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Collapse Postulates

20 Post author: Eliezer_Yudkowsky 09 May 2008 07:49AM

Previously in seriesSpooky Action at a Distance
Followup toDecoherence is Simple, Falsifiable and Testable

Back when people didn't know about macroscopic decoherence aka many-worlds—before it occurred to anyone that the laws deduced with such precision for microscopic physics, might apply universally at all levels—what did people think was going on?

The initial reasoning seems to have gone something like:

"When my calculations showed an amplitude of -1/3i for this photon to get absorbed, my experimental statistics showed that the photon was absorbed around 107 times out of 1000, which is a good fit to 1/9, the square of the modulus."

to

"The amplitude is the probability (by way of the squared modulus)."

to

"Once you measure something and know it didn't happen, its probability goes to zero."

Read literally, this implies that knowledge itself—or even conscious awareness—causes the collapse.  Which was in fact the form of the theory put forth by Werner Heisenberg!

But people became increasingly nervous about the notion of importing dualistic language into fundamental physics—as well they should have been!  And so the original reasoning was replaced by the notion of an objective "collapse" that destroyed all parts of the wavefunction except one, and was triggered sometime before superposition grew to human-sized levels.

Now, once you're supposing that parts of the wavefunction can just vanish, you might think to ask:

"Is there only one survivor?  Maybe there are many surviving worlds, but they survive with a frequency determined by their integrated squared modulus, and so the typical surviving world has experimental statistics that match the Born rule."

Yet collapse theories considered in modern academia, only postulate one surviving world.  Why?

Collapse theories were devised in a time when it simply didn't occur to any physicists that more than one world could exist!  People took for granted that measurements had single outcomes—it was an assumption so deep it was invisible, because it was what they saw happening.  Collapse theories were devised to explain why measurements had single outcomes, rather than (in full generality) why experimental statistics matched the Born rule.

For similar reasons, the "collapse postulates" considered academically, suppose that collapse occurs before any human beings get superposed.  But experiments are steadily ruling out the possibility of "collapse" in increasingly large entangled systems.  Apparently an experiment is underway to demonstrate quantum superposition at 50-micrometer scales, which is bigger than most neurons and getting up toward the diameter of some human hairs!

So why doesn't someone try jumping ahead of the game, and ask:

"Say, we keep having to postulate the collapse occurs steadily later and later.  What if collapse occurs only once superposition reaches planetary scales and substantial divergence occurs—say, Earth's wavefunction collapses around once a minute?  Then, while the surviving Earths at any given time would remember a long history of quantum experiments that matched the Born statistics, a supermajority of those Earths would begin obtaining non-Born results from quantum experiments and then abruptly cease to exist a minute later."

Why don't collapse theories like that one have a huge academic following, among the many people who apparently think it's okay for parts of the wavefunction to just vanish?  Especially given that experiments are proving superposition in steadily larger systems?

A cynic might suggest that the reason for collapse's continued support, isn't the physical plausibility of having large parts of the wavefunction suddenly vanish, or the hope of somehow explaining the Born statistics.  The point is to keep the intuitive appeal of "I don't remember the measurement having more than one result, therefore only one thing happened; I don't remember splitting, so there must be only one of me."  You don't remember dying, so superposed humans must never collapse.  A theory that dared to stomp on intuition would be missing the whole point.  You might as well just move on to decoherence.

So a cynic might suggest.

But surely it is too early to be attacking the motives of collapse supporters.  That is mere argument ad hominem.  What about the actual physical plausibility of collapse theories?

Well, first:  Does any collapse theory have any experimental support?  No.

With that out of the way...

If collapse actually worked the way its adherents say it does, it would be:

  1. The only non-linear evolution in all of quantum mechanics.
  2. The only non-unitary evolution in all of quantum mechanics.
  3. The only non-differentiable (in fact, discontinuous) phenomenon in all of quantum mechanics.
  4. The only phenomenon in all of quantum mechanics that is non-local in the configuration space.
  5. The only phenomenon in all of physics that violates CPT symmetry.
  6. The only phenomenon in all of physics that violates Liouville's Theorem (has a many-to-one mapping from initial conditions to outcomes).
  7. The only phenomenon in all of physics that is acausal / non-deterministic / inherently random.
  8. The only phenomenon in all of physics that is non-local in spacetime and propagates an influence faster than light.

WHAT DOES THE GOD-DAMNED COLLAPSE POSTULATE HAVE TO DO FOR PHYSICISTS TO REJECT IT?  KILL A GOD-DAMNED PUPPY?

