"Against" Realism

setAI

ehem:

using quantum computation to solve NP complete problems:

http://www.arxiv.org/abs/quant-ph/9912100
http://www.arxiv.org/abs/quant-ph/9801041
http://www.arxiv.org/abs/quant-ph/0508177

RandallB

Found it! --- NP stands for Nondeterministic Polynomial Time ...
NP-completeness difficult stuff.
But for this line of reasoning to confirm that QM and the MW interpretation of it (That MWI is an interpretation of QM may just be my opinion) is correct don’t we have to assume that the Classical view must be deterministic.
Has it been shown that Classical cannot be Nondeterministic, or is that something that is just assumed?

AnssiH

A bit off-topic but I have to make sure, don't the extra dimensions in string theory just refer to the fact that the strings would have to move/vibrate in more than 3 dimensions? (Which to me sounds like the dimensions could be just as well thought of as some completely different property than spatial dimensions, like an ordinary string could vibrate spatially and by "colour", etc...)

Yeah, definitely concepts like "size" need to be viewed critically here, but not only that, also we must view critically any sort of concept of particles. And the whole concept of "identity". Not only when we imagine identity to such thing as "photon", but even if we think about the universe as if it's one big continuous "fluid" where particles exists as stable standing waves (or whatever), we have still tacked identity to this "fluid". It may seem very obvious that something must have an identity in objective reality, but it must be noted that this intuitive view has bitten ourselves in the *** so many times on so many issues, that I'm becoming convinced that "identity" is a non-sensical concept as far as metaphysics is concerned. For example, it is completely arbitrary and without any empirical evidence, to assume that locations of space or spacetime have any identity to them. It is odd that physicists ever expected it to be so.

And having said that, even though we "kind of" understand the above, we still naturally imagine QM-situations in terms of things that have identity to themselves (instead of being stable patterns onto which one can arbitrarily tack identity, like onto a "standing wave" or a "shadow"). The fact that we consistently find such behaviour as we could expect a quantum mechanical electron to cause, does not mean there must "really" be a metaphysical electron. It just means there is some process causing this behaviour. Just like the fact that we consistently find our shadow to follow us, doesn't mean there actually is such an object with identity as a "shadow".

As a more concrete point in case, we can talk about how a photon, if energetic enough, can turn into an electron, or more vaguely, how energy can turn into matter (or vice versa), but is it not much more proper to understand that all these "fundamental particles" are not in fact fundamental at all. It is not like the energy as one fundamental thing just magically turns into some other fundamental thing (that has "fundamental inertia"). It's more proper to understand these particles as emergent features of whatever causes them, and their behaviour is also, after all is said and done, governed by their underlying causes (and I think one important question is going to be "what is charge metaphysically?").

Well, the problem with calling something an "illusion" is that it means one basically just refuses to give any cause to some phenomenon. Sure we should expect motion to be something different from what it readily seems, but even more so we should expect "time" to be something different than what it seems, because it is a concept that is derived from "motion". I get a rash from the interpretation that the flow of time is just "an illusion in a static spacetime", because that is the same as saying "reality is static and conscious experience is magic". I understand the need for the word in some cases but it really is very very dangerous word that ought to be avoided :)

That being said, what is very important to understand is that as long as one talks about the concept of spacetime, he must also remember that nothing moves in spacetime. We are so used to the idea of "motion" that otherwise astute people often confuse the concepts of "spacetime" and "motion" together in incoherent ways. For example when they talk about how a photon "moves back and forth" in spacetime.

It must be understood that if spacetime is what is used to describe motion, you cannot then assert that something is in fact moving inside spacetime, for you would need a new time dimension to describe that motion. The matter of the fact is that metaphysical spacetime and metaphysical motion are mutually exclusive concepts. We can only have one or another. And to assert that only our "consciousness" moves in spacetime is also an assertion about motion "within" spacetime, regardless of if you call it an "illusion" or not.

This is not just a minor mathematical problem that can be dismissed, but it in fact highlights very concretely the problems of such assumptions as the metaphysical existence of spacetime (strictly speaking, the observable predictions of relativity don't require spacetime to exist because relativity of simultaneity cannot be directly observed). I don't think anyone has been able to actually make any explanation about how the "illusion of flow of time" could be achieved if nothing is in motion in reality, but everybody are very willing to dismiss the whole problem as meaningless because you really don't bump into it until you get to the philosophy of the mind, which may seem unrelated to physics, but it is not.

(Let it be said that I understand our subjective experience is very different from its immediate "causes" in objective reality, which is why I say it is an emergent feature of its parts)

This is very interesting. Thanks.

-Anssi

AnssiH

Does anyone have more information about this?

-Anssi

selfAdjoint

Try here. A good general description of various double slit experiments including the buckyball one, and does elementary calculations using DeBroglie wave length.

kvantti

Yes, the extra dimensions first came up because they were needed to represent the one-dimensional strings. But the six extra dimensions can also thought to be the "landscape" in which the different universes of the multiverse exist:

http://www.world-science.net/exclusi...tiversefrm.htm

Yeah its funny, we can only observe the properties particles exhibit (mass, spin, charge etc.) and make models of the interactions and relations of those properties. So we don't acutally observe the particles, just their behaviour.
As I quoted Lee Smolin on the other forum, "a point in spacetime is not defined by its location -- its defined only by what physically happens at it." This is just fancy way of saying that we can't assing any specific "location" to spacetime itself; only to events in spacetime.

Are you referring to some hidden variable theory?

Particles are quantas of energy according to quantum field theory. Why this explenation isn't satisfactory to you? When a particle decays to other particles, its just different field interactions changing the energy (of the quantum field) into another form. In the case of a photon, the electromagnetic interaction "splits" the quanta of the neutral spin 1 field into two quantas of the charged spin ½ field if the conditions are appropriate for this kind of interaction to happen. According to QED atleast. Charge is the probability for the charged spin ½ field (or the electron field) to interact with the neutral spin 1 field (the em-field).

Conscious experience isn't magic; the quantum state of a persons consciousness just differs at every area of spacetime, giving illusion of the "flow of time". The entropy of the brain increases when "moving forward" in time, or in other words: the quantum state of the consciousness is more disordered in the "future" areas of spacetime. And consciousnes doesn't "move" within spacetime (as you suggested before), but instead consciousness exists at every area of spacetime where the persons brain exist; just that in different areas of spacetime, the quantum states of the consciousness differ from each other.

Yes. Nothing moves in spacetime. Motion can be viewed completely as an illusion: when you observe some object moving, you really just remember the "past" position of the object differing from the "present" position of the object. When this happens continuously, you see the object "moving".

Yup, nothing moves inside a static spacetime continuum, not even consciousness.

It has been explained. I just never realized your point until now... and now I feel stupid.

AnssiH

Yeah, exactly

Nah, I'm not very fond of hidden variable theories, at least not when they still assume particles are at all times entities with spatial stability (i.e. "like tiny balls").

I'm just saying that we shouldn't look at any observed stable pattern as more than just that; a stable pattern. Any stable pattern, like a shadow of a building or a standing wave inside a room, could be understood as a stationary entity because there is a sense of stability to their existence, but physically we can't say they are entities that are just "sitting there", but instead there are stable patterns whose stability is a result of an active process.

And such appears to be the case for matter as well. Matter is not something that is just "sitting there". There is an active process that keeps what we call an atom (or a buckyball molecule) spatially stable.

It is possible that the relative motion between such spatially stable patterns is mechanically explainable by some model that also explains just why is there such spatial stability, and such models are likely to make very different assumptions about what exists fundamentally (as compared to the standard model), and may give QM phenomena a completely deterministic footing. E.g. the locations where we observe electrons (or phenomena associated to electrons) are not necessarily required to be such places where an entity called "electron" would have had to move in any newtonian sense at all, and this assertion is, I believe, completely valid option for a realist.

So you could say my belief is that we just haven't figured out the proper model yet, but that we are capable of doing so by letting go certain particularly sticky assumptions about reality.

When you say "when this happens continuously", are you not invoking an idea of motion? (For there is no sense of something happening continously without pointing out continuous "moments" from spacetime)

Obviously it is very understandable idea that the "state of the brain is different at every area of spacetime" and it is only expressing the past at any particular "moment" we choose to point at in the spacetime, but even then, we cannot really say what is it - metaphysically - that is doing this choosing and pointing. Why do we ever feel like there is a "now" moment?

I believe the most popular way to understand spacetime is to just consider the future and the past to exist at all times (so to give a simple ontology for the relativity of simultaneity), and in such case all the states of the brain exist "all the time", and metaphysically there is no such thing as "now moment" at all except for our subjective experience. This is why Einstein said "time is just an illusion" etc...

