What is the current status of Many Worlds?

[AndreiB]

Can you tell me, how to get into that very universe, where the content of my account is spontaneously doubled by some event on the stock market? SCNR.

You don't need to get there. There is a "you" there already. So, just be happy for him!

 

[AndreiB]

In this spirit of confusion I'd love to hear what the thoughts on Many Worlds are in 2021 by everyone here at PF.

As far as I know there is no way to derive Born's rule in MWI, so the theory cannot make any predictions. There is no way to ascribe any meaning for probabilities in MWI.

 

[Demystifier]

Why is the Hamiltonian fundamental in classical mechanics? Newton was fine without it. Is Bohm's interpretation fine without the wave function?

You can define classical mechanics without Hamiltonian $H(x,p)$, but then you need something equivalent, e.g. the force function $F(x)$. The wave function is something similar, the closest classical analogy of the wave function is in fact the Hamilton-Jacobi function $S(x,t)$.

 

[AndreiB]

You can define classical mechanics without Hamiltonian $H(x,p)$, but then you need something equivalent, e.g. the force function $F(x)$. The wave function is something similar, the closest classical analogy of the wave function is in fact the Hamilton-Jacobi function $S(x,t)$.

So you can replace the wave function with a force that acts instantaneously between particles?

 

[Demystifier]

So you can replace the wave function with a force that acts instantaneously between particles?

No, in Bohmian mechanics you can't really do that. Bohmian mechanics is a law for the velocity, not for the acceleration.

 

[AndreiB]

No, in Bohmian mechanics you can't really do that. Bohmian mechanics is a law for the velocity, not for the acceleration.

OK, so if you modify Newton's second law so that the "force" does not determine the acceleration, but the velocity of the particle can you replace the wave function?

 

[Demystifier]

OK, so if you modify Newton's second law so that the "force" does not determine the acceleration, but the velocity of the particle can you replace the wave function?

Replace with what? I think nobody found such a mathematical object yet.

 

[AndreiB]

Replace with what? I think nobody found such a mathematical object yet.

You claimed that the wave function is not ontic. That means that it should be possible to describe it in terms of something else which is ontic. Or maybe we have a different understanding of what ontic means. Would you consider the forces in Newtonian mechanics as ontic?

 

[PeroK]

For me, this line of thinking is highly confusing. The entire goal of philosophy is to make things not fuzzy. The thing that changed in the renaissance wasn't separating philosophy from science, it was to establish concrete philosophical foundations for science. This was also the time when we began to established concrete philosophical foundations for mathematics. The revolution in science was due to a breakthrough in philosophy, not an abandonment of it.

This is such a travesty that I couldn't let it go.

The philosopher Henri Bergson, who didn't understand and wouldn't accept relativity, blocked Einstein receiving a Nobel prize for the theory of relativity.

https://nautil.us/issue/35/boundaries/this-philosopher-helped-ensure-there-was-no-nobel-for-relativity

Bergson himself got the Nobel prize for Literature (!) in 1927 and - like other philosophers - battled against the progress of science and mathematics in the mistaken belief that their own supreme intellect and powers of pure thought outweighed that of mathematics and empirical science.

Ironically, of course, any decent undergraduate of physics or mathematics can understand the theory of SR in six weeks or so. That's what it took me.

The lesson is clear: if you want to make progress in science and mathematics, you have to ditch philosophy and the philosophers and their non-existent powers to know the world through pure thought alone.

 

[martinbn]

My view on the many worlds is that, when it talks about many worlds existing and many copies of everything, it is just a pile of words. On the other hand the idea of a relative state interpretation without the philosophical nonsense is very atractive.

 

[Demystifier]

You claimed that the wave function is not ontic. That means that it should be possible to describe it in terms of something else which is ontic. Or maybe we have a different understanding of what ontic means. Would you consider the forces in Newtonian mechanics as ontic?

I would not consider the forces in Newtonian mechanics as ontic. $F(x)$ is nomological, as is the wave function.

 

[Demystifier]

My view on the many worlds is that, when it talks about many worlds existing and many copies of everything, it is just a pile of words. On the other hand the idea of a relative state interpretation without the philosophical nonsense is very atractive.

What's the "relative state interpretation without the philosophical nonsense"? Do you have a reference?

