Philosophical implications of quantum mechanics (warning: long confusing OP)

Great Debates
1

So, motivated by this thread, I’d like to share my troubles with the metaphysical implications of quantum mechanics. I’d especially like the materialists around here to clarify how they address these implications, and hopefully I’ll learn something useful in the process!

The specific issue that puzzles me the most is that of wavefunction collapse. Just to give a little background that might be needed, the fundamental quantity in quantum mechanics is the wavefunction: it’s what describes the state of any given system.

Now, suppose you have a free electron, and you measure its spin in the z direction. You’ll get either +1/2 or -1/2. Fine, dandy, no problems. Let’s assume we get +1/2: then the electron’s wavefunction is determined, and every single time we measure the spin in the z direction, we’ll get +1/2. What’s important to note is that by determining the spin in the z direction, I’ve lost all information about the spin in the x direction: this spin isn’t determined, and it’s a combination of +1/2 and -1/2 (the wavefunction is, in other words, a combination of states that have +1/2 and -1/2 spin in the x direction).

Now say I measure the x spin to see which one I get. I can’t predict beforehand what the answer will be, but it will be one or the other. That is, the wavefunction will collapse into a state of definite x direction spin: it actually changes when I look at it! :frowning: Further, I lose all information about the z spin that I had just picked up earlier by measuring. This troubles me enough as it is, but it gets worse. You see, suppose I put the electron inside the little device that measures the x spin but I don’t check the answer and instead immediately send the electron through the device that measures the z spin again. Now we find that I haven’t in fact lost the information about the z spin, and the wavefunction never collapsed! :eek:

So to sum up… The wavefunction is in some superposition of states. I measure something, and the wavefunction all of a sudden collapses to one particular state in my original superposition. But if I put it through the device that does the measurement but I don’t look, it doesn’t collapse.

Right, so having given general background that might or might not have been useful, here are the two big questions that trouble me.

  1. The wavefunction collapses to something definite, but you can’t predict what it will collapse to. Question: how does the electron know what to collapse to? I mean, it has to choose one or the other, so how does it make its choice?

  2. What’s so special about the act of doing the measurement? If the wavefunction only collapses when you make the measurement, who or what collapses it? After all, ultimately, I’m just a really huge collection of electrons and so forth myself; how do the electrons that make up g8rguy collapse the wavefunction of the other electron? Why don’t the electrons that make up a rock, or a flower, or a dead body do the same thing?

Thinking about these issues has gotten a very great many people hopelessly confused. The only way that I can reconcile myself with these issues is to propose that there’s something else going on. Some people like the “many worlds” interpretation, in which each time something is measured, a new universe is created for each possible measured value. I don’t see how this really addresses my frustration, and I’ve always thought it’s unnecessarily extravagant (I can’t even begin to imagine how many universes there’d have to be!), so I reject this one. Other people shrug their shoulders and don’t worry about it; I find myself unable to do this. There’s an idea due to Bohm that I don’t really know very much about in which things really are completely deterministic (thus addressing question 1), but for reasons I’ve never understood, it fell out of favor long ago, and in any event (and more importantly to me), it’s conspicuously silent on question 2.

Thus, I am led to assume that there’s something else out there to be accounted for, that this thing is evidently specific to conscious or sentience or something like that (since, as I mentioned, a rock/flower/corpse/etc doesn’t collapse the wavefunction), and that I am at a loss to explain what this might be, except that it would be awfully interesting if this is what we’d call the soul or something like that. I further conclude that maybe there is a ghod and he does play dice with the universe after all.

So the thing to debate here is just what precisely the philosophical implications of quantum mechanics are and whether my supposition (or any others that come up in the debate, for that matter) is even remotely reasonable.

[sub]We can instead, if you prefer, debate as to as whether g8rguy is on crack or not[/sub]

2

Hey dude, I had the same “worries” you had. Then after I realized that if you plug in Time=zero at all intervals the equations work out. That is T(sub 0)=undefined. The implication of this is that everything IS happening and that our view is one of an infinite number of views. An analogy would be that if you look at a cylinder from the oblique side…it looks like a rectangle in two dimensions. If you look at a cylinder from the top it appears as a circle. It is your observation that gives you the meaning of the object. However, the object is NOT two dimensional…but three dimensional.