But this view fails completely to account for what is it physically, that causes the "now moment" to exist in subjective experience. It must be something in the physical world causing this, yes?

For these reasons, I must consider the possibility that it really is "motion" instead of "time" that exists metaphysically. It is often stated that "for there to be motion there needs to exist time", but this is immediately invalid argument, because the semantical concept of "time" is what is derived from the fact that we observe motion. If things really are in motion and there really exists only present (not the past and the future), it would readily explain why the sense of "flow of time" exists in our subjective experiences.

Note that even if you consider it to be "time pointer" that "flows" in spacetime to give us the experience of "present moment", it is not meaningful at all to give any "speed" to this pointer. Regardless of its speed (or direction) through the static spacetime, the subjective experience "at the pointer" would be the same (for our sense of time depends on how reality is expressed physically in the brain). It is probably this fact that gives people confidence to the idea that time does not flow at all, but we should not forget that we would still need that "pointer" to exist, otherwise we have not given any explanation about why there is any subjective experience at all, and to me this just shows how the idea of time as a dimension is a non-sensical one and doesn't fit very well to ontological reality, even if it's a handy tool.

Consider the difference between "describing the motion of a physical system in an instantaneous manner, such as the brain in spacetime, and really experiencing the motion of a physical system; such as having a subjective experience. Consider this thought experiment:

If you take a snapshot copy of a physical brain and freeze all its motion (by some magic), does it still have a conscious experience of everything being still? No, for this would require thoughts (about stillness) to exist above physical motion.

If you wait for 10 minutes and take a snapshot of the state of the original brain, and modify the copy-brain manually into the same state, you have essentially inserted all the memories from that past 10 minutes into the brain, and if you now set the copy into motion, it surely would claim to have had a subjective experience of the past 10 minutes as if time was flowing smoothly.

But can conscious experience exist if time moves ahead in discreet steps? What if you do NOT set the brain into motion, but instead just project a new state onto it every 10 minutes? Would it still have a conscious experience of a smooth flow of time? What if you project a new state onto it once every year? Could you imagine the possibility, that while reading this, your experience right now of "this moment" is not real but is instead one that is "going to be updated into your brain a year from now"?

I think the more you think about these issues, the more inclined you become to consider the possibility that it is in fact motion that really exists, instead of a static spacetime block.

-Anssi

kvantti

That is possible.

Well, spacetime is a continuum, so even if there is no motion, there is continuity. We observe this continuity as motion.

Because we experience the increase of entropy in the brain as "flow of time" and "now" is just an illusion of this process. Try to remember what you did 0,1 seconds ago. Confusing?

You don't need to derive "time" from the concept of motion. You can just say that "time is a thing that enables the state of a system to change". But then again, a state of a system cannot change without motion.

I have thought the same from the perspective of the multiverse. In the multiverse, the quantum states of the universes actually are "snapshots" from the point of view of the observer. Every possible snapshot exists and these snapshots are connected with each other with the laws of nature. That is, when you have quantum states A and D, you can't get from A -> D without going thru B and C first. Same with the quantum states of the brains. The quantum states are seperated by Planck times (the multiverse is a discrete system). This accounts for "continous" conscious experience aswel.

So, again, I see no problem from the perspective I see things.

AnssiH

The question is how is it that we experience an increase of entropy as flow of time? Perhaps this has more to do with relativity and philosophy than with QM, but nevertheless, the important point to pick up is that it is not really a satisfying explanation to say reality is a static spacetime block where nothing moves (where the whole concept of "now" is non-sensical), and that it is the continuity that we observe as motion. Of course I understand how this continuity describes motion, but that is not the same as really producing an experience of motion.

For reality to produce an conscious experience of motion, something in physical reality must be different "now" from "a moment ago" (even if these are misleading concepts).

Consider your own subjective experience. You have an experience that "now" is different from "yesterday", and surely your subjective experience is caused by something that exists in reality? Something "real" is causing your experience, right? Surely then something in reality is in different state "now" than it was "yesterday". Even if you consider yesterday still exists in spacetime, you need that pointer to experience the "now". It is not possible that in reality absolutely NOTHING is in motion or changes, because that would require your subjective experience to be something that is not part of reality.

