So, which do you choose? Do you want to discuss MWI, or do you want to adhere to the "existence" which most reasonable people refer to? — Metaphysician Undercover

It's not an either-or. MW is just the ordinary language interpretation of QM.

That doesn't imply that things will therefore exist in the way that we might intuitively think. Who knew that things wouldn't have a precise position and momentum at the same time? They still exist, but we've learned new things about them.

The whole point your long and detailed answer skips over is the 'm' in mwi.

Many-Worlds does not propose infinite (or finite) branching universes. The branching is already integral to QM. — AndrewM

Right. So it says the 'many worlds' are already there, it was up to Everett to see the implication.

The Copenhagen Interpretation has to add a postulate to QM to prune the branches it doesn't want, which is the famous wave function collapse.

The wave-function collapse is not a theoretical postulate. We're not discussing physics, we're discussing metaphysics.

These are the kinds of considerations that motivate the Many-Worlds Interpretation.

The instrinsically grotesque nature of there being 'many worlds' is skipped over by the advocates; like, the strangeness of the idea that we're all part of an infinite 'hall of mirrors' is being skipped over, on account of the fact that it is 'mathematically convenient'. Don't you see how strange that is?

Some might say that the world-shattering thing was Everett's relative state formulation.

Neils Bohr was unmoved by it, and in my books his judgement counts.

So why, when the going gets tough, should we abandon what has proven to work and switch to the alternatives? It seems completely predictable that it will cause confusion.

We would hate confusion. Much better to be soothed than to be disturbed.

This has been an instructive debate. I have taken some of it over to Physics Forum.

So, I'm up to Everett now in the book I'm reading on quantum mechanics. The section on Everett starts with a couple of eminent physicists saying they think quantum theory must be incomplete. What occurs to me is, perhaps it is physics that is not complete, and that, maybe, this is because physics is not, in the end, a complete description of what is real. In other words, that what is real, is not physical.

...perhaps it is physics that is not complete, and that, maybe, this is because physics is not, in the end, a complete description of what is real. In other words, that what is real, is not physical. — Wayfarer

This is a most enjoyable thread to read: thanks to all the participants. Sorry I've been too busy to contribute. Here is Nietszche (from another thread really!):

...even physics is only a way of interpreting or arranging the world...and not a way of explaining the world. — Nietzsche

I have been fretting over the distinction between epistemology and ontology, surprised by its use in this thread. I don't think science in its practice deals with ontologies, and I don't think physicalists think so either. For example, I'm working on something about placebos. Scientific discourse about placebos uses 'beliefs' as data and refers to 'beliefs' in its hypotheses. But I don't think that commits physicalists to an ontology including mental terms like 'belief': they may perfectly well claim that such epistemic terms stand for an equivalent more fundamental physical term, or that the mental supervenes on the physical.

Conversely, there is nothing forcing someone who debates physics - while accepting the methods of science - into an ontology of one kind or another. There's a whole Stanford group of philosophers of science who would say this, including Dupre and...

...we have no grounds in our experience for taking our laws - even our most fundamental laws of physics -as universal. Indeed, I should say 'especially our most fundamental laws', if these are meant to be the laws of fundamental particles. For we have virtually no inductive reason for counting these laws as true of fundamental particles outside the laboratory setting - if they exist there at all. — Nancy Cartwright

That's the irony. Many-Worlds does not propose infinite (or finite) branching universes. The branching is already integral to QM. The Copenhagen Interpretation has to add a postulate to QM to prune the branches it doesn't want, which is the famous wave function collapse. — Andrew M

I'm going to quibble with you here. The Copenhagen Interpretation does quite a bit more than postulating wavefunction collapse in order deny reality:

1. Copenhagen explicitly denies the reality it purports to be describing. i.e. wavefunctions do not exist.

2. Because wavefunctions don't exist, neither does wavefunction collapse.

3. The Complimentarity Principle - the Principle that particles either exist as particles or waves, never both.

4. The Correspondence Principle. The Principle that QM is a subsidiary theory to classical Mechanics.

5. Principle of Acausality. i.e. the Born Rule and its algorithm.

6. Principle of irreversibility.

(7. Consciousness causes collapse) - in brackets because it is so embarrassing.

