Ken G said:
Dmitry67 said:
Fredrik said:
I think this is more or less exactly what I tried to say but was somewhat sloppy/inarticulate: When I talk of "branches" I refer to the sequence of labels j,j',j'',\ldots which are associated with (perceived/not perceived) measurement results. And when I talk about assigning "reality" to one of the branches I only talk about the sequence of measurement results, not necessarily the corresponding parts of the mixed state operator. As such the state operator and the laws that govern its (unitary) evolution is simply a calculational tool to obtain possible outcomes of a sequence of measurements (branches) and their associated probabilities p_jp_{j'}p_{j''}\ldots.
To be honest I think the issue is whether we can accept the probabilistic nature of QM: How can a theory describe reality and yet not predict (with arbitrary accuracy for a single experiment) what we observe. If you say that what we observe is what we mean by reality, then I don't think such a theory can ever be constructed. The options are to say (CI:) QM does not describe reality but we may use part of this construction to probabilistically describe reality, or (MWI:) QM describes reality but what we perceive is only a (probabilistically selected) part of reality.
I can't respond to this since the details don't seem to make sense. Let me make a different scenario:Ken G said:
And, to the best of my knowledge, there hasn't been much progress in trying to find such a physical law. CI might become interesting again if progress is made.
Really? I got the impression you cared very, very strongly about the old "reality is definite" mode of thought, because you keep saying things like
Assuming such a classification even makes sense, it falls in the same category that one would place its negation.
What if I see tails? Is that a nonunitary experience?
Ah! The state of the coin being pure is thermodynamically impossible! MWI most certainly does not predict that. In sufficiently "small" systems, though, we can and do see the superpositions. But there isn't much interest to that, because for sufficiently "small" systems, which pure states one calls a superposition is quite arbitrary.
You remember my game with the indefinite universe? I mentioned that the mathematics of the setup are identical to a different scenario with two universes and two experimenters. Worlds are a useful way to analyze a mixture, in the same way that Euclidean geometry is a good way to analyze vector spaces. (and that vector spaces are a good way to analyze Euclidean geometry!) Call it the theoreticians habit of actually naming the concepts they study, and sometimes naming after whatever other idea gave them inspiration.
Only in the bird's eye view. (and even then only in an ignorance interpretation of probabilities)Ken G said:
Yes, that's right, and what I am talking about is the frog's eye, because I'm distinguishing the moment before you look at the coin, and the moment after. Those are what is different from the frog's eye, they are not different from the bird's eye, and that's the whole problem when MWI gets explained from the bird's eye as you did above-- it misses our experience as frogs. As Fra made me see, what's different is the surprise. That's also why MWI is good rationalism and poor empiricism (and CI is good empiricism and poor rationalism), this is exactly the structural difference in those approaches.Hurkyl said:
That is just exactly what empiricism demands, yes-- the cosmological principle is a rationalist principle when taken as an ontology (it is an empiricist principle when you say "as far as we have seen so far, the universe behaves like this, and we have no reason to expect otherwise at the moment"). Note empiricism also does not assert that what is beyond the horizon is "unreal", it merely asserts agnosticism around what is beyond that horizon. Empiricism is being awake to the things that might change, i.e., what has not been observed yet that might be different from what has. It's true what Hurkyl mentioned-- this already requires some form of rationalism to be mixed in there, empiricism does require logic. But it tries to stay honest about what we know, and what we don't.Dmitry67 said:
True, as long as you bear in mind the distinction between "not real" and "unreal." In other words, empiricism does not say there is nothing inside an event horizon, or that the material we see crossing it disappears into a pandimensional void, or even that GR can't make predictions about what is in there. It simply says we don't know what is in there, because the universe has put up a "no trespassing" sign. There are other competing theories to GR, by the way, about what is going on inside event horizons, so this is the point of empiricism: we resist pretending we know what we have not empirically established. That is one of the clear lessons of the history of physics.
