I mentioned earlier that the Mach-Zehnder interferometer falsifies any idea that photons don't pass through transparent media.

It occurs to me that it takes a deranged zealot to claim that optical fibres don't transmit photons, particularly when used in ultra-secure quantum communication applications.

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.

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.

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

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:

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

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

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?

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.

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?

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.

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.

Some pertinent advice for the left, from the left.

Just taking a page from the Donald's own playbook. Didn't know you Trumpies were so sensitive to name-calling. — Real Gone Cat

And due to the endless name-calling, people stop caring what you say.

You describe yourself as a Positivist, i.e. you hold the view that all statements apart from those describing or predicting measurements are meaningless. Why do you care if photons exist, if the question is strictly meaningless? I think I covered that particular dinosaur theory.

Your theory of meaninglessness, along with the theories of the inapplicability of reason, and the theory of consciousness-induced-creation, are all generic ways of denying anything. You can even use them to deny that quantum theory is true.

You complain about abstractions and mathematics. Given a simple experiment such as the photo-electric effect, what mathematics and abstractions particularly trouble you?

Unfortunately, that required ignoring the mountain of evidence that he is grossly unfit to lead a local PTA, let alone a country with nuclear weapons. How can anyone choose that evil oompah-loompah over a sober adult is beyond me. He is simply a spoiled-brat 15-year-old. — Real Gone Cat

This is precisely the sort of name-calling nonsense that causes people to look more closely at Trump, then vote for him.

Scientific theories are meant to be ontological commitments, which means they can be tested (and potentially falsified). — Andrew M

To paraphrase... On making observations of fossils, paleontologists developed a theory of dinosaurs to explain fossils. They made an ontological commitment to dinosaurs - i.e. the theory *IS* that dinosaurs really existed, had real behaviour, and occasionally really died in such a way that their remains are preserved. The theory of fossils is actually a theory of dinosaurs, which no one will ever observe.

But there are alternative theories - how about that fossils only come into existence when consciously observed? Thus fossils aren't evidence of dinosaurs, but rather evidence of those particular acts of observation. Another theory is that dinosaurs are such strange animals that conventional logic does not apply to them. Or, how about the theory that it is meaningless to ask if dinosaurs were real or just a useful fiction?

None of those alternative theories are empirically distinguishable from the rational theory of fossils, yet we manage to reject them. Not so in QM unfortunately.

Ontological commmitment interpretations are the opposite, obviously. One takes the explanation or account to be literally picking out things in the world, just as they are. — Terrapin Station

So, being an instrumentalist, you would class dinosaurs as just an 'interpretation' of fossils, rather than actually having existed? Perhaps you think fossils only come into existence when they are consciously observed?

I challenge you to find anywhere in the formalism of Everettian Quantum mechanics mention of 'many worlds'. Go ahead!

The axioms of quantum mechanics say NOTHING about 'many worlds'.

Well, glad we got to the bottom of that, although it directly contradicts and answer you gave just above it. — Wayfarer

I challenge you to find anywhere in the formalism of Everettian Quantum Mechanics mention of parallel universes. Go ahead!

The axioms of quantum mechanics say NOTHING about parallel universes.

In non-technical terminology, what does a 'macroscopically definite state' consist of? — Wayfarer

I refer you to my post about macroscopically definite cats above.

So, for the umpteenth time, 'many worlds' means 'many worlds'? Yes or no? — Wayfarer

I reckon 'many worlds' must mean 'many worlds', what else could it mean?

Frankly, you can call decohered macroscopic superpositions whatever you like, it makes no difference.

Yes, there are parallel universes and we can find out about them.

Macroscopically definite states, just as the formalism indicates.

Text-book QM claims that Schrödinger's cat is in a macroscopically indefinite state - a superposition of being alive and being dead.

Everett claims that the cat is in a superposition of macroscopically definite states - a superposition of an alive cat and a dead cat.

Text-book QM claims the act of observation transforms the indefinite cat into a definite cat, by a process indistinguishable from magic.

Everett (actually bare quantum formalism) claims that any environment that interacts with the cat in superposition will itself enter a superposed state, whose components correspond to entanglement with a macroscopically definite cat. Decoherence guarantees that very rapidly, the components of the environmental superposition cease to interfere with each other.

And how does that connect with what Orzel (or I) have argued? — apokrisis

My apologies, I misread where Wayfarer's quote came from. It came from an article that Orzel did NOT like apparently.

Andrew, 'Worlds' doesn't begin with 'M', does it. The question was, what does "M" stand for?. And obviously the answer is 'many' - as in 'many worlds'. That is what it means, it refers to branching or splitting or multiple universes. — Wayfarer

Nope, it doesn't refer to that.

What Everett claimed is that the bare formalism of quantum mechanics may be treated in a straightforward realist way, without changing our general conception of science, or quantum mechanics.

So, here's the thing. According to text-book QM, when you have a macroscopic superposition, you declare indefiniteness. Under Everett, you accept multiplicity.

So it is clear Orzel indeed has you stumped because you can offer no analysis at all. But just saying "nope" is not going to get you out of the hole here. — apokrisis

Nope, nowhere in MW is the claim made that measuring the spin of an electron means "you have to build an entire parallel universe around that one electron, identical in all respects except where the electron went". Definitely nope, Nope, thrice NOPE!

If we were to survey physicists, what percetage do you think would say that they buy MWI instrumentally versus buying it as making a realist ontological commitment? — Terrapin Station

The old argument from consensus.

Only a minority of physicists advocate Everett. It's a scandal, which future historians will recognise as being an obstacle to progress. In fact Deutsch is on record, not only stating that Bohm could have anticipated Everett entirely, if only he had not equivocated about what is real and what is not in his theory, but that the quantum computer could easily have been invented in 1950s for the same reason. All the quantum mechanics was there, plus an extraordinary collection of towering geniuses.

Strange as it may seem, the nature of reality doesn't trouble most physicists, and few have any understanding of the importance of realism. Most shut-up-and-calculate, and whether they admit it or not, they do so as if they were dealing with reality. Methodological (or unconscious) realism works up to a point.

But, where it matters, i.e. where pretending QM is not about reality makes no sense whatsoever - particularly in the fields of quantum cosmology or quantum computation - then Everett may be consensus. Hawking is on record stating it is "trivially true".

Of those working on foundations, if Oxford U Philosophy of Physics dept. is anything to go by, then Everettians make up 25%. http://www.philosophy-of-physics.ox.ac.uk/

As quantum physics developed, it undermined common-sense realism or even scientific realism. Einstein wanted to see a fundamental material unit, not all of this wave-particle ambiguity and now-you-see-it now-you-don't magic tricks. It offended his sense of propriety. — Wayfarer

Many Worlds is realist.

All the MWI advocates seem to be ignoring this point. — Wayfarer

Sure, Many World advocates ignore that point.

http://www.cheapuniverses.com/

Orzel is also wrong. by the way.

The metaphysics is realism, which brings us back to Einstein and Bohr. — Andrew M

The realism is required by the epistemology of science.

except for it's not 'a theory', it is a metaphysic. — Wayfarer

No, it's a testable theory:

https://arxiv.org/abs/1508.02048

It is different from standard treatments of QM in that does not have the Born rule as an axiom. The Born rule is derived.

It has also made far reaching predictions - quantum computing, and predictions regarding conscious agents running on reversible quantum computers.

A rudimentary quantum computer is capable of performing vastly more calculations in parallel than if all the matter in the visible universe was made into a classical computer. In fact, that is an understatement. Where these parallel calculations occur, is not a metaphysical question.

By all means keep an open mind. Nonetheless, Everett's is the only theory that explains why we see quantum interference effects. So it is the theory to beat. — Andrew M

And as a result of MW being the ONLY explanatory theory that can reproduce all the results of QM, it is also the only testable theory.

https://arxiv.org/abs/1508.02048

Rather than being defensive, why not critique Orzel from your point of view? That would be more interesting. — apokrisis

I note you are unable to defend your baseless claims.

Orzel's understanding of Many Worlds has improved over the years:

http://scienceblogs.com/principles/2015/02/20/the-philosophical-incoherence-of-too-many-worlds/

And we are seeing MWI being defended in very fuzzy terms with talk of interactions, correlations, interferences, branches, — apokrisis

Really? Where?

Where is MW being "defended" by use of fuzzy terms?

It's possible that if I jump off a cliff, I will float to safety rather than fall to my death, — Sapientia

Sorry, but absent a parachute, that is impossible.

Newton's theory of gravity is wrong in the sense that it makes predictions that are demonstrably incorrect - for instance about the precession of the perihelion of Mercury. Under certain circumstances, Newton's theory is a good approximation. — andrewk

Newton's theory is wrong because it is a false explanation. It could be (and indeed was) protected from problematic observations by making ad-hoc modifications.

There is no force of gravity, let alone a force which instantaneously acts at a distance.

Under certain circumstances, Kepler's theory is a good approximation, as is geocentrism, or the flat earth.

Frozen block-time comes from the physicist Brian Greene. I don't know whether he came up with the interpretation, or just wrote about it in one of his books. — Marchesk

Not quite. The block-universe is a stationary space-time which must exist according to Relativity. So its originator was Einstein.

Quantum mechanics and General Relativity disagree with each other on this. According to QM, there are an infinite number of slightly interacting space-time blocks, and the one you will find yourself in next is in principle unknowable (even by God).

But sure, time doesn't flow in either of these structures.

Under MWI, entanglement is just correlation. In terms of the EPR experiment, there will be a pair of correlated opposite-spin particles on one branch and another pair on another branch and these branches are in superposition. When Alice observes the first particle, a process of decoherence occurs whereby Alice becomes correlated with the pair of particles on one branch (and similarly on the other branch). There is no spooky action at a distance because there is no action happening between the particles at all. — Andrew M

Under MW, entanglement is not just a (statistical) correlation. "Correlation" is the wrong word. It is the anti-explanatory word used by anti-realists to avoid any questions about why their algorithm works, particularly as the algorithm does not apply to reality, but rather what can be said about reality.

Rather, under MW, the physical mechanism by which the right branches encounter each other - in order to preserve conservation laws etc - is termed "information flow" or something similar. The process was fully worked out here: http://xxx.lanl.gov/abs/quant-ph/9906007

The difficulty is in coming up with a coherent interpretation that omits the other branches. If the other branches aren't real, then what causes the interference effects? — Andrew M

Quite!

Denial is always an option however, and to be consistent, the Copenhagen Interpretation denies all the branches!

Of course "branching" is just shorthand. What troubled Wheeler was branching-by-splitting, which not the current understanding of branching.

This thread is about whether what's seen 'through' the glass are the very same objects that would be seen if the pane was removed. — dukkha

You can prove that with a Mach-Zehnder interferometer.

Of course, the most important reason for adopting Many Worlds:

There exists no alternative explanatory theory to Everett-interpreted quantum mechanics which can reproduce the predictions of quantum theory.

So how do you know he talked about them? — Wayfarer

"The Interpretation of Quantum Mechanics: Dublin Seminars (1949-1955) and Other Unpublished Essays" Schrödinger 1995. p 19