Of course, as you know, Everett's theory doesn't make any of those assumptions let alone declare they are principles of reality.

Conversely, there is nothing forcing someone who debates physics - while accepting the methods of science - into an ontology of one kind or another. There's a whole Stanford group of philosophers of science who would say this, including Dupre and...

...we have no grounds in our experience for taking our laws - even our most fundamental laws of physics -as universal. Indeed, I should say 'especially our most fundamental laws', if these are meant to be the laws of fundamental particles. For we have virtually no inductive reason for counting these laws as true of fundamental particles outside the laboratory setting - if they exist there at all. — Nancy Cartwright — mcdoodle

Well, there is indeed "no inductive reason for counting these laws as true"- because there is no such thing as an inductive reason for any explanation, let alone for arriving at an explanatory scientific theory.

I must at your quote to my list of generic ways to deny reality - the direct appeal to fallacy.

It's not an either-or. MW is just the ordinary language interpretation of QM.

That doesn't imply that things will therefore exist in the way that we might intuitively think. Who knew that things wouldn't have a precise position and momentum at the same time? They still exist, but we've learned new things about them. — Andrew M

It is an either-or, you're just in denial. You're claiming that the only possible starting point for meaningful discussion, is the premise that things exist in the intuitive, common sense notion of "things exist". And you want to maintain this premise, while introducing the QM premise that things do not "have a precise position and momentum at the same time". Do you not see that this QM premise contradicts the common sense notion of "exists"? When there is contradiction, we have an either-or situation.

If you want to proceed in understanding the quantum reality, you must drop this ancient, outdated, notion of existence, which is inherently contradictory to the quantum reality. When "matter" was superseded by "energy" as the principle of continuity in the physical world, "existence" in the common sense notion of the word, was lost. Berkeley demonstrated that there is no necessity to the assumption of matter, it's just a useful premise. Aristotle introduced it as a way to account for continuity in an ever changing world. The assumption that "matter" is real makes continuity real. That is what is at issue here, what assumptions will we make to account for continuity?

Aristotle posits matter as the principle of continuity, it's the continuous thing which is real. Newton adapts the principle of continuity, in his first law of motion, to allow that the continuous thing is moving. Notice that the formulation of Newton's first law is such that the motion of the thing is that which is continuous, not the "matter", which refers to the very existence of the thing. the very existence of the thing is no longer addressed, just the motion of the thing is said to be continuous. Now, the continuity of existence is assigned to a description of the object, a formula, which describes its motion. Here, the continuity of existence is attributed to a form of the object, its motion, rather than using the Aristotelian principle which assigns the continuity of existence to the object's matter. Matter and form are two completely distinct aspects of the object.

Are you ready to proceed into the realm of "energy", in which the continuity of existence is firmly established to be inherent within the formula, the description which applies to the movement of the object? If so, we cannot turn back and try to assign to the object itself a continuity, without some mathematical principles, because this is to relate one continuity to multiple continuities. We've given up the Aristotelian notion of individual continuities for each and every object (matter), in favour of one universal continuity, energy. This continuity is expressed now as a wave function, and to relate the wave function to individual continuities, of individual particles, requires field mathematics.

Do you AndrewM, recognize that there is a fundamental incompatibility between the premise that there is just one continuity, and the premise that there is multiple continuities? These two premises are incompatible, contradictory. So, when we progressed from Aristotle's principle of matter, which assumes a continuity for each individual object (multiple continuities), to modern physics' principle of "energy", which assumes just one universal continuity for all objects, we crossed a gap of incompatibility. There are principles of relativity which bridge this gap, but the fact remains that there is an inherent incompatibility, and the bridge is just an illusion. This illusion creates a misunderstanding in those people who believe that the gap has been bridged. Now, when we proceed back across the bridge, to relate the wave function, which represents the one single continuity, to the multiple continuities of individual particles, through the means of field mathematics, we have that very same incompatibility. There is no bridge there, the bridge is just an illusion created by relativity theory.

It is an either-or, you're just in denial. You're claiming that the only possible starting point for meaningful discussion, is the premise that things exist in the intuitive, common sense notion of "things exist" — Metaphysician Undercover

How do you explain quantum interference if the other path does not "exist"? How can things that don't exist be physically causal?

