I really hoped for something other than sarcasm and dismissiveness. Maybe my expectations were misplaced.

Rather than getting upset, show that you understand what you are talking about.

Again, in what way does the event by event accumulation of a twin slit interference pattern (or even single slit diffraction pattern) depend on the rate at which one event follows another? Where does the formalism require such a dependence?

You seem to think that the interference pattern is caused by some kind of dependency of one outcome on all the others. It is the particles that are all physically interfering with each others statistics in some kind of spooky, nonlocal, time and space defying, fashion.

But that is wrong. It is about how each event is affected by its (observational) context. So it is about a single event and the exact set-up of the apparatus for that run. And it is the human experimenters who control the state of the emission source and the apparatus, so ensuring that the interference pattern will accumulate over multiple trials replicating "the same event".

What's annoying was that this is the issue that Orzel was highlighting - the impossibility of perfect repeatability in the real thermal world. Something is always slightly different about the world. And that to me is a promising angle from which to attack the absolutism of MWI.

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

The point is that a superposition constitutes many states and they are all necessary for the wave function to evolve.

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? — Wayfarer

Yes it seems strange because we intuitively think we live in a classical world. But we don't, we live in a quantum world. So the key to resolving that strangeness is to think of things (like particles, trees, cats, humans) as quantum systems, not classical systems.

This has been an instructive debate. — Wayfarer

Indeed - I've enjoyed the discussion.

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

Thanks Tom - great list!

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. — Metaphysician Undercover

It doesn't contradict it. This just comes down to Wittgenstein's private language argument which, as I recall, you reject.

The term "existence" has a public referent. We point to an apple and say that that is what we mean by something existing. Even though we update our knowledge about apples from time to time, we are still referring to the same ordinary, familiar, existing apples that we were before.

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. — Metaphysician Undercover

My apple, at the moment, may have a well-defined position. So it therefore will be in a superposition of momenta. This just means it's not a classical object, it's a quantum object.

There is only a contradiction if I say there is both an apple and not an apple at the same time and in the same respect, which is not what I'm saying here.

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

Quantum tunnelling between threads. It happens...

Rather than getting upset, show that you understand what you are talking about. — Apokrisis

Rather than telling me I must be a crackpot, please consider the point.

You seem to think that the interference pattern is caused by some kind of dependency of one outcome on all the others. It is the particles that are all physically interfering with each others statistics in some kind of spooky, nonlocal, time and space defying, fashion. — Apokrisis

I didn't say anything of the kind. What I was told on Physics Forum, is whether the particles are fired one at at time, or whether they are fired altogether, the end result is the same. So I am saying, it can't really be a result of 'interference', can it? Because if the interference pattern is not dependent on time, then it is also not dependent on proximity, is it? We are, after all, talking about 'space-time', so 'proximity' and 'duration' are two aspects of the same thing. So it's not actually 'interference' in the sense that interference in water waves is; that is, at best, an analogy for what it is. That is the only point I am trying to fathom at the moment, and I think it is quite in keeping with the 'Copenhagen Interpretation'.

It doesn't contradict it. This just comes down to Wittgenstein's private language argument which, as I recall, you reject.

The term "existence" has a public referent. We point to an apple and say that that is what we mean by something existing. Even though we update our knowledge about apples from time to time, we are still referring to the same ordinary, familiar, existing apples that we were before. — Andrew M

When one refers to "the apple", that individual is referring to a particular instance of temporal continuity in which the similitude of an apple is of the essence. In order that one can refer to 'the apple", it is necessary that this similitude appears for a duration of time. What constitutes the "existence" of that apple is that this similitude persists through a duration of time. If the similitude seemed to flash upon the scene for a simple yoctosecond of time, then was gone, we could hardly assign "existence" to the apple. "Existence" requires that the described thing has a temporal duration

My apple, at the moment, may have a well-defined position. So it therefore will be in a superposition of momenta. This just means it's not a classical object, it's a quantum object. — Andrew M

There is no such thing as your apple at "the moment", because as soon as you mention this moment, it is then the next moment.. You only have "an apple", if the same identifiable thing persist through an extended period of time, so this "existence" is not defined by a moment of time, it is defined by an extended period of time.


.

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. — apokrisis

Ok. so let's assume that there is no particle, I'm cool with that. Isn't that what you say here, "there is no particle"?

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. — apokrisis

Wait a minute, I thought the assumption was that there is no particle. Where did the particle come from?

Do you get the complementarity principle? Is one description right and the other wrong? Or are both a reflection of some chosen measurement basis?

And every photon is happy in their own possible world.

What I was told on Physics Forum, is whether the particles are fired one at at time, or whether they are fired altogether, the end result is the same. So I am saying, it can't really be a result of 'interference', can it? — Wayfarer

So are you saying the two paths of an individual quantum event don't interfere due to superposition?

And bear in mind that we are talking about the interference of probability waves. And also that interference is about the additive or cancelling effect of wave peaks and troughs arriving at a point of space and time - the detector screen.

