Interestingly, in topology, where you can imagine all sorts of exotic spaces, you can do just that. You can take two separated points on a plane and "glue" them together, making them one and the same point. You can do that with lines and surfaces as well. That's not to say that puzzling quantum mechanical correlations should be explained by weird space topology. (Although if someone were to produce a topological account, I would be open to it. I just doubt that it would be the topology of the physical space - configuration space perhaps?) — SophistiCat

Yes, that would avoid Bell's Theorem since the two surfaces would be part of the same local object. The idea is similar to ER=EPR where the two entangled particles are connected via a wormhole.

Susskind discusses this here:

Quantum gravity may have as much to tell us about the foundations and interpretation of quantum mechanics as it does about gravity. The Copenhagen interpretation of quantum mechanics and Everett’s Relative State Formulation are complementary descriptions which in a sense are dual to one another. My purpose here is to discuss this duality in the light of the of ER=EPR conjecture. — Copenhagen vs Everett, Teleportation, and ER=EPR - Leonard Susskind

Sean Carroll discusses his team's work on this at his blog:

A version of the ER=EPR conjecture is recovered, in that perturbations that entangle distant parts of the emergent geometry generate a configuration that may be considered as a highly quantum wormhole.
...
...as far as we know we’re the first to start directly from Hilbert space, rather than assuming classical variables, a boundary, or a background spacetime. — Space emerging from quantum mechanics - Sean Carroll

-

I don't have an unshakable commitment to quantum physics in its standard form, but neither do I have an unshakable commitment to the conventional metaphysical ideas articulated by Einstein. Like those physicists whom he opposes, I would consider relaxing some of those ideas if it helps us better accommodate lessons from physics.

What if we are now in the position of the inhabitants of Flatland who reluctantly conclude that they may in fact live in a Klein bottle? — SophistiCat

:up:

In short, I'm offering an alternative "solution" to the EPR paradox viz. that...someone (god? :smile: )...knows beforehand what the states of the particles are, we just don't know about it. The way the situation will evolve is that the experimenters who make the observation will erroneously infer that faster-than-light or instantaneous transmission of information had occurred but this is an illusion just like in the socks analogy. — TheMadFool

That apparently common-sense conclusion is just what Bell addresses.

In 1978 Bertlmann went to CERN, where he worked together with J. S. Bell.[1] Bertlmann always wore socks of different colours. In 1981 Bell wrote the article "Bertlmann’s socks and the nature of reality", where he compared the EPR paradox with Bertlmann’s socks: if you observe one sock to be pink you can predict with certainty that the other sock is not pink. Thus you might assume that quantum entanglement is just the same. However, this is a non-admissible simplification, and Bell in his article explains why.[2] — Bertlmann’s socks - Wikipedia

The philosopher in the street, who has not suffered a course in quantum mechanics, is quite unimpressed by Einstein–Podolsky–Rosen correlations. He can point to many examples of similar correlations in everyday life. The case of Bertlmann's socks is often cited. Dr. Bertlmann likes to wear two socks of different colours. Which colour he will have on a given foot on a given day is quite unpredictable. But when you see (Fig. 1) that the first sock is pink you can be already sure that the second sock will not be pink. Observation of the first, and experience of Bertlmann, gives immediate information about the second. There is no accounting for tastes, but apart from that there is no mystery here. And is not the EPR business just the same? — Bertlmann's socks and the nature of reality - J.S. Bell, 1981

By the phrase "spooky action at a distance", Einstein was referring to the phenomenon of quantum entanglement. — SupernovaGirl

Note that Einstein didn't mention entanglement when he used the famous "spooky" phrase below:

I cannot make a case for my attitude in physics which you would consider at all reasonable. I admit, of course, that there is a considerable amount of validity in the statistical approach which you were the first to recognise clearly as necessary given the framework of the existing formalism. I cannot seriously believe in it because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance.

I am, however, not yet firmly convinced that it can really be achieved with a continuous field theory, although I have discovered a possible way of doing this which so far seems quite reasonable. The calculation difficulties are so great that I will be biting the dust long before I myself can be fully convinced of it. But I am quite convinced that someone will eventually come up with a theory whose objects, connected by laws, are not probabilities but considered facts, as used to be taken for granted until quite recently. I cannot, however, base this conviction on logical reasons, but can only produce my little finger as witness, that is, I offer no authority which would be able to command any kind of respect outside of my own hand. — Einstein letter to Born - March 3, 1947 (via StackExchange)

Einstein's more general concern was the apparent non-local dynamics of wavefunction collapse which he raised at the 1927 Solvay conference. Entanglement is just a specific manifestation of that more general concern, and was first discussed in the 1935 EPR paper (with the term "entanglement" subsequently coined by Schrodinger).

What did Einstein mean by “Spooky Action at a Distance"? — Down The Rabbit Hole

Einstein is referring generally to an instantaneous measurement update (collapse) over a region of space which can involve just a single particle. As SEP notes:

If the argument developed in EPR has its roots in the 1930 Solvay conference, Einstein’s own approach to issues at the heart of EPR has a history that goes back to the 1927 Solvay conference.
...
On the supposition that quantum theory offers a complete account of individual processes then, in the case of localization, why does the whole wave front collapse to just one single flash point? It is as though at the moment of collapse an instantaneous signal were sent out from the point of collapse to all other possible collapse positions telling them not to flash. — The Einstein-Podolsky-Rosen Argument in Quantum Theory - SEP

Here are the relevant comments by Einstein from 1927:

But on the other hand, I have objections to make to conception II. The scattered wave directed towards P does not show any privileged direction. If |ψ|² were simply regarded as the probability that at a certain point a given particle is found at a given time, it could happen that the same elementary process produces an action in two or several places on the screen. But the interpretation, according to which |ψ|² expresses the probability that this particle is found at a given point, assumes an entirely peculiar mechanism of action at a distance, which prevents the wave continuously distributed in space from producing an action in two places on the screen.