Why does the Elitzur-Vaidman bomb-tester work?

Well, there is indeed "no inductive reason for counting these laws as true"- because there is no such thing as an inductive reason for any explanation, let alone for arriving at an explanatory scientific theory.

I must at your quote to my list of generic ways to deny reality - the direct appeal to fallacy — tom

Sorry, I don't know what you mean.

From premisses via inductive reasoning we arrive at conclusions. Premiss 1: There are well-demonstrated laws X in the lab. Premiss 2: Lots of things that are lawful in the lab turn out to be lawful outside the lab. Premiss 3: Laws X are one of those sorts of thing. Conclusion: Laws X apply all over the place.

How do you think lab findings end up as (supposed) neutrinos passing through me and you outside labs?

How do you explain quantum interference if the other path does not "exist"? How can things that don't exist be physically causal? — tom

If you read my posts, what I contest is the assumption that the particle, or any object in general exists. To talk about any paths of the object is pointless before we've established the existence of the object.

How can things that don't exist be physically causal? — tom

Causality is a description, and there is nothing which prevents us from making imaginary or fictitious descriptions.

Causality is a description, and there is nothing which prevents us from making imaginary or fictitious descriptions. — Metaphysician Undercover

Sure, but try making a fantasy or fictitious EXPLANATION.

Seriously, try it. If the bomb-tester is too complicated, then try constructing a fictitious EXPLANATION of the simple Mach-Zehnder interferometer.

You describe yourself as a Positivist, i.e. you hold the view that all statements apart from those describing or predicting measurements are meaningless. — tom

This is a good example of something I was saying to Wayfarer in another thread. He was asking why I didn't give an example of/quote some other published philosopher whom I agree with on the mind/body issue. I said that one of the reasons was that people then take one to wholesale subscribe to that philosopher's views, at least in the realm in question, and that's the case even when you explicitly try to preempt that misunderstanding. In the post that you're responding to, i said this:

That doesn't mean that I'm a logical positivst wholesale, and I certainly do not agree with them on the idea of meaning, etc., — Terrapin Station

Unfortunately with this:

Your theories of the inapplicability of reason, and the theory of consciousness-induced-creation, — tom

I'm not even sure what you're talking about.

You complain about abstractions and mathematics. — tom

I'm not sure what you're referring to there, either. Any comments I made about that would have been by way of an explanation (specifically with respect to "what's really going on" in my view); I wouldn't have been complaining about anything.

Sure, but try making a fantasy or fictitious EXPLANATION. — tom

A fictitious explanation is even easier than a fictitious description, because empirical evidence relates directly to the description, not the explanation. So I could provide a fictitious description of what I see out my window, suppose I describe a bicycle chained to a post. But this could be verified empirically, and determined to be fictitious. My explanation of why there is a bike chained to the post, a man put it there last night, or a woman put it there this morning, is an occurrence in the past, and therefore cannot be empirically verified. The explanation can be denied as fictitious only when it is determined that some elements of the description are fictitious. Either the description, "there is a bicycle chained to a post" is determined as fictitious, or the description of the man putting it there is determined as inconsistent with what is empirically determinable. The conclusion that the explanation is fictitious can only follow from empirical determination of fictitious elements in the description. Therefore any sort of fictitious explanation can pass as a possible truth, so long as consistency with the empirical evidence is maintained.

If you're trying to make a point, you should explain yourself more clearly, because what you have said so far appears as irrelevant nonsense.

From premisses via inductive reasoning we arrive at conclusions. Premiss 1: There are well-demonstrated laws X in the lab. Premiss 2: Lots of things that are lawful in the lab turn out to be lawful outside the lab. Premiss 3: Laws X are one of those sorts of thing. Conclusion: Laws X apply all over the place.

How do you think lab findings end up as (supposed) neutrinos passing through me and you outside labs? — mcdoodle

So, you are defending the assertion that:

"

we have no grounds in our experience for taking our laws - even our most fundamental laws of physics -as universal. — Nancy Cartwright

...by purporting that there is indeed an "inductive argument" for the opposite? Seriously?

For we have virtually no inductive reason for counting these laws as true of fundamental particles outside the laboratory setting - if they exist there at all. — Nancy Cartwright

"Virtually no inductive reason". What is that supposed to mean?

Your premises are a joke, surely?

A fictitious explanation is even easier than a fictitious description, — Metaphysician Undercover

Over to you. The Mach-Zehnder interferometer explained ...

So, you are defending the assertion that..(quote from Cartwright) — tom

No. I defend its coherence, I'm agnostic about whether it's true, it's obviously a radical opponent of metaphysical realism, but some realists go along with the sort of thing Dupre and Cartwright say about 'ontology'.

What I was doing was responding to you saying...

Well, there is indeed "no inductive reason for counting these laws as true"- because there is no such thing as an inductive reason for any explanation, let alone for arriving at an explanatory scientific theory. — Tom

...by asking you what you meant. I'm not being sarcastic, jokey or offensive. I genuinely don't know what you mean by the sentence I'm quoting. I tried to posit a banal way of constructing an inductive argument in the hope you would then show me what you meant. How do you arrive at an explanatory scientific theory other than by inductive reasoning?

This is a most enjoyable thread to read: thanks to all the participants — MacDoodle

Thanks! I took a question over to physics forum and made what I consider an original discovery. This is that the interference pattern in the double-slit experiment is not rate-dependent. In other words, whether the protons are fired singly or as a beam, makes no difference to the interference pattern. So that means that the interference is not dependent on time and space. Which suggests to me that the so-called 'wave function' is not something in time or space either.

In other words, whether the protons are fired singly or as a beam, makes no difference to the interference pattern. — Wayfarer

The interference is from the fact that the particle can take two possible paths through the twin slits. So it is about the particle and the apparatus, not the particle and all the other particles.

And the fact that you see a particle hitting the detector screen is the destruction of that wave function. The particle shows up at some place, and you can attach a probability to that place ranging from very low to very high.

So to "see" an interference pattern on the screen requires we collect some reasonable number of wavefunction collapses - the story of many individual particles trips through the probabilistic maze. But the point of the experiment is that even a single particle will behave like a wave - a superposition of a pair of probability waves.

But the point of the experiment is that even a single particle will behave like a wave - a superposition of a pair of probability waves. — Apokrisis

Right! That is what I have been thinking about. The question seems to be: how can a particle 'interfere with itself'?

So is there any sense in which the probability distribution is causing the individual particle to behave as though it is part of a beam of particles? It seems as if the probability distribution is itself like the so-called 'pilot wave' - in other words, it determines all the possibilities, but only in the sense of constraining the possible paths that any particle takes, whether individually or as part of beam. But because it is simply probability, or possibility, it is not something that actually exists; it is on the borderline of potentiality and actuality. So it doesn't exert any force, it is not causal in that sense, but causal in the sense of being a constraint.

You know, he also said this:

Buddhism does not promise, it delivers, while Christianity promises everything and delivers nothing.” —F. Nietzsche, The Anti-Christ

A relevant guest post on Sean Carroll's blog by philosopher David Wallace: On the Physicality of the Quantum State

Hang on Woz, I think you've crossed threads.

Lol, you're right I did. I'll just relocate that then...

If you're trying to make a point, you should explain yourself more clearly, because what you have said so far appears as irrelevant nonsense. — Metaphysician Undercover

The question seems to be: how can a particle 'interfere with itself'? — Wayfarer

The issue of course is that we have no good explanation in terms of concrete commonsense notions. So you are not going to get the kind of answer you are seeking in terms of things you think you understand.

But such caveats aside, there is no particle travelling through the apparatus. Instead there is an evolving wave of probability of detecting a particle that reflects the shape of the apparatus. If there are two slits that the wave has to pass through, then it "goes through both" and you get the resulting wave-like interference effect.

Remember that you get a wave-like defraction effect even if only a single slit is open. The slit causes particles to spray out across the detection screen. If the particles acted exactly like particles, they ought to just go straight through and burn a crisp hole in the one spot, not get smeared out across the screen.

So that is the wave~particle duality. We know that only one particle gets emitted, one particle gets detected. But on its travels, it acts like a classical wave and responds to the shape of the experimental apparatus accordingly.

It seems as if the probability distribution is itself like the so-called 'pilot wave' - in other words, it determines all the possibilities, but only in the sense of constraining the possible paths that any particle takes, whether individually or as part of beam. — Wayfarer

But don't forget the causal role being played by the apparatus here. There are some specific - classical - set of constraints being placed on the particle event. That may include experimenters making complicated delayed choice measurements with half silvered mirrors, or whatever.

So in the decoherence view, we can see this as being about the hierarchical nested constraint of quantum potential. The causality is contextual.

Start with a naked vacuum - the Universe in its most unconstrained state, without any kind of experimental apparatus. You still have some probability of an emission and absorption event. But it would be very random and patternless. The wavefunction would represent very little causal or contexual information beyond some probability of a patch of vacuum having an energetic fluctuation.

But now start to assemble an apparatus. You have a photon gun, or some other particle producing machine that heats up and is designed to produce quantum events at some controllable rate. Now you have a wavefunction that is becoming quite highly constrained by its "classical" context. It is like corralling pigs in a pen and then creating a small gate which you can open. Pigs will start to fly out in a predictable direction.

Then start adding in slits. This is like creating another pen with another gate. The pigs that happen to make a straight bee-line towards the next gate will fly through, but are then free to bend off once they are past. If there are two such gates, the pigs will form an interference pattern as they eventually smash into some distant wall set at an appropriate angle across their path of flight - a further act of constraint.

So the wavefunction itself is the product of some environmental arrangement, some set of constraints that give shape to a "process". And the collapse is then just taking that constraint a further step. It is placing an end-stop by insisting that absorption happens "right now" due to some overwhelming constraint, like a particle detector screen.

The quantum weirdness then comes in because no detector can ask every question of nature that you might expect of the one event.

In the classically-imagined world, the particle (or wave) would have some exact position and momentum at all times. But in the quantum reality, you can't answer both questions at the same time with complete certainty. So the weirdness lies in the fact that the environment can causally constrain events up to a point. But that ability to create exactness runs out before classicality believes it should.

And as I say, even a single slit results in quantum uncertainty. The narrowness makes it certain that any particle had to come through it. But at the detector, you have to pay for that certainty by losing certainty about the momentum.

There you are standing waiting for your pigs to come flying straight through your maze of gates. But while you now the pigs can only come through the gate, they are then free to veer off randomly once their path is not constrained. And so veer off they do.

The issue of course is that we have no good explanation in terms of concrete commonsense notions. So you are not going to get the kind of answer you are seeking in terms of things you think you understand. — Apokrisis

I do get that. Note these quotes.

We know that only one particle gets emitted, one particle gets detected. But on its travels, it acts like a classical wave and responds to the shape of the experimental apparatus accordingly. — Apokrisis

And is that the wave that is described by the Schrodinger equation?

So the wavefunction itself is the product of some environmental arrangement, some set of constraints that give shape to a "process". — Apokrisis

But I'm thinking, it can't be a product.

The fact that 'rate is not important' strikes me as being an important point.

Consider this thought-experiment - set up two double-slit experiments. In one, fire the photons off sequentially, i.e. one at a time. In the other, send them as a beam.

Then send the results to a third person.

Would that person be able to tell which was which? According to what I am told on Physics Forum, the answer is 'no'.

So if the pattern is not rate-dependent, then by implication the cause of the pattern is not a function of time.

What do you think?

So if the pattern is not rate-dependent, then by implication the cause of the pattern is not a function of time. — Wayfarer

You mean the pattern isn't the function of other particle histories. The pattern is simply a function of the fact the same maze, the same apparatus, imposes its constraints on a sequence of highly identical events.

So it is the design of the system that makes it rate-independent. You could stick the equipment in a cupboard for a thousand years, pull it out, and the quantum statistics would be unchanged.

Perhaps you are confusing entanglement and superposition in your understanding of what is going on?

...http://backreaction.blogspot.co.nz/2016/03/dear-dr-b-what-is-difference-between.html

You mean the pattern isn't the function of other particle histories. — Apokrisis

The pattern is dictated by the wave function. That will be so regardless of which apparatus or set-up you're using. The equation which describes the distribution is not dependent on the apparatus, although I imagine that the particulars of each set-up might produce variations because of the distances involved etc. But the underlying determinative cause is the wave equation itself - however the wave equation is not a material cause, as it is not something which exists, it's simply a pattern of probabilities, as the name says. The ontological status of the wave function is the outstanding issue in all of this, it is what lead to the 'relative state formulation' in the first place. So I think the real sticking point is, how can a probability be causally efficacious. Isn't that what the whole argument is about? That's what Einstein kept saying to Bohr - 'God doesn't play dice'. He made a slogan out of it.

The reason why the rate-independence is significant, is that the behaviour of individual 'particles' (not that they're actually particles) is described by the wave-function, whether they're together or separate. In other words, whatever is causing that, is independent of space/time, or, that duration and the proximity of 'particles' are not factors in determining the result. Or so it seems to me.

That's not confusing super-position and entanglement, although what I'm starting to think is that the 'rate-independence' of the pattern, and the so-called 'entangled states', are actually two aspects of the same underlying cause.

Thanks! I took a question over to physics forum and made what I consider an original discovery. This is that the interference pattern in the double-slit experiment is not rate-dependent. In other words, whether the protons are fired singly or as a beam, makes no difference to the interference pattern. So that means that the interference is not dependent on time and space. Which suggests to me that the so-called 'wave function' is not something in time or space either. — Wayfarer

The wave-function is the Face of God, or the Greater Context of the Truth if you prefer, that which none may know in all its glory. It is where the context and content meet with their identities becoming conflated and indeterminate. That's why for all practical purposes photons express the same behavior as their own shadows being instantly absorbed and emitted and displaying no preference even mathematically for any direction in space or time. Its a question of how humble their contents and contexts are relative to the observer which is why both shadows and quanta can express apparently acausal behavior. It means they should be measurable for both bandwidth potentials using differentials and juxtapositions for integrals that, combined, form a self-organizing system.

The pattern is dictated by the wave function. That will be so regardless of which apparatus or set-up you're using. The equation which describes the distribution is not dependent on the apparatus, although I imagine that the particulars of each set-up might produce variations because of the distances involved etc. — Wayfarer

...and you can't see how you just contradicted yourself?

In the real world, every set-up is particular, and so a particularisation of the wavefunction equation.

But the underlying determinative cause is the wave equation itself - however the wave equation is not a material cause, as it is not something which exists, it's simply a pattern of probabilities, as the name says. — Wayfarer

The equation is the useful, in the limit, generalisation or abstraction which describes no actual world until some numbers are plugged into it, just like the laws of motion.

You are making the mistake of reifying it and then treating that reification as a mysterious further concrete part of nature. Platonism redux.

So it is not simply a pattern of probabilities until some actual numbers have been plugged into the equation.

So I think the real sticking point is, how can a probability be causally efficacious. Isn't that what the whole argument is about? That's what Einstein kept saying to Bohr - 'God doesn't play dice'. He made a slogan out of it. — Wayfarer

The sticking point is that probability is irreducible. The wavefunction is the tool that limits the extent of the weirdness in useful fashion. But in the end, it can't be eliminated by just an equation. The equation - even if total information is plugged into it - can only point its finger to roughly where to expect a particle to be. So the question is how does that residual uncertainty ever get eliminated by a "real collapse".

The reason why the rate-independence is significant, is that the behaviour of individual 'particles' (not that they're actually particles) is described by the wave-function, whether they're together or separate. In other words, whatever is causing that, is independent of space/time, or, that duration and the proximity of 'particles' are not factors in determining the result. Or so it seems to me. — Wayfarer

Well you are wrong. It is an important point that the particle "goes both ways" even if it was a one-off, never to be repeated, experiment.

The problem is you can't see that just from observation of the one event.

That's not confusing super-position and entanglement, although what I'm starting to think is that the 'rate-independence' of the pattern, and the so-called 'entangled states', are actually two aspects of the same underlying cause. — Wayfarer

So with next to no demonstrable understanding of the theory, you have convinced yourself you have stumbled on the missing link which has eluded a century of physicists?

Isn't that the definition of crackpot?