a objective reality, then I would like to see a fool proof formula that guarantees that any two arbitrary observers will always see the same reality when consuming different subsets of the information flow (note that two observers can't typically make the SAME observation), and explain how the actual comparasion takes place.

Also it is completely unrealistic to think that a finite observer can consume *and retain* all the information in the universe. I think the continuum hypothesis is another questionable fact.

Also, what exactly is a probability - in terms of something real measureable and retainable to a real observer? If it's not an idealisation, what is it?

The axioms of probability applied to reality is a clear idealisation - but a damn good one I agree. I think anyone who doesn't agree with that isn't looking close enough.

Considering the swampy ground we are all on, I don't see why it's obvious that there is an objective reality, and how this statement can be verified?

My opinion is rather not that objective reality will never be found, it's that util it actually IS found, it remains in the clouds and the current reality is based on this uncertainty. At least mine :)

/Fredrik

 

[Mentz114]

Friend:

This correspondence between the probability considerations in our head and the inteference of possibilities in nature may indicate that nature really does operated by the same logic that we use in our minds.

That's quite a leap to make, given the uncertain status of current theories. There is a debate about whether the ultimate reality is deterministic and we just don't interface completely with it. Check out the later works of Gerhard t'Hooft ( Nobel Laureate in Physics).

Which brings in Fra :

Also it is completely unrealistic to think that a finite observer can consume *and retain* all the information in the universe.

I agree. From there it's a short step the the 'incomplete information' hypotheseis of tHooft.

Also, what exactly is a probability - in terms of something real measureable and retainable to a real observer? If it's not an idealisation, what is it?

Yep. I would call it a psychological construct and I don't grant it physical existence outside our heads.

Considering the swampy ground we are all on, I don't see why it's obvious that there is an objective reality, ..

Does this not contradict your earlier statement ( first quote ) where you refer to the 'universe' ? Surely this is objective reality by another name ?

My opinion is rather not that objective reality will never be found, it's that until it actually IS found, it remains in the clouds and the current reality is based on this uncertainty. At least mine :)

Yep. Even the best physical theories are approximations, and always will be because, as you we agree, the Universe is a lot bigger and more complicated than we are.

 

[Fra]

Also, what exactly is a probability - in terms of something real measureable and retainable to a real observer? If it's not an idealisation, what is it?

Yep. I would call it a psychological construct and I don't grant it physical existence outside our heads.

So we agree that the probability formalism is sort of an idealisation. Then the question is, how come it is so successful? and how can we improve it?

In my opinion, probabilities are like optimal bets. And for reasons already mentioned, it is not straightforward to define an objective measure of "best", for several raasons.

But still, the basic problem is... we are stuck with incomplete information, and lack of solid references... so it seems we both need to build are references AND then use that references to place bets. How is this done, in the best way, to make sure we survive? If we can't figure out anthing better, we can also just try anything at will, and we die when in constructive disharmony with the environment.

I agree it's a bit violaition of terminology but I think of subjective probabilites as subjective odds, and I'm still working on my own understanding here but I definitely do think that these odds can be given a more solid interpretation (but not fundamentally objective). The fact that subjective observers can still coexists and communicate, lacking common univeral reference is a mystery but I think also the key to crack the nut.

Considering the swampy ground we are all on, I don't see why it's obvious that there is an objective reality, ..

Does this not contradict your earlier statement ( first quote ) where you refer to the 'universe' ? Surely this is objective reality by another name ?

I see your objection. What I am suggesting is that the reality is an emergent and fundamentally subjective thing, but "subjective" IMO does NOT refer just to human brain. The subjectivity concept here, to me, also includes for example the perception of things relative to say a particle. I picture that this particle relates and reacts to the environment and the relations are represented by the particles internal state relative to the environment. However, for an outside observer the particles internal state is seen as a superposition of emerged possibilities only.

If you picture a communication problem, I picture an observer, a particle, or any subsystem to act like a transciever. But the transciever itsel is "sefassembled" and keeps changing. Clearly the self-desctructive transcievers will not live on.

Yep. Even the best physical theories are approximations, and always will be because, as you we agree, the Universe is a lot bigger and more complicated than we are.

I agree with this. And this is exactly what leads my to my position. This is why the theories themselves are not fundamental. The more fundamental thing seems to be the method or physics that govern the evolution of the theories. I see it as a information problem, a learning problem, where we are crippled by insufficient and dynamic memory.