Why would I, these are quite clear tenets of empiricism. To be clear, I do not wish to claim that empiricism has it all right and rationalism has it all wrong-- rationalism has had its successes too. My actual point is we need to be aware when we are adopting one perspective or the other, because I've found that rationalists often think they are "just doing physics", and seem to have completely missed the two-headed nature of this discipline.
I completely agree with essentially everything you said, but let me suggest a different construction for the CI case. Since you started the MWI situation with what we will call reality, we can do the same for CI:jensa said:
Eqblaauw said:
Except that is not what I proposed at all. The issue keeps coming back: you are not getting that the reality we perceive is nonunitary, even though unitarity does tell us how our statistical expectations toward reality evolve while we are not looking at that reality.Hurkyl said:
I don't believe you understand anything I'm saying about "definiteness", because you don't seem to be able to "get" empiricism at all. Empiricism has a beautifully simple view of what is definite-- what is definite is what is measured. Yes there is much difficulty around issues like measurement uncertainty, and the role we can attribute to hypothetical observers, but the core idea is pretty simple in practice.
I haven't the vaguest idea what you are saying here, the classification makes obvious sense. The classification we are talking about is distinguishing a t parameter in a theory from our experiences of measuring time. What I can't get my head around is why you can't get your head around that distinction.
Correct. Either outcome is nonunitary, that's just exactly right.
You are again missing the distinction between an experiment that results in a mixed state of outcomes, and one that results in the perception of a definite outcome. Your syllogism overlooks a key assumption you made-- that the perception of a definite outcome is possible. So you assumed the evolution was nonunitary. So actually what you just proved is "assuming evolution is nonunitary, unitary evolution predicts a non-unitary outcome." I'm not surprised by that.
Absolutely not, it's your rationalism creeping in again. What do we actually see, and what is the jump of inference you are making? What superposition do we actually see? Never, we never actually see a superposition of anything, that's the whole point. We see interference patterns in an ensemble, but the individual outcomes are always collapsed-- we never actually see a superposition. Reality confounds us every time-- just like it did with the aether.
If you're talking about the frog's eye view, then why did you bring up the bird's eye view?Ken G said:
(hint: it looks like a definite outcome)Hurkyl said:If you're talking about the frog's eye view, then why did you bring up the bird's eye view?
You've confused yourself. Look carefully at what you have argued -- you denied my description of the frog's eye view on the grounds that the bird's eye view looks different. And then you complained about the very idea of discussing the bird's eye view because it's not the frog's eye view!
If you want to consider the frog's eye view of a mixed state, try looking through the frog's eyes.
This last post makes it look like you're talking about a notion roughly synonymous with "precision". That's so totally not what I'm talking about -- it is not what the "definite" in "definite outcomes" refers to.Ken G said:
Do we actually see "spin up around the x axis"? Then in exactly the same sense, we actually see the superposition "|z+\rangle + |z-\rangle".Ken G said:
Hurkyl said:
It seems to me that an explanation that explains everything is more or less the only definition of the "right" explanation I can think of. But I agree that often when we think we explain everything, it is only because we have carefully chosen what we want to explain such that it matches what we do explain, and that is a trap.Eqblaauw said:
Um, to contrast them.Hurkyl said:
Here's how I translate everything you said: "you are noticing a difference between the frog's eye and the bird's eye view, and asking which perspective is the one science should be framed from." Yes, guilty as charged.
No, not at all. The frog's eye view of a mixed state looks like a coin that the frog hasn't looked at yet. That's just exactly what it looks like. I think this is your primary stumbling block to seeing basically everything I'm saying, so we should look closer. You are actually saying that there is no difference in the experience of knowing that a coin has been flipped, and adopting the natural attitude that it is in a definite state, but not knowing what that state is-- and looking at the coin to know what state it is in. I would say those are very clearly different experiences, and each experience has a name-- the first experience is called the experience of a "mixed state", and the second is called the experience of a "definite outcome."If you want to consider the frog's eye view of a mixed state, try looking through the frog's eyes.