Given that, in what sense is it not analogous to wave interference in classical mechanics?

And given that, why would you expect the rate of producing individual events to make some kind of difference to the accumulation of an interference pattern at the detector?

I'm not declaring anything, I'm exploring a question.

Here is the relevant exchange from the Physics Forum:

afcsimoes: "So, if we made a first double slit experiment using a beam and a second experiment firing the same amount of particles but on a one by one basis, then we wil finish with two concrete objective and real identical images of an interference pattern?"

bhobba (moderator): "Yes".

Wayfarer: "Thanks! So from this, can I presume that the interference pattern is not rate-dependent, i.e. the rate at which the photons are emitted doesn't affect the distribution?"

bhobba: "Yes".

('bhobba' is one of the science advisers on physics forum. I asked some other questions as well, to which the answer was (predictably) 'go and read these six books'. Fair enough, but I'm only addressing a single point, I'm really not trying to solve physics problems per se. It's a strictly philosophical question as far as I'm concerned.)

So are you saying the two paths of an individual quantum event don't interfere due to superposition? — Apokrisis

One of the well-known problems of the double-slit experiment is that particles fired singly seem to act as though interference is happening. But how can interference occur when there's only one particle? It's one of the notorious difficulties of quantum mechanics. So I'm not saying 'they don't interfere due to superposition'; I'm saying that what appears as 'an interference pattern' isn't really interference at all - where it would be exactly that is if it really were water waves or sound waves.

So, it is analogous to the interference of waves in a medium, but here there isn't a medium! So the reason it is perplexing is because, there are waves, but nothing for the waves to be 'in'. The 'waves', so called, really are probability distributions, not actual 'waves' at all. The equation models both them and material waves, but they're of a different nature to waves in water, because there's no medium. They're not really waves, in the same sense, and for the same reason, that electrons are not really particles.

Now the reason I say that is compatible with the Copenhagen Interpretation is that there are many statements along similar lines from them: 'What we observe is not nature itself, but nature exposed to our method of questioning', said Heisenberg. Whereas, Einstein wanted to insist that there were something objectively real and (crucially), 'mind-independent', of which QM was an incomplete description. So he wanted to see 'nature itself' and was annoyed when Bohr and Heisenberg said 'no can do'. So that is really a big argument. I don't claim to have solved or discovered anything, but I think what I'm saying is at least close to the heart of the 'dispute between Bohr and Einstein'.

One of the well-known problems of the double-slit experiment is that particles fired singly seem to act as though interference is happening. But how can interference occur when there's only one particle? It's one of the notorious difficulties of quantum mechanics. So I'm not saying 'they don't interfere due to superposition'; I'm saying that what appears as 'an interference pattern' isn't really interference at all - where it would be exactly that is if it really were water waves or sound waves. — Wayfarer

But again, this isn't a physical interference of the kind we imagine with classical material waves. It is the analogous "interference" of probability waves. And it is the "interference" of all the possible paths a single particle could take. And it is the "interference" which is both constructive and destructive. So it builds up probability densities as well as knocks them down.

So there is little point trying to apply some simplistic and materialistic understanding of the word "interference" here.

The 'waves', so called, really are probability distributions, not actual 'waves' at all. The equation models both them and material waves, but they're of a different nature to waves in water, because there's no medium. They're not really waves, in the same sense, and for the same reason, that electrons are not really particles. — Wayfarer

Right.

Now the reason I say that is compatible with the Copenhagen Interpretation is that there are many statements along similar lines from them: 'What we observe is not nature itself, but nature exposed to our method of questioning', said Heisenberg. Whereas, Einstein wanted to insist that there were something objectively real and (crucially), 'mind-independent', of which QM was an incomplete description. — Wayfarer

But that's ancient history. Today we know for sure that you have to give up either localism or realism. And probably have to give up both (in some sense).

However your posts here were making some kind of deal out of interference patterns not being rate-dependent. And it is not clear why you think that is relevant to the interpretation issue in any form.

If you have a wave machine making an actual wave of water in the lab, and the wave passes through twin slits, the split wave produces an interference pattern. So it is not an issue that we are talking about individual trials.

But a quantum twin slit experiment results in only a single particle like event at the detector screen. And the interference pattern disappears if the path of the particle is observed. So that's the weirdness that realism would have to explain away, and the weirdness that a CI-style pragmatism simply gives up trying to explain in terms of real world mechanism.

Not being rate dependent is not part of the weirdness. It would instead be weirder still if the particle-event was affected also by every other event both before and after it. How could we even calculate any statistics if we had to take the entire past and future of the Universe into account?

your posts here were making some kind of deal out of interference patterns not being rate-dependent. — Apokrisis

The point that interests me about 'rate dependence' is this - what is varied if the same amount of energy is released one photon at a time versus being released all at once? The only difference between the two trials is duration (=time). So if there is no difference in the end result, then it shows time is not a factor in the formation of the pattern. Doesn't that strike you as being significant?