My personal idea is that each observer, can only resolve a certain complexity. The organisation of the memory is under constant equilibration. Coupled to this is new input and released output (interactions with the environment). I have some thinking where the expectations of the probabilities are in fact coded in the observers internal state. (with observer here I mean any system, a particle, or system of particle - not just a human). The "processing" is I pictured a sort of "stochastic process", coupled to unexpected input, and a bit random but still controlled emission/radiation or information. The dynamics needs to be worked out, but in principle I imagine the following improvement to the normal probability theory.

The observers internal state (represented but the state of it's microstructure), limits the size of the probability space (no continuum is allowed). A small particle can in my thinking simply not simultanesouly relate to the entire universe (I think this will have impacts on some renormalisation problems - there will be "natural" cutoffs, but they won't be hard cutoffs). Therefor the wavefunction of the entire universe, gets a very special meaning. The limit is imposed by the complexity of the observer itself. This is one reason for the "subjective reality" as I refer to it.

Next, there is the concept of uncertainty and change. The observers microstructure can be used to encode also patterns of change, and when stored in the same microstructure I think there willl exists a relation between the different effective probability spaces.

The probability space itself will in my thinking, sort of take on an observable character. But the probability space is then inherently subjective (== observer relative).

/Fredrik

 

[vanesch]

Well, typically I would think that possibilities are by definition things that could happen but do not necessarily happen.

Probabilities are lack of knowledge. What's the probability that Napoleon lost at Waterloo ? It's only when we didn't know that we could eventually assign it a probability ; that is: we could lump the event in a bigger bag of similar events which all were compatible with the knowledge we had, and then we could look at the ratio of "favorable outcomes" to the total number of events in the bag. So a probability is the combination of two things: the event at hand, and the bag of "equivalent" events, satisfying all the information we have about it. A probability is not a property of a single event, which happens one way or another. After the fact, there's no point in assigning probabilities to outcomes. Napoleon lost, with 100% certainty.

Now, lack of knowledge doesn't mean that somehow that knowledge would be possible to obtain, but we don't have it: this assumption is determinism. It is very well possible that in all of nature, as it is NOW, there is no way to tell what a future event will bring. But that future event will happen in one way or another, and there doesn't need to be a mechanism for that. Nature can just be a "big bag of events", where things "just happen" the way they happen, with no "machinery behind it". But it is not because we could, in 1814, only lump in Napoleon's future battle in a bag of similar (real or hypothetical) battles, and that we could only say, in that bag, that in about 40% of cases, he would loose, that there were realities to these other outcomes.

So it is not because of a probabilistic nature of the description of future events that the alternatives have to "exist" in some way. They only exist on paper because we had a bag of possibilities, starting from our current knowledge.

The reason for considering existing alternatives in quantum theory (the MWI view) is NOT inspired because of the probabilistic nature of its outcomes, it is because of the way the formalism arrives at these probabilities.

 

[Fra]

I agree to a certain extent with friends view.

You've made a crucial distinction - does the universe 'consider' anything, or just happen ?

It is equally valid to ask wether human brain really "consider" anything, or wether it just obeys the laws of physics and the "consider" is a purely subjective sensation, and that the human brain happens to be very complex but still operated by the same principles?

In a certain way, I think nature just happens, but "considerations" can probably be defined for an arbitrary system in the sense of internal equilibration and preservation of successful configurations in relation to an environment. This need not involve human brains.

The simplest possible case is a mictrostructure that serves as a storage devices. The state of the microstructure will either be self-preserving in the environment, or not. This will I think imply a selection. A stable system is one which sort of is in maximal agreement with the environment.

I think of the probabilities, implemented in the microstructures as combinations or distinguishable states. And all things are subject to change and revision. A certain environment will "select" stable systems. But there is also a feedback in the environment by any system.

My objection to the critics to the relational ideas is that this necessarily has to all take place at the human brain. I have no problem to in principle imagine this for a generic system. The "knowledge" of the environment an observer/system has, is completely represented by it's internal configuration - as this is "selected" during interaction with the environment which ultimately leads to maximum equilibration or "agreement".

Nature doesn't "think" - it just seems to take the shortest path, or most likely path - as judged from the subjective viewpoint - but I think this will as the complexity increase give the appearance of "intelligence". But it has IMO nothing to do with anything "human", divine or anything such. It's still fundamental reality.

/Fredrik

 

[Fra]

"Shortest path" in my thinking is essentially nothing but similar to occams razor or the principle of minimum speculation, and the measure "minimum" is subjective - two observers will generally first of all have difficult to even communicate their measures, but also to agree since they are conditional on different things. But this subjectiveness is I think exactly the reason for the non-trivial dynamics that result.

