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([personal profile] ceb Apr. 28th, 2017 11:47 am)
Just posted off my first Pay It Forward present (ref: [personal profile] venta look out!
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([personal profile] jack Apr. 27th, 2017 02:16 pm)
How to adjudicate when the GM and player have diverging expectations?

Someone has to act as arbiter, and by default that's the GM, but when the GM decides, what should they decide?

I have no one answer, but a few principles.

If it doesn't matter much, get it out of the way quickly, and defer any discussion about the rules till later.

If the player had a particular expectation, try not to undermine them. I think this is one of the most important things to try to deal with in the moment.

If the player misunderstood an explanation and tried to jump across a 100" wide chasm not a 10" wide chasm, you may need to clarify some other things, but at a minimum, you probably want to say, "you'll just fall to your death, do you want to do something else?" not "are you sure?" "uh, yeah, why?" "ok, you fall to your death".

That applies whether you have someone who knows what the official rules say and was relying on it. If they've set up a shot that depends on the cover rules working the way the rules say and you've never previously altered, it sucks for them to have that yanked out from under them if you improv something instead. Or whether you have a new player who doesn't know what's covered mechanically or not, and tries to do something dramatic like swinging on a chandelier that in-rules doesn't provide any combat advantage. In both cases, the player shouldn't have a hissy fit, but also in both cases, it's your job to do the best you can in the spur of the moment to allow the player's action or give a good substitute. FWIW, I would allow the first player their interpretation of the rules that once, and if it kills an important NPC, I never rely on an important NPC surviving. And for the second player I'd do something like, "make a dex check, if you succeed, attack with a modest bonus (or choose to knock the enemy back)". That fits the sort of action they wanted.

If it's a one-off, it probably doesn't matter much. If it's going to come up repeatedly (eg. rules for hiding), get past the immediate problem, and then review the situation later. Check what the rules really say. Decide if you'd prefer those, or some modification. Check with the player if they have a sensible request, and if so, consider if it makes sense. Then make a decision, make it clear and stick to it.

If you're not sure which rule to go with? Look for easy to adjudicate (if it doesn't matter, you can always go with what's in the book). Look for fun -- the beginner is right, random stunts should TOTALLY be in lots of combat, and it's a flaw in the rules they're not. Look for ones that avoid breaking a tone you're evoking. Look for which way your players would prefer.

Part of this is just, how to make good rulings in the heat of a moment whichever side you come down on.

Part of it is, where do you draw the line between "what happens because of common sense" and "what happens because what it says in the rules". There's a gulf of people's expectations. Both in terms of tone (is this action adventure where heroes do things humans MIGHT be able to do? Or more like an epic norse legend, where great heroes wrestle sea-serpents?) and in terms of pedantry (do you expect the GM to allow an unconscious villain to have their throat slit? or rely on the weapon rules on how much damage that deals?). There's an amount you can stretch to accommodate different players, but only so far: beyond that, you just have to accept you want to play different things.

It's important to figure out if that's happening or not. You can totally have a tone that has character drama all over the place, *and* swashbuckling *and* fart jokes (see: all of Shakespeare). But if 4/5 players want wall-to-wall drama and one wants fart jokes, it may well not work. And the same in reverse.

Likewise, you can easily have some characters who chose well-optimised powers for their class, and some who chose whatever felt cool, and as long as there's not a big difference in power, it's fine. But if some characters want to hand wave away combat to get to the character interaction, and the other characters want to use the class abilities they just levelled up into, it's a stretch to keep both happy. Sometimes you can, sometimes you can't.

But that's often the underlying dynamic when players react in very different ways, they're focussing on different parts of the adventure, and you want to give both what they want, but avoid what you give one player obviating what the other player wants. Eg. if conversation is always pointless when combat happens, people who want to learn about NPCs are screwed. If you let one character do things because they're cool, but everyone else sticks to the rules, the other players are eclipsed. Can you do both, or not?
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([personal profile] jack Apr. 27th, 2017 02:07 pm)
I saw this recommended online somewhere and the premise was v my sort of thing so I gave it a go.

Bob is a hacker who gets lucky rich, signs up for cryogenic suspension, and at some point in the future is scanned and turned into an AI in a semi-theocratic-dystopian future. This is before that tech becomes reliable or cheap, so it's only used where an AI is needed and the subject doesn't have much choice, specifically running a space probe.

The generally comedic tone allows a lot of interesting premises to be examined which I've rarely seen in other books, like automatically using multiple copies of the most effective uploaded personality, instead of using each once each.

