The branching is intrinsic to QM. — Andrew M

But it's not. It is the result of a simple conjecture: 'hey, what if the wave collapse DOESN"T OCCUR?' That's all it is. One of the implications of the wave function not occuring is that there must be gadzillions of different universes, or that the universe 'splits' whenever a measurement is made. But those who advocate it, don't seem to get how bizarre this is. 'Look at the math', they say.

Everett’s scientific journey began one night in 1954, he recounted two decades later, “after a slosh or two of sherry.” He and his Princeton classmate Charles Misner and a visitor named Aage Petersen (then an assistant to Niels Bohr) were thinking up “ridiculous things about the implications of quantum mechanics.” During this session Everett had the basic idea behind the many-worlds theory, and in the weeks that followed he began developing it into a dissertation.
The core of the idea was to interpret what the equations of quantum mechanics represent in the real world by having the mathematics of the theory itself show the way instead of by appending interpretational hypotheses to the math. In this way, the young man challenged the physics establishment of the day to reconsider its foundational notion of what constitutes physical reality. ...

Everett’s radical new idea was to ask, What if the continuous evolution of a wave function is not interrupted by acts of measurement? What if the Schrödinger equation always applies and applies to everything—objects and observers alike? What if no elements of superpositions are ever banished from reality? What would such a world appear like to us?

Everett saw that under those assumptions, the wave function of an observer would, in effect, bifurcate at each interaction of the observer with a superposed object. The universal wave function would contain branches for every alternative making up the object’s superposition. Each branch has its own copy of the observer, a copy that perceived one of those alternatives as the outcome.

Here is where I get off the bus. I just think it's conjecture gone mad. Sure, given that there are all these branches, then 'the math works'. But there's something the matter with the basic intuition behind it.

That article I'm quoting from, on Scientific American, notes that Neils Bohr did eventually agree to speak to Everett.

In the spring of 1959 Bohr granted Everett an interview in Copenhagen. They met several times during a six-week period but to little effect: Bohr did not shift his position, and Everett did not reenter quantum physics research. The excursion was not a complete failure, though. One afternoon, while drinking beer at the Hotel Østerport, Everett wrote out on hotel stationery an important refinement of the other mathematical tour de force for which he is renowned, the generalized Lagrange multiplier method, also known as the Everett algorithm. The method simplifies searches for optimum solutions to complex logistical problems—ranging from the deployment of nuclear weapons to just-in-time industrial production schedules to the routing of buses for maximizing the desegregation of school districts.

It was in doing the math for the 'deployment of nuclear weapons' that Everett made his fortune. Not that it did him a lot of good. He died aged 51, an embittered alchoholic hardly on speaking terms with his family, leaving instructions in his will to have his ashes put in the garbage.

Sure, he might have been a brilliant mathematician, but there was something seriously wrong with his intuition, in my opinion.

Modern speculative physics is the very same thing, sophistry. It is highly educated individuals simply seeking money to support their stream of false information. If they are to be rousted, as the sophists which they are, where else to start this movement other than a philosophy forum?

A point is reached where the person who (or the public opinion which) decides whether the money flows into the coffers, has to take the "truth" on faith, rather than understanding it in person. From this point on, the more inaccessible the sophistry, the better. The money continues to flow regardless, on faith alone. The problem then becomes looking as though you are doing something worthwhile, to justify the diversion of resources. It was in the mediaeval monasteries where this was perfected. They devised a scheme whereby the worth was to be realised in the afterlife (buying your way into heaven), so there was no way to test it.

So in this case perhaps we should be looking for the worth of the funding, are the money dispensers taking it all on faith? What is the worth they are expecting to arrive?

