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Quantum Mechanics for Programmers

kim.oyhus.no

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Re: Quantum Mechanics for Programmers

#31

Post by madhadron »

This puzzles me extremely. There are very insightful statements like

> One does not deduce them like one do in math. The physicists who actually did this stuff apparently knew this, and considered the math more akin to toying with the models to see what happens, to see if they could get better models

Which is absolutely true. Part of the problem with quantum mechanics texts is that they're almost all descended from Oppenheimer's lectures (via Schiff's book) to graduate students who already knew this, and just needed someone to brain dump the latest techniques.

But then it's mixed with really basic misunderstandings, like

> Many physicists like to believe that this makes the underlying model irrelevant; that the matrix behaviour, its eigenvalues, is the only thing that matter. You will encounter lots of this in books about Quantum Mechanics. This however is not science, because it ignores Ockhams Razor; the models shall be the simplest ones. A sparse matrix is simpler than when it is Fourier transformed, or put into atom orbitals. (I thank Eliezer Yudkowski who gave a reminder that Ockhams razor belongs here too.)

Quoting Eliezer Yudkowski is a useful heuristic for not taking someone seriously, but this quote implies that the author missed the whole point of linear algebra. And is falling into the traps described by Theorem IV in van Kampen's [Ten Theorems about Quantum Mechanical Measurements](http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=617...).

Re: Quantum Mechanics for Programmers

#32

Post by empath75 »

Xcelerate wrote: post #14
monktastic1 wrote: post #7

Earlier quoted context omitted.

It is generally agreed (except, perhaps, by the strongest champions of the decoherence program) that decoherence does not completely solve the measurement problem. Some good references here: http://physics.stackexchange.com/questions/295527/decoherenc... It helps explain the loss of interference, but it does not resolve the question of why and how we see one particular outcome.

> that decoherence does not completely solve the measurement problem It's kind of funny how the problem keeps getting pushed to higher levels of "meta": If you consider the experimenter and his system, measurements of (non-eigenstate) quantum systems appear indeterministic to him . However, the state of [experimenter + system] is governed by an entirely deterministic equation that follows a reversible, unitary path t…

I've long thought that the measurement problem is a problem with the interface between consciousness and reality and that it's more of a psychology problem than a physics one.

Re: Quantum Mechanics for Programmers

#34

Post by monktastic1 »

codethief wrote: post #25
Xcelerate wrote: post #19

Earlier quoted context omitted.

> Furthermore, plenty of physicists don't actually grasp the fundamentals of their own field I once met a professor at a quantum chemistry conference who argued with me that I could not converge on the exact eigenvalues of a helium atom (assuming a simplified Hamiltonian with a few Coulombic terms). He stated the oft repeated mantra that "the Schrödinger equation can't be solved for any element other than hydrogen",…

> Another professor […] once said that the single particle wave function is more fundamental than the multi-particle wave function. Nevermind […] his research […] where the molecular wave function can't be well approximated using a product of single particle wave functions Depends on what you mean by "multi-particle wave function". The way it is usually understood (I think), it includes all possible tensor products o…

Tensor products only describe the separable (i.e., unentangled) states.

Re: Quantum Mechanics for Programmers

#35

Post by B1tchard0 »

This article could have been written by an algorithm. Everyone knows the meme about Quantum Mechanics being incomprehensible, like, ~"if you understand quantum mechanics, you don't understand quantum mechanics".

Quantum Mechanics requires randomness, because determinism is scary. Both probability and fate are functions of time, and time is the most interesting thing to look at. Generally, Time is ignored, or at best "accounted for".

As a programmer I think time is more interesting than particles or fields or probabilities of wave-function whatever

Re: Quantum Mechanics for Programmers

#36

Post by hota_mazi »

It's puzzling to see the author call himself multiple times a scientist while lending so much importance to Occam's razor (which is spelled differently in the article, not sure if it's an alternative spelling in his language or a mistake).

Occam's razor is not a law. It's not a fact. It's a simple suggestion if you're looking for a starting hypothesis.

Not sure which way to start to investigate a phenomenon? Pick the simplest one and verify that one. It doesn't mean it's right, it doesn't mean it's wrong, just that it's a reasonable first guess.

But not a proof. Not a fact. Just a guess that's statically more likely to be right.

Re: Quantum Mechanics for Programmers

#37

Post by AgentME »

B1tchard0 wrote: post #35

This article could have been written by an algorithm. Everyone knows the meme about Quantum Mechanics being incomprehensible, like, ~"if you understand quantum mechanics, you don't understand quantum mechanics". Quantum Mechanics requires randomness, because determinism is scary. Both probability and fate are functions of time, and time is the most interesting thing to look at. Generally, Time is ignored, or at best…

>Quantum Mechanics requires randomness, because determinism is scary.

Isn't the many-worlds interpretation generally regarded as deterministic?

Re: Quantum Mechanics for Programmers

#38

Post by defined »

hota_mazi wrote: post #36

It's puzzling to see the author call himself multiple times a scientist while lending so much importance to Occam's razor (which is spelled differently in the article, not sure if it's an alternative spelling in his language or a mistake). Occam's razor is not a law. It's not a fact. It's a simple suggestion if you're looking for a starting hypothesis. Not sure which way to start to investigate a phenomenon? Pick the…

Occam is the Latinized version of Ockham, as in "William of Ockham" [1].

[1]: https://en.m.wikipedia.org/wiki/William_of_Ockham

Re: Quantum Mechanics for Programmers

#39

Post by platz »

empath75 wrote: post #32
Xcelerate wrote: post #14

Earlier quoted context omitted.

> that decoherence does not completely solve the measurement problem It's kind of funny how the problem keeps getting pushed to higher levels of "meta": If you consider the experimenter and his system, measurements of (non-eigenstate) quantum systems appear indeterministic to him . However, the state of [experimenter + system] is governed by an entirely deterministic equation that follows a reversible, unitary path t…

I've long thought that the measurement problem is a problem with the interface between consciousness and reality and that it's more of a psychology problem than a physics one.

ok, but I don't think that is what Xcelerate is quite saying here
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