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Apr. 25th, 2017 @ 10:28 am Invitation: Roleplaying taster session this saturday (29th) afternoon
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.

Pitch

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.

Invitation

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.

Future

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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Apr. 25th, 2017 @ 09:48 am Inbox non-zero
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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).

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Apr. 24th, 2017 @ 10:21 pm QM: Why it's mysterious that electrons go round corners
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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.

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Apr. 24th, 2017 @ 09:17 pm QM: Probability waves are kind of mysterious but not as mysterious as people make them sound
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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?

Conclusions

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.

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Apr. 23rd, 2017 @ 05:56 pm QM: Quantum eraser experiment
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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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Apr. 23rd, 2017 @ 05:12 pm Why Quantum teleportation isn't mysterious
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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.

Takeaways

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?

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Apr. 21st, 2017 @ 10:39 pm Roleplaying diversity quota
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...Collapse )

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Apr. 21st, 2017 @ 09:56 pm Roleplaying
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.

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Apr. 20th, 2017 @ 11:11 pm Random GM reminders to myself, mostly session planning
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.

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Apr. 20th, 2017 @ 07:21 pm QM: Why wave/particle duality is no more mysterious than cat/lion/horse duality
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Lions

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".

Electrons

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.

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