Same with “space-time” whereas we see things in a 3 dimensional “space” with time running (!) as a “fourth-dimension”. If time were zeroed out in the quantum equations all the “problems” we have fall apart.

I don’t believe in “observational collapse”. We do however, seem to have an observational point of view…and if we could see everything without regard to time which, admittedly is very difficult it would be easier to conceptualize QM.

The Idea that time doesn’t “exist” is explored in several magazines lately. Check it out using a google search.

3

And yet you resist multi-dimensional string theory… :shrug: :wink:

(this is really fucking long, but necessary to answer your questions as I perceive them)

I am always amused at the metaphysical interpretations of QM; although, I am skeptical about the existence of consciousness so I am skeptical about any theory which requires it, as some flavors of meta-quantum mechanics (hereafter MQM: nice palindrome :)) seem to.

Penrose in “The Emperor’s New Mind” had some interesting ideas about collapsing wavefunctions as a result of observers, though he was decidedly ambivelant about what, exactly, an observer was (was, of course, to maintain tense; no death is implied).

I often consider MQM as a study of useful information and that any information which is not “used”—that is, any quantum information which does not have a deterministic effect—is an undecidable proposition. This is why, IMO, when we “ask” a wave question we “get” a “wave answer” (consider crystal electon scattering with and without position detectors yielding seperate interference patterns).

The problem with the Information MQM Idea (IMQMI—gotta keep that palindrome!) is that “information” is seemingly not well defined. In the electron scattering experiment we can fire one electron at a time and still yield an interference pattern, and it is doubtful that the path swept out by that electron had no effect on the intervening space… isn’t it?

Of course, even in standard QM we run into the problem where we really don’t know that the electron we fired out of the gun is the same electron that hit the detector screen. Between any two “questions” literally anything can happen, just so long as we don’t ask what happens in between. In this case, our electron could have anihilated with a virtual anti-electron whose fluctuational twin is now “real” by this act, all the way across. Hell, it could be that nothing really “moves” per se but is really a series of creation/anihilation along what we perceive to be a continuous portion of space.

Your second question is possibly loaded: “Why don’t the electrons that make up a rock, or a flower, or a dead body do the same thing?” Who says they don’t? For example, I place a rock in a Schrodinger Box (the same one the cat would be in, but animal rights activists won’t let us suject cats to life and death simultaneity) close it, count to ten, then open it again. Viola! A rock. The same rock, as far as I can tell, but again, each and every “particle” in the rock could have been exchanged with new particles. The very same thing is happening to us each and every instant. So the question is: what makes you think we are so special as observers? We are subject to the same happenings.

IMQMI (a term I just coined for this thread as a useful descriptor) requires that the only questions which have answers are questions that are actually asked. Any question like, “What is the electron doing,” which is asked by scientist A to scientist B, is really a question about a question; that is, correctly phrased, the question becomes “What would the electron be doing if we looked to see what the electron was doing?” Meaningless question as far as the electron is concerned; it has no obligation to answer a hypothetical.

We see the macro world because we interact with it, all the while asking questions. So then, it seems, IMQMI requires that the observer is any wavicle which requires a answer to do something.

And so we come to the big question: what started it all? QM brings us a First-Mover question more strongly than any scientific theory I’ve ever been privvy to. Hume once mentioned that the implicit assumption in all of empiricism is that “things will continue to happen as they have happened,” that is, there is some underlying causality. Standard deterministic causality is destroyed by the existence of wavicles, but enhanced causality remains. When we ask a question, we get an answer. Furthermore, when we ask the same question again we still get an answer.

What follows is only necessary to read if you want my opinion about what the universe is, and explains why forces unite and relies heavily on the anthropic principle, so don’t read it if you don’t care.

erl’s first rule of causality: all questions have answers. Each time we measure spin, we find spin. Each time we measure position we find position. It is meaningless to pose a meta-question about anything else because, until that question is asked, there is no answer. Why should there be? Without a Universal Observer like Gods or Goddesses (or singular, or us monotheists) the meta-question is strictly meaningless. We didn’t ask, so we cannot know. If we measure the position of an electron, get our position answer, then wonder “Yeah, sure, but how fast was it going?” the IMQMI answer is “there is no such thing as ‘fast.’” Why not? Because no one was asking.

While IMQMI requires a First Mover, the First Mover need not be a God, it only needs to be a God Particle; that is, a GP is a strict particle or wave which is not itself subject to waveform collapse. It asked the first question, even if that question was “will this wavicle destroy me?” From there, it seems, we might have a chain reaction of questions flowing from a single particle. Consider:

“Will this wavicle destroy me?”
“Yes.”

The act of destruction brought about a new wavicle which itself was not a GP but was now a passive observer as a causal chain of question asking. It alone could collapse quite a few waveforms by asking questions in its general vicinity such as: “Did I absorb a photon?”

Now the answer is even more interesting. Consider, first, the ‘yes’ case.
“Yes.”
“Who wants it?” (since electrons seek the lowest energy state) Not only that, but for it to have absorbed a photon that photon must have followed some path… actually, any number paths, just so long as the paths brought it in contact with our Non-GP observer. The path the photon followed is a meaningless question to the electron because it only cares whether it “has” it or not, not where the photon came from. It just needed to follow a path to get there, the electron is unconcerned about anything else.

Consider the “no” answer and we see a very similar question. each and every photon must have avoided that electron right up until the moment it asked that question. Note that the only restriction the photons have is that they did not interact with that electron. They could do whatever they wanted so long as they didn’t interact with the electron.

erl’s second rule of causality: all wavicles are limited in the number of questions they can ask. No wavicle can ask all questions. Note that the mapping of “question” with “force” is becoming explicit. Electrons are fundamentally uninterested about questions involving integral spin. It simply does not have the capacity to ask that question. The “force particles” that we find, such as the bosons, are even more limited to the questions they can ask.

erl’s third rule of causality: there is no system of particles that, when combined, can ask all questions. This follows directly from two but is possibly unintuitive. We would say that a system of particles would collectively “know” all the answers at any instant in time. But is this really the case? Quite simply, no. Systems do not ask questions so they do not have answers. “But erl, if all waveform callapse has backwards ripples in time surely there must exist a combination of particles which would collapse everything!” No! Impossible. Yes, the past is determined, but the future isn’t. At any instant we ask a question we get a determined answer, but then the next instant comes along and there are a whole new set of questions to ask. Because wavicles are only bound by the questions they asked, there is no forward causality. The next state a system is in to ask questions aout the present/past (whose distinction is uninteresting in IMQMI) is in no way dependent on its previous state until the question is asked. Also, consider that any experiment we perform to ask questions are going to rely, fundamentally, on such particle interactions, and so we can only get those answers. Unless we can come up with a particle which can ask all questions simultaneously (which violated known QM rules, for it would require that a wavicle could be in simultaneous spin states; that is, integral, half-integral, and so on) the future remains open and we are stuck in a state of epistemic incompleteness. As the universe gets larger, as our study of relativity seems to demand, the questions particle can ask that have “yes” answers grows smaller and so the possbilities are larger.

This is why we see “force unification” at higher energy densities. The higher the energy densities are the more “yes” answers there are (and “yes” answers generally require a state, whereas “no” answers generally allow for multiple states) and so the more deterministic the universe is. The boundries between the force particles disappear because the backwards collapsing of one question requires other questions have certain answers all the way around.

What IMQMI requires: one, an indeterminate number of force particles (depending on the universe in question); two, vacuum fluctuations of zero average energy density; three, a GP; four, expanding space in which wavicles can ask questions.

The form of the GP is a question for further inquiries about inquiries about inquiries but is essentially a meta-metaphysical question easily resolved by “resorting” to the anthropic principle. The multi-worlds interpretation says that each and every wavicle is some IMQMI’s GP, but the distinction is uninteresting. It is entirely possible that in some world (accepting the multi-world theory) there is no such thing as future indeterminancy, but we don’t live in that world, our GP is gone, and speculation about it is fruitless empiricly.

Also, let us consider the four requisites for my IMQMI by asking “why” to each of them. The first one is simple enough in principle. With no forces there are no questions and so there is no universe to speak of. Two, vacuum fluctuations are necessary for the “jumping” of states, the only way IMQMI accounts for motion (more appropriately termed “apparent motion”). The third requirement is simply axiomatic, but as the multi-worlds meta-metaphysic demonstrates it can be “abstracted” away. Four is necessary for the world we live in, but nothing more. Actually, all four “why” questions are only sufficiently answered by the anthropic principle; IMO there is no reason why any state exists, and there is no particle which could ask such a question so it is strictly meaningless anyway.

So, g8rguy, with the above in mind let me answer your two questions within my IMQMI framework.
[li]The wavefunction collapses to something definite, but you can’t predict what it will collapse to. Question: how does the electron know what to collapse to? I mean, it has to choose one or the other, so how does it make its choice?[/li]~~It doesn’t know what to collapse to per se. Its next state is entirely undetermined. Any appearance of motion, or of finding “the same electron doing stuff” is not well-formed for no such particle exists which could ask such a question. The state it comes to when it asks a question is limited by the distances involved in the questions it can ask and that are asked of it (try not to think of electrons as wavicles existing over time; they only seem to be that way).

[li]What’s so special about the act of doing the measurement? If the wavefunction only collapses when you make the measurement, who or what collapses it? After all, ultimately, I’m just a really huge collection of electrons and so forth myself; how do the electrons that make up g8rguy collapse the wavefunction of the other electron? Why don’t the electrons that make up a rock, or a flower, or a dead body do the same thing?[/li]~~Wavicles collapse themselves. You are no more special than a rock, it only seems that way because you think you are asking questions which have answers when, in reality, they don’t.

Whew! I think I had better quit now before I get back into my “the universe is a game” theory which was not well-received here, but perhaps might be better understood now by those who participated the first time…

4

Hey, I never claimed to be consistent in which things I find troubling… :slight_smile:

Yeah, this troubles me as well. Who knows what’s really going on?

I was confused by what you were saying for a long long time, and then I realized that we’re talking about different things! Yes, of course a rock could be exchanging electrons and what not, and so am I, and so is the IPU. What I meant was that a rock obviously can’t make measurements. But it’s made up of the same kinds of things that we are, so why is it that the electrons and so forth that make up erl can cause the wavefunctions of other electrons to collapse, but (as far as we can tell) the electrons that make up erl’s sock can’t?

Hmm… a good point, and I have to agree. If I know what the electron’s wavefunction is, I can tell you what the wavefunction itself is doing, but that’s not the same thing as telling me what the electron is doing, eh?

Again, I agree, on the face of it. I am, physically, nothing more than a collection of various electrons and nuclei and so forth. So there certainly is a wavefunction [sym]Y[/sym][sub]g8rguy[/sub]. How [sym]Y[/sym][sub]g8rguy[/sub] interacts with [sym]Y[/sym][sub]rest of world[/sub] to make measurements is utterly and hopelessly beyond me, but it must do so, because I can make these measurements.
I’m going to need to take some time to digest the rest of your post (thanks for replying, by the way), but here’s a few quick comments…

Right, but we could ask “how fast are you going, little electron?” and we’d know how fast it was going. We could come back three days later and ask “how fast are you going now, little electron?” and assuming that there was nothing around to interact with it, we’d find it was going just as fast as it was when we last asked, and no faster. No, there’s no answer to “okay, so where were you?”, but why is it that the minute we do ask where it is, we get an answer, and we lose the answer to how fast it was going?

Yes! This is the “ghod” that I alluded to towards the tail end of the OP. I am not alone! :smiley:

Okay, but do the rock wavicles ask questions? Supposing that the g8rguy wavicle is asking stuff which has no answers, are the rock wavicles doing the same thing? I mean, if I put a hamster in with my spin measuring device, would that have an effect on my experiment? What if I spoke hamsterese and asked little Bandit what just happened?
dierson, I’m still trying to figure out what you’re saying as well (I’m a little slow when it comes to this kind of thing, and writing up the blasted OP gave me a terrifying headache), but when I plug t=0 into my equations, I normally get things like [sym]Y/sym = [sym]Y/sym, which while obviously true isn’t very helpful. And I have a hard time with the idea that time doesn’t exist, since it certainly seems pretty obvious that it does…

5

Do you have a cite for the claim that if you put the electon in a measuring device, perform the measurement, print out the measurement, but don’t look at the printout, then that doesn’t collapse the wavefunction?