/Fredrik

 

[Mentz114]

Vanesch said:

After the fact, there's no point in assigning probabilities to outcomes. Napoleon lost, with 100% certainty.

If MWI is true, it is possible to define a probabilty measure to this outcome ! Ie the ratio of the number of universes he lost in, to the number he won in.

Seriously, there seems to be a general consensus in this thread that there's a limit to what we can understand.

Fredrik:

Nature doesn't "think" - it just seems to take the shortest path, or most likely path - as judged from the subjective viewpoint - but I think this will as the complexity increase give the appearance of "intelligence". But it has IMO nothing to do with anything "human", divine or anything such. It's still fundamental reality.

Sounds OK. But we could get side-tracked trying to define 'intelligence' ( a human centred concept).

 

[Fra]

Yep. I would call it a psychological construct and I don't grant it physical existence utside our heads.

I agree that probability as per the normal "probability theory" is an idealisation, and the main idealization(=the problem) lies IMO in two main points

1) There is no finite measurement that can determine a probability. The infinite measurement series with infinite data storage seems unrealistic.

2) The other quite serious problem is that the event space itself, is not easily deduced from observations. So not only is there an uncertainty in the probability (the state) but also an uncertainty of the probabiltiy space itself (the space of states).

Again considering a larger space of possibles "spaces of states" solves nothing to principle, it just make another iteration using the same logic and it could go on for ever unless we have another principle that prevents this. So point 2, seems o suggest that reality is somehow an infinite dimesional infinitely complex thing (or at least "infinite" to the extent of the entire universe). This seems to make it impossible to make models because the models would be infinitely complex and is thus nonsensial. But the stabilizing factor is that the bound of relational complexity prevents this. A given observer can I think only represent a finite amount of information amount, and we need frameworks that can handle this.

So in this sense, I think even the probability spaces we tihnk of can be observable, but the observational resolution is limited by the observer himself, unless the observer keeps growing and doesn't release relations/storage capacity. Because even thouhg we have witness our past, the memory is bound to dissipate. We can't retain all information we have ever consumed - it makes no sense. So another "decision" on what to discard needs to be made (minimum loss).

To me the challange is to understand how effective probability spaces and effectively stable structure are emergent in this description, and also how the effective dynamics is emergent from this picture. I am sufficiently convinced it can be done to try it, but it seems hard.

/Fredrik

 

[Hurkyl]

For example. In normal QM, the probability space itself is assume to be objective and known with certainty - this alone does not quite IMO comply to the basic idea that we should deal with information at hand, and that information is always induced.

The state space is algebraically derivable from the relationships between different kinds of measurements. This is one point of the C*-algebra formalism; once we write down the measurement algebra as a C*-algebra, we can select a unitary representation, which gives us a Hilbert space of states. Or, we can study representation theory so as to catalog all possible unitary representations. And this approach covers all cases -- by the GNS theorem, any state can be represented by a vector in some unitary representation of our C*-algebra.

If you like to think there exists a objective reality, then I would like to see a fool proof formula that guarantees that any two arbitrary observers will always see the same reality when consuming different subsets of the information flow (note that two observers can't typically make the SAME observation), and explain how the actual comparasion takes place.

We're doing science, not formal logic! A fool proof formula is an unreasonable demand; what we do have is empirical evidence. Not only the direct kind, but it is a prediction of quantum mechanics, which also has mounds of experimental evidence.

Also, what exactly is a probability - in terms of something real measureable and retainable to a real observer?

If, when repeating an experiment many times, the proportion of times that a given outcome is seen converges almost surely to a particular ratio, then that ratio is the probability of that outcome in that experiment.

 

[f95toli]

We need to be carefull when we talk about "probabilities" here. There is a significant difference between classical probability theory and the probabilitstic interpretation of QM, they are not mathematically equivalent (which has been known for a long time, von Neumann even proved it around 1930). The reason is essentially that there are non-commuting operators which is why we use psedudo-distributions in QM such as the Wigner distribution; the latter is the closest thing you can get to a classical distribution but has some very "non-classical" properties, it can e.g. be negative.
Hence, if we assume that QM is a more "fundamental" theory than classical physics, ordinary probability theory can't be used.

 

[vanesch]

Vanesch said:
If MWI is true, it is possible to define a probabilty measure to this outcome ! Ie the ratio of the number of universes he lost in, to the number he won in.

Or better, the ratio of the squared sum of hilbert norms of the universes he won in. There's no a priori need to introduce a uniform probability distribution over "universes" ; or, in other words, there's no need to assign equal probabilities to universes with different hilbert norm.