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Quantum Mechanics for Programmers

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Re: Quantum Mechanics for Programmers

#41

Post by stan_rogers »

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…

Ockham is arguably the proper spelling when the name isn't being rendered in Latin; Ockham is where William was from.

Re: Quantum Mechanics for Programmers

#42

Post by dragonwriter »

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…

> It's a simple suggestion if you're looking for a starting hypothesis.

While it can be used to select priority for exploring hypotheses, it's at least as valuable as a method of choosing from among models with equal explanatory power once they've been tested and established to have equal explanatory power.

Re: Quantum Mechanics for Programmers

#43

Post by TheOtherHobbes »

defined wrote: post #38
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

Which must be the correct spelling, because it's shorter.

Re: Quantum Mechanics for Programmers

#44

Post by [deleted] »

defined wrote: post #38
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

[deleted]

Re: Quantum Mechanics for Programmers

#45

Post by HeavenBanned »

Xcelerate wrote: post #19
doubleunplussed wrote: post #12

Earlier quoted context omitted.

I'm a quantum physicist (well, we don't say that, I'm an atomic physicist, but for anyone not aware it is 99% quantum mechanics we do all day), and the MWI isn't universally accepted, but it's not universally rejected either. Plenty of important physicists interpret quantum mechanics that way, and I do too (I am not important though). That's not to say I'm confident it's correct , just that it's the most sensible way…

> 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",…

this comment chain is getting legendary rn ...best of HN for real. i'm wondering what max tegmark was saying about computers simulating the MWI and physicists confirming/nonconfirming MWI via computational simulation.

Re: Quantum Mechanics for Programmers

#46

Post by Razengan »

doubleunplussed wrote: post #12
monktastic1 wrote: post #3

Hmm he seems to imply that MWI is the "right" interpretation, and that the measurement problem is solved. Most physicists would not agree. If you follow the link to his MWI description, there's this gem: > But fortunately, I knew computer science, which most physicists do not know, with the Church-Turing thesis, which roughly states that anything physical can be simulated by a computer. But that is not what the Churc…

I'm a quantum physicist (well, we don't say that, I'm an atomic physicist, but for anyone not aware it is 99% quantum mechanics we do all day), and the MWI isn't universally accepted, but it's not universally rejected either. Plenty of important physicists interpret quantum mechanics that way, and I do too (I am not important though). That's not to say I'm confident it's correct , just that it's the most sensible way…

I'm a layman and I don't really understand much of this, but I'm really intrigued: What's the general consensus in your field on the existence of more than 3 spatial dimensions?

Seems to me, that there are a few phenomena that appear to be more or less random. Could they be perturbations caused by activity in dimensions we cannot perceive?

Re: Quantum Mechanics for Programmers

#47

Post by eutectic »

krastanov wrote: post #13
aphextron wrote: post #10

The more I learn about physics and math, especially with regards to quantum theory, I start to get really freaked out. The amount of "neatness" to the universe is staggering. How there's no "inbetween" at the smallest scales. Everything is discrete. The fact that simple arrangements of symbols on a screen can perfectly describe this behavior is mind blowing. It leads me to think there's no possible way we're not livi…

Minor nitpick: We definitely do not know whether everything is discrete. There are plenty of quantum mechanical phenomena that do not have discrete spectra (you can have light of any wavelength for instance (with some caveats at the extremes of the energy scales)). We also do not have theoretical or experimental proof that space-time is discrete at the Plank length-scale - all we know is that our current theories bre…

Luboš is known for being extremely hostile in all his opinions. :)

Re: Quantum Mechanics for Programmers

#48

Post by foldr »

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…

>So now you consider the system of [experimenter 2 + [experimenter 1 + system]], and we've got infinite regress — a.k.a. the measurement problem.

At the risk of sending things off an a huge tangent, it's interesting to see physicists recognizing that an infinite regress is, at least sometimes, unsatisfactory (even though there is of course nothing incoherent per se about the concept of an infinite sequence). Physicists usually tend to give short shrift to metaphysical arguments that rule out certain states of affairs on the grounds that they would involve an infinite regress of a problematic kind. But the logic you're using to argue against decoherence as a solution to the measurement problem is very similar to e.g. Aristotle/Aquinas's argument that the causal hierarchy must have a terminus. I'm not saying that in an attempt to start an argument about God. It's just interesting to see similar reasoning used in such different domains. (And of course in neither domain is it entirely clear that the reasoning works.)

Re: Quantum Mechanics for Programmers

#49

Post by adrianratnapala »

Razengan wrote: post #46
doubleunplussed wrote: post #12

Earlier quoted context omitted.

I'm a quantum physicist (well, we don't say that, I'm an atomic physicist, but for anyone not aware it is 99% quantum mechanics we do all day), and the MWI isn't universally accepted, but it's not universally rejected either. Plenty of important physicists interpret quantum mechanics that way, and I do too (I am not important though). That's not to say I'm confident it's correct , just that it's the most sensible way…

I'm a layman and I don't really understand much of this, but I'm really intrigued: What's the general consensus in your field on the existence of more than 3 spatial dimensions? Seems to me, that there are a few phenomena that appear to be more or less random. Could they be perturbations caused by activity in dimensions we cannot perceive?

For first question: I'd say pop-science does a surprisingly good job of conveying the consensus on extra dimensions -- they are a totally reasonable possibility, but their effects are to be felt in realms far beyond the realms that experimental physicists can study well.

But if they exist, they probably have important (but unknown) effects. And your proposal that they explain randomness is a good example of that. But to me it doesn't feel right.

Quantum randomness somehow doesn't seem to be of that kind. Perturbations from unknown dimensions might well look like randomness, much link an RNG in a computer. But that is still masquerading as a classical random process -- it would not show the weird correlations found in QM.

Re: Quantum Mechanics for Programmers

#50

Post by adrianratnapala »

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…

> quantum systems appear indeterministic to him. > However, the state of [experimenter + system] > is governed by an entirely deterministic equation ...

This sort of thing only makes sense in the context of many-worlds QM, and it is amusing how many professed non-many-worlders say such things.

We often describe quantum systems using an entirely deterministic (Schroedinger) equation. But we don't know in what sense that equation describes the physical state of the experimenter + system, or in what sense it is "just" a probability model.

If you choose to include the whole thing as physical reality, then you are left with all the terms in the equation -- and thus all of Everett's multiple worlds. Fine, that is a logically coherent position. But it's not the only one.

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