Because so far as I know, the use of the measuring device counts as an observation, regardless of whether an intelligent entity examines its output.

-Ben

6

Ah, but we cannot make measurements either! What we can do is ask wavicles “wavicle” questions… they make the measurements. A rock is just as much a measuring device as you are; how could it not be? The real measuring device are the wavicles… hell, that’s what we use to ask the questions! Anything made of wavicles is a measuring device by implication.

IMO, there is no room for “speed” or movement in IMQMI because there is no motion. Everything is discrete quanta, and we relate velocity to energy… but how do we determine velocity? By asking wavicle questions. IMO our concepts are fuzzy because what we ask taints the answer by loading the question. “how fast is the electron going?” Well, we “know” that its momentum is its rest mass times its velocity, so lets smash it into something and measure the change in momentum, which must be conserved. So we do our smash, but what do we ask? “How much did the target’s momentum change?” No, we just ask it “What is your momentum right now?” and create information from that result to answer our question which cannot be answered.

There are a limited number of questions we can ask about particles because there are a limited number of questions particles can ask about themselves. A photon, for instance, can ask “how many other photons are there with me?” while an electron cannot (pauli exclusion principle for fermions).

So at each instance in time each particle asks all its questions. If any question’s answer will not require a state then the state is undetermined. As an example, let us consider a single photon in an otherwise empty universe of appreciable size (appreciable to us, anyway). Every single one of its questions based on interactions is a “no” so the photon is free to occupy all states. And it will since nothing limits it.

We run into trouble by asking what we think are meaningful questions, but our interpretation is flawed. For instance, if a wavicle can only have four significant pieces of information attached to it (four properties which have particular states) then we can only ask it four questions. No more, but possibly less. And of course, it can only ask four questions itself (IMO all particles ask all their questions every instant). So long as nothing is required of it then it is free to do everything it can. When we measure position, for example, it is meaningless to postulate spin because we didn’t ask a spin question. As far as we are concerned it was in both spin states; because there was no spin-answer then there is no spin.

Consider what we are asking about when we probe individual wavicles… are we asking about them or about their states? I mean, when we come down to it, do protons exist or just quarks? Do quarks exist or just the bosons responsible for the strong force mediation? How would we tell the difference? What question could any particular wavicle ask that would shed some light on the subject?

See, here is where we start running into trouble. IMQMI has no method of asking questions about collections of particles because it would need a particle to ask that question. Unless there is a g8rguy particle or a hamster-in-the-wheel particle, the question is meaningless (to the universe). It isn’t that we couldn’t answer the question, we just couldn’t do it by referencing wavicles. (I understand that my explanation is pretty sparing because I don’t go into real detail about multiple-wavicle systems whose questions seem far more complicated than I am doing them justice, but it is the IMQMI principle I want to get across: we can only ask a particle a question at any instant, and only get answers to question it can ask, no more, no less.)

My prediction, if IMQMI is correct, is that gravity will never be quantized (properly renormalized), because that would make gravitons particles which can ask all questions (that is, unless the quantization of gravity demonstrates it cannot act at infinite distances, in which case we are still safe inside IMQMI) by implication. Even the HUP won’t save us completely (unless I can find a way to incorporate it into IMQMI successfully, which I haven’t outlined above).

Ben, I have had my doubts about the integrity of that experiment too, but that is because I always asked myself about the electron scattering experiments… surely, even if we didn’t put a detector there, the electron must interact (through the electromagnetic force) with particles all along its path, right? Do you feel that there is something to scientists and other humans that collapse waveforms? What do you mean by measurement? That electron scattering experiment is the primary cause of my above-outlined IMQMI. What makes QM so perplexing are the ideas of continuity and causality, neither of which exist in my opinion (at least, not causality as we usually describe it).