There's a bunch of space exploration which is solid and pleasingly up-to-date, but not otherwise spectacular.

Bob is an example of the sardonic-witty low-self-esteem hacker who shows up in lots of books. An archetype I like, but have got sick of. The sexist comments are fewer than The Martian, but still not zero.

If you like this sort of thing, you will probably enjoy it a lot, but if you don't, it probably won't persuade you.
When the Kindles first came out and Colin was an enthusiastic subscriber, I had a go and didn't really get on with it. But recently, [personal profile] juliet mentioned that Kindle screens are different now, and I had another go and discovered that I quite like the kind he has. So he offered to buy me my own (because I could borrow his but what I mostly use the app for is situations that I don't know in advance that I'll definitely need a book or a magazine, and I'm guessing that's what I'll use the device for as well). It'll make packing for holiday significantly easier, too, as a large part of what goes in my bag is Enough Books.

Annoyingly, I seem to have lost my ability to read Lightspeed in organising this but that should be easy to fix.

Anyway, I kind of feel like I win at shopping. I needed to buy something from Argos, next door. So I ordered that on the way, then I went into Curry's to check which Kindle I wanted (because I wasn't sure) and ordered that from my phone, went next door to Argos and picked up my stuff, returned to Curry's and picked up that. There was a bit of a wait in Curry's, but only because there was no queue in Argos. Total waiting time less than five minutes. Curry's didn't have the case I wanted, so I ordered that from Amazon in the waiting time.
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([personal profile] jack Apr. 27th, 2017 10:38 am)
A long time ago, there was a DnD module tomb of horrors, and every so often since there's been some controversy about it.

AIUI, it was the equivalent of playing a computer game on iron-man difficulty, with no saves, only one life, etc. It was designed for experienced players who wanted a really deadly challenge, often at conventions where there might be an audience.

The general features are (a) there's a lot of challenges that involve player decisions, not specific skills, whether the characters are appropriately really really careful about everything they do. (b) when something goes wrong, it's usually very deadly.

That meant, if you expected "fair" to mean "forgiving", it's really really not -- if you're the slightest bit incautious, you'll likely all die immediately. But if you expected "fair" to mean, "your death stem directly from your decisions" then it is more so than most adventures[1].

But if you don't know that, there is a lot of ire between people who loved it, people who think this is "the one true way" of how a session should be, and people who tried it and became incredibly resentful. It's good that the far end of a bell curve exists when that's something some people want to find, even if *most* modules should be somewhere left of it.

I did once play with a GM who played a few sessions of it inbetween campaigns. I liked the idea, although I usually like roleplaying with more story.

[1] There are some flaws where it might not be completely fair, or ambiguous descriptions, etc, but less than most modules at the time iirc.
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([personal profile] jack Apr. 26th, 2017 06:32 pm)
DnD 4e and 5e introduced the idea of skill challenges. Basically a unified framework for handling various things other than combat or parallel to combat that should involve more back and forth than a single roll, like a chase scene, or defusing a bomb.

The idea is, instead of a single "defuse bomb" roll, you need multiple things, open the panel without setting something off, find the deadman's switch, choose the right wire, cut it.

And these might be things that require a variety of skills.

4e designed a version which really rubbed me up the wrong way. It optimised for designing a scenario that could be run mechanically for different groups and present a particular level of challenge, and assumed that each challenge would be defined by "achieve N successes before X failures, using skills A, B, C or D".

I've only skimmed the rules for 5e but it seems to be somewhat more freeform. Because I thought this was a *great* idea, basically codifying something that a good GM would do automatically, but I really didn't like the way it was hard-coded, and presented to the players up-front.

Ideally, it should be obvious without specifying to the players. For the bomb, maybe each failure makes the bomb arm itself, then begin flashing, then finally explode. You don't know for sure how many steps, but you can tell things are getting critical. (And if you're aiming for fun rather than challenge, the GM can escalate or descelate the requirements according to how challenging this encounter should be compared to other ones that have happened this session.) It should be obvious which skills might apply, but they might lead to different paths -- a knowledge skill might open up an easier path to success, not count as a success/failure itself; different skills might stack or not; etc.

Or it ties into combat, each failure makes combat more difficult (it makes the platform you're standing on move dangerously or lets more enemies catch up), or you need to coordinate making skill rolls with other characters doing combat.

If you're improv'ing, that's all fairly easy to do, even though it's hard to spec in advance.

