290 karma · joined August 15, 2014
No, not enough. This is a consequence of its interacting only gravitationally or via the weak force. Much of the distribution of visible matter is down to electromagnetic interactions that effectively allow it to collide and slow down, whereas dark matter naturally wouldn't do that, or at least would take a drastically longer time to do so.
One might more generously say that dark matter is a proposed explanation for many measurements deviating from predictions based on visible matter in a way very consistent with the existence of large amounts of non-electromagnetically-interacting matter.
I don't think there's anything fundamentally ridiculous about this. For instance, while you characterise it as 'radically' different to any matter that we observe directly, the neutrino has most of the relevant properties, and e.g. supersymmetry has been noted to include dark matter candidate particles. While one may doubt that supersymmetry is actually correct, I think it demonstrates that the combination of properties (massive + electromagnetically inert + maybe weak force interacting) isn't necessarily a problem.
We don't know what dark matter is, or if it even is a kind of matter rather than e.g. modified gravity (though modified gravity has many problems of its own), but I think it is a common mistake that people are so eager to associate it with aether on the grounds only of what they find 'elegant'.
Edit: Also, the notion of a kind of matter that can hardly be observed is not particularly weird or 'arcane'. For instance, neutrinos have many of the right properties. I think they are ruled out as dark matter candidates mainly because their mass is too low to fit with observations.
But why should we accept this? Why does it justify pages like this one, that don't need javascript but deliberately fail if you don't enable it?
Do you have a reference for why this should be? A quick search yields results suggesting only the opposite (for instance, https://superuser.com/questions/738848/does-more-ram-usage-c...).
I do see why you argue this way, and I might agree except that I also would give weighting to the moral point he's making. Staff like this are systematically exploited, and working to contract is a classic way to try to demonstrate why they should be better supported - it's a direct attempt to make a larger point, not just a random choice to annoy a few students.
It doesn't change the context that the instructor isn't being paid to do it - he says he's already spent more time on the course than contracted. From his point of view, it's not an unreasonable request that he should not spent more of his (insufficiently remunerated) time on even small issues.
> and would be understandably pissed off if I was given no opportunity to collect an exam I'd taken.
But does that make it reasonable to blame a guy who's not paid to help you for not helping you?
I do understand the nature of your point, but I don't think any of the original argument is actually affected by the size of the task he's refusing to do.
Edit: To be clear, you can make games in vanilla kivy just fine (and it's probably much more performant than pygame), but kivent is a dedicated game engine with more efficient graphics internals and nice things like chipmunk integration.
It's not simply the existence plea bargains that is coercion, I don't think anyone would argue that, and it's easy to find situations where plea bargains can be good things.
But, this is not the point of the criticism - it is also easy to think of situations where plea bargains could be used to distort justice rather than to make it efficient. Wikipedia has a good discussion of this at https://en.wikipedia.org/wiki/Plea_bargains#Controversy .
You can disagree that these criticisms are a problem in practice, that is fine and something that could be discussed, but you must recognise that plea bargains could in principle be used in a coercive way, and that many people fear that this happens in practice.
My understanding was that plea bargains are criticised in the context of being offered as an alternative to fighting the case against a very significantly tougher sentence, so that you might win but you're much worse off if you lose. The criticism is then that there is certainly duress - not literally forcing your hand, but forcing a choice that is unreasonable given the nature of the crimes and (so is the claim) encourages confessions by people that are innocent or even just an overall sentencing distribution that ends up being a bad fit for the crimes.
I could have understood wrong previous discussion of this though, or perhaps the problematic cases are not widespread.
The concern with changing it is that you could simply make things worse, even if on the surface more meritocratic. For instance, if it just ended up filled with the same career politicians as the commons and just agreed with everything they said. Of course it could end up better as well, in principle, but I'm not sure the government could be trusted to implement things that way.
This isn't actually the case - Bell's theorem and subsequent verification demonstrate only that a theory of local hidden variables cannot be successful - the local part means that faster than light information transfer doesn't occur. You're allowed to have a pilot wave interpretation if it's nonlocal.
I think this is actually a problem with these experiments - it's nice that they work, but we already knew pilot wave mathematics could describe quantum mechanics, with the caveat that nonlocality is necessary to explain everything. I don't think this nonlocality is (or can be) expressed in the fluid experiments, so presumably they can't actually replicate QM.
Bell's theorem remains true, but pilot wave theory achieves the quantum results by sacrificing locality instead of hidden variables.
> how does the description of entanglement as "spooky action at a distance" not violate those?
It's just a name, and an old one at that. I suppose if you ascribe it to non-locality then it really does involve something FTL on some level, but even with a standard locality-preserving, no hidden variables theory, no information travels faster than light so you don't actually hit a FTL problem. The strange thing is that the quantum state appears to behave consistently regardless of its spatial extent, which is weird.
> How long do you think it would take to reason intelligently about it?
I would have thought that someone in a PhD mathematics program would be well equipped to understand the mathematics - maybe the hard part is finding a good resource that takes things in a good order. I'm afraid I can't really recommend anything, though Feynman's stuff is probably good.