7

I suppose I should mention for completeness that speed certainly can exist, just not to a particle. All particles are static in position and either exist or don’t exist, but certainly we can see a path of force, so to speak, act across a specific path.

We can then quantize that force and treat it like a wavicle again, which puts us back in a state of no-motion IMO.

I don’t want to talk over my own head here, I just want to mention that our concepts about the nature of things aren’t always answerable by observing the particles themselves. I suppose that is the best way to sum up my previous two posts without speaking gibberish. No particle can give up all information because we need a particle to get that information to get that information, etc ad nauseum.

There is a level of abstraction we put in place to discuss the fundamental nature of reality which creates information we didn’t actually get from the experiments, and cannot get from experiments because that information either isn’t there (we made it up) or the things we are questioning can’t “know.” At some level it ceases to be of value to use empirical methods of theory creation and resort to synthetic determination because, somewhere in our abstraction, we’ve slipped information in that isn’t there to be gathered.

8

Don’t y’all think you’re taking what is really a poetic metaphor a bit too literally? The wavefunction collapse image is a way of visualizing what is going on, but not really what is going on. Ben, of course is right: any interaction with anything is “observation”, so therefore the statement of what is going on without observation is unprovable and unknowable.

Personally, I find that the metaphysical implication of QM (and potions of string theory as well) is that some information is unknowable … that ultimately the scientific method is valuable but insufficient. It shows that for all the value of science, sciencism (science as religion, as an answer to all questions) fails, because we cannot have acsess to all information. The same conclusion results from cogitation about black holes. We canot know what is beyond the event horizon. If a particle and its antiparticle are created out of the quantum foam at the edge of the horizon, and one is sucked in and one escapes, then information about one half of the pair is forever lost to us … its wave function is lost to us … and according to Hawking is lost forever even as the black hole radiates new particles.

That some things are extant but unknowable. By definition unobservable. And yet there. This is the unescapable conclusion made within high level physics. And brings us round to its also being the premise of theism … not in the mythologic God sense, but in the simultaneously more primative and advanced sense … God as the ultimately unknowble and yet always present.

9

IANAP (I am not a physicist) but I think the problem is that you’re imposing a macro level set of rules about “objects” to a micro level where things don’t work the same way.

If I had a water hose and was spraying water across the concrete floor, and the water was flowing through two different drain gratings, you’d have no particular trouble setting up measuring devices that measure water flowing into drain #1 and drain #2; you could also (given sufficiently sophisticated equipment) tag a particular molecule of water and determine WHICH of the two possible drains it was going down, which will be one or the other but not both.

These things don’t surprise you because you expect a stream of water to use both drains simultaneously, and you expect a molecule of water to be indivisible (under these circumstances) and therefore to go down one or the other.

But suppose the entire stream of water were a single indivisible object? You try to tag it, and by demanding a fixed location through the act of measuring, you get one; but unlike single indivisible objects in the macro world, it can flow like water down two different drains as long as a fixed location parameter isn’t being demanded of it by your measuring devices?

Like employees whose work flow doesn’t correspond to the categories on the forms their supervisors make them fill out, the water’s answer to “location” questions is insufficient to describe what’s really going on, mainly because the available answers don’t permit a fully meaningful answer.

10

Nobody understands quantum physics. You just get used to it.
Richard Feynman

11

g8rguy wrote:

Well, there’s your first problem. The electron’s spin in a particular direction will only be +1/2 or -1/2 at the instant you measure it. Later, after interacting with other particles or fields, it can be indeterminate again. In fact, the way you’re measuring the electron’s spin interacts with the electron, so it can cause your next measurement of the same electron’s spin to be different!

… and there’s your second problem. It is not the act of OBSERVING the spin, per se, that collapses the wavefunction. It is the act of the electron interacting in any situation where its spin matters. When your device “measures” the x spin, the electron has to interact with it in such a way that its x spin actually matters. It is at that moment that the electron’s x-spin wave function collapses.