 

[martinbn]

What's the "relative state interpretation without the philosophical nonsense"? Do you have a reference?

I didn't say the relative state interpretation. I said a relative state interpretation.

 

[Morbert]

I think MWI as a project was completed by Consistent histories.

MWI showed us how decoherence can let us assign probabilities to possible worlds/histories, and how QM treats these possibilities on equal footing apart from their probabilities.

But you need an exotic ontology underlying these probabilities. Consistent histories showed us i) how we can recover our intuitive understanding of these probabilities as likelihoods for mutually exclusive alternatives, as opposed to needing all alternatives to actually exist, and ii) How to more rigorously quantify the decoherence between worlds.

 

[vanhees71]

The paper defining the original relative-state interpretation by Everett or rather the version of Everett's view revised due to the advice of his thesis adviser J.A. Wheeler, who was a declared Bohr disciple, is

https://doi.org/10.1103/RevModPhys.29.454

 

[Demystifier]

I didn't say the relative state interpretation. I said a relative state interpretation.

What's a relative state interpretation without philosophical nonsense?

 

[PeterDonis]

Can you tell me, how to get into that very universe, where the content of my account is spontaneously doubled by some event on the stock market?

Sure, just invest in the right stock.

 

[*now*]

RQM involves relative states. This is an early paper, there could be further developments since,
https://link.springer.com/article/10.1007/BF02302261
Published: August 1996
Relational quantum mechanics
Carlo Rovelli
International Journal of Theoretical Physics volume 35, pages1637–1678 (1996)
Abstract
I suggest that the common unease with taking quantum mechanics as a fundamental description of nature (the “measurement problem”) could derive from the use of an incorrect notion, as the unease with the Lorentz transformations before Einstein derived from the notion of observer-independent time. I suggest that this incorrect notion that generates the unease with quantum mechanics is the notion of “observer-independent state” of a system, or “observer-independent values of physical quantities.” I reformulate the problem of the “interpretation of quantum mechanics” as the problem of deriving the formalism from a set of simple physical postulates. I consider a reformulation of quantum mechanics in terms of information theory. All systems are assumed to be equivalent, there is no observer-observed distinction, and the theory describes only the information that systems have about each other; nevertheless, the theory is complete.
https://arxiv.org/abs/quant-ph/9609002

 

[Jarvis323]

This is such a travesty that I couldn't let it go.

The philosopher Henri Bergson, who didn't understand and wouldn't accept relativity, blocked Einstein receiving a Nobel prize for the theory of relativity.

https://nautil.us/issue/35/boundaries/this-philosopher-helped-ensure-there-was-no-nobel-for-relativity

Bergson himself got the Nobel prize for Literature (!) in 1927 and - like other philosophers - battled against the progress of science and mathematics in the mistaken belief that their own supreme intellect and powers of pure thought outweighed that of mathematics and empirical science.

Ironically, of course, any decent undergraduate of physics or mathematics can understand the theory of SR in six weeks or so. That's what it took me.

The lesson is clear: if you want to make progress in science and mathematics, you have to ditch philosophy and the philosophers and their non-existent powers to know the world through pure thought alone.

You're talking about groups of arrogant Philosophers, not Philosophy.

There have also been arrogant groups of medical doctors that rejected the merits of hand washing with tragic consequences. The solution wasn't to abandon medicine.

Philosophy has given us the scientific method, formalization of computation, logic, and axiomatic systems in mathematics.

You really want scientists to ditch the scientific method, and you want mathematicians to ditch logic and axioms?

You can't expect to make progress by reason and intelect alone, but how much progress can you make without it at all?

 

[PeterDonis]

You're talking about groups of arrogant Philosophers, not Philosophy.

Even Philosophers should recognize this logical fallacy, namely No True Scotsman.

Philosophy has given us the scientific method, formalization of computation, logic, and axiomatic systems in mathematics.

Nope. None of those things were given to use by Philosophy. The scientific method, to the extent that term even has a definite meaning, was given to us by scientists. Formalization of computation, logic, and axiomatic systems was given to us by mathematicians. The fact that some of the people who contributed to those things also billed themselves as philosophers does not mean Philosophy gets to take credit for those things.

You really want scientists to ditch the scientific method, and you want mathematicians to ditch logic and axioms?