 

Part of The Quantum Physics Sequence

Next post: "If Many-Worlds Had Come First"

Previous post: "Quantum Non-Realism"

Comments (59)

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Comment author: Ben_Jones 09 May 2008 10:13:48AM 5 points [-]

I suppose that suggesting 'other' amplitudes must collapse or cancel just because we don't remember them is like suggesting the spaceship disappears once it leaves our light cone because we've lost contact with it. You're adding an extra element of complexity for no apparent reason. Never thought of it that way really. Unless I've missed the point entirely....

Main thing I've learnt from this series: the human brain must be really badly suited to understanding how nature works on the lowest levels. How else to explain our most basic laws being split into 'interpretations'?

Question - is there absolutely no communication between one world and another? Does this rule out any testable predictions?

Comment author: Shane_Legg 09 May 2008 10:30:36AM 13 points [-]

I distracted my proto-AGI for a moment and asked it to take a minute to explain this to me.

The reason for collapse, apparently, is quite simple: while most of the fundamental laws of physics are all nice, linear and elegant, keeping track of all these wave forms quickly becomes computationally intractable, even on the machine that's simulating our universe (PhD candidate Zirro's request to uses the department's new infinitely powerful super computer for his project was apparently turned down as they are still trying to simulate AIXI). Anyway, once the wave form starts to interact with too many things a subroutine kicks in and simply collapses the matrix representing the wave. Yeah, it's an ugly hack, but Zirro's A+ in epistemology means getting a B in universe simulation isn't too much of a problem for him.

Comment author: FeepingCreature 23 November 2012 01:45:01PM 1 point [-]

The amusing/scary thing is, if ancestor simulations are possible then this is probably true.

Comment author: RobinHanson 09 May 2008 11:44:00AM 1 point [-]

or the hope of somehow explaining the Born statistics

That does seem to be the main legitimate reason for considering collapse theories. But I agree that avoiding splitting humans probably is an important driver.

Comment author: Ben_Jones 09 May 2008 12:55:01PM 0 points [-]

Shane,

Did vit mention how the simulation goes about choosing which wavefunctions to collapse and which to continue processing? Is it based on how 'interesting' the resulting universe turns out? If so, should I be dancing on tabletops?

Also, is Zirro's own universe a simulation itself? How do the wavefunctions in the top-level universe decide what to do?

Comment author: eddie 09 May 2008 02:09:09PM 6 points [-]

Ben: It's simulations all the way up.

Comment author: Bob5 09 May 2008 02:29:36PM -2 points [-]

It seems that many physicists are strongly biased to deterministic theories, and that this is a prime selling point for MWI. So we have a configuration space that comprises every possible state of the universe. And we have a wavefunction over that space which evolves deterministically. So game over: there is no novelty in the universe. There is no meaningful distinction between past, present or future; they are just points on the trajectory through the configuration space, any one of which is completely determined by any other along with the universal wave equation. How boring. I think this is more of a bug than a feature.

I've already said a little about what kind of interpretation I prefer. It's along the lines of Lande's theory. Realistic interpretation of the wavefunction; reality as a single point in configuration space, and random time evolution under the influence of the wave equation.

Comment author: kamenin 09 May 2008 03:11:54PM 0 points [-]

To me, science is bound to explain human experiences by explaining qualities of the objects that form the world (I hope it's not too far fetched, I just made it up). Some qualities can be observed, even if it takes an LHC, some can't, at least we don't have any idea yet how. If then the world splitting can't be observed at all and all we know is our single resulting world then I guess science's task is to explain this single world. At least, from inside the single world that may look like the main task of science. I may be wrong, that's my thoughts right now.

In entangled systems, those systems only keep being entangled because they're experimentally protected from outside influences. I always understood collapse as a result of special interactions of the wave with the surrounding, particularly interactions which expose particle-like features of the wave-particle. It has nothing to do with distance or size. And I think that can be shown really nice in the double-slit experiment. So right there, there's no possibility in collapse theory that our brain or consciousness could be the referee of wave collapses. Before it gets to the brain, the wave function obviously has to interact. That's also an argument against the Earth's being a wave function. Wave and collapsed wave, in my understanding, explicitly behave differently, so we can't say it was a wave all along, we just never knew it.

Finally, if you substitute collapse for world splitting, wouldn't then world splitting produce the same effects and fulfill your last list quite as well as the collapse interpretation?

Nice series, really like it!

Comment author: Eliezer_Yudkowsky 09 May 2008 04:14:09PM 5 points [-]

@Ben: The communication exists but it's exponentially tiny. Not 20th decimal place, 10^20th decimal place.

Bob: It seems that many physicists are strongly biased to deterministic theories

No, physics is strongly biased toward deterministic phenomena. There is no known law in all of physics that is non-deterministic. I eliminate collapse fantasies because there is no observed phenomenon that cannot be explained as well without collapse as with it.

Kamenin: Finally, if you substitute collapse for world splitting, wouldn't then world splitting produce the same effects and fulfill your last list quite as well as the collapse interpretation?

NO, DAMN IT!

Many-worlds does not involve a special, extra, 'splitting' postulate. It is simply the pure, unaltered result of applying the same equations that are known to govern microscopic phenomena, which equations happen to result in superpositions (experimentally verified) and would logically result in macroscopic superpositions (experimental verification in progress).

So, #1, above all, the fundamental physics of many-worlds is experimentally nailed-down. It consists simply in supposing that the same rules govern at all levels. We know quantitatively what those rules are for microscopic cases. There is no theoretical doubt as to when and under what circumstances decoherence should happen - it's all in the equations already, though in practice we may have trouble doing the math.

With that said,

Macroscopic decoherence is linear, unitary, differentiable, local, CPT symmetric, probability-current conserving, deterministic, and relativistic JUST LIKE ALL THE REST OF PHYSICS, DAMNIT!

Comment author: kamenin 09 May 2008 04:45:49PM 2 points [-]

@ E.Y. O.K., no need to damn something or someone -- I think I'm almost there. I still have a blockade at this point: The splitting world describes the world from a all-knowing top-down perspective from where everything looks linear, unitary etc. But from our encapsulated one-world perspective we see this as a series of nonlinear accidents: particles hit at one point, only one point, given by the probabilities governed by the wave function. Entanglement breaks when we measure it. So what I meant was, the splitting produces the illusion for us that the world is non-linear. Wouldn't you say that from our perspective we would never be able to discriminate between both positions, if the non-linearity is true or if it's just an illusion of an superordinate process? I cannot see how you could get experimental verification from within this one world. Or as long as we just want to describe our one world, how we could get better results than by calling the non-linearity 'collapse' and go on with our maths.

If I missed something along the line, I'm really willing to learn.

Comment author: Bob5 09 May 2008 04:55:50PM 3 points [-]

So to preserve the illusion of determinism, which is not observed, you concoct the illusion of multiple worlds, which are also not observed. (feel free to imagine the preceding in all caps, to reflect my righteous indignation).

Comment author: Wiseman 09 May 2008 05:18:42PM 1 point [-]

4 points:

If collapse actually worked the way its adherents say it does, it would be: 1. The only non-linear evolution in all of quantum mechanics. 2. The only non-unitary evolution in all of quantum mechanics. 3.... WHAT DOES THE GOD-DAMNED COLLAPSE POSTULATE HAVE TO DO FOR PHYSICISTS TO REJECT IT? KILL A GOD-DAMNED PUPPY?

Not a valid argument. The physics of the universe are what they are, at the microscopic and macroscopic levels. If it so happens that there is some non-GR-violating non-locality going on (don't complain, just cause you can't imagine it, doesn't mean it's not possible), then your list above simply would be wrong, and there would be no violation of "traditional physics" to complain about.

In any case, since from the perspective of each world we have non-determinism, and the only world we are acting on is our own, why is it necessary to explain many worlds for the purposes of AGI?

Well, first: Does any collapse theory have any experimental support? No.

Neither does MW, they are both interpretations.

I'm going out on a limb on this one, but since the whole universe includes separate branching “worlds”, and over time this means we have more worlds now than 1 second ago, and since the worlds can interact with each other, how does this not violate conservation of mass and energy?

Comment author: Normal_Anomaly 30 April 2012 05:50:16PM 4 points [-]

Wiseman left ages ago, but I'm taking a stab at this question because 1) I want to know if my answer is right, and 2) other people who read it might want to know the answer too.

since the whole universe includes separate branching “worlds”[sic], and over time this means we have more worlds now than 1 second ago,

As far as I can tell from this sequence, the number of worlds that exist over time, or at least the total amplitude, is constant. Multiple "past" configurations contribute amplitude to the same "present" configuration. Any given "past" configuration also contributes amplitude to multiple "present" configurations. The scare quotes are because neither the question nor the answer makes much sense if one considers timeless physics.

Comment author: shminux 30 April 2012 10:19:22PM 0 points [-]

As far as I can tell from this sequence, the number of worlds that exist over time, or at least the total amplitude, is constant.

If you take the MWI literally, each world splits all the time, so the number of worlds would increase. Of course, there is no point counting what we cannot observe, not even in principle.

the total amplitude, is constant

Depends on what you mean by that. But yes, one can certainly express the MWI in a way that preserve unitarity over multiple worlds.

Multiple "past" configurations contribute amplitude to the same "present" configuration.

Probably not in this sense. The world splitting process ought to be a tree graph, with no cycles. Scott Aaronson explains it better.

The scare quotes are because neither the question nor the answer makes much sense if one considers timeless physics.

You may want to ponder how rational it is to refer to an exciting idea that was never fleshed out as if it were a real physical model.

Comment author: dlthomas 30 April 2012 10:31:22PM 1 point [-]

Multiple "past" configurations contribute amplitude to the same "present" configuration.

Probably not in this sense. The world splitting process ought to be a tree graph, with no cycles. Scott Aaronson explains it better.

My understanding is "Yes, but only if the resulting 'present' configurations are identical, which basically never happens when things get big."

Comment author: shminux 30 April 2012 10:52:54PM -2 points [-]

That's what Scott says, yes. There is related to Poincare recurrence, something that happens probably just as often as two worlds combining.

Comment author: YVLIAZ 04 September 2012 09:04:04PM 1 point [-]

I'm going out on a limb on this one, but since the whole universe includes separate branching “worlds”, and over time this means we have more worlds now than 1 second ago, and since the worlds can interact with each other, how does this not violate conservation of mass and energy?

The "number" of worlds increases, but each world is weighted by a complex number, such that when you add up all the squares of the complex numbers they sum up to 1. This effectively preserves mass and energy across all worlds, inside the universal wave function.

Comment author: shminux 04 September 2012 09:16:49PM 0 points [-]

This effectively preserves mass and energy across all worlds, inside the universal wave function.

Even if this were true, conservation of energy across the worlds is not a good argument for or against MWI. There is no reason it should be conserved over non-interacting entities. Also note that energy in our expanding Universe is not conserved (or even well-defined) globally.

Comment author: DonGeddis 09 May 2008 05:21:34PM 4 points [-]

Bob: But multiple worlds are observed, in subatomic phenomena. That's what superposition is. There is experimental evidence for multiple worlds.

Determinism is also observed, at the subatomic level.

So the alternative is: (1) It's exactly the same at the macroscopic level (= decoherence), or else (2) Something new, with no experimental evidence, must be happening at the macroscopic level (= collapse).

Comment author: Luke_A_Somers 30 April 2012 02:52:15PM 5 points [-]

Not sub-atomic. Multi-atomic. Poly-atomic. Just not macroscopic.

Comment author: DonGeddis 09 May 2008 05:24:53PM 0 points [-]

Wiseman, re: conservation of mass/energy. What's your answer for the simple cases, like the double-slit experiment? When you start, you have a single photon. When "it" passes through the slit(s), apparently there are at least two "things", one going through each slit. Does this mean the single photon became two photons, and violated conservation of energy?

Probably not...

Comment author: Wiseman 09 May 2008 05:41:20PM 1 point [-]

Bob: But multiple worlds are observed, in subatomic phenomena. That's what superposition is. There is experimental evidence for multiple worlds.

How does the experimental evidence favor MW over a possible collapse function with non-GR-violating non-locality?

Comment author: DonGeddis 09 May 2008 06:32:03PM 8 points [-]

Wiseman: How does the experimental evidence favor MW over a possible collapse function with non-GR-violating non-locality?

Because, at the subatomic level, no "collapse" is ever seen. At the subatomic level, there is always a distributed amplitude of position and momentum throughout all space, and it evolves deterministicly. When a photon hits a half-silvered mirror, it both gets reflected and also gets transmitted at the same time. That's basically what a "multiple world" is.

If you just put a detector in the paths, you'll never realize that the multiple worlds exist. You'll only either (apparently) detect a reflection or a transmission. You'll never detect both. But there's no question that the single photon is both transmitted and reflected.

How can you tell? By recombining the paths, causing constructive and destructive interference between "identical" particles and/or configurations.

At the subatomic level, these "multiple worlds" do exist.

At the macroscopic level, decoherence says "the exact same thing is happening to the humans; nothing different". But notice that even in the subatomic realm, you can't notice the multiple worlds until you recombine paths with identical configurations. The "problem" is that, in the macroscopic world, you never get identical configurations, so you never see constructive and destructive interference from the "multiple worlds".

MW in subatomic experiments really shouldn't be controversial. You just follow the equations. Evolve the waveform. There is always superposition between multiple outcomes. Collapse never happens. Surely you realize the theory/model for the subatomic quantum case?

The MW "interpretation" merely says that nothing changes in the macroscopic case. It's exactly the same as the quantum case. (Remaining to be explained: the Born probabilities.)

Comment author: Bob5 09 May 2008 08:13:39PM 2 points [-]

Don Geddis: I don't agree that "multiple worlds are observed, in subatomic phenomena. That's what superposition is." That is your preferred interpretation. I prefer to think that the wavefunction is real, but it is a function over potential configurations, only one of which is real. Superposition reflects the influence of other physically equivalent configurations. I would not call my interpretation a "collapse" interpretation. The wavefunction is always there, in the sense that nature "knows" the probability amplitude for points in configuration space other than the that represented by the real state of the universe.

I am also puzzled by your statement that "determinism is observed". It most certainly is not. When an atom is in an excited state, the time and direction of the photon emitted is essentially random. Isn't it more satisfactory to just acknowledge this than to postulate an infinity of other worlds being spawned for every possible direction and time of emission?

Comment author: Caledonian2 09 May 2008 08:21:44PM 0 points [-]

Bob, what makes you think there's a difference?

Comment author: Bob5 09 May 2008 08:45:40PM 1 point [-]

Caledonian: There is no difference at the level of predictions, because I'm not calling for any new laws of physics beyond QM. It's a matter of what makes sense as interpretation.

Comment author: Caledonian2 09 May 2008 08:53:51PM -1 points [-]

'Interpretation' is irrelevant, Bob. If they have identical consequences, they're equivalent no matter what you choose to call them.

Comment author: Cyan2 09 May 2008 09:32:56PM 2 points [-]

Caledonian, two current theories may have identical consequences and yet suggest very different directions for refinement. For example, a theory which postulates a fundamentally deterministic universe suggests that we look for causes of observable events, whereas a theory which postulates a fundamentally random universe includes events for which it would be fruitless to search for a cause.

The theories are not equivalent, because they have different implications about the next sensible step in understanding the universe.

Comment author: Dustin2 09 May 2008 10:11:31PM 1 point [-]

'Interpretation' is irrelevant, Bob. If they have identical consequences, they're equivalent no matter what you choose to call them.

You're confusing metaphysics with epistemology AGAIN.

Comment author: Nick_Tarleton 09 May 2008 11:23:52PM 1 point [-]

Quantum suicide might allow for subjective checking of MWI.

Comment author: Dustin2 09 May 2008 11:55:57PM 1 point [-]

There is no difference at the level of predictions, because I'm not calling for any new laws of physics beyond QM. It's a matter of what makes sense as interpretation.

The reason for that lack of difference is that every interpretation of a physical theory is an attempt at reifying the theory in some sense. Each interpretation must conform to the theory at every level of examination since the interpretation is an ascription of a certain ontology to that theory, not a modification of that theory. But it isn't the ontology which predicts things, it's the model which we've attempted to reify that does that, so no amount of experimentation is going to reveal any difference between two interpretations of the same theory. Nonetheless, those two interpretations are not equivalent. I cannot find, by way of experiment, any difference between any two interpretations of quantum mechanics, but we need only find one which asserts the metaphysical reality of wavefunctions and one which does not to see that they do not, in fact, entail precisely the same body of claims and are therefore not equivalent.

Comment author: Caledonian2 10 May 2008 03:09:17AM 1 point [-]

Attaching an empty concept to a thing doesn't differentiate between them. The idea of 'metaphysical reality' is meaningless.

The various interpretations don't just make the same predictions for the phenomena we know about, but they have no known implications that vary between them. They are equivalent. The descriptions of the mathematical processes differ, but the function they implement are the same. They're precisely the same thing with a different superficial appearance. That's all.

Something that looks like a duck, and walks like a duck, and sounds like a duck, and behaves in all ways like a duck, IS A DUCK. It's the function of a thing within the set of interactions with the universe that determine identity. Talking about something that behaves in all ways like a duck, but is somehow metaphysically different, is not only wrong-headed but silly.

Comment author: Robin_Z 10 May 2008 03:48:44AM 4 points [-]

...wait, the collapse postulate doesn't suggest different results? In order for collapse to occur, the amplitude-summing effect we see at the level of particles would have to vanish at some point. Which implies that above that point, "interference" effects will vanish.

We might have a hard time running the experiment, but that sounds like a different result to me.

Comment author: Dustin2 10 May 2008 03:49:32AM 1 point [-]

You aren't paying attention. Theories make predictions, interpretations of theories do not. In any case, suppose we grant you your little maxim. Then, if we can't tell the difference between an interpretation which claims that wavefunctions and their collapses are real and one which explicitly claims that they are not real by experiment, they're equivalent. Your maxim has just given us that wavefunctions are metaphysically real if and only if they are not.

And, in any case, someone who reacts against metaphysical realism should also take the brain in the vat hypothesis seriously, and you have no grounds for saying that something which is measured in all ways to be like a duck is, metaphysically, a duck. And that's fine. I'd agree. But if you don't want to play metaphysics, don't. Don't claim that two different ontologies are equivalent when they clearly aren't. Just don't reify the physical model. Tell anyone who purports to have a reification of a physical theory that they're committing a fallacy of reification and be done with it. You can't have it both ways.

Comment author: Caledonian2 10 May 2008 04:01:33AM -1 points [-]

Theories make predictions, interpretations of theories do not.

That's precisely the point!

Arguing over the 'interpretations' is pointless. Even if we could identify a difference in the implications, we don't have any relevant data that would permit us to distinguish them. So there are no grounds for rejecting or accepting any one of them - doing so is departing from rational skepticism.

We don't even have a difference of implication between the interpretations. So there isn't even a theoretical distinction between them.

Are you a professional philosopher by any chance, Dustin?

Comment author: DonGeddis 10 May 2008 04:55:47AM 2 points [-]

Bob wrote: I prefer to think that the wavefunction is real, but it is a function over potential configurations, only one of which is real. Superposition reflects the influence of other physically equivalent configurations. I would not call my interpretation a "collapse" interpretation. The wavefunction is always there, in the sense that nature "knows" the probability amplitude for points in configuration space other than the that represented by the real state of the universe.

Bob, I'm having a hard time assigning semantics to your words. What does it even mean, in general, for a mere "potential" non-real thing (like your configurations), to influence the "real" world? What is reality, other than things that affect the real world? How can a "potential" thing cause real effects in the real world?

What does it mean for there to be a "probability amplitude" for non-real things? If they are non-real, wouldn't their probability (of "being real", presumably) be zero? What is that a probability of, if it isn't of reality?

I know the meanings of the individual words you've written, but the way you put them together sounds like nonsense. "Colorless green ideas sleep furiously", that sort of thing. Your theory doesn't seem "wrong" to me, so much as not even meaningful.

If I'm mistaken, perhaps you can help me out by explaining what it might mean for something to not be "real", and yet to affect "reality". That seems to be an inherent contradiction to me.

Comment author: Dustin2 10 May 2008 06:27:49AM 0 points [-]

So there isn't even a theoretical distinction between them.

You were making perfect sense right up to this sentence (I suspect that's because you were just rephrasing something I've already said). That sentence, though, has sadly brought us back to where we started: your perpetual conflation of metaphysics with epistemology. Scientific theories and ontologies aren't the same thing. If you think the latter is baseless, that's probably right, but I'd think that would give you added incentive in making sure that you understand the difference between a model and the reification of that model.

By the way, you still have a contradiction to explain away.

Comment author: Will_Pearson 10 May 2008 08:04:25AM 0 points [-]

"Theories make predictions, interpretations of theories do not. In any case, suppose we grant you your little maxim. Then, if we can't tell the difference between an interpretation which claims that wavefunctions and their collapses are real and one which explicitly claims that they are not real by experiment, they're equivalent. Your maxim has just given us that wavefunctions are metaphysically real if and only if they are not."

I'm sympathetic to caledonians position at least for non-theoretical physicists (one position might be better than the other for trying to find better theories). My way out is that, "real" is not a predicate that can be attached to "collapse".

Comment author: Caledonian2 10 May 2008 01:56:38PM -1 points [-]

The Koan of Master Foo

It is recorded that once, when Master Foo was iterating along a beach, he came upon two of his disciples arguing by a computer processor. "It is subtracting positive 1", declared the first. "No; it is adding negative 1", asserted the other. Master Foo answered them thus: "Not incrementing, not decrementing — Equalizing!" whereupon both were enlightened.

Ben Jones, the spaceship DOES disappear once it leaves our light cone. What do you imagine dis-appear means, that you think it's not what the spaceship does?

Our universe has an edge. Throw something over that edge, and it ceases to be. You might as well say that it doesn't disappear if we break the First Law of Thermodynamics and utterly unmake it - which is what we're doing, as it happens.

Comment author: Dustin2 10 May 2008 03:43:12PM 1 point [-]

Throw something over that edge, and it ceases to be.

Sweet Jesus! Observers in asymptotically flat spacetime don't ever see something go over an event horizon. They just see it get pancaked onto the thing. Interestingly, in proper time, you're still probably wrong.

Comment author: Dustin2 10 May 2008 03:44:01PM 0 points [-]

And by the way, Zen master, you still have a contradiction to explain away.

Comment author: Eliezer_Yudkowsky 10 May 2008 04:09:05PM 1 point [-]

Dustin, Caledonian is the local troll. Don't bother.

Comment author: Caledonian2 10 May 2008 04:24:33PM 0 points [-]

There is no such thing as "metaphysical reality", the concept is empty, and it's meaningless to question whether things possess the property.

The different 'interpretations' give the same results for everything we can observe, and the same predictions for the things we can't yet observe. They are logically equivalent. They are the same thing with different appearances. It is nonsensical to say that one is true, or that another is not true. They are all equally true.

If someone can locate a prediction that one makes that another does not, THEN we will recognize them as logically distinguishable. If someone can produce evidence compatible with some but incompatible with others, THEN we can begin to speak about some being or and untrue.

As it stands, asking about such matters is like asking whether the ice cream is 'metaphysically 'atop the pie, or the pie 'metaphysically' beneath the ice cream. The phrases are different - surely the things they describe must be different, too!

NO. Metaphysics is nonsense, and the question incoherent.

Comment author: Cyan2 10 May 2008 06:01:37PM 1 point [-]

The different 'interpretations' give the same results for everything we can observe, and the same predictions for the things we can't yet observe. They are logically equivalent. They are the same thing with different appearances. It is nonsensical to say that one is true, or that another is not true. They are all equally true.

I never thought I'd see Caledonian affirm the existence of angels, even if all they do is use Maxwell's equations to figure out how to push on charged particles, but there it is in black and white. Wow.

Comment author: Caledonian2 10 May 2008 09:15:04PM 0 points [-]

I never thought I'd see Caledonian affirm the existence of angels,

And you never will, barring some truly remarkable evidence.

You seem to have misunderstood. Having an invisible, intangible, etc. etc. dragon in your garage IS having no dragon in your garage. Having quantum collapses IS having Many Worlds... unless and until you can demonstrate that the two are different in some way. And it cannot simply be noting that you use different phrases to refer to them, because that's not a property of the phenomena, just how you choose to talk about them.

When it can be shown that they have different, operational implications, then they will be distinguishable. Until that time, they aren't. Arguing over which of two indistinguishable things is correct is fundamentally wrong - they both are.

Comment author: Robin_Z 10 May 2008 09:43:33PM 0 points [-]

Having quantum collapses IS having Many Worlds... unless and until you can demonstrate that the two are different in some way.

...

I do not believe that word means what you think it means.

Comment author: Cyan2 10 May 2008 10:30:08PM 0 points [-]

Caledonian, my position is that the claim that there is no dragon in my garage and the claim that there is an undetectable dragon in my garage are logically inconsistent, not logically equivalent. From my perspective, the logical equivalence you are insisting on really does require you to ascribe Maxwell's equations + angels the same credence you ascribe to the bare Maxwell's equations. Kooky.

Comment author: Dustin2 10 May 2008 11:11:24PM 1 point [-]

Having quantum collapses IS having Many Worlds

Good God, he's even making up his own contradictions now.

Comment author: Caledonian2 10 May 2008 11:22:23PM 0 points [-]

Cyan, the 'angels' are a completely empty concept with no meaning and no implications. Saying that your model has Maxwell's Laws plus angels is just a fancier way of saying it has Maxwell's Laws - it's like putting leading zeros on a number, or double negatives in sentences. It doesn't change the value of anything, it's just a somewhat silly elaboration. As ridiculous as such behaviors are, I don't see any reason to prohibit them.

It's when people insist that the dragon-without-actual-properties is somehow 'metaphysically distinct' from simply not having a dragon that they fall into error, as opposed to mere silliness.

People may use whichever 'interpretation' they prefer, because they're all the same. It's the people who insist that one of the interpretations is fundamentally better than the others, without producing new evidence that shows there is actually a difference, who are wrong.

Look at it this way: if I show you a given pattern in Conway's Game of Life, and ask you what the grid looked like one step earlier, how would you respond? (To simplify the thought experiment, let's restrict the size of the grid to something finite.)

Comment author: Wiseman 10 May 2008 11:30:17PM 0 points [-]

Dustin: "Good God, he's even making up his own contradictions now."

That is a meaningless comment, and adds nothing to this discussion. The whole point I believe, of Caledonian's argument is that the statement "MWI -is- collapse" is not a contradiction, so long as the differences in the theories/interpretations of QM can never be substantiated with experimental evidence, ever, because the theories themselves don't allow for it, rather than we just haven't seen those experiments yet.

That said, I don't think that's the case with MWI. If you are saying something about reality that supposedly is true, and has an effect on the rest of reality, I find it unlikely that if it were true, it wouldn't eventually result in experimental evidence that proved that.

But if it can not be shown that MWI would result in experiments that explicitly differentiated it from non-local collapse, than Caledonian's point remains valid, or at least valid enough that there's no reason to be nasty about it (Eliezer, Dustin).

Comment author: Dustin2 11 May 2008 12:39:13AM 3 points [-]

The problem here seems to be a deliberate conflation of "logically equivalent claims" (which are two sets of claims entailing precisely the same set of statements entirely independently of whether those statements are a good or even testable model for a physical pheonomenon) and "physically equivalent states" (which are two ostensibly different states which are the same at every level of examination), or a deliberate conflation of the model of a phenomenon with the phenomenon itself. This conflation is, in either case, completely solipsistic, and arguing with solipsists is futile.

I'll leave the two of you to congratulate yourselves on being both brains in vats and not brains in vats at the same time.

Comment author: Cyan2 11 May 2008 02:17:49AM 0 points [-]

Caledonian, it's not that I don't understand what you're saying, it's just that I don't agree. I think I'll have to leave it there since I want to avoid fruitless arguments over the meanings of words.

Comment author: Nick_Tarleton 11 May 2008 04:36:57AM 0 points [-]

Even if there is a difference between a completely undetectable dragon and no dragon, does anybody care? I can see ethical implications MWI (multiverse theories in general, really) might have even if they're not testable, analogous to the ethical implications of things not disappearing when they cross the cosmological horizon; but in the absence of any mention of practical reason, so much focus on interpretations seems unjustified.

Comment author: DonGeddis 11 May 2008 05:15:00PM 6 points [-]

Re: MWI (!)= Collapse.

But isn't this easy? They don't actually have the same logical implications. It's simple to find (theoretical) experiments that would distinguish them.

MWI implies that you'll see inteference phenomena at all scales, and without humans involved. It's hard to set up the experiment, but you can imagine a double-slit experiment with a macroscopic baseball, for example. According to MWI, if the configuations are the same, there will be interference.

Collapse implies some transition point, based on something. There are different versions of it. One of the originals said that it was consciousness, which has implications for humans being part of the experimental setup, and also suggests that AI will fail. AI (someday) succeeding is probably an observation that contradicts the consciousness-causes-collapse theory.

Even the more modern collapse theories suggest something about scale. So a baseball double-slit experiment would distinguish MWI from that collapse theory.

This isn't invisible dragons in a garage (except insofar as the collapse folks keep changing the goalposts every time their current theory is invalidated). Nor even the spaceship-over-the-horizon problem. This is really a case where the two interpretations agree on the subatomic consequences, but disagree on extending them to macroscopic scales.

There are testable differences between the theories.

Comment author: BogdanBelcea 19 December 2011 10:07:19AM 6 points [-]

The research to demonstrate quantum superposition at 50-micrometer that Eliezer was mentioning has been published in March 2010 :D

Comment author: Kenny 14 March 2013 04:33:11PM 0 points [-]

And the results seem to be that macroscopic interference was observed.

Comment author: vitaly 18 April 2013 02:02:27AM 0 points [-]

What about treating the collapse as the Bayesian probabilities update in light of the measurement (new evidence)?

Comment author: hairyfigment 18 April 2013 02:14:48AM 0 points [-]

I think Bell's theorem rules out exactly this reading. Unless you just redefine probability to include all the math of QM, but I feel inclined to call that a vile heresy.

Comment author: PrawnOfFate 18 April 2013 02:20:17AM 0 points [-]

Dropping the Bayes, subjective interpretations of collapse as receipt of information are not ruled out.