However, if you replicated the 'single photon' type of trial in a water tank, it would mean that you would release one 'quantum' of energy at a time in the water tank. For the next trial, release the same amount of energy in a single wave event. I would have thought that this would make a big difference to the pattern in the water trial, but not so for electromagnetic energy. Would it? Maybe I should take that back to physics forum. It sounds like a cool type of 'physics experiments for beginners'.

there is little point trying to apply some simplistic and materialistic understanding of the word "interference" here. — Apokrisis

I don't think I did that. I am saying, to imagine probabllties as actual waves is to do that.

...it shows time is not a factor in the formation of the pattern. Doesn't that strike you as being significant? — Wayfarer

Again, who is saying time is a factor in the sense that multiple events need to accumulate for there to be quantum interference?

Do you get the complementarity principle? Is one description right and the other wrong? Or are both a reflection of some chosen measurement basis? — apokrisis

Complementarity applies to the attributes of an object. To say, as you did, 'there is no particle travelling through the apparatus" is to say that there is no object called "the particle" to which the complementarity principle may be applied. To then speak of the paths of the particle is simple contradiction. The object being referred to exists as a wave particle duality, so if there is no particle travelling through the apparatus it really doesn't make any sense at all to ask questions concerning which way the particle goes.

So, it is analogous to the interference of waves in a medium, but here there isn't a medium! So the reason it is perplexing is because, there are waves, but nothing for the waves to be 'in'. The 'waves', so called, really are probability distributions, not actual 'waves' at all. — Wayfarer

This is the dilemma which special relativity gives us. The principles of this theory deny the possibility of a real medium for electromagnetic waves. It is impossible that there is a medium for light waves, or else the special theory of relativity would be an incorrect representation. Light must always maintain the same velocity relative to objects, so there cannot be a medium, or else the object would have its velocity relative to the medium, rather than relative to the waves.

But the physicists who interpret special relativity do not allow for the possibility that the medium may actually be attributed to the object, that the object might actually be the medium itself. This would allow that the object maintains a constant velocity relative to the light waves, and also that these waves have a medium. Instead, physicists produce an artificial medium, space-time, which is completely separate, conceptual, it is unreal, and this unreal medium is the only place where the waves can exist. I think that this is an unreal representation of reality which creates false models. Instead of understanding electromagnetic waves as a property of objects, they are understood as the property of a conceptual medium, space-time, and this produces a categorical separation between the waves and the objects. The object itself, the real mind-independent object, has no real position in this conceptual medium.

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

All David Wallace's work is first class, and this talk particularly accessible:

How do you arrive at an explanatory scientific theory other than by inductive reasoning? — mcdoodle

It is impossible to arrive at an explanatory scientific theory via induction. For details see "The Logic of Scientific Discovery" by Karl Popper, or, appropriately to this thread, this succinct exposition.

https://arxiv.org/abs/1508.02048

But that's ancient history. Today we know for sure that you have to give up either localism or realism. And probably have to give up both (in some sense). — apokrisis

Unless you subscribe to Everettian QM, in which case you retain both.

I'm sure you spotted I was being deliberately tendentious in some of the points in the list. I did this because I have given up any hope that critics of Everett know enough about QM to notice.

Does anyone think the MWI, leads to notions of solipsism for any particular observer?

Kinda a reductio ad absurdum if you may...

Does anyone think the MWI, leads to notions of solipsism for any particular observer? — Question

Quite the opposite! Everettian QM is observer-independent, furthermore, you only exist in an infinitesimal slice of the multiverse.

I find it solipsistic and incomprehensible to view every entity existing in a multiplicity of states in the multiverse. Doesn't one wavefunction entail another or do these wavefunctions exist/evolve independently?

who is saying time is a factor in the sense that multiple events need to accumulate for there to be quantum interference?

The question is, what causes the interference? With actual waves, the interference is a consequence of kinetic energy which varies with proximity. But in this case, the patterns are not dependent on the proximity of the particles to one another. So what is causing the pattern is not physical energy but purely probability.

I find it solipsistic and incomprehensible to view every entity existing in a multiplicity of states in the multiverse. Doesn't one wavefunction entail another or do these wavefunctions exist/evolve independently? — Question

I'm gong to make a list of the arguments against Everettian QM that appear in this thread. The argument from personal incredulity is most of them.

There is only one wavefunction.

the post on Sean Carroll's blog was dated 2011, and refers to the 'PSR paper', which argues that the the probability wave is physical. You may recall a long and circular debate a year ago on Philosophy Forum about that.

Sounds like something you say in a cult. Never mind me, I never got past understanding how one defines an or a ? 'observer' in QM.

To say, as you did, 'there is no particle travelling through the apparatus" is to say that there is no object called "the particle" to which the complementarity principle may be applied. — Metaphysician Undercover

It may seem a subtle point, but what I said was there was no (classically-imagined) particle. There was "an evolving wave of probability of detecting a (classically-imagined) particle that reflects the shape of the apparatus".

So I was trying to highlight the irreducible quantum contextuality of the existence of any "particle".