In my opinion, one can remove this objection only in the following way, that one does not describe the process solely by the Schrödinger wave, but that at the same time one localises the particle during the propagation. I think that Mr de Broglie is right to search in this direction. If one works solely with the Schrödinger waves, interpretation II of |ψ|² implies to my mind a contradiction with the postulate of relativity. — Quantum Theory at the Crossroads Reconsidering the 1927 Solvay Conference, p487 - Bacciagaluppi, Valentini

There's also a nice discussion of Einstein's comments on p89 of Travis Norsen's Foundations of Quantum Mechanics (Chapter 4 - The Locality Problem).

God and the universe do not add up to two, any more than my envy and my left foot constitute a pair of objects.
— Lunging, Flailing, Mispunching - Terry Eagleton — Wayfarer

That's the spirit!

What ways have we tried to divide the mind? — TiredThinker

Alice had half a mind to tell Bob what she really thought of him. Bob is in two minds about whether to go to the party. As well as being mindful, one can also act mindlessly. One can change their mind and occasionally lose their mind.

This use, as well as being the ordinary idiomatic use, is also found in Aristotle and stands in contrast to the Cartesian use.

Talk of the mind is concerned with the distinctive rational powers of human beings and their exercise.

Once this is clear, it becomes evident that the domain of the idiom of ‘mind’ coincides roughly not with that of the Cartesian mind – the domain of consciousness, but with that of the Aristotelian rational psuche. The Aristotelian psuche is not a kind of entity, and the question of whether the organism and its mind are one thing or two is, according to Aristotle, as absurd as the question of whether the wax and the impression on it are one thing or two. The possessor of a mind is an animal of a certain kind, namely a human being. To have a mind is not to be in possession of a kind of entity. It is rather to possess a distinctive range of powers. — Human Beings – The Mind and the Body: Wittgensteinian-Aristotelian Reflections - Peter M.S. Hacker, 2007

How would an anti realist explain why the particle acts differently when collapsed vs uncollapsed? In the double slit experiment for example. — khaled

They wouldn't explain why.

Bohr: "It is wrong to think that the task of physics is to find out how nature is."

Heisenberg, "We have to remember that what we observe is not nature herself, but nature exposed to our method of questioning."

If all it was was a book keeping device for our own sakes, then you’d expect the electrons to act the same way collapsed or uncollapsed no? — khaled

At least on Copenhagen, you can only ask about what you observe, not how reality is. There is no unifying picture, just a wave picture or a particle picture depending on the measurement context (complementarity).

Bohr: "We must be clear that when it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly so concerned with describing facts as with creating images and establishing mental connections."

Heisenberg: "for visualisation, however, we must content ourselves with two incomplete analogies - the wave picture and the corpuscular picture."

That the Copenhagen interpretation is anti realist is news to me. I’m curious where you got that? — khaled

See the OP video at 55:00 - Copenhagen is on the anti-realist side. Note that it's anti-realist about the wavefunction. Reality itself is not denied, but is beyond our ken.

But I think the so-called 'wave function collapse' is not necessarily something that happens objectively - it's not a literal change of state. It's not that matter exists in some non-collapsed state, waiting for someone to measure it, so it can collapse and thereby begin to exist. The issue arises from reconciling the wave-function equation, which describes the state of the object before it is measured, with the act of measurement. — Wayfarer

If you look at Jim Baggott's categorization of wavefunction anti-realism versus realism at 26:40, he notes that psi does not collapse at all on an anti-realist view (which includes Copenhagen). At 55:00 he categorizes both physical collapse theories (GRW, etc.) and consciousness-causes-collapse (von Neumann–Wigner interpretation) on the realist side. Which is to say, collapse (when the wavefunction is real) is a physical process - whether triggered by matter or mind.

Conversely on an anti-realist view, the wavefunction is a book-keeping device that is useful for making predictions but not for revealing nature. As Baggott quotes Bohr at 29:30, "It is wrong to think that the task of physics is to find out how nature is." It is just the book-keeping device that is adjusted ("collapses") when an observation is made - but there is no physical collapse implied.

One of the odd spin-offs of this, is that David Deutsch is Everett’s #1 fan. His first book, Fabric of Reality, or something, is an impassioned plea for the reality of many worlds, and an implicit condemnation of all the bone-headed dinosaurs who can’t accept it. — Wayfarer

Your comment reminded me of this quote:

I think the argument for Everett’s theory is incontrovertible now. It seems to me that there is as much evidence for the existence of parallel universes as there is for the existence of dinosaurs. The logic for the evidence in both cases is very similar. No-one has ever seen a dinosaur, we’ve only seen fossils, and similarly, no-one has ever seen a parallel universe, but we have seen interference phenomena. And just as there is no other explanation of dinosaurs, so there is no other explanation for interference phenomena. And what most physicists do nowadays is they adopt what is called the “shut up and calculate” interpretation. Which says just use the equations to predict the outcome of experiments but do not ask what brings about those outcomes. Which is just the same logic as saying, “Do not ask what brings about fossils.” — David Deutsch

To those who might know, does the following interpretation of Schrodinger's wave function have any validity: — Enrique

I don't know - are you referring to an objective collapse theory?