But it's not. It is the result of a simple conjecture: 'hey, what if the wave collapse DOESN"T OCCUR?' — Wayfarer

You are misrepresenting QM:

Copenhagen - Wavefunction collapse does not occur.
Many Worlds - Wavefunction collapse does not occur
De Broglie-Bohm - Wavefunction collapse does not occur
Modal Theories - Wavefunction collapse does not occur
Relational Theory - Wavefunction collapse does not occur
Statistical Interp. - ....
Ensemble ...
Many Minds
Consistent Histories

Get the idea?

The only theories that ever employed wavefunction collapse as a process in nature are von Neumann's theory of consciousness causing collapse, GRW - which is NOT quantum mechanics and does NOT work, and the Transactional interpretation.

Oh, but of course, wavefunction collapse also happens to be falsified.

Copenhagen - Wavefunction collapse does not occur. — tom

The WIkipedia entry on the subject states that:

According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured, and quantum mechanics can only predict the probabilities that measurements will produce certain results. The act of measurement affects the system, causing the set of probabilities to reduce to only one of the possible values immediately after the measurement. This feature is known as wavefunction collapse.

Further down in the same article, it is stated that:

During an observation, the system must interact with a laboratory device. When that device makes a measurement, the wave function of the systems is said to collapse, or irreversibly reduce to an eigenstate of the observable that is registered.[12]

The reference there is to this quote by Heisenberg:

It is well known that the 'reduction of the wave packets' always appears in the Copenhagen interpretation when the transition is completed from the possible to the actual. The probability function, which covered a wide range of possibilities, is suddenly reduced to a much narrower range by the fact that the experiment has led to a definite result, that actually a certain event has happened. In the formalism this reduction requires that the so-called interference of probabilities, which is the most characteristic phenomena [sic] of quantum theory, is destroyed by the partly undefinable and irreversible interactions of the system with the measuring apparatus and the rest of the world.

Sure sounds like 'wave function collapse' to me. But, as you know, Wikipedia is a user-edited resource, so if you believe it's wrong, go ahead and edit it.

The WIkipedia entry on the subject states that: — Wayfarer

In metaphysical terms, the Copenhagen interpretation views quantum mechanics as providing knowledge of phenomena, but not as pointing to 'really existing objects', which it regarded as residues of ordinary intuition.

Such joy being reduced to selecting quotes from the same wikipedia page!

Copenhagen, and neo-Copenhagen theories such as Consistent Histories, are purely epistemic. The wavefunction is not part of reality, and certainly collapse is not.

Do we really have to repeat these threads over and over again? Local realism and non-local realism have been falsified by several no-go theorems. Copenhagen survives because it is not a theory about what is real, rather it is a theory about what can be said about what is real. Many Worlds survives because the no-go theorems do not apply to it.

This is the whole point of the famous Bohr-Einstein debate. Einstein could not accept that QM was not about "elements of reality", whereas Bohr claimed "the quantum world does not exist".

And, as we have repeated, and repeated, a theory that is explicitly anti-realist cannot provide an explanation. The ONLY explanatory theory that exists, which agrees with QM all the way up through field theory and the Standard Model is Many Worlds.

A famous quote from Bohr:

There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature

Of course, Einstein, Everett disagree, though I think Deepak Chopra agrees.

This blog is worth a look.

http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

Such joy being reduced to selecting quotes from the same wikipedia page! — tom

So, the first quoted passage is incorrect, in your view? (I ask because it seems to contradict what you said in the post before).

Local realism and non-local realism have been falsified by several no-go theorems — tom

But these are all intepretations. When you say that something has or hasn't been falsified, all you're doing it is interpreting it in accordance with your chosen metaphysical view, which any statement about what the theory means must be. Everyone sees the same data, the only thing being discussed here is what it means.

The wavefunction is not part of reality, and certainly collapse is not. — tom

I interpret the wave-function as a distribution of probabilities. Is that not correct?

a theory that is explicitly anti-realist cannot provide an explanation. The ONLY explanatory theory that exists, which agrees with QM all the way up through field theory and the Standard Model is Many Worlds. — tom

That's only because of a pre-commitment to the kinds of explanations that must be real. Again, it's a metaphysic masquerading as science. It all comes down to a very literalistic understanding of what must be considered 'real'.