I said on twitter, skill challenges are a great idea, but I find it more fun if it's "how the GM designs the scenario" not "a mechanic the players need to be familiar with". Now I think of it, I see the same contrast with "what monsters you encounter". That easily can be pre-specified, and the players know, basically, the mechanics are "here's the monsters who exist" or "they spawn every two rounds" (as in 4e)[1], and know everyone faced a similar challenge. Or it can be improvised -- if the players faff around, the reinforcements arrive early, if they players have a lucky plan to bar a door, they can't come in, etc, etc. (as I'd like it).

[1] This makes sense from a tactical combat perspective, but I found very frustrating. Every 2 rounds skeletons climb out of a sarcophagus. No, you can't look inside. No, you can't judge how many skeletons could fit inside. No, you can't judge what sort of spell or effect is responsible (well, you can, but you can't expect it to matter). No, you can't try to block the lid. It's screaming "accept the premise and desperately avoid imagining being there". Except that if you do that, you have no way to judge "having the infinite spawning skeletons finished or will they continue" and are punished for guessing wrong. I feel like you could have 90% of the effect by saying "there's a pile of bones, a skeleton assembles itself out of them, there's still 3/4 of the pile left" or "the sundered skeleton parts begin to reassemble themselves" or "the air shimmers and a skeleton warrior sprouts from the ground".
ceb: (squee)
([personal profile] ceb Apr. 26th, 2017 02:57 pm)

In 50 years time we will look back on this as second only to the washing machine in the revolutionising-womens-lives stakes.

(IHNJ, IJLS "labour-saving device")
liv: In English: My fandom is text obsessed / In Hebrew: These are the words (words)
([personal profile] liv Apr. 25th, 2017 08:50 pm)
I made the classic mistake with Passover this year, of getting worked up and stressed about the practicalities of it instead of preparing spiritually. Actually it all went completely fine, but it wasn't until the last day of the festival, when all the organization was over, that I actually remembered to feel joy and celebration for being free.

contains religion )

Monday was just wonderful, though. That was when it really started to sink in that not only was I actually happy at being redeemed from slavery, but I am incredibly joyful and grateful to have such an excellent family. Both the ones I grew up with who are so great to celebrate Pesach with, and my family of choice who are incredibly supportive about joining in with my festivals and including me in theirs in a really respectful and non-pressurey way. We played D&D with [personal profile] jack GMing, something we've been meaning to do for ages and just not had time for, and it was really fun and relaxing.
Last post, I decided that what's "really there" for fundamental particles is typically a quantum thing, specifically, a probability wave of possible values a particle can have which appears to collapse into one particular place only when its interacted with.

However, this "collapse" sounds very suspicious. If two different particles emitted from the same particle decay (or something?) are known to have opposite spins, but not what those are, do you get all the usual wavelike behaviour, can each self-interfere, etc? Yes, of course. And yet, when you finally measure them, lo, the spins are still conveniently opposite.

Something that looks like collapsing to a single answer seems to happen, because when we measure them, we always do get a single answer. But that's not an event. If you measure one, does a spooky force reach out across the room to force the other to collapse at the same time? Does it collapse the value you measure, but still allow other properties of the particle to continue being multiple? That looks awfully like what happens, but it should seem wrong to start with, even before you ask "if you measure one particle, does the other know to wait until you interact with it, but store the answer you're going to find until then" and "if you measure them both a long way apart, does the collapse rush faster than the speed of light (aka backwards in time) to make sure both answers agree with each other?"

Any theory involving particles "knowing" or "waiting" or "choosing" depending on how you measure them sounds very unlike physics.

And yet, the particles go on behaving like probability waves until you measure them, and if they came from a shared source, then when you measure them, they DO agree. Just as if this spooky shit was happening. What might be going on?

Hypothesis 1

Whenever one particle collapses, a spooky force travels faster than the speed of light to the other particle, and then hangs around telling it what value it will have when it's finally measured.

This *works*, but hopefully you can see why it doesn't seem correct.

Hypothesis 2

Just like hypothesis 1, but we try to avoid thinking about it. This is not really satisfying, but it works and is a pragmatic default for many physicists. (Sort of Copenhagen interpretation?)

Hypothesis 3

Even while a particle is still smeared out across a probability of many potential positions/values, it has a hidden property which tells it how it's *going* to collapse when something interacts with it. Like, not necessarily "hidden", but basically some sort of determinism.

This is roughly Hidden variables interpretation (right?)

This would be fairly satisfactory except that it turns out it's impossible.