Yes, that works fine for me, we only see eigenvalues. That is very much the point I'm making.BruceW said:
So are you finally adopting the long-standing tradition of formulating physics from the bird's eye perspective because it's much easier to understand and compute with, and deriving the frog's eye view from it?Ken G said:
The indefinite outcome position allows for it to be a mixed state after the frog has looked at it.
I've corrected the above quote to say what I'm actually talking about.
I agree, it's not precision, we're both idealizing precision. We have heads or tails, there's no measurement uncertainty here. Those are the eigenvalues, they are all we ever experience (the mixed state before we look is an experience of other eigenvalues from which we infer a kind of missing information about the coin, and from the eigenvalues we do get we assemble a notion that the coin is in a definite state and we just don't know what it is). Here's the key point: eigenvalues are nonunitary. MWI gives us no account as to why we only experience eigenvalues, and I described a hypothetical progress of scientific knowledge where that might have come as rather a big surprise, had we expected evolution to be unitary in the first place. In that scenario, clinging to unitariness would have been clinging to the "god frame" of Lorentz's aether, justifying the way the LET analogy works for me.Hurkyl said:
Yes, you can take information-free expressions involving X if you like. I can also wash all the paint off a Van Gogh using bleach. So what?
That's not the bird's eye view, that's the rationalist view. I believe I see the problem here-- there are really 3 views we are talking about, but thinking that there are only 2 is creating confusion. Here are the three views, I will express them from the empiricist perspective:
I already dispelled that syllogism by pointing out where you assumed that it was only possible to perceive "heads" or "tails", which is the entire reason that the outcomes are nonunitary. So you embedded the assumption that the only possible outcomes were non-unitary, and then used that to prove a theorem that was in fact part of your assumptions. See if your theorem works if the possible experiences of the state are "heads", or "tails", or "a superposition of heads or tails." Where is the proof now?
You have a bizarre interpretation of what a mixed state is, that's all I can say. Most likely it is so rationalist a stance it can't even conceive of empiricism. So let's concentrate on eigenstates and superposition states, it seems we can get to the heart of the nonunitarity of our experiences perfectly well in that language.Hurkyl said:
Yes, I'm fine with all those, they are essentially the empirical bedrock of objectivity and the meaning of an eigenvalue. The second one is most key, that one is equivalent to the statement "experience is nonunitary."
Yes, I can't think of anything to add at present.
Good. All of those propositions are also valid in the sort of indefinite outcome interpretation I'm talking about.Ken G said:
I am not following the significance you attach to this statement. If no experience can distinguish between definite and indefinite outcomes, then the empiricist says there is no difference, and labels all experiences as definite outcomes. Yes, that is indeed just what empiricists do. So? The question remains: why is a superposition experienced neither at the frog's eye level, nor at the bird's eye level, but only at the god's eye level? Note that to the empiricist, there is no god's eye level of perception, because perceptions are done by perceiving agents that we actually understand.Hurkyl said:
The connection between unitary evolution and experience proposed in MWI and other similar interpretations quite explicitly depends on the fact that our experiences are described by mixed states; I suspect whatever plan you wish to propose won't have anything useful to say on the subject.Ken G said:
I don't see how, unless you presume the ontological position that, in the bird's eye view, "I saw tails" is either bird's eye true or bird's eye false.
Why does your empiricist care? Why does he bother making any assertions at all? What criteria does he use?Ken G said:
Travis_King said:
This sounds pretty strange to me. In the case of QM, we don't even know how to derive the frog's view from the bird's view. Even in classical SR and pre-relativistic classical mechanics, I wouldn't say that we have a tradition of deriving the frog's view from the bird's. Instead we do a lot of talking about inertial frames. Isn't that a frog's view concept? (The coordinate independent statements of GR would be an example of a bird's view in classical physics).Hurkyl said:
Simple-- the empiricist wishes to use science to describe his/her experiences. Not the experiences he/she imagines he/she could have under different circumstances, like your qubit experimenter, but rather the ones we actually have. This is just the point. I'm afraid that everything you say about what a scientist is sounds to me like someone who is pretending to be experiencing something other than what they are actually experiencing, and focusing on explaining the pretend experiences rather than the real ones. You want the god's eye view, but never experience it, and you just say "no bother, I'll pretend I'm experiencing it, because that pretense fits in better with my rationalistic objectives." Yes, I get that, it's all you are really saying to me-- you have rationalistic objectives and simply see no point in empiricism.Hurkyl said:
As I understand the term "frog's view", not at all. For simplicity, consider the familiar example of the twin paradox. The frog's view is that Terrance experiences the (relativistic) Doppler effect -- through his telescope he watches Stella celebrate 8 birthdays over 16 years, and then 8 more birthdays over the next 4 years. He doesn't "see" the constant time dilation factor described by his inertial reference frame -- he has to do the calculations to plot his observations relative to that frame.Fredrik said:
Okay. We have seen both definite outcomes and indefinite outcomes describe his/her experiences.Ken G said:
These are good examples, and it shows us we have an interesting issue here-- just what is the frog seeing anyway, and are some frogs getting a "preferred view"? It is indeed traditional to tell new students "don't worry about centrifugal forces, noninertial frames will only confuse you." But is that the core principle of relativity, that noninertial frames should be avoided? No it isn't-- that's the "old way of thinking." The new recognition is that sometimes frogs accelerate, yet they should be just as reliable a witness to what is "really happening" as those who are not. Hence, we need theories of physics that explain the experiences of inertial frogs, and noninertial frogs, and they need to be the same laws. That's what Einstein didn't like about the "special" in SR, and I suspect that was as much his motivation for a general theory of relativity as the desire to treat gravity.Hurkyl said:
I still have no real idea what you even mean by an "indefinite outcome", it sounds like an oxymoron to me. Let me ask you this: do you actually believe that when you, personally, flip a coin, and look at it, the outcome you perceive is a mixed state of heads and tails? And do you call that a definite or an indefinite outcome?Hurkyl said:
Science doesn't tell you, language does. We experience outcomes. We define that word "definite" to go with that. That's it, there's not even a role for science yet. Science comes in when it is time to understand and predict the outcome.
Again, that is neither dogma, nor assertion. It's just language. Definite means we know it. That's it, that's what it means. So my "dogmatic assertion" is that we know our experiences. I suppose I could see that as "empiricist dogma", but it's certainly a pretty tame variety. Nowhere near as radical as "when I flip a coin I perceive both outcomes I just don't know that I do", which is more or less what you seem to be saying.
First of all, I have never once ridiculed you, you are quite mistaken there. My efforts have been simply to get you to see that you are so radical a rationalist that you cannot seem to even conceive of empiricism. That's not ridicule, I really don't think there's anything wrong with your position. I just want you to see it is radical.
Way off. The whole point of "proper time" is that it is just precisely time that is locally experienced. Absolute time was always the rationalistic notion, proper time was always the empirical version. That's what I mean that rationalistic theories like Galilean relativity disappear overnight, but observations, like proper time, do not.
I have no idea where you got this idea.Ken G said:
What idea are you referring to? I was saying that the lesson of relativity is that all observers are in some sense "equally positioned", whether inertial or not, to bear true witness on what is happening, and what's more, they should all be able to apply the same laws to explain what they see. That seems like a fairly natural interpretation of relativity to me, do you differ?Hurkyl said:
Not quite, I'm saying that our observations are closely related to our own perceptions. Understanding them is then something different. The role of empiricism is to say what reality is, the role of rationalism is to understand what empiricism has already told us is the reality. That would be how I sort the two. Your perspective seems to exactly reverse that.
