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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??
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([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.
jack: (Default)
([personal profile] jack Apr. 21st, 2017 10:39 pm)
I wish I was not so amateur at this. I think it's worth me thinking and talking about it, but I'm sorry when that comes across as unhelpful.

Read more... )
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([personal profile] jack Apr. 21st, 2017 09:56 pm)
Again, my brain has got totally wrapped up in roleplaying. Except, I feel enough more confident GMing I may actually do something about it this time. I want to finish session with osos, and get some more one-shots in, and consider running something regular (maybe once a month). Ideally something where (a) there is an ongoing arc, so I don't need to do too much worldbuilding when I'm busy but (b) each session is self-contained, so it can be with "whoever's free", and not feel like it's only worth it if you come to all. Maybe mixed with some pure one-shots if I have cool ideas. "You travel in a boat or spaceship but not all of you leave at every port" would work well). I have *too many* ideas, but hopefully can decide on something practical to try out.
Especially for a one-shot or a new party, strive to have the first few minutes include (a) some kind of positive choice by the PCs to establish them as making choices, not just doing what you say and (b) include a FLASHING NEON OBVIOUS HOOK SAYING "HERO'S GO HERE" so the players have an immediate goal/challenge to work towards. I keep trying to make this much much more obvious and still falling short.

Remember pcs and npcs may have ranged attacks, make sure encounter is sensible if so.

If a PC has helped or angered an NPC organisation, note it down, it may not be anything, but it might be a useful hook later.

This is a big different-style-for-different people, but for me, when I'm thinking for 5e or 3.5e, plan a variety of encounters some of which will be bypassed or won in one lucky action, don't try and make each separate combat equally difficult. (Many people play the opposite, that each combat should be a separate winnable tactical challenge.)

Understand what players are likely to want, not in terms of free gifts, but in terms of what they want to achieve with their character.

Don't usually fudge things after they're already in play. If one lucky roll can wipe out the the monsters or the party, it can be too obvious if you adjust it on the fly. But do design flexible encounters that can be included or not, so if the first half is harder/easier than expected, you can rejig the overall difficulty to be about what you wanted by including or leaving out some of the encounters later.

In general plan lots of small things, and only include what fits well at the time. Make up locations, NPCs, backstory, history, cool NPC speeches, cool environmental effects... so they're there when you want to use them or when the players ask. But don't commit yourself to what you'll include on the spot, trust yourself what to pull in or leave out as it comes up, or what to replace with a better idea.

On a smaller scale, the same for objects, NPCs, locations, etc. Sketch a bunch of detail, and tell the players *some* of it, and more as needed. Just make sure you clearly separate some scene-setting with a nice clear understanding of "there's a big ogre here" :)

Likewise, don't plan a linear sequence of events, plan a physical layout or a political situation, plan at least one "obvious" path through, with an end the players will get to eventually, drop them in, and let things happen. They'll generally explore *most* of it, and whatever happens last can be the finale, if it's what you expected or not. It usually falls into place as a reasonable story for the session, and fits a lot better because the players feel like their choices were right, not like they were just guessing what you intended.

And feel free to plan some set pieces of a dramatic showdown in the ballroom. But if the players get horribly sidetracked and then blunder into the BBEG on the rooftop instead, don't try to force it, cannibalise the relevant parts to the new rooftop encounter, and save any other cool ideas for another time.

Imagine Aaliyah and Bruce lived somewhere no-one had ever seen a lion. One day Aaliyah travels somewhere there are lions and comes home and tries to describe it to Bruce. She probably says things like, "it's like a domestic cat, but the size of a horse".

Now, that's not a perfect description. But it's not bad. I think most people in Bruce's position will get the idea. There's some new sort of animal, one he hasn't seen before. Which is like a cat in many ways (pounces, plays, body shape, etc), and like a horse in some other ways (bigness, mane). And a few ways it isn't really like either (earth-shaking roar). He knows there's a lot about lions he doesn't understand. But he's not confused that there *is* some new creature he doesn't know a lot about, that sometimes looks like a horse and sometimes like a cat.

Specifically, he doesn't stand around saying, "Wow! Isn't it so strange and mind-bending that there is some mysterious animal that is both a cat and a horse AT THE SAME TIME? No-one on earth could ever understand lions".


Now, I'm not sure, because I don't really understand quantum mechanics. But as far as I've been able to tell, this is basically the case for electrons too.

I don't know what electrons are. But whatever it is, it's some physics thing which really, really doesn't behave how our intuition for macroscopic objects says objects should behave. And in particular, sometimes it acts really, really like a small solid object ("a particle"). For instance, it bounces off things, it exists at a particular place (sort of), etc. And sometimes it acts really, really like a wave. For instance, when it goes throw a narrow gap or round a corner, it diffracts and creates interference bands.

As far as I can tell, this is all "wave particle duality" means. The thing that's really there is... quite weird. But if you try to shoehorn it into "specifically as a physical object" category, you get all sorts of further confusion[1]. It's not sometimes one, and sometimes the other. Nor both at the same time. It's *like* a particle, sometimes a lot, sometimes a little. And *like* a wave, sometimes a lot, sometimes a little. And occasionally not a lot like either.

What actually *is* it? There's a lot I don't understand, but I was coming to that.

Footnote [1]

Part of the reason this is so confusing is that it doesn't act like a *single* object. Rather it acts like an object where you have some smooth probability function describing where it might be, but as if that distribution of probability was a physical thing that things could happen to. See following posts.
liv: cast iron sign showing etiolated couple drinking tea together (argument)
([personal profile] liv Apr. 20th, 2017 07:38 pm)
OK, this is UK party politics, please feel free to skip. In short, I am looking for Labour supporters to convince me to vote for your party.

what is the point of Labour? )

I will of course be researching all this stuff for myself, but I really want to be convinced, which is why I'm asking people who are pro Labour to guide me in where I should be looking. And to take the opportunity to counter the media bias against Corbyn. I do kind of like that he doesn't toady to Murdoch, but being willing to insult the Daily Mail isn't enough if he then goes and votes for terrible policies.
jack: (Default)
([personal profile] jack Apr. 20th, 2017 10:28 am)
Liv: I was thinking a ranger fit my character in most ways, but I'm a sailor not a tracker.
Liv: I'm not sure what skills to take.
Me: It's ok. Take survival, that deals with "wilderness-type-stuff" including a lot of appropriate things and some others like tracking. We'll switch out "wilderness-type" for "ship-related".
Me: It's not like there's going to be a lot of tracking.
Me: (sotto voice) Except in the first session. I didn't really think this through.
Liv: What?
Me: Nothing.
Me; (sotto voice) Maybe someone will spontaneously volunteer to play the ship's cat.
Liv: What?
Me: Nothing.

Cleric: We don't have a proper tracker, but it looks like the footprints go that way.
Fighter: My rating is about the same as yours, but that sounds right to me.
Cleric: OK, now... I'm not sure.
Fighter: Me neither.
Wizard: I don't have survival or a wisdom score worth mentioning, but I roll high.
Wizard: I'm not expect, but maybe we should look for footprints in the soft mud by the stream, about 2 yards that way?

Cleric: Whew, that was an eventful stream-crossing
Cleric: Maybe I should have cast "detect traps"
Cleric: Wait, or does that only count if someone put an unpleasant surprise there? If it just happened, it doesn't find it? Would it have worked?
Me: That's a very philosophical question.
Cleric: I mean, someone like an NPC. "God" doesn't count.
Cleric: Nor "GM".
Me: Oh. Then no.
ghoti_mhic_uait: (Default)
([personal profile] ghoti_mhic_uait Apr. 20th, 2017 08:19 am)
Yesterday at 11am, Judith asked if she could take Spanish classes. I muttered something affirmative, she said great, here's Jasper's mum, she organises them, talk to her, by the way it's tomorrow at 10am. So this afternoon, Judith was excited.
"Benedict, I'm going to take Spanish classes!"

Andreas heard, and said "I already speak Spanish!" before approaching B and greeting him "Bonjour, mon frère."
liv: Bookshelf labelled: Caution. Hungry bookworm (bookies)
([personal profile] liv Apr. 19th, 2017 02:39 pm)
Seemingly DW exploded while I was away over Passover. Hi, everybody who suddenly showed up after many years' hiatus. I'd be delighted if this burst of activity lasts, even if the reason for it is a very sad one. Anyway, I'm just about caught up on reading, and have quite a backlog of posting which I'll try to get to in the next couple of weeks.

As for reading, though:

Recently acquired: My family have basically turned Passover into a massive book exchange. So let's see if I can reproduce it. lists of book presents ) Recently read: All the fishes come home to roost by Rachel Manija Brown ([personal profile] rachelmanija). (C) 2005 by Rachel Manija Brown, Pub 2006 Hodder & Stoughton Sceptre, ISBN 0-340-89881-X.

This was a birthday present from [personal profile] rmc28, and I got to it on Good Friday this week, when I was taking a breather from all the Passover stuff, and had a bit of a cold and wasn't feeling up to go out and look for more exciting activities than spending the Bank Holiday sitting at home reading.

All the fishes come home to roost is a memoir of a really horrendous childhood that manages to be uplifting rather than miserable.

detailed review )
jack: (Default)
([personal profile] jack Apr. 18th, 2017 02:44 pm)
We had a seder for the immediate polycule. Ghoti was amazing at producing food (including little jelly israelites crossing a jelly sea parted to reveal a seabed of matza), and plagues (including the utahraptor (?) who was the firstborn of its family). And everyone including the children was amazing at asking questions.

We played a long-delayed sequel to our first roleplaying session. I feel a lot more confident I get most of the 5e rules now (for lower levels) and could GM for other people. Thank you ever so much to liv, ghoti, colin, B and J for playing!
jack: (Default)
([personal profile] jack Apr. 18th, 2017 11:42 am)
Previous session http://cartesiandaemon.livejournal.com/951049.html

I have fictionalised the write-up somewhat, because different things are fun to read than to play, and in case any of you come when I run this scenario again.


GM: ... and that's why levelling up in 5e is simpler than most previous editions.
GM: In theory.
GM: So, anyway, the captain,
GM: The ship's captain, not army Captain Amelficus, veteran of the elf wars, one semi-successful diplomatic mission, and the adventure of the lightly-crispy fried toad-seals.
GM: Summons you to a meeting of the captain, a few trusted passengers, the first mate, and the heretofore unmentioned second mate, played by Liv.
Second mate: I'm friends with the ships cat.
Second mate: I'm a lot like Bel Thorn, but I use "they" pronouns not "it" pronouns.
GM: She thanks you for help before.
GM: And lobs some simple hooks to draw you into the conversation
GM: And says, in a SHOCKING TWIST, the journals you found hint at the location of POWERFUL MAGICAL ARTIFACTS. On this VERY ISLAND.
Ship's Captain: And, um, I don't want to impose on you further, but since (a) you've already proven your trustworthiness (b) TREASURE (c) you're the PCs, how would you feel about, tracking it down and bringing it back?
GM: I warn you, there may be a a variety of level-appropriate encounters, probably just enough to bring you to level 3.
GM: And take the first mate, because she knows about it. And I don't trust her.
First mate: Blah blah blah I am untrustworthy blah.
GM: Or leave her behind, because I don't trust her. I haven't decided.
GM: First mate: I will leave the room now. Absolutely definitely.
GM: First mate: And not ambiguously leave the room in a fashion which leaves most players uncertain about who is actually present for the next scene.
Ship's Captain: And if you wouldn't mind, maybe just once sleep in the store room where the journals, treasure, etc are stored, just in case first mate tries to abscond with them.
GM: In the actual session, I did quite well remembering which NPC was which, but I'm using titled in this write up for your convenience.
GM: And if you could all just debate this question amongst yourselves for a bit to get invested in the adventure, that would be good too.
Party: OK, sounds good. We bed down.
GM: Whew. OK, thank goodness. When I told you to prepare your character sheets assuming you'd recovered max health, I really hoped we wouldn't get any combats with your hitpoints still where they were um last year.

Read more... )
jack: (Default)
([personal profile] jack Apr. 13th, 2017 03:38 pm)
Whatever time you start, apologise for being late, but contrast the situation to other people's tradition which would have been even later.

Argue whether you should avoid eating things like rice which are absolutely definitely not leavened bread, but there is a tradition of avoiding them. Agree that everyone coming to the seder agree that you shouldn't avoid them, but decide to avoid them anyway just in case.

Don't eat anything until you're explicitly told to eat it. Don't finish any cup of wine until the last one.

Announce how Rabbi Hillel invented the sandwich.

"Seder" originally comes from Hebrew meaning "Judiciously skip ahead without telling anyone the page number because everyone has different books"

Try have everyone recite things in unison using different translations.

Explain the story of the first passover and the exodus from egypt, but repeating that every year would get a bit repetitive after several thousand years, so spend most of the time telling stories about other people telling the story.

Argue whether parting the red sea and letting the israelites get halfway across and then stopping and letting the water roll back over them could reasonably be construed as "sufficient" or not.

Tell everyone you don't usually exchange presents before exchanging presents.

Sing the jewish version of Partridge in a Pear Tree, starting "One is our God, in heaven and on earth."

Just when you've got used to switching between english and hebrew, to shake things up, there's suddenly an aramaic forerunner of House That Jack Built, that ends with God destroying

Sing the jewish version of the House that Jack Build about a little goat, that ends with God destroying the angel of death.

The year you first came was the first time people did the animal noises while singing, but because it's been every year you've been there, you're firmly convinced that's a tradition about eighteen hundred years old.

Comment that that's a recent addition to the passover liturgy (recent in this context meaning "a continuous tradition of barely more than 400 years").

Stay up too late discussing different interpretations.
pseudomonas: (Default)
([personal profile] pseudomonas Apr. 11th, 2017 01:59 pm)
More in due course about life &c., but an admin note: I'm no longer crossposting to Livejournal, for the same reasons as everyone else.