This is not very mysterious or controversial, but involves more simple probability than I can manage to wade through. Look up the EPR paradox or the Bell inequality. The idea is, you choose something like polarisation angle that could be measured at many different angles. You randomly choose to measure at different angles for two particles known to have opposite polarisation. There are various correlations between the probabilities when you measure the two particles at an angle to each other (the detectors neither parallel nor orthogonal). You can prove that no possible hidden value would make all those correlations true at once, but QM does and that's what's actually observed.

I can't really prove this to myself, let alone anyone else, but AFAIK no reputable physicists doubt that it's correct, only maybe what it means, so I'm willing to accept it as true.

There are still edge cases, like, people argue whether the experiments have ABSOLUTELY DEFINITELY proved this spooky collapse effect would have to go faster than the speed of light, rather than going at a possible speed (but depending what exact moment sets it off, etc). But I don't find any of that very persuasive. A spooky collapse effect which is triggered by measuring a particle and goes at the speed of light or below, while not ABSOLUTELY DEFINITELY ruled out, doesn't sound at all likely. I don't think anyone seriously expects that if they make the distance apart in those measurements a bit bigger, they'll suddenly get difference results: that's not how you expect physics to happen.

Hypothesis 4

Those weird quantum probability waves don't only exist for tiny particles, they happen just the same for everything including macroscopic objects, humans, etc, but you can't observe the effects except for tiny things (because to see interference you need something isolated from other particles, and you need to be able to detect its wavelength, which is way too small for anything bigger than a molecule).

I'm still working on understanding *why*, if that's true, it produces the effects we see. But most physicists, even ones who don't like this line of reasoning, seem to agree that it *would*.

This makes everything above non-mysterious. How does the collapse effect move around? It doesn't. Every "collapse" is just another probability thing of a scientist (and all the other macroscopic stuff) interacting with a particle and becoming two never-interacting possible scientists, one observing A, one observing B. We know both happen. We know, when we measure things light-hours apart and then compare notes, that we will be comparing notes with the version of the other scientist who observed the opposite polarisation to what we saw, while our shadow twin will be comparing notes with the other scientist's shadow twin.

The multiple non-interacting versions of the macroscopic world are called "many worlds" or "parallel universes" which admittedly makes them sound very implausible.

It seems like, this leaves some things to ponder, but resolves a very large part of the things people find mysterious. And yet, many physicists really don't like it. I need to read the bits of Scott Aaron's book about different interpretations[1], because I trust him to know more about this than me and he doesn't seem convinced.

Footnote [1]

The hypotheses above are called interpretations. I don't know if my ones exactly map onto the real ones. The name is because they all predict the same results, and yet seem quite different.

You can argue, "they're the same", but I don't quite agree. See for instance space outside our light cone -- we have no way of observing it, so the hypotheses "it's got physics just like ours but with different stuff there" and "it's all purple unicorns" are both possible, and yet, the first one seems a lot more like actual reality.

In both cases, it sort of doesn't matter, but you can imagine (a) which answer is most plausible, most useful, easiest to work with, or least ridiculous (b) if we're wrong and there IS some difference, which one would actually be found to be the one that exists.
You should be able to select multiple pokemon from your reserves when choosing which pokemon to fight with.

When you're training a friendly gym, the default pokemon selection should avoid pokemon very slightly higher CP than the ones you're fighting that automatically reduce the prestige gained by 40%.

"Vaporeon used hydropump" should always come slightly before the special move takes effect, rather than slightly after.

If your pokemon is on 5% health and you switch to another pokemon and that one is knocked out, its default replacement should be the *next* one, not the one which will be knocked out instantly. (Is there a shortcut for "next pokemon" without going through the pokemon select screen?)

If your switch pokemon and while you're in the pokemon select screen, your previous pokemon faints or you forget which pokemon you started with, and you click frantically click a pokemon again and again trying to select it and nothing happens, it should select that pokemon even if it's the one already selected.

If you select "run away" there should be a quick gesture to do so in a single click, without needing to get to the "yes" button before your next pokemon is knocked out too.
This has so much I love.

An interesting space empire, full of detailed calendrical minutae, customs, etc, etc.

A mathematically gifted protagonist struggling to serve loyally as a minor officer in the infantry.

A legendary rogueish maybe-monster.

The empire is built on basically mathematically-based magic, following particular social codes (both on an "infantry formation scale" and a "society as a whole" scale) allows various exotic technologies to work that wouldn't otherwise, including more powerful weapons and other tech that enables the empire to function at all.

I had some reservations too, which may contain spoilers, so will be moved into a follow-up post. Please make any comments which contain spoilers on that post too.
After running a couple of roleplaying sessions with quad & family, I would like to try to run something regularly in addition to whatever I run with them. I'm probably going to aim for once a month depending on interest.

I'm going to start by running a lightly revamped version of the DnD 5e one-shot I ran for quad before.


Passengers on a ship, driven far out to sea in a storm and beached for repairs on an abandoned island. 30 years ago it was home to a pirate lord, Erik Twicecursed and his BFF Grignir Hammerhead. While repairs succeed, the captain asks for volunteers to explore the abandoned and reputed-cursed pirate lair.

There may be treasure. There will almost certainly be combat encounters. Hilarious misunderstandings of the skill system and trigger happy party wizards are not guaranteed, but likely.

DnD 5e. For people new to roleplaying I will give you a pregenerated 1st level character sheet but suggest you invent a character who's more interesting to you, and change any specifics accordingly. If you're familiar with the system you're welcome to generate a 1st level character however you like.


This Saturday 2pm. It may run into the evening, in which case we'll probably have pizza.

If you're interested, comment here or email me by midnight Fri, and I will send you directions. (North cambridge, but may be lifts available if transport is an issue.)

You don't need to bring anything. If you're excited to do so anyway, things that could be useful: bring 5e books if you have them; read a little about 5e online; think about a character concept, not so much detailed background, as what they like doing and how they might be connected to other characters (member of ships company? bodyguard? relatives?)

Also let me know if you'd be interested in future one-shots or campaigns.


I have a campaign in mind following this session, but think it makes sense to schedule several one-shots and see which people are interested in coming back to.

People were very enthusiastic about my putative vorkosigan campaign, and I would really, really like to run that, but it will not be this weekend, it needs more prep time. But if you're interested and think you could actually make time to come, please let me know. (If it happens I plan a series of connected stand-alone sessions, so I might well be able to run one if I'm in london for the day, even if other sessions take place with people in Cambridge.)
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([personal profile] jack Apr. 25th, 2017 09:48 am)
I realise I've had *another* shift in habits.

Now I'm keeping a daily/weekly todo list more as standard, any emails I need to reply to on a specific timescale get duplicated into that system.

But that means I've shifted to starring emails that need a reply, and going through them occasionally, and the rest of my inbox has gone back to being "everything I've received recently0-ish that might be relevant". But mostly without the problem of "agh the important emails got lost".

Of course, gmail divides that into five folders: primary; social media notifications; corporate mailing list type stuff, and a couple of others. I could do something similar with filters. But it would be harder to cope if those were all muddled together. Non-starred mail in primary tends to be "conversations which are relevant in the next few days but don't need a reply right now". I tend to use social media notifications for marking comments I'd like to reply to, although that's fiddly. And the others rarely need any action (if they do, it's usually important and I move it into primary).
To expand on the point in the previous post, is it right that electrons bend round corners, like sound etc? Aka diffraction? This is how electron microscopes work, right?

That means that a probability wave is an actual thing, right, not a description of a particle? Does it?

But if so, how can anyone cling to the idea that they're a particle with a particular position. Particles don't do that. Do they?

And yet, there's massive amounts of effort to come up with interpretations of quantum mechanics that retain the "in a particular position" idea. Or the idea of hidden variable theory seems to be that the electron is in multiple places at once, but when you finally measure it, it was predetermined what value you were going to find[1]. If you've *already accepted* the multiple-places-at-once thing, AND the wave-physically-exists thing, what do you gain by assuming it then suddenly stops doing that at some unspecified point?

[1] "Predetermined" to avoid the "spooky action at a distance" problem, of, if you have a probability wave describing *two* particles (say, emitted in opposite directions with opposite spin), and measure them waaaaaaay far apart, how do they "know" what value to take to ensure they end up opposite, when there's no way for a signal to travel between them. Leaving aside the absurdity of a "hey, collapse this way" message even if it were slower than light.
Hypothesis 1: Electrons are tiny objects that have a specific position

Evidence: If you bounce something off an electron it hits the electron in one place. For all the talk of "in multiple places at once", you never shoot something at an electron, it bounces off the electron, and it bounces off the electron *somewhere else*.

Evidence: There's always a particular number of electrons. You never have two and a half electrons.

Hypothesis 2: Electrons are waves

Evidence: If you have an electron "orbiting" an atom, it's not at a particular place, it's smeared out over a whole sphere (or sphere-ish shape?) round the electron aka "an electron shell". Indeed, if you have two electrons in an electron shell, I don't know if you can even tell them apart, just that there's two. In metal, ALL the electrons are ALL OVER. They really don't have a particular position.

Evidence: If you fire one at a corner of an object, they diffract round it (is that right??)

Evidence: If you fire one through one or two narrow slits, you get interference bands, where "electron from here" and "electron from *here*" combine to give a dark band of "no electrons detected". This happens to waves. It does not happen to objects.

Hypothesis 3

This takes longer to explain. Imagine you have an object, but its position isn't certain, you're doing a calculation like, "if there's an x% chance it's here, and a y% chance it's there, and it bounces off this, then it might be anywhere along this line with a chance proportional to the distance..." etc. We do that all the time instinctively. But we mostly expect that the object actually *is* in one particular place, we just don't know what it is.

Suppose that instead of a mathematical convenience, what an electron *actually is* is a probability distribution like that, except for:

(a) When something interacts with it, it interacts with one point in the distribution chosen with the relative likelihood of that point, and from then on only that matters. Except if the other particle is of uncertain distribution too, then you get a probability distribution over both of them, until you actually check at least one of them.

(b) The probability distribution changes obeying equations which mostly describe a particle moving in a straight line (or a curve according to a force acting on it), except that it's all continuous, and if you have a sharp corner, the probability spreads out round it (as if the particle's path was bending).

(c) The probability not only has a magnitude, it has a direction (usually represented as a complex number, where the actual probability is the magnitude). If two probabilities have opposite signs, they cancel out. And it changes as it moves, analogous to wave oscillating, eg. light consisting of electric field waxing while a magnetic field wanes, etc.

The third point (c) is par for the course for waves: waves almost always involve something oscillating in both directions away from a rest point. But it's very spooky to see with things that look like particles: if there's a 5% chance of an electron hitting this particular point on a screen having gone through slit A, and a 5% chance of an electron hitting this particular point having gone through slit B, what's the chance of it hitting that point at all? Well, it might be 10% or it might be 0% or it might be somewhere between, depending

Evidence: Everything above in both previous hypotheses

Evidence: Everything behaves like a particle even if you didn't expect it (eg. light has photons)

Evidence: Everything behaves like a wave even if you didn't expect it (eg. you can fire small molecules through slits and see them do wave-like things like interference).

Evidence: The cancelling-out thing. You can construct this out of specific particles with clearly defined values (qubits) in building a quantum computer, and this is exactly how you find probabilities behaving. (Right?)

Correct me?

Is (b) really true? That's what it looks like from what I've read. But is that basically accurate?

If not, where have I gone wrong?

If so, it seems such an obvious "this is how we know these probability thingies actually exist" why isn't it front and centre in more explanations?

Is the description of probabilities right?


Hopefully I will think myself through some more examples. But this is the major point to get your head around first with quantum mechanics.

I think everyone would say the first two hypotheses are more natural. But they don't fit the evidence. The third hypothesis fits ALL the evidence, even though the hypothesis itself looks screwy.

And as far as I can tell, physicists still argue about which parts of this are actually there, and which are mathematical descriptions of something else, but agree that if you take Hypothesis 3 and just assume everything works like that, then you get all the right answers.
liv: alternating calligraphed and modern letters (letters)
([personal profile] liv Apr. 24th, 2017 01:20 pm)
So the wonderful amazing [personal profile] ghoti_mhic_uait gave me a proper alto recorder as an afikoman present. I am slightly awkward about it because an actual musical instrument is a bit bigger than the sorts of things my family generally expect as Passover presents – it's a gift-giving occasion, yes, but it's not anything like on the scale of Christmas. But I am also really really happy, it's the most absolutely perfect present.

babbling about me and music )

And I'm allowed to play the recorder. Just like I learned with piano all those years ago, I don't have to be a brilliant performing soloist, I can just play because I want to. And with work, with amazingly satisfying work, better than any video game, I can get to the point where my playing sounds at least pleasant. But I do in fact want to focus on more social sorts of playing, not learning a bunch of sonatas to a mediocre standard.

So does anyone have any recs of social sorts of music? Melodies of songs, perhaps, or even something aimed directly for people who want to play recorder to accompany singers? The readthrough people have a songbook, right, with dots in? Would it be possible to obtain a copy? I'm happy to pay for music but I'm spoilt for choice so I need some ideas first. And I am somewhat interested in online tutorials though I think I can mostly learn fine just by practising pieces, cos it turns out I know how do that. I like baroque music a lot, and there happens to be quite a lot available for recorder, but I am not wedded to only playing baroque, any style is fine, and I'm quite positively interested in recorder versions of pop music, if that exists. (And if it's set for descant, well, all that rusty music theory means that I do in fact know how to transpose.)
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([personal profile] jack Apr. 23rd, 2017 05:56 pm)
There's an experiment. "Quantum eraser". This is "me asking advice", I don't understand it to explain it.

It involves, producing two entangled photons, and doing the double-slit experiment on one of them with a different polarisation-changing filter over each slit. Repeat lots of times and see if you get an interference pattern, or actually not, because the polarisation-changing filters make the photon not destructively-interfere with itself (because the two states "at this point coming from slot A" and "at this point coming from slot B" are no longer exactly the same).

The mysterious bit is, if you put a linear polarisation filter in front of the *other* photon, this ruins the polarisation and the interference pattern goes away. Which looks like a specific physical effect of waveform collapse. People go to lots of effort to make sure that the same effect applies if you make the path between the other entangled photon and the "linear polarising filter or not" really long, so you make that choice *after* the other photon hits the screen, and yet, still seems to affect it.

This seems really mysterious. In fact, it sounds so mysterious it's actually impossible.

But what I was missing was, every diagram has a "coincidence counter" which only counts photons if one from each path both arrive (at the same time, if the paths are the same length, or at corresponding times otherwise). This seems like a standard precaution, to ensure you're only counting the actual photos, and not stray cosmic rays or whatever.

And yet, normal two-slit experiments don't (seem to?) need to use one.

And specifically, the linear polarising filter *throws away* half the photons, which means that at the screen you DON'T get an interference pattern. Whereas if you only look at the half of the photons which correspond to ones which passed the linear polarising filter, then you DO. (If you look at the OTHER half of the photons, you'll see an opposite interference pattern, which adds up to a smooth non-banded pattern of photons if you overlay the two halves).

What actually happens does (as always) correspond to "things only interfere if they're smeared out over multiple potential possible values (in this case two different paths through the slits), if you've already interacted with them, then not". And I don't quite follow what *does* happen because I've not tried to follow the equations. But the whole "mysterious effect travels back in time causing waveform collapse" seems to just not exist, except in how people choose to interpret the experiment.

So, I'm confused, many physicists seem to agree this is important, but I don't quite see how.

And "you get exactly the same experimental results but only look at half of them according to the result of the other entangled particle" seems a really important concept but all explanations seem to leave it out and say "you get a different result" instead. Do I understand that right??
jack: (Default)
([personal profile] jack Apr. 23rd, 2017 05:12 pm)
This is a bit earlier in the sequence than I'd intended but I wanted to rant about it.

What is so-called quantum teleportation?

Imagine you have a small particle. If this were a classical world, you could measure everything about it (it's speed, it's spin, etc), and then use a bunch of fiddly experiments to recreate one (or more) new copies of it that had all those same properties. Of course, it's *practically* impossible, to scan the state of millions of particles so this actually only happens to single particles (or we mass-manufacture consumer goods, but we don't try and make sure they all have corresponding atoms in the same place in each).

As we live in a quantum world, you can't "measure everything about it". Electrons don't exist at a particular point, they exist as a wave of possibility in a sphere round an atom, and only when another particle interacts with them, does it interact with them at one particular place on that sphere. Each photon isn't "in a particular place", even if you have a single photon you have a very very very faint beam of light and if you repeat the experiment, you find "places a photon hits" and "places the beam of light would cover" are the same thing. If you have a qubit made up of a single atom, you can measure its value as 0 or 1, or send it through a quantum logic gate, and find out about the parts of its state you can't measure directly *instead* but you can't do both.

Hence, in a quantum world, even in theory, it's weirder to construct a new particle the same as an existing particle, because you can't "measure everything, and then move the new particle so it has all those values".

So you *can't* make multiple copies.

What can you do

However, it turns out, there *is* a way of making an exact copy of a particle's property. You create two other objects (photons?) with opposite values for polarisation or something, even though you can't measure what that value is. (aka "an entangled pair", although all "entangled" means is "they have the opposite polarisation even if you don't know what it is"). You interact the original with that one and measure some values. Those values don't tell you what the property is (because if it WAS one particular thing, you'd have destroyed the information you were trying to copy). But you can apply them to a new particle via the second entangled particle. And you don't know what the state *is*, the original particle no longer has it, but the new one does.

That is, "You might imagine that you could copy a quantum electron the same way you could copy a classical particle by measuring the values and applying them to a new electron. But you can't, that's actually a meaningless concept. Knowing that, you might give up. But there's a way to do sort-of do that."

Specifically, "quantum teleportation" means "there's a special and fiddly way you can construct a new particle exactly the same as an old particle, but only EXACTLY ONE, and it destroys the original state". As in, you can do SOME of what you'd expect to be able to do to a classical particle, but not all of it.

What doesn't it mean?

What doesn't it mean? Firstly, it means "teleportation of quantum", not "teleportation by means of quantum". It doesn't give you some magic way of scanning macroscopic objects or reconstructing them elsewhere. It just means that, if you happened to already have one, you might be able to copy quantum states too.

Secondly, nothing anyone cares about day-to-day is encoded in quantum states. It might matter for quantum computers. Maybe for quantum cryptography. Certain scientific experiments. That sort of thing.

If you actually cared about quantum states, this might be exciting. Suppose brains encoded what they did in something like a quantum computer. Then startrek teleportation would only be normally impossible because you can't scan a human like that, not logically impossible. However, brains don't do anything of the sort[1].

If you care about startrek-teleporting a human, you probably want to end up with the same DNA molecule. But you probably don't need each atom to have the same quantum state. So it doesn't really matter.


A: Startrek is awesome, right?
B: Yeah.
A: But teleporting people is impossible right?
B: Pretty much. I suppose there might be some way discovered, but it doesn't seem very practical.
A: But, doesn't quantum say something about this?
B: Oh right. Yes, it says if you care about replicating all the quantum states in the transportee, you can only have one source (which is destroyed) and one copy.
A: That seems fair. That's how it works in startrek.
B: Well, it rules out "lets keep a backup of our most valuable engineers and seconds in command". Which did happen in startrek but only by accident.
A: Oh yeah, I guess.
A: So, *do* I care about replicating the quantum states in the transportee?
B: No, not really.
A: So quantum doesn't really change the answer?
B: No.
A: What about "quantum teleportation". Doesn't that let you... teleport people?
B: No. It just means, you CAN do the up-to-one perfect-quantum-states copy (assuming you have a way of teleporting people at all).
A: So why do people keep writing news articles about it?
B: Because it sounds startrek-y.
B: And to be fair, is relevant for how QM works.

Footnote 1

How do I know that? Well, I might be wrong. But firstly, maintaining atoms in a particular quantum state which can encoded a qubit used for quantum computing needs a whole bunch of vacuums and stuff. MAYBE brains could do that, but it seems unlikely. Sorry Penrose, I know you're a genius and I'm not, but I don't believe you.

Secondly, quantum computers have certain distinguishing features. They're about the same as classical computers for most problems. Notably, most every-day stuff. Also, NP-complete problems they're not significantly better. However, they ARE better than normal calculations for some specific things, like factoring numbers with thousands of digits, and other maths problems which share some features in common with that. If you look at a human brain, do you think, "boy, that's optimised for simple but powerful heuristics used for catching balls, recognising objects, and social interaction, but is mediocre at factorising incredibly large numbers"? Or the reverse?

Thirdly, there's no reason to think brains DO have quantum information used in any particular way. If they did... it wouldn't change anything significant. It wouldn't make the free will argument any different. It wouldn't give them a magical insight into parallel universes (as awesome as Anathem makes it sound). So why would you think that?
ghoti_mhic_uait: (Happiness isn't happiness without a viol)
([personal profile] ghoti_mhic_uait Apr. 22nd, 2017 11:57 am)
When I was a teenager, I got kind of into musicals. I'd been in performances of Joseph and Oliver and Salad days, seen Les Mis and Cats, and played various bits of various other musicals. I listened to the casette if I could get hold of it, and I played around with the scores to learn about others. Maybe even watched the film, if there was one.

I haven't so much in recent years, I haven't made time for theatre in any of its guises, beyond singing the children to sleep with a song from Porgy and Bess, but you can imagine my delight when I finally realised that it was not a new biography of Lewis Hamilton that my friends were raving about, but rather a musical about Alexander Hamilton.

It is, in my mind, the best kind of musical - the kind where you understand everything by reading the score or listening to the recording. I don't so much like the kind with lots of talking because back when I didn't have any money or a TV, that meant I missed everything. I'm not happy with how Hamilton's bisexuality is glossed over, but the rest!
I love how Benedict could walk through and pick out the hip hop references I missed. I love how it feels so much like the musicals of my youth, there's a clear family resemblance between all of the genre, despite the difference in actually musical texture.

So, when [personal profile] rmc28 said, there's an amdram performance of one of Miranda's other musicals nearby, I jumped at the chance to go. The musical was Bring It On, a story of cheerleaders and athletic competition and making it through the school years.

cut for minor spoilers )
ETA: and I think Cross The Line has jumped straight into my 'favourite song from a musical' slot.