> Why would the measurement of Up/Down spin destroy information about Left-Right spin in the classical case?
It wouldn't, if you like, which would make it another thing that would be different in classical mechanics, though it's a little strained because it's assuming a lot about quantum states being like classical states.
In quantum mechanics the different spin operators do not commute, which means if you measure it in the vertical direction (and get e.g. up) then in the left-right direction, you get each of left or right with 50% probability. But then if you measure it in the up/down direction you don't get up again, you get up/down each with 50% probability, the original state is irrelevant. This is obviously different to your marbles, which just have letters that don't change.
> Can a spin be not 1 or -1? Could it be in between?
No. When you measure the quantum state you get an eigenfunction, though the state before collapse could be a superposition. Indeed, this is the case for different directions - spin up is a superposition of equal parts spin left and spin right in the horizontal spin basis, which is why you get each direction equally if you measure it in that direction.
> Doesn't that capture everything?
You're still trying to encode everything in a hidden variables theory, where the quantum states secretly know everything beforehand about what it will do, but the observer can't access the information without performing specific measurements. This immediately fails as above, because the quantum states inherently don't have fixed up/down and left/right components and each measurement in a different basis gives a random result.
You can try to fix things by adding more complex rules about the letters on the marbles changing when you read them, but it turns out there are fundamental limitations on what physical results any such theory can predict. This is famously addressed by Bell's theorem (as in, seriously famously, this is really important), which demonstrates specific limitations on what physical results are allowed by such models, and experiments have shown that quanum mechanics does breach these limitations. I'm not sure how to explain more simply what's going on though.
(Strictly, we can allow hidden variables (though more complex than a predetermined left/right and up/down as above) by breaking the speed of light to let the separated states communicate instantly, but this brings up its own problems.)
We can see this by considering two electrons in an entangled spin state - say, one is spin up, and the other is spin down, but the entangled state means you don't know which is which, only that Alice and Bob will get consistent answers when they measure the spin in the vertical direction. At this point, everything maps fine to the two-half-coins idea, all we know is that they have opposite spins.
What's different in the quantum case is that Alice and Bob could instead decide to measure the spin in the left/right direction. Following the rules of quantum mechanics, a given spin up or down state has an undetermined spin left/right state, so when you measure the spin in the left/right direction it has exactly 50% chance of being each one.
If the original states were really just like the coin halves, this new measurement would be simply uncorrelated between Alice and Bob - they'd start with different states (up or down), but the left/right measurement would destroy that information and they'd both get a random answer because the individual elecrons end up with an individually random left/right spin direction.
The reality is actually different; if we do the measurement maths on the quantum state rather than assuming it's predetermined like the coins, it turns out the left/right spin is still entangled. That means that when Alice and Bob measure the spin in the left/right direction, they'll always find that one of them gets left and the other gets right. This would not be possible if the quantum states were predetermined like the coins.
So, the coins analogy is not a bad way to understand some of the basics of what you expect, but it absolutely is not a fully accurate description of what's going on. Maybe you already knew that, but I wanted to be clear that there's very much more to entanglement, because this is the source of several common misconceptions.
(Of course quantum teleportation is a further thing again, but the extra non-classical mathematics of entanglement are still important, it's not just coin halves.)
I don't disagree in general about some of the flaws of LaTeX, but am I missing something about this one? Using maths in a caption works fine.
This is a remarkably short sighted attitude. I mean, maybe there is totally no problem with the shirt, but it's just a false argument to say 'I saw some women in science so there is no problem'.
I don't think anyone can prove it right now, only find it plausible or probable. Of course that's a long way from proof, but the opposite is also true - can you demonstrate that this shirt, in the context of a wider trend of what people can and do wear, does not affect the number of women in science?
> Did the female student's lecture attendance/signup rate plummet since that interview?
This is disingenuous, I'm sure you know that no criticism of the shirt is because this specific, individual incident would be perceived to be of overwhelming importance for any given statistic, and I think your attempt to portray things this way is a strawman or a horrible misunderstanding. As above, it is the example of wearing this shirt in the context of wider trends in what people do (and wear) that people are criticising. You can still disagree with them, but at least disagree on a point you didn't just make up.
Of course there are probably plenty of people for whom being told this kind of thing is itself a stimulus that can help to modify their behaviour, but I worry there's another class of people (or even just people in specific contexts) to whom being told to exercise self control is not much different to telling someone with depression to cheer up. Potentially well meaning, but fundamentally the wrong way to approach things.
(To relate to this specific article, I don't see why it shouldn't be a very reasonable point that popular window managers etc may really not be optimised for productivity - not necessarily for you, but for some significant number of people. It's easy to say 'oh they can just change it then', but maybe most of them will never think about it or even realise it's possible unless the issue becomes publicised more widely.)
Any debate about the interpretation of quantum mechanics refers to to this question of what really happens, not to any details of what QM actually predicts will happen. That is, until/unless experiments are devised to separate these philosophical explanations, but nothing much has happened on this front for decades.