Ken G said:
I would modify this slightly, to clarify some important distinctions. To be an observer requires more than just being "part of the collection", there is some requirement that the observer must "process information like we do" to count in a way that is useful to our use of the term. So you're right that a tree can in some sense observe itself when it falls down, but for it to count in our term, it must "observe itself the way we would." We have no idea how a tree is really observing itself, if the phrase even means anything-- instead, we must "put ourselves in the place of the tree" before we can claim the tree is acting like what we mean by an observer. I'm not placing arbitrary constraints on the language, I honestly don't see how term "observer" could possibly mean anything else, and still hold any kind of empirical meaning to us.Fra said:
I would actually start the "frog" lower in the hierarchy-- no communication with other frogs, just interactions with the non-observers. The "raw experience" of a single frog.
Here I would agree the bird's view assembles frog's views, including the views we consider hypothetically (like "if a frog were there, what would it see"). But note this is a very specific type of information, so even if we assemble it all, it's not all the information (unless we define this to be information, that's a subtle issue I won't take a position on). The key point is that the god's eye view is something quite different, because it does not ask "what would a frog see", it just asks "what is." The god's eye view is the view of the rationalist, it is a conceptual framework for talking about truth (rather than an empirical one). The "many worlds" are, to me, a quintessentially example of a "god's eye view", and so is the whole Tegmark hierarchy of multiverses. Tegmark is in effect placing himself in the position of god, that his rationalist perspective can "see" what empirical interactions cannot. I'm not saying he has a god complex, I don't really mean any religious overtones-- I'm saying he is a dyed-in-the-wool rationalist.
Realism is actually something quite a bit different. It is defined as people who "take their perceptions at face value", such that what is real is what we have access to. The key tenet of realism is that our limitations do not actually limit us, because they are fundamental to us, so we basically shouldn't care about any reality that is outside our limitations. So there's a subset of realists who are empiricists, who say that what is real is exactly what we perceive (I would call that Einstein's brand), and there is a subset who are rationalists, who say that what is real is the god's eye view accessible to our reason (I would call that Tegmark's brand). None of these are "naive realists" (http://en.wikipedia.org/wiki/Naïve_realism), who say that reality is exactly what we perceive it to be, there's no need for us to reinterpret reality based on either other observer's points of view, or over-arching conceptual principles. It's the "show me" brand of realism taken to its logical conclusion, and I don't think anyone in this discussion espoused that brand.
Exactly. That's why I feel an empiricist would need to bring in a new concept, the "god's eye view", to treat what rationalists are talking about.
Here I disagree with what I believe you are saying. In relativity, it is actually codified right in the laws (rationalistic laws at that) that what the laws must be built from are frog's eye views, fed into a rationalist machine called "compute the invariants." That's why relativity can still be interpreted (by an empiricist) as completely empirical-- it is a theory that acts only on what are demonstrably frog's eye views (it takes as input only things frogs could not only perceive, but also communicate about-- the invariants are functions of only things that are local and communicable to frogs). That's where spacetime comes from-- locality + communication.
Yes, I agree that is conventional for both empiricists and rationalists, and is the approach I take too.
Yes, I see what you mean. But here I would substitute "rationalist" where you have "realist." The empiricist is still being a realist when they admit that laws must be built from invariants even though no one sees the invariants, because the empiricist rejects the rationalist idea that there "really are laws" in the first place. Instead, the empiricists says that there "really are observations", but that we must try to build laws or we can't use the observations effectively. The laws are from us, not nature (though of course they are constrained by nature or they won't work). The advantage of this approach is that the laws can change, as they do, and the empiricist never has to say "OK, we were wrong before, but we have it right this time." That stance just gets kind of embarrassing after too many centuries! (But the rationalist has many successes to point to, mysteriously many, so I don't claim this means empiricists are "right" and rationalists are "wrong", my goal is only to elucidate the consistency packages involved.)
I agree that is the empiricist stance, but I wouldn't call it non-realist, only non-naive-realist. The empiricist is a realist whenever they say "there is a reality that is accessible through observation", or "if there is any reality that is not accessible to observation, it is angels on the head of a pin to us." They can admit that this reality is quite subtle and surprising, and needs to be kind of cobbled together in an intelligent way that looks for things like invariants and unitary principles. However, these principles are never the reality-- they are always our efforts to make sense of the reality.
That's what I would call rationalism.
The way I used "observer" I already had in mind the generalization you refer to. However in my view, even a quantum system is a perfectly good observer. However, to understand how this process information, is identical to the problem of understanding it's action; just like we in current theory have an action for the standard model. This action exactly encodes how "matter processes information about other matter and fields" - or at least so goes my conjecture.Ken G said:
To avoid misunderstanding: I described tis picture, but I do not share it. See above (*)Ken G said:
Ken G said:
I agree you don't need realism to make observations useful, it is objectivity that you need, by which I mean borrowing cautiously from the rationalistic construct of "laws" that are observer independent. To have empirical objectivity, we first need to accept all observer's testimonies as valid descriptions of reality, and then we need to find functions of those observations that strip off the observer dependence, like 4-vector norms. The latter is need to have laws that are observer independent. Note how empiricist this program is-- the laws are not the reality here, because reality is observer dependent, and the laws are not. This is just the goal the empiricist sets out for laws-- how well it works is another matter, and is accepted as mystery by empiricists. Of course, rationalists don't see it as mysterious that laws work, because they think the laws are the reality. But they have their own problems, not the least of which is the fact that laws change but observations don't.Fra said:
Actually we agree here-- I didn't mean "must build laws from invariants" to mean "nature decrees they must do this", I mean they "must" if they want to achieve the goal of laws that do not reference observers. My point is that observations "must" by their nature refer to observers, but it is our desire as scientists to build laws that do not refer to observers, so we "must" do that to be successful. It's a different kind of "must", I agree.
Yes, I can buy that, if we further stipulate that the goal is to establish observer-independent rules for reaching those expected equilibria. Here's where the rationalist says that the observer-independent rules of engagement are the reality itself, but the empiricist says they are only the reality of our desires as scientists to make sense of what is happening.
Here we have a key juncture-- we can go CI and say that there is no quantum world, meaning that there is no negotiation for atoms because atoms don't negotiate-- the laws we seek express the goals of our own intelligence, so that is the only kind of negotiation we can refer to when making those laws. That would be my approach. You seem to have a more rationalist/empiricist mixture in mind, where the fundamental talking points of the negotiation are empirical, but you can contemplate how an atom might involve itself in such a negotiation, that can be given some meaning for you. I don't say that can't work, I just hold more of the Wittgenstein view (if a lion could talk, we wouldn't understand it anyway).
I agree that the highest purpose of an interpretation is not to understand reality better, because it is the theory that is the attempt to understand reality, whereas the interpretation is just how we understand the theory (and the interpretation can turn into a kind of pretense of knowing what we do not know, that's my sole beef with MWI). The highest purpose is to guide the way forward to the next theory, that actually will understand reality better (and make us feel foolish for adopting essentially mystical interpretations like MWI or the way some people talk about CI).
I agree that people who talk about CI-esque "collapse" as if it was a real transition of some kind don't understand what (I believe) Bohr was saying. It's not very satisfactory to say "the wave function is real, and its collapse is real", that's why many people reject CI but that's not really what CI says at all. CI says the wave function was never real, so it can't "really collapse", and MWI says it was always real, so it can't collapse either. They actually agree that collapse is a disconnect, they just align with different ends of the disconnect. But CI might say that we cannot reject the implicit reality of the classical background, because that is just how we think, and if we imagine we are thinking any other way (even abstractly as in MWI), we are really just engaging in classical modes of thought in more beguiling disguises. That is how I would personally characterize Hurkyl's descriptions of experiences of mixed states.
Ken G said:
Ken G said:
