A Private View of Quantum Reality
wired.com
wired.com
I mentioned this in another comment, but I particularly like "Quantum Mechanics as Quantum Information, Mostly"
I think either the author messed up the concept badly, or what is more likely, the proponent of this 'QBism' doesn't get it.
He appears to think spooky action is just lack of information - something like "if I open the box and see white marble, you must have the black one". Possibly haven't read or doesn't understand EPR thought experiment (which shows how by choosing to make a certain kind of observation, what he and thus the other guy sees).
Looks like pseudoscience to me.
More generally, QBism is not a hidden variable theorem in any sense. What the article glosses over is that QBism does still require a modification to standard probabilities that (when combined with Baysian/information theoretic reasoning) gives you the measurement probabilities you actually see in the lab.
Chris Fuchs' writeups are pretty fantastic: http://perimeterinstitute.ca/personal/cfuchs/
Specifically, "Quantum Mechanics as Quantum Information, Mostly" is a short and fun introduction (okay, 32 pages, but pretty easy reading).
> A grain of sand falls into the shell of an oyster and the result is a pearl. The oyster's sensitivity to the touch is the source of a beautiful gem.
> Last year, I watched my two-year old learn things at a fantastic rate, and though there were untold lessons for her, there were a sprinkling for me too.
A better reading material is the solution of a simple exercise, that explains the difference between the usual approach and the QB approach. (Is there any differences in the results?)
Someone has suggested the double slit experiment, because it's nice and easy to explain with words, but the continuous distribution makes the calculations difficult. I prefer the three Stern-Gerlach experiments because it's discrete and the math is easier. I think I read that experiment in a Feynman book, but I don't remember the exact citation. (The SG in the middle is the equivalent to the double slit.)
I just found this PDF that explain clearly the situation: http://docslide.us/documents/spin-and-quantum-measurement-da... . It's the "Experiment 4" (subsection 1.2.4, page 10). Can you explain the differences between the usual and the QB approach in this experiment?
In particular, things like collapse of the wave-function (for example) present some difficulty for (b) -- not for (a) -- which is what QBism is trying to address. It's also why you don't get problems to solve here, and why I recommended "Quantum Mechanics as Quantum Information, Mostly". Yes, it's written casually (have a look at Fuchs' and others' publications on the arXiv that made it to scientific journals if you want fewer asides about children) but the casual nature is because this is about how we view the problems in the first place, and why we make the calculations we do, not how to carry out the specific calculations.
Consider this (example stolen from Fuchs, somewhere): We knew the correct equations of special relativity years before Einstein came along -- that's why it's called the Lorentz transform, not the Einstein transform. But Einstein's genius was to boil things down to two laws (within an inertial reference frame, typical laws of motion hold, and the speed of light is the same in all reference frames). From there we moved from simple calculations that we already knew how to do to a much deeper understanding of the subject. That's what Fuchs' and others working on interpretations of QM are trying to do -- not change the way we make calculations, but understand why the laws are the way they are in the hopes of extracting something new and different from that knowledge.
In QM you can describe a quantum state with a wavefunction (to incorporate quantum ignorance) or a density matrix (to incorporate both quantum and classical ignorance). (A for classical ignorance only, one would just use probability vector).
States than can be described with just a wavefuctions are called pure states. And many-world interpretation revolves around having _only_ pure states (so, while being unsettling, does not add other assumptions and is, well... more pure). In QBsim pure states are not singled out.
Having said that, if you are coming to QM, QBism will protect you against a lot of BS. :)
And BTW: I remember my meeting with Chris Fuchs. It was a very illuminating story how did he turned from a (sinful) frequentist to an (enlightened) bayesianist. And how we should focus on knowing and not knowing things, rather that consider reality as an abstract thing.
A --bit-- lot of shameless self-advertisement:
- Hydrogen ion and classical vs quantum not-knowing: https://johncarlosbaez.wordpress.com/2015/03/13/quantum-supe...
- My quantum game - I want _show_ how does quantum mechanics work http://quantumgame.io/ (just a sign-up list; I will release alpha this Sept)
- in my PhD thesis I coined qubism (for a plotting scheme for quantum states), only to realize later that a similar word is already taken; chapter 3 of http://arxiv.org/abs/1412.6796: "The name qubism (inspired by Cubism, the art movement) should not be confused with QBsim (quantum Bayesianism)"
Without math, many-world interpretation is a ridiculous absurd, and an Ockham's nightmare. With - well, it's pure QM _without_ adding additional assumptions.
Just never forget that Ockham's razor has absolutely no basis in science. Also, what one person finds a simpler or more elegant theory, another person might not; in that sense it is quite arbitrary.
But one can quantify the complexity of a theory as the number of bits required to compute all of its predictions. In that sense, the MWI is the least complex version of QM, because, as stared pointed out, it's just the basic math of QM with nothing added on. All of the other interpretations add something on, which means requiring more bits for computation.
There are ways of making it formal and precise. See section 3 in this chapter from Judea Pearl's book: http://bayes.cs.ucla.edu/BOOK-99/ch2.pdf or for a more lightweight discussion that happens to be in my tab stack atm, see https://probmods.org/occam's-razor.html
I understand people think they're being helpful with the knee jerk "that's not science" response to someone asserting Occam, since the principle is often abused/overused, but the academic perspective on this has been much richer for decades now. It's not fair to just sweep that away with a ba-humbug.
It was certainly not my intention to impress an opinion on anyone else. Everybody here has the brains to think differently.
I'll be happy to see my comments proved wrong; please provide proper argumentation.
To elaborate a little more on my original point: the razor has proved useful as a guidance for thinking, and historically it has helped us to avoid going into paths that are not worthwhile, but there is absolutely no guarantee. In fact, the razor might even prevent us from going into paths that are fruitful. So, I'd be cautious about it. That was all, basically.
"Minimum Description Length Induction, Bayesianism, and Kolmogorov Complexity" (Paul Vitanyi, Ming Li)
And so one does not consider what a person, nor any collection of as yet inscrutable minds, finds simpler. Instead, the question is posed to a rigorously formalizable third party: https://en.wikipedia.org/wiki/Solomonoff%27s_theory_of_induc...
The proposed theory would seem to indicate that it's possible to get the real world into a state similar to an out-of-sync network game. Some games can get into a state where the player states have diverged, but the players are still connected. Is this article claiming that the real world can do that? That should be testable.
> My fellow QBists and I instead think that what Bell’s theorem really indicates is that the outcomes of measurements are experiences, not revelations of something that’s already there.
I studied the Bell inequalities at the university, but I have no cue about what this sentence means.
http://motls.blogspot.com/2015/06/is-quantum-reality-persona...
In that interpretation, QM is seen as the only way to do physics when you represent your knowledge of a system using probabilities. Measurement instruments are a choice among all the physical systems, and what we consider good physical instruments lead to QM "axioms".
This is elaborated here: http://cc3d.free.fr/tim.pdf.
In other words, for any probabilistic physical framework it seems to me you are going to need to put a magical 'sampling' or 'observation' somewhere.
Making this explicit is one of the reasons I like Bohm's formulation: https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory...