Lost Causes of Theoretical Physics (2003) • Hacker News Board

Re: Lost Causes of Theoretical Physics (2003)

#51

Post by naasking » Sat, Mar 03, 2018, 4:12 PM UTC

Retra wrote: post #11

IntronExon wrote: post #5

Earlier quoted context omitted.

From other sections it seems clear that the author is a devout adherent of The Copenhagen Interpretation, aka objective wavefunction collapse; this is a close relative of the baseline non-Interpretation “Shut Up And Calculate.” People like that are generally utterly unmoved by anything short of a rigorous mathematical formulation, which works for them in QM where “rigorous mathematical formulation” is pretty much all…

I would argue that expecting QM to satisfy a human need for ontology is about as useful as expecting general relativity to satisfy a human need for sexual gratification. It's easy to find a way to be dissatisfied: just want more out of things. But it doesn't make sense to always expect to get what you want. Some things simply won't provide. As long as QM is providing a means to achieve accurate predictions and precis…

> As long as QM is providing a means to achieve accurate predictions and precise language, it is doing its job perfectly. It is not responsible for satisfying a (potentially irrational) need for ontological interpretation.

What a strange position. Clearly some things exist, since we're here, we're discussing the subject itself, and so on. Defining what "to exist" actually means would seem to be the central rational pursuit of physics. This is an ontology.

The focus on prediction is merely a proxy to the ultimate goal.

Re: Lost Causes of Theoretical Physics (2003)

#52

Post by naasking » Sat, Mar 03, 2018, 4:16 PM UTC

millstone wrote: post #26

gizmo686 wrote: post #10

Earlier quoted context omitted.

QM is a mathematical model. Many worlds is an intuition to understand that model. There is a pedagogical question on if many worlds is a useful mental model to have. There is also a philosophical question of if many worlds better captures the essence of the model relative to Copenhagen. We can also flip it around. Why should we think of QM in terms of the Copenhagen when it makes to testable predictions.

Wouldn't you consider the Born rule to be a testable prediction (though in an admittedly weak sense of simply being postulated)? If the Born rule were found to be violated, it would invalidate Copenhagen but not MWI, which IMO means Copenhagen is more falsifiable.

> If the Born rule were found to be violated, it would invalidate Copenhagen but not MWI, which IMO means Copenhagen is more falsifiable.

All quantum mechanical interpretations depend upon the Born rule. A violation of the Born rule would rule them all out, except perhaps Bohmian mechanics which allows the possibility of non-equilibrium states, but we have no idea if those can be created.

Re: Lost Causes of Theoretical Physics (2003)

#53

Post by naasking » Sat, Mar 03, 2018, 4:19 PM UTC

gonehome wrote: post #31

millstone wrote: post #25

Earlier quoted context omitted.

The price that MWI pays for this minimalism is that it loses some contact with reality, i.e. physical experiments. Basic physical observations like "some measurements are non-deterministic" are quite difficult to explain in the MWI. Reality is inconvenient.

I don't think that's true - it takes that into account, it just looks like it collapses because you're in the world with that state - not seeing the entire picture. MWI accounts for it appearing that way while in actuality the wave function never collapses. Max Tegmark gives a pretty accessible description of this in his book - Our Mathematical Universe, and Eliezer Yudkowsky does a decent job with a general explanat…

> I think the Copenhagen interpretation is now considered wrong by most physicists.

Recent surveys suggest that most practicing physicists still pick Copenhagen as their default, mainly because that's what they were taught and QM foundations have no implication on their actual work.

Re: Lost Causes of Theoretical Physics (2003)

#54

Post by ajkjk » Sat, Mar 03, 2018, 5:08 PM UTC

naasking wrote: post #50

ajkjk wrote: post #3

Earlier quoted context omitted.

After skimming the whole thing, I was relieved to see that the argument against Many Worlds was the only one I considered invalid. It took the form of "It's not even a testable theory", rather than "it has mathematical deficiencies". Well, of course, no one's saying it's testable necessarily, but for various aesthetic and intuitive reasons it still seems valid. Just don't expect predictions from it and you'll be fine…

> After skimming the whole thing, I was relieved to see that the argument against Many Worlds was the only one I considered invalid. You should consider the Bohmian criticisms invalid as well then. Many have argued that de Broglie-Bohm is "many worlds in disguise", so if the criticisms the author levels against Bohmian mechanics are true, then they apply to MWI, but if they don't apply to MWI, then they don't apply t…

Oh yeah. Probably, yeah. I glossed over that one because its criticisms were strangely technical for a theory that, iirc, just rephrases regular quantum theory.

Re: Lost Causes of Theoretical Physics (2003)

#55

Post by ajkjk » Sat, Mar 03, 2018, 5:08 PM UTC

John_KZ wrote: post #43

whatshisface wrote: post #33

Earlier quoted context omitted.

Pilot waves, multiverse and Copenhagen are fundamentally ineligible for experimental support, at least with respect to each other. They lead to the same numbers, meaning than an experiment that agrees with one will also agree with the others. It's something like trying to tell the difference between 2x=2y and x+2=y+2. The "support" in the article is really just a physical system that obeys (as a macroscopic approxima…

While the current formulation details of the pilot wave theory doesn't allow for new predictions, a better formulated one will. I strongly believe we'll see the breakthrough in the coming 10-15 years. Quantum mechanics are statistic predictions and it's about time we treat them as such.

Why do you strongly believe that?