Thanks!

BTW, it's worth noting that Bell's Theorem makes three assumptions - locality, counterfactual definiteness (i.e., hidden variables or classical realism) and freedom-of-choice (in what measurement to perform).

So rejecting hidden variables need not imply rejecting locality. For example, Copenhagen, RQM, QBism, Many Worlds and Consistent Histories are all local interpretations.

So when you say the probabilities that QM predicts, do you mean via the Schrodinger wave function and/or matrix mechanics? — Enrique

Yes.

If, like me, you've heard about, and read up on, the famous Bell Inequality experiment, then my guess is, unless you're physics grad, that you won't understand it. I, too, don't understand it, but my understanding of it is now a little better than it was before listening to the presentation below. — Wayfarer

OK, there's a challenge. I'll see if I can explain Bell's Theorem on an intuitive level. I'll use coins instead of particles.

Suppose Alice and Bob have one each of a pair of coins that have been prepared in an entangled state. Due to their entanglement, if the coins are measured by devices tilted at the same angle (say, 120 degrees) then Alice and Bob will observe the same outcome, i.e., they will both observe heads or they will both observe tails. Whereas if the coins are measured by devices tilted at different angles then, per the probabilities predicted by QM, they may or may not observe the same outcome.

What explains those correlations, even when the coins are separated by large distances? Perhaps the coins communicate instantly (Einstein's "spooky action at a distance"). Or perhaps the coins have definite orientations (i.e., heads or tails) for every possible measurement angle - which any actual measurement simply reveals.

Let's assume the latter (called local hidden variables) and test it. The experiments will involve a measuring device for each coin. Each measuring device can be tilted at an angle of 0, 120, or 240 degrees prior to measurement. Only experiments where the relative angle between the measuring devices is 120 or 240 degrees will be conducted (we already know that the outcomes will be the same when the relative angle is 0 degrees, i.e., when the devices are tilted at the same angle).

Now consider the possible coin orientations for each potential measurement angle. (1) They could be heads for all three angles. (2) Or tails for all three angles. (3) They could be heads for two of the angles and tails for the other angle. (4) Or tails for two of the angles and heads for the other angle. That exhausts all the possibilities.

For the initial two cases, measuring each coin at different angles will always return the same outcomes (e.g., both heads, or both tails). For the final two cases, measuring each coin at different angles will return the same outcome 1/3 of the time (e.g., for HTH the three possible combinations are HT, TH or HH).

Note how the measured coin orientations are the same either 100% of the time or 1/3 of the time. That's Bell's inequality - the measured coin orientations are the same for at least 1/3 of the times that the experiment is performed.

However QM predicts the same outcome 1/4 of the time (cos^2 120 = cos^2 240 = 0.25). Thus QM violates Bell's inequality.

When this is tested empirically, the same measurement outcomes are observed 1/4 of the time as QM predicts. Therefore the assumption of local hidden variables is mistaken.

or else concede that I'm in pain, but no part of me is experiencing any pain, which of course is an absurdity. — RogueAI

No, that's the fallacy of division. It doesn't follow that something predicable of the whole should be predicable of any of the parts.

In this case, one's body parts are not living organisms, so it's absurd to attribute experiences to those body parts.

↪Andrew M
People (or bats) have experiences, not brains or minds.

A person is made up of many things: arms, legs, organs, tissue, brain, etc. If I stub my toe and experience pain, where exactly in my body is that experience taking place? Not in my pinky. Not in my kidney. — RogueAI

The pain is in your toe (unless it's referred pain). But no experience is taking place in your toe. It is you that is experiencing pain (or is in pain), not your toe.

If you want to know what caused you to have that experience, then you look at factors like the place you were in when it happened (say, your backyard) and what you stubbed your toe on (say, a rock).

You can also investigate physiological factors, such as the role of the brain and nervous system.

But at no point does it make sense to say that an experience such as the above happened in your mind, or in your brain, or in your toe. People have experiences like kicking a football, or watching a sunset, or stubbing their toe and they happen in particular environmental contexts.

You don't believe experiences happen in the mind? If not, then where? In the world? If so, then specifically where in the world do experiences (or experiencing, if you prefer) happen? The brain? — RogueAI

No, not in the brain. Where do I kick around a football with my kids? In the park, or my backyard. People (or bats) have experiences, not brains or minds. From Smit and Hacker:

Suppose that I see a red tomato, do I then experience a red tomato in my brain? Is this experience a neural state of my brain? Saying so is incoherent, for there is no such thing as experiencing a red tomato in my brain. It does not make sense to answer the question where I experience the red tomato by saying: ‘Here’, while pointing to my head (as opposed to pointing at the fruit in the garden). Similarly, it can not be said that the hippocampus is the locus of remembering, for an answer to the question ‘Where and when did you remember that …?’ is given by saying: ‘While I was in the library’; not by saying: ‘In my hippocampus; where else?’. — Seven Misconceptions About the Mereological Fallacy: A Compilation for the Perplexed - Harry Smit & Peter M. S. Hacker, 2013

Experience is a subjective thing. — RogueAI

As I'm using the term, experience is "practical contact with and observation of facts or events".

Kicking a football around with my kids is an experience. So is watching a sunset. These experiences are interactions between myself and (other entities in) the world, not events in a private Cartesian theater.

When you unpack "1. A bat experiences the world when it uses echolocation.", you're saying there's an experiencer (the bat), and it has experiences. — RogueAI

That's right. Like a human being, a bat is a living organism that has the ability to perceive and interact with its environment (albeit with differing sense modalities).

Those experiences are therefore the bat's subjective experiences. — RogueAI

Not if subjective means "in the mind" as opposed to "in the world" which in this context is a Cartesian distinction, not an ordinary or natural distinction. As I'm using the term, an experience is an interaction by a perceiving creature with things in the world.

If you're not a dualist, and you believe experiences are real, how are they real? — RogueAI

People ordinarily regard what they do and see as the primary candidates for what is real. For example, I'm sitting at my computer, thinking about your comments and typing a reply. That's my current experience.

Huh, we do have echolocation technology. — Athena

Yes, so conceivably echolocation technology could be embedded into the brain and body so that a person could see (so to speak) with their eyes closed. Things would look different via that sense modality since the information received would be different.

I like
Jack Cummins
— Jack Cummins
example of people with mental health problems. Here our bodies are the same but our experience of life is different. I think it is hugely important we know without question that our experience is not the same as another and our understanding of what the other is experiencing is very shallow. — Athena

Indeed, empathy depends on recognizing points of difference as well as points of commonality.

1. There is something it is like to be a bat.

2. However much I learn about the objective world I can never know what it is like to be a bat.

3. Therefore there is something in reality that is outside of the objective world.

Do you agree with the argument? — Aoife Jones

No. The argument assumes there are objective and subjective worlds, which a non-dualist rejects.

Here's a similar argument that doesn't assume dualism:

1. A bat experiences the world when it uses echolocation.

2. Regardless of human knowledge, human beings can never know what it is like to experience the world as a bat does.

3. Therefore there is something in reality that is beyond human knowledge.

In the future, could we be augmented with echolocation technology and so experience the world as a bat does (at least in that respect)? If so, then premise 2 would be false.

But if premise 2 entails being a bat (note the be in the original argument) in order to experience the world as a bat does, then premise 2 would be true. This is just an identity claim. But, by that criterion, I would also never know what it is like to be any other person, since I am not them.

I think, under normal considerations, that identity criterion is too strong. We do know what it is like to experience the world as other people do and even as other creatures do in particular circumstances, however imperfectly (e.g., when suffering an injury).

"Latest" I wrote. But the truth is a combination of Bohmian Mechanics and the Schrödinger–Newton equation causing the collaps. It depends in the mass of the measuring apparatus. The cat is heavy enough. — SolarWind

Fair enough. Is that different to the Penrose interpretation?

The Schrödinger cat thought experiment was conceived in order to refute the Copenhagen interpretation, specifically the idea that the act of "observation" or "measurement" reduces or "collapses" the wavefunction. I am sympathetic to the attempt, I don't believe in the magic of observation either. But to me, it seems Schrödinger forgot a tiny little detail, which is that his cat was an observer too and therefore (according to said Copenhagen interpretation) could collapse the wavefunction inside his box, all by himself. — Olivier5

OK, but the basic point of Schrodinger's thought experiment was that if it doesn't make sense to imagine macroscopic phenomena being indeterminate, then it shouldn't make sense to imagine atomic phenomena being indeterminate either. After presenting his thought experiment, Schrödinger says:

It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks. — The Present Situation in Quantum Mechanics - Erwin Schrödinger, 1935

...

Now, fluorescence is considered a quantic phenomenon, so this finding above that chlorophyll can "entangle" with photons doesn't seem so new to me. — Olivier5

From the article, "According to study co-author Tristan Farrow, also of Oxford, this is the first time such an effect has been glimpsed in a living organism."

And regarding future experiments, "Several research groups, including those led by Gröblacher and Farrow, are hoping to take these ideas even further. Gröblacher has designed an experiment that could place a tiny aquatic animal called a tardigrade in superposition—a proposition much more difficult than entangling bacteria with light owing to a tardigrade’s hundreds-fold–larger size."

Actually Schrödinger's cat was an attempt to prove that observers cannot be the cause of anything quantic happening. — Olivier5

Sorry, I'm not sure what you're saying. Can you clarify?

The line is my consciousness at the latest, because I experience only one world. — SolarWind

OK, so consciousness causes collapse, on your view? Or something else?

How come Schrödinger did not see that his cat was just as good an observer as he was, pray tell? — Olivier5

I'm sure he did. But the thought experiment is not about what the cat observes, it's about where the line is drawn (if at all) for when a system stops being in a superposition of states.

Thought experiments mean very little, especially when poorly thought through.

E.g. what Schrödinger forgot in his famous mind experiment is that the cat is just as valid an observer as his master. — Olivier5

I'm pretty sure Schrödinger and Wigner had carefully thought their ideas through. What is relevant are the implications of those thought experiments for differentiating and testing various interpretations and theories.

A cat, or a human being for that matter, is not just an observer. She is also a biological system. Nobody has ever solved the Schrödinger equation for biological systems, it's far too complicated. We can barely compute it for simple molecules, like water. If you want to apply QM to life, you got a lot of very very hard "shut up and calculate" to do. — Olivier5

Perhaps Schrodinger's Bacterium?

