bkcooper

Yes. Bell's theorem doesn't forbid hidden variable theories (in fact, he has a publication preceding his famous result explicitly demonstrating a hidden variable theory that could reproduce QM measurements on a two-level system), just local hidden variable theories. In his collected papers, Bell often remarks that he feels Bohm's interpretation should be more widely studied.

It's a good question why it's not. My understanding, though I'm not well versed in the subject, is that there are some pretty severe shortcomings to it, particularly when you start considering systems with many particles. I've read some of Bohm's writings to try to understand it and as far as I got I found it pretty underwhelming; it seemed more like a bookkeeping trick than any sort of real insight.

It's also worth pointing out that there are distributions for which the central limit theorem doesn't hold (e.g. the sum of samples from a Lorentzian distribution will again be Lorentzian, not Gaussian.)

This is possible. But I think it's less about this and more about status marking. Joining the pile on is often a quick, cheap way to demonstrate that you care about the right things.

I've really enjoyed this book so far, so thanks!

And, as it has been seen on our entry level numerical physics course, learning programming, numerics and physics the same time is really quite hard.

Yeah. My feeling is that the numerical side of things is a lock to get short shrift in this type of course. In my own education, there were certainly lots of nods at numerical work, but they really undersold the subtle difficulties of doing numerics well.

The aspect of this that interests me most is related to a classic observation that, for most people learning physics, it's hard to separate difficulties with the physical content and difficulties with the mathematical content. The distinction between these is vague, but the separations like "set up the differential equation" vs. "solve the differential equation" that this functional style suggests seem like a good approximation to "physics" vs. "math."

There's a bot with several wins in Dungeon Crawl Stone Soup, another roguelike. The combinations it has won are pretty rote, but it's still very impressive, particularly since I don't think it's even capable of knowing that much about the game (it uses Lua handles to pick up information about the state and I believe there's a fair chunk of the game that isn't exposed that way.)

I disagree. In a textbook, it is very unlikely (and would be a sign of a badly written book) that there are terms in a displayed equation that are genuinely undefined. The worst case scenario is that they are not defined immediately next to the equation and presume that you have read the preceding material.

Re: the tourists, Metro in DC has an approach that I assume is for charging tourists more, which is that paper farecards (instead of the reusable SmarTrip card) get a surcharge of $1 on each trip. They're very open about the surcharge, so if you don't like it, then you can get a SmarTrip; however, it would then take a pretty involved computation to end up with zero balance at the end.

I'm actually pretty favorable toward the DC policy. Increasing tourist revenue (who probably are going to be pretty willing to pay slightly more for limited subway use) in a tourist-heavy spot seems like a reasonable approach to subsidizing the heavier commuting users of the system. With Metro specifically that may not be a huge deal because so many people have their commuting paid for as a benefit, but I like the basic idea.

ii and iii are the big issues for me (and obviously interwoven.) While it's not an original observation, one aspect of ii) that is especially bad is that most people probably have a distorted perspective on how good they are when they are starting out. The pool you will actually be competing with is probably much stronger than you realized.

In discussing some of these issues with a friend of mine, he said that he thought a good solution would be to substantially cut graduate enrollment and fill the labor gap with an increase in staff scientist positions. I think there's a lot to recommend that, but I can't say I see it realistically happening.

[1] http://arxiv.org/abs/math/9404236

I think that will be fairly tough. It's been a while since I looked at D-Wave, but aside from the whole "is it quantum" question about their stuff, their fabrication always seemed like a real strength. They had tons of on-chip circuits for addressing all of the qubits, and building devices with that many Josephson junctions that work is not easy. The comment that some of their material choices are probably limiting coherence is almost certainly true (this was one of Martinis's big contributions from ~10 years ago). But translating processes of that complexity to cleaner setups seems like it's going to require some real fabrication fu. I certainly wouldn't put it past Martinis, but it's ambitious for sure.

See Michael Nielsen's answer elsewhere in the comments for why this is not the case.

Another question is why L3-L3' red beam - the image info carrying beam - is fed into NL2 crystal thus providing a chance to physically affect formation of NL2-D5-L6 yellow beam, ie. to exchange information.

The interference requires us to not know which path the photon took way back at BS1, in that diagram. The probability of pair formation in the nonlinear crystals is quite low, so with very high likelihood, only one of the crystals will be responsible for producing a pair of photons (including the yellow signal photon.)

Suppose you did not route the imaging photon through NL2. Then observing an output photon at D3 would tell you that the pair production happened at NL2 (since there is no way for the imaging photon to get there.) This will destroy the interference pattern of the "yellow" photons. That is why the beam is sent through NL2.

In the setup of this experiment (see Fig. 1 of the arXiv link), there are two conversion crystals labeled NL1 and NL2. These convert the pump laser into two longer wavelengths, referred to as the signal wavelength and idler wavelength. The object is probed at the idler wavelength, but the interference depends only on photons at the signal wavelength.

Going much further than that gets tricky, because you will usually need more development in math in concert with the physics. The omnibus "engineering mathematics" type books will cover a lot of it but I don't really like them. Boas's Mathematical Methods in the Physical Sciences would be something I would look at. For more detailed looks at electromagnetism and quantum mechanics, I (and many others I know) really liked David Griffiths's textbooks. The Feynman lectures make an excellent supplement to these for the different perspective and interesting physical insights.

--- The time budget is extremely sensitive to how much you already know about the subject. If you're generally up on the literature in an area, it is often much easier to isolate the chunks that are genuinely new to you and thereby grok the paper very quickly. In a new field, even several hours to really read a paper might not be enough, depending on how much backtracking you need to do to understand core ideas.

--- In physics, the conventional wisdom (which I agree with) is that the main thing to do when checking out a paper is to look at the figures. These are generally chosen to highlight the most important points of the paper and will often quickly convey what was measured/calculated, how the effect scales, etc.

That artificiality is why I don't really like that approach, though. It's a brand of thinking that generally works only on artificial problems, because the key component ("you wouldn't be asking me this if it didn't have a well-defined answer") doesn't exist on most problems. Proving that it's constant and then using the r -> 0 trick to calculate the constant is much more satisfactory to me.

EDIT: My best guess as to what's going on is that they want to display the for-else idiom which could be useful in other contexts (e.g. if you don't want to return anything from inside the loop and can't break out that way.) It's a kinda surprising idiom; I had forgotten you could even do that in Python and at first thought it might be a misindentation until I realized the logic would be wrong if the else paired with if.

Sure, but Boltzmann's ideas were famously controversial at the time. I don't think they represent a good measure of mainstream practice at the time.