This is another logical fallacy that even Philosophers should recognize, namely the Straw Man.

 

[Jarvis323]

Even Philosophers should recognize this logical fallacy, namely No True Scotsman.

You've missed the mark on this one. I was pointing out the conflation between philosopher and philosophy. This is the mistake you're making now.

Nope. None of those things were given to use by Philosophy. The scientific method, to the extent that term even has a definite meaning, was given to us by scientists. Formalization of computation, logic, and axiomatic systems was given to us by mathematicians. The fact that some of the people who contributed to those things also billed themselves as philosophers does not mean Philosophy gets to take credit for those things.

It sounds like your concern is with which group of people get credit for something, and which identify they place on themselves.

 

[PeroK]

Philosophy has given us the scientific method, formalization of computation, logic, and axiomatic systems in mathematics.

There's no doubt that mathematics and the natural sciences began as part of philosophy - but, that was the problem. Real progress only began when science and mathematics were freed from religion and philosophy.

The great advances in mathematics in the 19th century are all mathematical. There's no great philosophy behind real and complex analysis, differential geometry and vector calculus, for example. It's just hard-nosed mathematics.

To take three concrete examples from the 20th Century: General Relativity, Goedel's Incompleteness Theorem and the Turing machine. Wittgenstein and Popper could not possibly have produced anything so definitive and concrete. Not by doing philosophy.

I know Wittgenstein wrote and thought about mathematics, but because (unlike Einstein, Goedel and Turing) he didn't actually do mathematics, there is nothing left to show for his efforts. He was never going to produce the theorems that settled the question of mathematical decidability, for example. Undecidability would have remained a point of philosophical debate, rather than an established theorem.

That's the difference. Philosophy can never really resolve anything - and, perhaps the endless shifting sands are what philosophers like about it. And, perhaps, that's what makes them generally poor scientists and mathematicians.

 

[Jarvis323]

There's no doubt that mathematics and the natural sciences began as part of philosophy - but, that was the problem. Real progress only began when science and mathematics were freed from religion and philosophy.

The great advances in mathematics in the 19th century are all mathematical. There's no great philosophy behind real and complex analysis, differential geometry and vector calculus, for example. It's just hard-nosed mathematics.

To take three concrete examples from the 20th Century: General Relativity, Goedel's Incompleteness Theorem and the Turing machine. Wittgenstein and Popper could not possibly have produced anything so definitive and concrete. Not by doing philosophy.

I know Wittgenstein wrote and thought about mathematics, but because (unlike Einstein, Goedel and Turing) he didn't actually do mathematics, there is nothing left to show for his efforts. He was never going to produce the theorems that settled the question of mathematical decidability, for example. Undecidability would have remained a point of philosophical debate, rather than an established theorem.

That's the difference. Philosophy can never really resolve anything - and, perhaps the endless shifting sands are what philosophers like about it. And, perhaps, that's what makes them generally poor scientists and mathematicians.

Maybe our disagreement is simply about what philosophy is and what it isn't. I think I may be thinking too literally.

To me, Goedel's Incompleteness Theorem is a work of philosophy. And the Church Turing thesis that underpins the Turing Machine is also in my opinion.

 

[PeterDonis]

I was pointing out the conflation between philosopher and philosophy.

If Philosophy does not mean what philosophers actually do, then it's a meaningless term. Anyone can make it mean whatever they want by just saying that the doings of any "philosopher" who doesn't do what they want Philosophy to mean don't count as Philosophy. That's what you were doing.

It sounds like your concern is with which group of people get credit for something, and which identify they place on themselves.

You're the one who said Philosophy gave us all these great things. That's a claim of credit. I was simply pointing out that it's not a justified claim of credit.

 

[Jarvis323]

If Philosophy does not mean what philosophers actually do, then it's a meaningless term.

This is a highly imprecise and logically problematic statement. But since we aren't philosophers I guess we don't use logic anyways?

That's what you were doing.

This isn't at all what I was doing.

 

[PeterDonis]

Maybe our disagreement is simply about what philosophy is and what it isn't.

Quite possibly, yes. See below.

To me, Goedel's Incompleteness Theorem is a work of philosophy. And the Church Turing thesis that underpins the Turing Machine is also in my opinion.

I have never seen anyone else take this position; everyone else that I'm aware of considers these to be works of mathematics, not philosophy. Of course you are free to adopt your own idiosyncratic definition of "philosophy" for your own use, but that doesn't mean you should expect everyone else to go along with it.

This is a highly imprecise and logically problematic statement. But since we aren't philosophers I guess we don't use logic anyways?

This isn't at all what I was doing.

Evidently we disagree, and it doesn't look like our disagreement will be resolved here. Which is fine, in this particular forum it is understood that many topics discussed will not be amenable to a definite resolution. But, once again, while you can adopt your own definitions of terms for your own use, that doesn't mean you should expect everyone else to use them.

 

[Jarvis323]

When an architect uses the pythagorean theorum, it seems not controversal that they are doing math.

I don't see why it should be different for philosophy. If a physicist uses logic or inductive reasoning, they are doing philosophy. Maybe it is more complicated, due to connotations about philosophy?

I sense that here people have certain branches of philosophy in mind, e.g. metaphysics.

 

[PeterDonis]

If a physicist uses logic or inductive reasoning, they are doing philosophy.

I think most people would consider logic and inductive reasoning to be general tools applicable to a variety of disciplines, not philosophy. If they are part of any particular discipline, I think most people would say that discipline is mathematics.

 

[PeterDonis]

When an architect uses the pythagorean theorum, it seems not controversal that they are doing math.

No, they are doing architecture, using math as a tool. One can similarly do philosophy using logic and inductive reasoning as a tool. That does not mean logic and inductive reasoning are philosophy, any more than math is architecture.

 

[Jarvis323]

I think most people would consider logic and inductive reasoning to be general tools applicable to a variety of disciplines, not philosophy. If they are part of any particular discipline, I think most people would say that discipline is mathematics.

I guess maybe you're right. I've been taking people's rejection of the use of philosophy in physics as a rejection of the tools of philosophy, or formal methods of reasoning in general, in physics.

It's still not clear to me where the line is between using/doing philisophy, and just using tools that were origionally developed as tools of philosophy. Philosophy is generally the study of discovering truth and knowledge, and its tools are methods of reasoning and analysis. I guess every discipline used to be a branch of philosophy.

I'm still not exactly sure what people are rejecting when they say they reject philosophy in physics. It would help to be more precise.

 

[PeterDonis]

tools that were origionally developed as tools of philosophy.

I don't think logic and inductive reasoning were originally developed as tools of philosophy. If they were originally developed as tools of anything, it was mathematics.

Philosophy, perhaps, has used these tools to try to discover propositions with more generality than any other discipline, which is both a strength and a weakness. It's a strength because the more general a proposition is, the more ways you can use it. It's a weakness because the more general a proposition is, the less it is likely to be able to tell you. In science, in particular, I think the weakness weighs much more than the strength.

 

[Demystifier]

I don't think logic and inductive reasoning were originally developed as tools of philosophy.

They were. https://en.wikipedia.org/wiki/Term_logic

 

[Lord Jestocost]

Remind me - what does ontology mean?

When it is allowed to answer:

Ontology is an easy concept. Maybe, some get mixed up with the term “ontology” because there is a meta-question which questions – so to speak – the basic question of ontology itself. David J. Chalmers puts it in a nutshell in “Ontological Anti-Realism”:

“The basic question of ontology is ‘What exists?’. The basic question of metaontology is: are there objective answers to the basic question of ontology? Here ontological realists say yes, and ontological anti-realists say no.” [bold by LJ]

That’s it. It’s only the meta-question which unsettles physicists who cling with ferocity to the concepts of daily life, which – in the scientific language of physics – may be refined to the concepts of classical physics.

 

[haushofer]

It is? Then what is considered the "modern" formulation of Bohmian mechanics? I thought the whole point of BM was to have a deterministic equation for the time evolution of particle positions, just like in classical mechanics. To do that you need the quantum potential.

No, determinism is not the primary concern of BM; ontology (a realist's form of it) is.

 

[PeterDonis]

They were. https://en.wikipedia.org/wiki/Term_logic

Aristotle may have been the first to explicitly codify these tools, but he wasn't the first to discover or use them. The Greek geometers were already using them (and the Greeks weren't the first to do geometry either), though they did not systematize their use of them until Euclid, who was a rough contemporary of Aristotle.