In essence, it appears certain photons were simultaneously hitting and missing photosynthetic molecules within the bacteria—a hallmark of entanglement. “Our models show that this phenomenon being recorded is a signature of entanglement between light and certain degrees of freedom inside the bacteria,” [Marletto] says. — 'Schrödinger's Bacterium' Could Be a Quantum Biology Milestone

Total energy=1/2E+1/2E=E
— Andrew M

So at every branching, the total energy of the universe is divided by 2? And likewise with its mass, I suppose. Since there is a gigamongous number of branching per nanosecond, it follows that if the MWI was true, our universe would become empty of all matter and energy quite rapidly, like in a few seconds. — Olivier5

Here's a possible way to think about it.

Consider a superimposed photo. The number of times that the photo is superimposed doesn't change the amount of material in the photo. There is still only one photo, but it can be described from different points of view. Further, a filter could potentially be applied such that you see one definite picture (or slice).

This idea reflects the math of superposition. Suppose I have a vector (which can be visualized as an arrow) that points north-east. It's just one thing. But I can also consider it as a linear combination of one vector pointing north and another vector pointing east. Now there are two things. But nothing has really changed. I'm just describing the original vector in a different way.

Now suppose that you have a quantum coin that is in a superposition of heads and tails. In MWI, whether it is one coin (like the north-east vector) or two coins (like the north vector and east vector) is just a matter of how you want to describe it.

What MWI says is that you, the observer, are a quantum system just like the quantum coin. From an isolated observer's viewpoint (see Wigner's Friend), you become entangled with the quantum coin when you measure it. The universe still contains the same energy that it did before, but it now looks different from your point of view compared to the isolated observer's point of view (where they describe you as in a superposition of measuring heads and measuring tails).

the photon still interacts with the apparatus at the slits
— Andrew M

Not the photons passing the slits. — Olivier5

Those photons as well. Amplitude for every possible path through the apparatus contribute to the observed interference pattern - including when the photons are emitted one by one. The characteristics of the apparatus (such as the positions and widths of the slits) determine the paths the photon can take and thus the specific interference pattern.

Even with photon detectors at the slits, the resulting photon position information can be erased, restoring the interference pattern.

The issue can be simplified by considering a Mach-Zehnder interferometer where there are only two possible paths. Photons sent one at a time through an MZI will exhibit wave interference even though they interact with components of the MZI itself (such as beam splitters, mirrors and sample liquid on the paths).

What Dirac is talking about is the superpositions of wavefunctions. Waves can add to one another, as in sound1 + sound2 = sound3. — Olivier5

OK, we're on the same page then. You seemed to be saying you could think about QM without that.

how would you describe the double-slit experiment without assuming superposition?
— Andrew M

I would assume that the photon behaves as a wave until it interacts with something, at which point somehow it behaves as a particle. — Olivier5

Without detectors at the slits, the photon still interacts with the apparatus at the slits. Yet an interference pattern is still observed.

For an even simpler example, when a photon interacts with a beam splitter, the interaction is described by a wave function (i.e., there is amplitude for both the photon transmitting and reflecting). This is exploited by Mach-Zehnder interferometers, for example.

So your assumption can't be correct.

Why the average and not the sum? What is the argument here? — Olivier5

Because that reflects the contribution of each branch to the wave function.

Superposition is a fundamental principle of quantum mechanics, regardless of interpretation.
— Andrew M

No, it's not. — Olivier5

You're mistaken. From Paul Dirac's classic textbook:

The discussion in the preceding section about the limit to the gentleness with which observations can be made and the consequent indeterminacy in the results of those observations does not provide any quantitative basis for the building up of quantum mechanics. For this purpose a new set of accurate laws of nature is required. One of the most fundamental and most drastic of these is the Principle of Superposition of States. We shall lead up to a general formulation of this principle through a consideration of some special cases, taking first the example provided by the polarization of light. — The Principles of Quantum Mechanics, Ch.1: The Principle Of Superposition, p4 - Paul Dirac

Also you haven't said what your alternative way of thinking about QM is. For example, how would you describe the double-slit experiment without assuming superposition?

Interestingly, the conservation of mass and energy would seem gigumongously violated by this constant burgeoning of a gigumongous number of new universes. — Olivier5

Just to reiterate @fishfry's point with a simple example. In MWI, the total energy of the universe is the weighted average of the energies of each branch. Suppose that there is only a single branch and the total energy is E. Now suppose that the universe splits into two branches such that:

$|\psi\rangle = \sqrt{\frac{1}{2}} |Branch 1\rangle + \sqrt{\frac{1}{2}}|Branch 2\rangle$

When an observer measures the energy, they will measure (approximately) E. So, from the observer's point-of-view, energy has been conserved on their branch. To calculate the total energy of the universe, it is necessary to square the amplitude of each branch and multiply by their respective energies. So:

$Total\space energy = \frac{1}{2}E + \frac{1}{2}E = E$

So the total energy of the universe has also been conserved.

are you going to change the philosophy? Are you going to stick with the straightforward way of reading a scientific theory as just telling us what the world is like
— Interview with David Wallace

In the classic physics era, massive objects were supposed to attract one another at a distance, without any physical chanel of interaction between them, as by magic. Even Newton thought this was a problem, that the world could not possibly be that way, with actions at a distance. And yet the likes of Wallace were for two centuries quite happy to see Newtonian gravity as "the way the world was like"...

A scientific theory makes predictions about how the world behaves in quantitative terms. It doesn't tell you "what it's like" ontologically or qualitatively, never did, never will. — Olivier5

That would be an instrumentalist view of science, but Wallace takes a realist view, i.e., that a theory represents the structure of the world.

Newton thought that the "action at a distance" aspect of his gravitational law was a problem because he was also a realist. As are and were many scientists, including Einstein.

Wallace again:

Answering “yes” to the second question basically commits you to overturning a really pretty solid consensus in philosophy of science that scientific theories really do have to be understood as making claims about what the world is like, and aren’t just shorthands for claims about how experimental devices work. (And it’s a consensus that I think pretty much all scientists share when they’re not actively philosophising. Are there really astrophysicists who think that the reason for talking about stars is to model patterns of detections on photoplates, not vice versa?) — Interview with David Wallace

I don't think superposition of states is a good way to think about QM. — Olivier5

Superposition is a fundamental principle of quantum mechanics, regardless of interpretation. What alternative would you suggest?

Another consequence is that, everytime I pee, I create thousands of universes, just to account for where the droplets may fall. — Olivier5

Yep. As David Wallace puts it, the alternatives are to change the physics or to change the philosophy.

What’s the advantage of the Everett interpretation in particular? Here’s one way to put it. In trying to interpret quantum mechanics, you’ve got two yes/no choices to make. Choice one: are you going to change the physics? Are you going to stick with the Schrodinger equation and the quantum state, or are you going to add dynamical collapse processes or hidden variables or backwards-in-time interactions or something? Choice two: are you going to change the philosophy? Are you going to stick with the straightforward way of reading a scientific theory as just telling us what the world is like, or are you going to start saying “a scientific theory is just a predictive algorithm for experiments” or “observers can’t just be modelled as physical systems” or “ordinary logic is wrong” or something? If you answer “no” to both questions, you’re stuck with the Everett interpretation, because the Everett interpretation is just the “take quantum mechanics completely literally” interpretation. — Interview with David Wallace

All I'm arguing is that it's naive to argue that MWI is making more assumptions; the core of MWI, explained in terms of Schrodinger's cat, is that there's nothing privileged about Schrodinger opening the box versus the cat.
— InPitzotl

MWI says that there are infinite worlds, while Schrödinger assumes his cat can't be dead and alive at the same time. Can you spot which assumes less and which assumes more? — Olivier5

In the mathematical formulation of quantum mechanics there are usually six postulates, listed here.

However it is possible to simplify the formulation by omitting (at least) the collapse postulate - postulate V in the link. That is the sense in which MWI requires less assumptions (read: formal postulates) than other interpretations.

The consequence is that every physical event is described by the Schrödinger equation - measurement is not singled out for special treatment.

2 - the faster than light experiments conducted by Nicolas Gisin across lake Geneva which demonstrated that particles of light travelling away from each other in opposite directions (twice the speed of light) were still able to communicate instantly - (or technically, at least 10,000 times the speed of light). — Gary Enfield

2 New one to me, I'll have to look it up. Is it yet another case where QM and relativity clash? — jkg20

This refers to quantum entanglement of distant particles. Einstein called it "spooky action at a distance". QM just says that the measured values of entangled particles (including at a distance) will be correlated. It specifies no mechanism for how that occurs, which is an interpretational issue. Some interpretations reject locality (such as Bohmian Mechanics), others reject realism (in Bell's sense).

In theoretical physics, quantum nonlocality refers to the phenomenon by which the measurement statistics of a multipartite quantum system do not admit an interpretation in terms of a local realistic theory. Quantum nonlocality has been experimentally verified under different physical assumptions.[1][2][3][4][5] Any physical theory that aims at superseding or replacing quantum theory should account for such experiments and therefore must also be nonlocal in this sense; quantum nonlocality is a property of the universe that is independent of our description of nature.

Quantum nonlocality does not allow for faster-than-light communication,[6] and hence is compatible with special relativity and its universal speed limit of objects. However, it prompts many of the foundational discussions concerning quantum theory, see Quantum foundations. — Quantum nonlocality - Wikipedia

↪Andrew M I like this, and it reminds me of my own take on many things. In philosophy of time I'm sort of both a presentist and an eternalist, in different senses. On ontology more generally I stand by both the positions that all there is nothing to reality but empirically observable stuff and that all of reality is itself an abstract mathematical object. And yeah, regarding quantum mechanical observations, I can see a Copenhagen interpretation or an Everett interpretation as equally valid, depending on perspective. In all of these issues I've listed here, the main difference is between a first-person perspective and a third-person perspective on the same thing. — Pfhorrest

Yes. What I think is also needed is a reframing that doesn't depend on those dual first-person/third-person perspectives. I find Aristotle a useful resource here.

I've heard the Sanskrit term "advaita" (nondualism) and am often tempted to use it to describe this type of thinking — Pfhorrest

I'm not particularly familiar with Eastern non-dualism. However on Aristotle's hylomorphic view, mathematical objects are abstractions of empirically observable stuff, and not separable from that context (though they can be considered separately, as mathematicians do). I'm not sure if that really differs from your own conclusions, but perhaps a different way of getting there.

I always like this one:

What did you do to the cat, Erwin, It looks half dead.
— Mrs Schrodinger — Wayfarer

:up:

I heard that in one world, Wigner's Friend adopted Schrodinger's Cat, and they lived happily ever after. That'd be the world I'd choose, although I probably won't have the chance. — Wayfarer

About that cat, I have good news and bad news...

↪Steve Leard Have a read of The Multiverse Idea is Rotting Culture — Wayfarer

Have you tried the Zen Anti-Interpretation of Quantum Mechanics?

I hold that all interpretations of QM are just crutches that are better or worse at helping you along to the Zen realization that QM is what it is and doesn’t need an interpretation. As Sidney Coleman famously argued, what needs reinterpretation is not QM itself, but all our pre-quantum philosophical baggage—the baggage that leads us to demand, for example, that a wavefunction |ψ⟩ either be “real” like a stubbed toe or else “unreal” like a dream.

...

You shouldn’t confuse the Zen Anti-Interpretation with “Shut Up And Calculate.” The latter phrase, mistakenly attributed to Feynman but really due to David Mermin, is something one might say at the beginning of the path, when one is as a baby. I’m talking here only about the endpoint of the path, which one can approach but never reach—the endpoint where you intuitively understand exactly what a Many-Worlder, Copenhagenist, or Bohmian would say about any given issue, and also how they’d respond to each other, and how they’d respond to the responses, etc. but after years of study and effort you’ve returned to the situation of the baby, who just sees the thing for what it is. — The Zen Anti-Interpretation of Quantum Mechanics - Scott Aaronson

If that theory could be established as a fact what would it say about our concept of reality, in particular our viewpoints on death. For example, if other dimensions are spun up off of events which occur here does that mean that when i die here i am deceased on all planes. — Steve Leard

No, each branch is independent. What someone does on one branch (including when they die) has no effect on any other parallel branch. [*]

If not, could our search for what we think of as the "soul" be somehow related to a connection between dimensions. — Steve Leard

No, from your branch you have no connection to other parallel branches.

Everett's amoeba analogy is useful to get a sense of how Many Worlds works. As Everett put it, 'Each time an individual splits he is unaware of it, and any single individual is at all times unaware of his "other selves" with which he has no interaction from the time of splitting.'

--

[*] In principle, an isolated observer could observe another person's (or cat's) parallel branches in superposition, which would exhibit interference effects for the observer. But an individual person (or cat) can only influence their own branch. See the Schrodinger's Cat and Wigner's Friend thought experiments.

Where is a real-world instantiation of the square root of -1? — TheMadFool

$i$ appears in the Schrodinger equation:

$i\hbar\frac{\partial}{\partial{t}}|\Psi(t)\rangle=\hat{H}|\Psi(t)\rangle$

Using Collingwood's presupposition analysis:

1) You are assuming there is such a thing as "the water molecule itself", as opposed to, say, one single Schrödinger equation describing the whole universe. — Olivier5

You are assuming those two notions are opposed. But, yes, I assume at least the first.

2) You are in your mind conceiving ONE such molecule, so you are already counting right from the start. — Olivier5

Yes. And you are assuming that the quantity of something (say, the number of atoms in a water molecule) depends on what you conceive of or count.

And so on...

So we all make assumptions. But that doesn't imply that what we're talking about - water molecules, say - have a dependency on our assumptions - or even on our existence. Though, of course, if someone's assumptions are false then they might not actually be describing anything in the world.

Otherwise aren't you effectively saying that the world isn't real, but mind-dependent?

No. If one considers one's own mind as real, then things that are mind-dependent can be perfectly real so the distinction "mind vs real" does not apply. — Olivier5

Do you consider that the world is mind-dependent?

All I am saying is that numbers are concepts. They are made in the mind. Otherwise, who's counting? — Olivier5

Human beings such as you and I are counting. How would that imply that numbers (and in this case, the number of atoms in a water molecule) depend on one's mind?

Do you consider that the world is a concept?

My question is not about how to use logic on forms, but how does logic itself emerge from the geometric (spatial) shape of things. — Olivier5

Aristotle's logic is grounded in our observation and investigation of the world (i.e., Aristotle is seeking to understand the nature of things). So logical principles such as the LNC and LEM emerge from that observation and investigation. For example, a thing is not observed to both have some characteristic and not have it at the same time and in the same respect.

Also form (Greek: morphe or eidos or idea) is not merely about how a thing looks to us, but about a thing's deeper structure and organization that shapes the material (and which might only be "seen" in our speech). For example, human beings are reasoning and language-using creatures - that is their shape (or pattern) that we can describe in speech. As Joe Sachs puts it:

Morphe never means mere shape, but shapeliness, which implies the act of shaping, and eidos, after Plato has molded its use, is never the mere look of a thing, but its invisible look, seen only in speech (Aristotle's Physics 193a 31). Idea, from the same root as eidos, is used primarily when technical discussions within Plato's Academy are referred to, but the English words "idea" and "ideal" are distortions of it, suggesting something that can only be present in thought, which no-one who used the Greek word intended. — Joe Sachs (translator of Aristotle's works)

Note that "speech" in the above Aristotle's Physics quote is the translation of the Greek logos. From Wikipedia:

Logic comes from the Greek word logos, originally meaning "the word" or "what is spoken", but coming to mean "thought" or "reason". — Logic: History - Wikipedia

So a possible answer to your question is that our reasoning in natural language just is an informal logic. Our language, and consequently logic, emerges as a result of our interactions with things in the world.

Per the above example, the quantity of atoms is independent of mind (real), but dependent on the atoms (immanent). So the quantity doesn't have an independent existence.
— Andrew M

This is a mistake. Before you can count anything, you have to set the boundaries of what you want to count. Those boundaries are not real, they are postulated, conceived by the person counting. — Olivier5

I choose what to measure and how to measure it. But when I do so, that I measure three atoms in a water molecule doesn't depend on my mind, it depends on the water molecule itself.

Otherwise aren't you effectively saying that the world isn't real, but mind-dependent?

For instance, I fail to see how to ground logic on forms. — Olivier5

Here's a reference that I think gets at what Aristotle was doing.

Criticisms of Aristotle’s logic often assume that what Aristotle was trying to do coincides with the basic project of modern logic.
...
Aristotle, however, is involved in a specialized project. He elaborates an alternative logic, specifically adapted to the problems he is trying to solve.

Aristotle devises a companion-logic for science. He relegates fictions like fairy godmothers and mermaids and unicorns to the realms of poetry and literature. In his mind, they exist outside the ambit of science. This is why he leaves no room for such non-existent entities in his logic. This is a thoughtful choice, not an inadvertent omission. Technically, Aristotelian science is a search for definitions, where a definition is “a phrase signifying a thing’s essence.” (Topics, I.5.102a37, Pickard-Cambridge.) To possess an essence—is literally to possess a “what-it-is-to-be” something (to ti en einai). — Aristotle: Logic - IEP

The point here is that, for Aristotle, form is not separable from substantial things (except in an abstract sense). So logic about forms is, basically, logic about things that we investigate naturally. For example, what-is-it-to-be a human being? Well, what differentiates us from other animals is our language and reasoning capabilities. A word signifying that might be "rationality", i.e., what-it-is-to-be a human being is to be a rational animal. So that's a definition. But note that rationality isn't itself something substantial like a Cartesian mind. It is instead a formalization of one class of things (human beings) in terms of a broader class of things (animals), with a differentiating criterion (rationality).

This then becomes the ground for developing logic, such as:

All human beings are animals.
Socrates is a human being.
Therefore, Socrates is an animal.

I think it's important to know that it wasn't a prediction. It was instead a note for how regions should act in the face of fat tail risk and uncertainty. You don't buy house insurance because you predict your house will burn down next year. You buy it to protect yourself against that possibility, and because the potentially bad consequences are much greater than the cost of the insurance.

This is where having experts and advisors that understand the nature of pandemics is important. The president's call shouldn't depend on being able to predict the future since no-one can.

No one from either side of the aisle would have advocated mass shutdowns of international travel when it was most needed.. probably mid-February.. That would have taken foresight and wisdom no one had. — schopenhauer1

Some experts were advising the US to close borders in February 2020 and earlier. And the US did close their borders to China on January 31st (albeit leakily - foreign nationals only, and ignored Europe until mid-March).

Here's some foresight and wisdom from January, 2020. Not just for this pandemic, but for the next one.

Clearly, we are dealing with an extreme fat-tailed process owing to an increased connectivity, which increases the spreading in a nonlinear way [1], [2]. Fat tailed processes have special attributes, making conventional risk-management approaches inadequate.

..

Together, these observations lead to the necessity of a precautionary approach to current and potential pandemic outbreaks that must include constraining mobility patterns in the early stages of an outbreak, especially when little is known about the true parameters of the pathogen.

It will cost something to reduce mobility in the short term, but to fail do so will eventually cost everything — if not from this event, then one in the future. Outbreaks are inevitable, but an appropriately precautionary response can mitigate systemic risk to the globe at large. But policy- and decision-makers must act swiftly and avoid the fallacy that to have an appropriate respect for uncertainty in the face of possible irreversible catastrophe amounts to "paranoia," or the converse a belief that nothing can be done. — Joseph Norman, Yaneer Bar-Yam, and Nassim Nicholas Taleb, Systemic risk of pandemic via novel pathogens – Coronavirus: A note, New England Complex Systems Institute (January 26, 2020).

it's easy to start imagining minds and numbers as things with distinct and independent existence.
— Andrew M

Yet a water molecule was composed of three atoms prior to the emergence of humans in the universe, violating that dependency.
— Andrew M

Aren't you contradicting yourself in those two paragraphs? In the first you say numbers have no mind- independent existence, and then you say the opposite in the second para. — Olivier5

No. Per the above example, the quantity of atoms is independent of mind (real), but dependent on the atoms (immanent). So the quantity doesn't have an independent existence.

I think we can do better than Aristotle. — Olivier5

Maybe, but it's worth noting that Aristotle's project was very different to Descartes'. Aristotle was seeking to provide a natural and investigative account of living organisms (what they have in common and what differentiates them), whereas Descartes was seeking a foundation of certainty against the skeptic. From Hacker again:

Aristotle’s profound account of psuche was concerned with demarcating the animate from the inanimate, with the classification of the animate into (very general) categories according to the classes of powers that characterize living beings – the vegetative psuche and the sensitive psuche being the powers that characterize plant and non-human animal life. What is distinctive of humanity over and above the powers of the vegetative and sensitive psuche is the rational psuch – the ability to reason and to act for reasons. To have a mind, according to the Aristotelian-scholastic tradition, is to have an intellect and rational will. It is to be able to reason, to apprehend things as affording reasons for thinking, feeling and acting. It is to be able to deliberate, decide or choose what to do or believe, and to modify one’s feelings and attitudes, in the light of reasons. These far-reaching and complex powers are corollaries or consequences of being language-users. — Human Beings – The Mind and the Body: Wittgensteinian-Aristotelian Reflections - Peter M.S. Hacker, 2007