Physics concerns what we can say about nature — Neils Borh

Shocking statement, isn't it. But probably not as shocking as the Bohr Family Coat of Arms:



I'm sure Deepak would think that was cool. ;)

It's more that in this matter I'm excruciatingly aware of how much I don't know. — Wayfarer

Well stated, that is exactly Socrates' attitude, and the position we should all take, including the high level physicists. Many already have this attitude with respect to limited branches in the field, the key is to expand this principle to all areas, even fundamental assumptions. Start with the premise "I know nothing", and justify every premise before proceeding.

Knowledge is a journey which proceeds into the unknown. The destination is unknown. Each premise, or assumption, is a fork in the road, the option to proceed or not. Do I take this road or not? There's a map of sorts, because I can look ahead, with my limited comprehensive capacity, and see where it has brought others. Are they coming to a dead end? What other options do I have? Have some others taken other roads? The nature of possibility is that there are always other options. The roads less travelled are not so well cleared, they must be sought. Where they might be exposed, who knows (tpf?). Perhaps I'm already beyond the turn off, I missed it because it was the less travelled road, so I have to go back and find that fork. Perhaps individuals slip off the well travelled road at different points all along, seeing the dead end ahead, adopting different assumptions which are not the same as each other, but are inconsistent with the well travelled road, then they start to come together again on a different well traveled road, off there in the distance somewhere, as they establish consistency with each other. Should I create my own turn off, or go all the way back looking for a more well travelled turn off?

It is better to have no understanding than a misunderstanding. Misunderstanding is the illusion of understanding, the believe of understanding which is really not understanding, it is mistaken. Misunderstanding robs one of the capacity of choice. All appears as understood, but it is not. Under the illusion which is called misunderstanding, there is no choice as to which road to take, the certitude involved with the confidence of knowing, and the appearance of understood, denies that possibility. But the confidence is misplaced, involved with misunderstanding rather than understanding.

A point is reached where the person who (or the public opinion which) decides whether the money flows into the coffers, has to take the "truth" on faith, rather than understanding it in person. From this point on, the more inaccessible the sophistry, the better. The money continues to flow regardless, on faith alone. — Punshhh

It's really always taken on faith, the western system is an honour system, built on strong moral principles, honesty, with trust and faith entwined with honesty. Though there are some exceptions to the rule, honesty is not the problem, physicists who are being funded to do their research truly believe that they are proceeding in the right direction. The vast majority of the money comes from the consumers, industry follows this, and hires physicists and engineers to get the competitive edge. In universities, learning institutions, and publically funded research centres, there is more freedom of direction for the researchers. Here, it is probably not so much the case that the physicists go in the direction that the money is, but the money goes in the direction of where the physicists' minds are.

The real issue I believe is misunderstanding, and this is honest mistake. The sophistry which Socrates exposed was real honest misunderstanding, at the institutionalized level. The sophists truly believed that they knew these things, and were proceeding in the honest and good way by educating others. What he demonstrated was that they really did not know what they professed to know. This opens the door to doubt and skepticism. But the point is that unlike deception which is relatively easy to determine, honest mistake is extremely difficult to identify. Fundamental principles are firmly believed, and maintained by the community, to the same degree whether or not they are actually true. There is no essential difference between a true fundamental principle and a false one, they both play the exact same role in the community. To expose a false one requires applying the principle to something outside of the system within which it is currently employed. That's what Socrates did, he took fundamental principles which were being employed in various fields of technology, and said look what happens when I employ this principle in another field, absurdity results. Why do you cling to this principle as if it is a truth? Clearly it is not.

So, the first quoted passage is incorrect, in your view? (I ask because it seems to contradict what you said in the post before). — Wayfarer

It's just standard guff written about an theory whose sole purpose is obfuscation and denial. I really couldn't care less about it, so can't be bothered forming an opinion. Save to say, the article makes the epistemic nature of Copenhagen explicit later on.

But these are all intepretations. When you say that something has or hasn't been falsified, all you're doing it is interpreting it in accordance with your chosen metaphysical view, which any statement about what the theory means must be. Everyone sees the same data, the only thing being discussed here is what it means. — Wayfarer

Your primary source of knowledge, Wikipedia, has articles on Bell's theorem etc.

Bell - local realism falsified
Leggett - non-local realism falsified

It has been shown by experiment that both local and non-local realist theories disagree with Reality. Quantum Mechanics has never been shown to disagree with Reality.

PBR - The wavefunction cannot be interpreted as a probability distribution over real states.

I don't believe any experiment has been performed to test PBR - i.e. to test whether reality agrees with Quantum Mechanics or any theory that regards the wavefunction as real probabilities, but no one doubts the result.

Actually, PBR does have implications for Many Worlds - it means Many Worlds is correct.

I interpret the wave-function as a distribution of probabilities. Is that not correct? — Wayfarer

To claim you have an "interpretation" of a topic you know so little about is bizarre.

Meanwhile my impression of MWI is that it's ad hoc to preserve determinism.

Meanwhile my impression of MWI is that it's ad hoc to preserve determinism. — Terrapin Station

That is almost funny.

I made a list of the rather low-quality "criticisms" of many worlds, but I'm not sure where this fits in.

It doesn't seem to fit precisely with "criticism by personal incredulity" which cover almost everything. This one seems to be a combination (or should that be superposition) of "ignorance" + "willful misrepresentation".

Here's a test too see if I'm correct:

1. Name the ad-hoc modifications to QM employed by Many Worlds
2. Identify where it is non-deterministic.

I like how you respond to that, but completely ignore the problem that Deutsch only defines "computational equivalence" for machines in the paper that supposedly "proves" the CTD principle.

I like how you respond to that, but completely ignore the problem that Deutsch only defines "computational equivalence" for machines in the paper that supposedly "proves" the CTD principle. — Terrapin Station

Why is that a problem?

Oh I get it, how do you know the machines exist when you're not looking at them.

Why is that a problem? — tom

Because the CTD principle isn't supposed to be only about machines, is it?

Because the CTD principle isn't supposed to be only about machines, is it? — Terrapin Station

It's only about machines.

It has been shown by experiment that both local and non-local realist theories disagree with Reality. Quantum Mechanics has never been shown to disagree with Reality. — tom

What does "disagree with Reality mean"? Do you have an assumed Reality which a theory either agrees with or disagrees with?

t has been shown by experiment that both local and non-local realist theories disagree with Reality. Quantum Mechanics has never been shown to disagree with Reality. — tom

Why the capitalised 'Reality'?

It's only about machines. — tom

I thought it was claiming that a universal computing device can simulate every physical process? Not every physical process involves a machine, unless he's claiming that everything is a computing device, but you explicitly denied that he was stating that.

It's just standard guff written about an theory whose sole purpose is obfuscation and denial. I really couldn't care less about it, so can't be bothered forming an opinion. — tom

That refers to the Wikipedia article on the 'Copenhagen Interpretation.' This is an open-source encylopedia, so anyone is entitled to edit it. But apparently it is 'so incorrect' that it's not even worth an opinion about, let alone editing or updating it.

Let's not forget that the main claim of 'many worlds' is that there are, in fact, many worlds. It's not simply mathematics, it's a metaphysic.

To claim you have an "interpretation" of a topic you know so little about is bizarre. — tom

You can learn a lot by asking questions and gauging the responses.

Let's not forget that the main claim of 'many worlds' is that there are, in fact, many worlds. It's not simply mathematics, it's a metaphysic. — Wayfarer

it's not a claim, it is a testable deduction...for the umteenth time.

Some intellectual honesty would be a peasant surprise!