12

Except in the experiment(s?) he is discussing, the function collapsed ONLY when the results from the measuring device were analyzed by scientists, and NOT when the measuring device was taking measurements but the scientists “forgot” about them.

13

I do not think such an experimental result is possible.

14

I’ll see if I can dig it up… it was just done in GQ a little bit ago but I don’t remember the final analysis of the experiment…

15

You know, I knew I was going to state the OP in a way as to confuse someone. Sorry, Ben, let me try again.

I’m thinking specifically of the old Stern-Gerlach experiments. A magnetic field is appled in some direction, and the spin then interacts with the magnetic field. So if I send an electron with spin +1/2 in the z direction through an SG device with a field in the z direction, the electron will be deflected up, and I can thus tell that it’s spin was +1/2 (if the spin was -1/2, the electron would move down).

Now if I send this same electron through a device with a field in the x direction, the +1/2 (x) and the -1/2 (x) components of +1/2 (z) interact with it differently, and I pick out one or the other; the wavefunction has collapsed.

There’s a variation due to Feynman (I don’t know if the experiment has been done or not, but I suspect it must have been by now) in which you send a +1/2 (z) electron through an SG device with a field pointing in the +x direction for half of it and a field pointing in the -x direction for the other half. Then again, the electron should have components that bend off up and down. If I block, say, the down path, the electron will come out with spin +1/2 in the x direction; the wave function has collapsed again. But if I do the same experiment without the block, the electron will come out with spin +1/2 in the z direction instead. But the interactions in both cases are the same; the only difference is whether I look at it or not. Clear?

I’ll give you the cite for this tomorrow morning when I can grab one of my text books (they’re at the office, and I’m at home).

Incidentally, this should clarify what I mean for you, too, tracer. The way I measure the spin doesn’t change it; if I have specificed S[sub]z[/sub] and the interaction is B*S[sub]z[/sub], then S[sub]z[/sub] is conserved, so that every single time I measure it, I’ll get the same answer (remember: it’s a free electron and the only thing it has to interact with is the magnetic field). Later, when I ask about S[sub]x[/sub], that’s not conserved. Evidently, though, when I put the electron through this x direction field a la Feynman’s thought experiment, even though S[sub]x[/sub] is what matters, S[sub]z[/sub] is still what gets conserved. That is where the confusion lies.

DSeid, that’s interesting. One of the many many hypothesized explanations of quantum mechanics is a so-called “hidden variables” interpretation, in which we just haven’t included all possible information in our formalism yet and if we included these extra variables, we’d not have these problems. There’s some work due to Bell which rules out global hidden variables but not local ones (I believe; it might be vice versa). I admit that I like the hidden variables approach philosophically, but I’m not sure it’s meaningful scientifically because in 75 years of work, no one’s come up with anything yet.

16

This relates to a different post Does God Need Witnesses?

Midrash apparently long ago concluded that God is a wavefunction that only collapses into “God” upon observation by human experience:

In Isaiah 44:8 it is stated that God says “you are my witnesses. Is there any god then but Me?” Which Midrash interpreted as meaning “If ‘you are my witnesses’ then I am God; but if you are not My witnesses, then, so to speak, I am not God.”

Again, not my point of view, but interesting, I think.

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Other way 'round, g8r. Local hidden variables (that would be consistent with special relativity) are ruled out, global ones are possible, but “violate” special rel. This is not neccessarily a problem - if such “violations” are unobservable, we’re still good to go. The problem, as you say, is that noone has made it a workable theory yet. (The Bohm stuff works for QM, but hasn’t been extended to quantum field theory, where particles can be annihilated and created.)

IMO (and IAAP) the “collapse” idea should be avoided entirely. QM is really telling us about the probabilities of different outcomes of a given experiment. In other words, if I do the same experiment 1000 times, I will get spin-up (say) 500 times and spin-down 500 times, give or take. If I add a component to the experiment (send the particle through a second Stern-Gerlach, for example) I am doing a different experiment. The results of the previous experiment are irrelevant - I have to begin again with the rules of QM and re-calculate all the probabilities. No “collapse”, just probabilities. As DSeid said, the wavefunction is only a metaphor, or, rather, a calculational tool. It isn’t a physically existing object about which the question “did it collapse or didn’t it?” can be asked. (See the textbook by Leslie Ballentine for more on this view - be warned, it is a graduate level text.) All of the paradoxes of QM can be dealt with this way. (Which is not to claim that all the philosophical issues are thereby resolved…) In particular, you never need to bring “consciousness” into it.

Anyway, I don’t think we need to call for ghod to resolve the issue. The world works in a much more mysterious way than anyone could have imagined - so what? There was never any particular reason it should be understandable according to a simple mechanical model. So, the mechanical model works well up to a point, then we have to call in QM to go any further.

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Ah. It’s been rather a while, so I couldn’t remember which was gone, and as I had no reference material on hand to check. Thanks for the correction.

Yes, quite, I do understand this (IAAP myself). But I’ve always been bothered by how the probabilities can instantaneously change from, say, 1/3 to 1 upon measurement. It’s simplest to not worry about how this happens, because we have no way of knowing, but in my odder moods, I do worry about it. Since it happens to fit into my personal philosophical framework reasonably well…

Well, but wouldn’t you say that if you had a free electron in an eigenstate |+1/2[sub]z[/sub]> = 1/sqrt(2) * ( |+1/2[sub]x[/sub]> + |-1/2[sub]x[/sub]> ) and measure S[sub]x[/sub], you’ll have changed the wavefunction in doing so? I can predict the probability for both values; it’s even odds, of course. But I only get 1 of the 2 when I measure it. Why? I must get one or the other, after all, and it’s that getting one or the other that I find both interesting and irritatingly opaque. (In other words, when I actually measureS[sub]x[/sub], I get +1/2 or -1/2; if I did the experiment many times, I’d tend to get the two in equal amounts. But each time I measure it, I get a specific value; how does this come about?)

Eh, I don’t know if I’d go that far. After all, while the wavefunction isn’t an observable, its norm-squared is an observable, so it can’t be entirely divorced from physical meaning, right?

Thanks; I’ll look into it.

Riiiight, but while there’s no particular reason it should be understandable according to a simple model, I strongly feel that it ought to be understandable according to some model. As of now, we can calculate things with QM, but of course we don’t really understand it in the way we understand classical mechanics or electrodynamics, and I think we ought to be able to do so. That’s a philosophical claim; I make no bones about the fact that there’s no science to it.

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It sounds like we’re closer together on this than I thought at first.

Yes, the wave function changes, but this doesn’t bother me since I think of the wave function as representing the information I possess about the system. Of course, when I make a new measurement, the information I possess changes.

Not divorced from physical meaning, no. But I don’t interpret it as a physical entity. It summarizes what I know about the physical system.

And I agree with you - it does bother me that we have no mechanical model that works for QM, which is why I think these discussions are worthwhile. My “so what?” was facetious; I’d like to have a deeper understanding of the processes described by QM, too. My feeling is that such an understanding might follow the lines of gauge invariance. A vector potential is not physical, since a gauge transformation changes the potential without changing the physics, but certain quantities that are calculated from the potential are physically meaningful (e.g. electric field, integral around a loop). So in QM, maybe we can find a mechanical model that isn’t relativistically invariant, but the non-invariance, like a gauge transformation, never shows up in physically relevant quantities. If anyone knows how to do this, please let me know. :slight_smile:

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Thing is g8rguy a person such as yourself is willing to believe in QM and not believe time is “UNDEFINED”…your saying that you “KNOW” time is real!

I understand…it isn’t easy to think OUTSIDE THE BOX the fact remains that the QM mechanics will agree mathematically with Time(sub zero)=undefined.

Hawkings admits that time could run backward without any problems.

I don’t see the problem with T(sub 0)=undefined…in actuality this makes the MOST SENSE!

Why? Because time is a construct…not unlike Numbers. To say that “Time OBVIOUSLY exists” is an “inside the box” evidence. Let’s examine a molecule in a singularity… time stops! OR DOES it… Time is a fabrication of mankind. Don’t say “Time OBVIOUSLY exists” PROVE it does! …ha ha…you can’t! that is what makes QM work! t=undefined.