So what I'm saying is that if you believe there is a spacetime, you have to commit to this idea absolutely before it is a valid ontological interpretation, and in that case you lose all sense of motion from reality, UNLESS you posit there is also pointer that moves in spacetime (so to make difference between today and yesterday for a given subjective experience), which then again is in conflict with the idea that there is no motion, but only a spacetime.

And to postulate that spacetime is static but pointer is in motion is not very elegant; why would there exist both, metaphysical motion and spacetime?

Yeah, that's the problem. Sure, it is not readily given that time is derived from motion, but what is given is that we can only expect to have either real time-dimension or real motion, but not both.

If we choose it is time dimension that exist, then the problem is, like you said, the state of the system cannot really change without motion. Of course the only system we really know to exist "in motion" is "subjective experience". Can it be different from one moment to the next if there is no motion?

But if we choose it is motion that exists, it becomes little bit clearer. We stroll around the earth and observe motion. We may notice that each time a pendulum swings, our heart beats exactly 4 times, or a rotating wheel does exactly 5 revolutions. So we assume the "time" it takes for the pendulum to swing is constant (at least as compared to all the other physical systems around us).

So just now, by comparing the motion of different systems we have built a concept of time, and we might say "I'll run around the building in 50 pendulum swings". This doesn't mean there had to be "time dimension" underneath it all to make this running possible, for we could expect "motion" to be something that "just exists" in a fundamental sense. (Albeit it is still non-sensical to talk about the "speed" of this fundamental motion)

Does there exist a metaphysical "now" moment in MWI, or is reality still a set of static spacetime blocks?
If its latter, you still need something to change when subjective experience does.

kvantti

I can't help but repeating myself: it's an illusion. The way we experience "the flow of time" is the only way we can experience it. For example, when your reading this text the entropy of your brain increases when it records the information you're reading. Because of the information your brain has recorded you have more memories of events, like reading this text. This gaining of new memories increases the entropy of your brains and gives an illusion of "flow of time". The fact that we experience "a present moment" is due to the fact that we can't remember the future; your brains haven't yet recorded future events. When the future events are recorded, you experience them as being in the "present" and after that, when your brains have recorded more events, in the "past".

Something is different between "a moment ago" and "now" (from the perspective of subjective experience): the amount of information stored in your brains.

You don't need a pointer. The "now" is at every point of spacetime. The "nows" of your brains (and thus your consciousness) just differ from each other.

Yes, it can. You just have to keep in mind that "subjective experience" is determined by the amount of information you have acces to and while the amount of information in your brains increases, you experience time "flowing".

The problem with only three dimensions is that the state of a three dimensional space can't change unless there is time; you would have only static 3D space. So, if you wan't to describe events in three dimensional space you need to use time, and the time component can be described as an extra dimension, giving total of four spacetime dimensions.

Nope, there is no "now" in the MWI. You could say that "reality is a static multispacetime block". This "multispacetime block" is the multiverse. This is a simplified way to see it and it doesn't describe all the properties of the multiverse.

AnssiH

Hmmm, we aren't making much progress... Let it be said, that I used to think of flow of time as an illusion much like you describe. I understand why people think this way. But some philosophy reveals that this view is not unproblematic at all. You must dig way deeper to really see the problems, and in particular form strong understanding about how we comprehend anything with semantical concepts and how we build those concepts in a mechanical sense.

So, let's see if we can clarify this a little bit from another angle. I'll try to proceed with careful steps. It doesn't matter if we disagree or not after this.

This is certain; We cannot claim "time must exist fundamentally, because otherwise there would not be motion".

We cannot claim this, because just like we can assert that "time" is what exists fundamentally (without cause), we can assert that "motion" is what exists fundamentally. The choice between is - to an extent - arbitrary. Just because our comprehension is based on concepts and classifications of reality, and because we need to use the semantical concept of "time" to express motion, does not mean reality works with semantical concepts also. We are forced to invoke the semantical idea of "time" to talk about "motion", but motion can still "really exist" without any fundamental entity like "time" dictating this change.

Otherwise we could also say that "numbers" or "vectors" must exist fundamentally, claiming that without numbers and vectors there could not exist "clusters of bananas" or "velocity addition", etc... Just that we need some concept to express something in reality doesn't make it of fundamental existence. (Note that any conscious experience is also a case of expression of reality, caused by the brain)

So we can establish that the choice between "time" and "motion" is somewhat arbitrary. Still agree?


Another thing that is almost certain is that "fundamental time" and "fundamental motion" are mutually exclusive; both cannot be fundamental.

I say "almost certain" because it is conceivable to imagine that time exists as a static dimension and it is read by a pointer/worldline that moves. It's conceivable but not very elegant, for various reasons.

If anything is allowed with motion, we could just as well expect it is the physical things, on which our subjective experience is based, that are in motion. If nothing is allowed with motion, this would include our subjective experience which certainly is "something". And more importantly, once we have described the structure of spacetime, our semantical concept of "motion" (of worldline) becomes meaningless as an explanation to the change in the subjective experience. The subjective experience could not detect which way this "motion of worldline" happens, because the worldline is not a homunculus entity (it is not "fundamental consciousness"). This well-known argument about the static existence of spacetime actually puts fair amount of mud on the idea that "time" is a prerequisite of motion.

So, to get any further with the issue, we must assume that "time" and "motion" cannot BOTH exist as fundamentals. Still agree?

At this point, people who have chosen the path of "fundamental time", are forced to resort to the claim that the flow of time in subjective experience is "an illusion". This they justify with the comfortable fact that reality is just an expression of the past in the brain at any given moment. But this claim does not so much explain anything as it ignores the problem. None of the states of the brain would be more "real" than any other state, yet in subjective experience one is, at a time, more real than others. Clearly this needs more words.

And here we get to the hard parts. It is difficult to explain it all briefly, but I'll try.

The issue is not so much about "how the expression of reality exists at any given moment", but to explain how is it that within subjective experience there is motion, if "nothing is allowed with motion". It is one thing to imagine the whole spacetime history of a brain, and another to understand a process of conscious experience occurring to that construction. When you have assumed that it is time that exists fundamentally, ontological descriptions of reality tend to get very muddy very quickly.

Considering the philosophy of the mind, it quickly becomes clear that it's better to understand consciousness in the sense that we are NOT conscious of "successive moments", but rather we are merely conscious of the "change" that happens. This becomes concrete in many cases. Any sensory stimulation must have a spatial AND temporal aspect to it before you can be conscious of it (the patterns in the neurons must actually change). The semantical concepts our brain builds are always juxtapositions of each others (They make sense without "fundamental meaning" only because there are "differences" to them; something is what something else is not). In many many ways, our subjective experience is about change, and for this reason it is absolutely impossible to really comprehend anything without invoking an idea of motion or change. You simply will not be able to describe subjective experience without invoking some idea of motion or change at some point. We are so used to change, that sometimes it takes considerable effort to just notice this conflict.

To say "...the entropy of your brain increases..." is invoking an idea of motion. To say "...the fact that we experience 'a present moment' is due to the fact that we can't remember the future" is invoking an idea of motion; it suggests one to imagine a metaphysical "moment" that is "real" at one particular "instant" but not at another instant.

At the face of it this all may seem like an indication that "time" could really be what exists fundamentally, just beyond our comprehension, but as you get closer and closer to understanding "static time" in an absolute sense (as in there is no motion anywhere at all), it merely clarifies the fundamental aspect of the problem of change within our subjective experience.

Subjective experience is caused by reality. Agree? If nothing changes in reality, nothing is causing change in subjective experience. This looks like a dead end.

Although, like I said, the correct choice between "fundamental time" and "fundamental motion" is not given. It could still be either one. But what is given is that if you build your model of reality around fundamental motion, things get very much clearer (Albeit any ideas about the "absolute speed" of that motion are still non-sensical).

And with current empirical knowledge, you can choose to do that. Like I said, it actually is NOT at odds with relativity, because relativity does not allow for direct observation of relativity of simultaneity. You can understand all the observable time effects as different relative speeds of the physical motion/processes (in different environments), although the more "descriptive" way to express this mathematically is probably much less elegant than Lorentz-transformation (Mathematical elegance is different from ontological elegance).

We still need to use the concept of time to "comprehend" motion semantically (to express it), but we must understand that it really is just a semantical concept, and reality does not work on semantical concepts. It just works under some fundamentals, of which we try to make sense by building semantical models of reality, that are always incorrect to some extent, because they are merely an expression of the real thing. Map is not the territory.

I hope that was not too confusing. It really is difficult to be brief with such a massive subject as this.

kvantti

Yeah and I think I know why: you see things from a Newtonian point of view while I see things from the point of view of relativity. This conversation would go on and on without progress, because we just see things too differently. You see problems where I don't and vice versa.

I'm too tired to answer your whole post at the moment, I had three hours of sleep last night, and now I'm off to take a nap. Be back later etc.

AnssiH

Well I guess then we are just going to have to disagree.

Although, if you find the reality of static spacetime likely, why do you consider MWI to be simpler than this:

http://www.physicsforums.com/showthread.php?t=130623

Isn't it simpler to just assume that light (and everything) exists in spacetime in static sense just the way we find it to exist, instead of imagining a model of many worlds that would produce the same behaviour? After all, you have to think about the trajectory of light as "single object" in spacetime, then why couldn't it exist fundamentally just the way we find it?

kvantti

That is basically same as saying "we don't know how things work, they just are the way they are". The static spacetime approach doesn't explain why we observe the world as indeterministic even though it should be deterministic from the point of view of a static spacetime.
The MWI is the simplest physical interpretation for explaining quantum mechanics. This is a fact. People don't see this because the change in paradigm is so huge, so incomprehensible, that they reject it straight handed. But the fact is that the MWI is a consequence of a very simple postulate: the mathematical formulation of QM describe the behaviour of a quantum mechanical system; not just probabilities of different behaviours (as in Copenhagean). From this postulate emerges the whole idea of the multiverse.

I like to think that the mathematical formulation of classical mechanics describe the way macroscopic systems behave. Same with quantum mechanics.

AnssiH

Well it's true that spacetime interpretation doesn't say anything about the indeterminism by itself (although it probably would be quite trivial to make all kinds of assertions about it that would be basically impossible to confirm), but as of the "we don't know how things work, they just are the way they are", that is the case with all models. Especially when we talk about ontological interpretations, they are literally just cases of selecting different "things" to exist fundamentally (like multiverse). This is what I critizised earlier in this thread and I certainly don't see reason to commit to any particular selection of "fundamentals".

Well I personally don't have any problems in making paradigm shifts, since I am convinced that any worldview that we are capable of is essentially a circle of beliefs; not fundamentally attached to any sorts of truths. And for the same reason I think it is just wrong to encourage anyone to commit to any interpretation, and whatever interpretation is the "simplest" really depends on what sorts of problems you are tackling (and to an extent how familiar you are with some interpretation).

For example, earlier you mentioned that Deutsch challenges doubters by asking "where else do the calculations happen if not in other worlds since there are too many degrees of freedoms for one universe" (or something like that). This particular idea about how many degrees of freedom there are is assuming that a photon experiences one particular moment in a newtonian way (in which moment there are this or that many degrees of freedom). But it is not very difficult to understand the same system as if the photons bouncing "back and forth" in spacetime are affected by the "future" measurement of each others. The degrees of freedom all exist in single universe now, but it doesn't really make sense to say that the calculations happen in many worlds anymore. At any rate, the observable behaviour of the system is the same in either cases. This is true for any model; you can always build arbitrary number of mechanisms to explain any behaviour.

I believe this postulate would hold true for spacetime interpretation too...(?) The critical difference seems to be different terminology and different concepts to refer to time, and that with spacetime interpretation the idea about information transfer is different from "just particles"; it is rather a connection over all space in one universe instead of series of lines in many universes. Very similar, but so very different... :I

kvantti

No, it isn't the case with all models. Some interpretations explain the physical behaviour behind quantum mechanical phenomenon, others don't.

The multiverse is a direct consequence of the postulate, not some tought up concept.

I'm not encouraging anyone, I'm stating a fact. The Occams razor decides which interpretation is the simplest.

It doesn't matter which quantum effects the quantum computer uses to calculate, photons or molecules, but it matters that a qubit can be in a superposition of state, ie. in the states |+1> and |-1> simultaenously. Either you interpret that qubits are in these states simultaenously in one universe or that they exit in only one state in one universe and in the other state in another universe, and that these universes superpose if the qubits are in decoherent state.

Nope, the postulate is specific to MWI only:

http://en.wikipedia.org/wiki/Many-wo...tation#Outline

AnssiH

It is the case with all human models about anything at all, not just QM interpretations. This is just elementary philosophy. A model is a set of "fundamentals"; something that is not caused but "just is" (and from which all the observable phenomena spring).

In the case of MWI, it doesn't explain how multiverse exists, it doesn't explain how photons exist, it doesn't explain why the universes affect each others the way they do. It says "they just do", which is what any other model says about their fundamentals.

Any explanation of any physical behaviour is at the bottom of it all an assumed set of fundamentals that are "not caused".

You can argue that some models explain more with simpler elements (note the history of the models of an atom, or the evolution from geocentric model of universe to heliocentrism to current ideas). Can we say that MWI explains more with less? How do we even measure that its fundamentals are simpler than those of other models? The meaning of "simplicity" is not unambiguous here.

And also, how can we make sure that MWI doesn't break reality into too small pieces? After all, it posits all this happens by things that we cannot directly observe, and these things also have functions that could also be broken into smaller and smaller elements. How do we judge where should the peeling end?

Also, any human idea is directly based on other ideas and vice versa, in a self-supporting fashion. This is why human understanding is "semantical" and capable of novel predictions. And this is also why any idea makes sense only if you have assumed a certain set of "truths". How can we measure that the particular set of assumptions - that make MWI possible - are true?

These are all important questions when we talk about ontology, and MWI is ontology more than "just physics".

And these above issues need to be understood at much deeper level than most people do. Most people do not appreciate what it means to claim something is "true". Even "true" and "false" are metaphysically non-sensical concepts, and I don't mean this in a naive way of "we cannot really know if this or that is true", but I mean the very method of classification of reality into "fundamental elements" is the only method with which an animal can make any predictions about its environment, but it is also always an arbitrary form of expressing reality. In many concrete ways that are not readily appreciated, just looking at an apple is a case of believing there is an apple there. Because you can only be conscious of your worldview, not the reality directly.

So, I just see it happening all the time that people assert something they believe in as "undeniable truth", without understanding it is undeniable only in so far that some other assumptions in their particular worldview are true. If the existence of god has been an undeniable truth your whole life, your proof of this is that world exists (for it could not without "the creator"). And it is fairly easy to see the circular fashion of the logic behind intelligent design, but all models are fundamentally like that. This is a restriction of semantical understanding.

Even when the postulate is that the formulation describes directly a QM system, you still have to interpret what are the fundamental elements whose behaviour the formulation describes. This is nothing more than an interpretation. In spacetime interpretation we could also say that the formulation "describes directly what really happens". Now, I hear you when you say "it is not the probabilities that the formulation describes", and I tend to agree; copenhagen says too much and is probably incorrect. But MWI doesn't make anything fundamentally differently; it just posits "these are the things that exist" and draws a relationship between those things and the mathematical formulation about the observable effects.

So I don't know how you can claim MWI is not a thought up concept. It includes many many many assumptions that it holds true, before it can get to the final conclusion about many worlds. I know this automatically because human thinking is like that. This should not be too difficult to see.

(And this is why it is immediately erroneous to claim that a working quantum computer proves MWI. Just because you understand its behaviour by the assumptions made by MWI doesn't mean it cannot work in any different fashion)

This is what I'm talking about. Little bit more philosophy into the picture please. Just what do you think are facts? And do you understand that Occam's razor can also be used by anyone just the way they please? I could say that by the Occam's Razor, I wish to cut out the many worlds and just have the one we can actually remember. And when you ask me to explain QM behaviour in single world, I can just claim that the nature of light, and everything, "just fundamentally exists" in advanced & retarded sense, until there exists a thermodynamically irreversible event. All I've done is selected another arbitrary set of fundamentals and no natural observer can demonstrate the difference.

...or you look at the nature of light and matter completely differently; i.e. understand their existence with different underlying concepts. (Note; this is not a hidden variable idea. This says more about reality than some hidden variable theory. It mostly says a photon is a particle as much as a rainbow is an object)

In the end I just want to stress that I am not refuting MWI as invalid, but I am very very worried about people getting emotionally attached to different sorts of models too much, and not really understanding why any model is necessarily just an arbitrary set of fundamentals, and cannot directly be shown true by the very nature that these models exist. For as long as you do not appreciate this fact, you do not abide to scientific philosophy, but to religious philosophy. You can never truly "unlearn" whatever set of assumptions holds your worldview together until you understand just how does your worldview exist. And if you can't do that, your thinking becomes rigid (and breeds reptiles of the mind, as Blake puts it ;)