I thought it was claiming that a universal computing device can simulate every physical process? Not every physical process involves a machine, unless he's claiming that everything is a computing device, but you explicitly denied that he was stating that. — Terrapin Station

The universal machine can simulate every finite physical process.

it's not a claim, it is a testable deduction...for the umteenth time. — tom

A deduction is only as sound as its premises. What is your definition of Reality?

I went through this in detail in above (or in the thread where we first discussed this if it wasn't this thread). Deutsch definies simulation in terms of computational equivalence, and he defines computational equivalence in terms of computational devices ONLY. There's no definition of what computational equivalence is for something other than computational devices, with the upshot that there's no definition of what a simulation is for something other than computational devices, so just what it amounts to to simulate a physical process that's not a computational device isn't even addressed in the paper that's supposed to be proving that every finite physical process can be simulated. I brought all of this up already, but you had ignored it.

it's not a claim, it is a testable deduction. — tom

Whenever you go into detail of what it's 'testability' amounts to, it is always along the lines of a deductive argument about 'what the observations mean'. Deductive arguments are by nature not amenable to falsification. Nobody disputes the accuracy of the predictions made by quantum physics, but it is precisely 'what the observations mean' which is at issue. If you google the term 'wave-function metaphysics' you get a number of books, and a wide range of interpretations. So if it's a matter of intellectual honesty, you're obliged to acknowledge that dissenting interpretations exist. Repeating your belief over and over again does nothing to change that.

But it's not. It is the result of a simple conjecture: 'hey, what if the wave collapse DOESN"T OCCUR?' That's all it is — Wayfarer

There is a lot more to the issue than that. There is nothing at all in QM that implies or predicts wave function collapse. Copenhagen doesn't postulate wave function collapse, it wholesale denies that the wave function is real. That is, the philosophy of the Copenhagen Interpretation is anti-realism. It's worth repeating the quote by Bohr which makes it very clear what anti-realism entails:

There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature. — Bohr

Meanwhile my impression of MWI is that it's ad hoc to preserve determinism. — Terrapin Station

The determinism is built-in to QM - the wave function evolves deterministically according to the Schrodinger Equation. And self-locating uncertainty is a prediction of QM.

Copenhagen has to deny the reality of the wave function to avoid that determinism and it cannot explain measurement uncertainty. If you take the pilot wave route, determinism is preserved, but it posits hidden variables which, as you may guess from the name, there is no evidence for.

Bell - local realism falsified
Leggett - non-local realism falsified

It has been shown by experiment that both local and non-local realist theories disagree with Reality. Quantum Mechanics has never been shown to disagree with Reality. — tom

Just to clarify this, Everettian QM is a local realist theory. What Bell's theorem falsifies are realist theories that depend on local hidden variables.

There is a lot more to the issue than that. There is nothing at all in QM that implies or predicts wave function collapse. Copenhagen doesn't postulate wave function collapse. — Andrew M

According to the Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured, and quantum mechanics can only predict the probabilities that measurements will produce certain results. The act of measurement affects the system, causing the set of probabilities to reduce to only one of the possible values immediately after the measurement. This feature is known as wavefunction collapse.

The second edition of Everett's thesis was published as “Wave Mechanics Without Probability'. Why do you think it was called that?

The second edition of Everett's thesis was published as “Wave Mechanics Without Probability'. Why do you think it was called that? — Wayfarer

Because Everett considered the wave function to be real and the world as not inherently probabilistic.

But a consequence of that is that the world 'splits' at the point of measurement, and/or that there are countless 'parallel worlds'. Once again - doesn't that seem intuitively strange to you? What does it say about other 'fundamental laws' like the conservation of energy?

Why do you think the probabilistic nature of the wave-function is sufficiently troublesome to consider such an alternative?

Because Everett considered the wave function to be real and the world as not inherently probabilistic. — Andrew M

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From ~25mins for the purely QM stuff.