doop

I don't think it really helps - you're already working in something like a probabilistic formulation. If you want to use a quantum mechanical justification for it then you need to look at some sort of non-unitary evolution.

Besides that, I don't think anybody is really arguing that the correlations are actually lost after a collision, just that it's usually a good approximation to treat them as if they are.

It's lost at Boltzmann's "molecular chaos" or "Stosszahlansatz" step. If f(x1,x2) is the two-particle distribution function giving you (hand-wavingly) the probability that you have particles with position and velocity coordinates x1 and others with coordinates x2, then Boltzmann made the simplification that f(x1,x2) = f(x1) * f(x2), ie throwing away all the correlations between particles. This is where the time-asymmetry comes in: you're saying that after two particles collide, they retain no correlation or memory of what they were doing beforehand.

Laser C or Lattice C maybe?

Why does this otherwise excellent series always depict electrons as red and protons as blue when everybody knows it’s the other way round?

The Falcon was a nice machine (I still have one!) although it suffered from the characteristic Atari penny-pinching: still no MIDI thru port (on a machine which was otherwise amazing audio-wise - same DSP as the NeXT!) and while the new video modes were great, they used comparatively more RAM and were somewhat held back by the fact it still had a 16-bit data bus.

The OS didn't take anything like full advantage of the hardware, but any serious users at the time would have piled on extensions/addons/replacements like MagiC.

This page was written by Anu Dudhia, who for many years was celebrated by the giant graffiti saying "ANU IS GOD" on the side of Donnington Bridge in Oxford.

Find a style of music you enjoy listening to, then go to a club that plays it, and start dancing. Keep doing that.

You might find that your taste shifts a bit over time, and that's fine, and it's fine to shop around a bit: the point is to try to find an environment where you can lose yourself in the music. If you're very self-conscious about your dancing then try to find a more underground scene (I started off in industrial/EBM and moved on to psytrance): partly because people are just more serious about the music and less about trying to hook up, partly because even if you're the world's worst dancer it won't matter because people will just assume you're having a great time because you've taken lots of drugs. Be considerate, give people space, and stay hydrated.

Once you've found your groove - once you've found yourself whooping as the beat drops, once you've found that weird moment where the dancefloor moves in unison and dissolved yourself into it, once you've exchanged exhausted happy grins with the person next to you as the lights go up at 7am - then, if you want to, you can start focussing on technique, on learning new tricks and moves, but it doesn't really matter by then. It's not a competitive sport; the point is not to be good at it, the point is to do it.

Drugs are neither necessary nor sufficient.

Great article! Also:

> I’ve never heard of a family being divided because its members dance different styles

Anyone who believes this needs to go watch Strictly Ballroom (1992) with all possible urgency.

I was also somewhat sceptical about dancing until in my early 20s I made the discovery that nightclubs were not necessarily just places where people went to get shitfaced, but that there were places run by and for enthusiasts of the music - that going out and dancing for eight hours straight was not just something you could do but that was incredibly enjoyable as well.

A huge amount of what has been good in my life since then has, one way or another, come from going out and dancing. Amongst (many) other things, I'm confident that I'm a better programmer for it: the usual arguments (blah blah, lowers stress, default mode network) deployed in favour of meditation also apply to dancing. It won't work if you're forced into it, and I don't think it's cool to do so, but that's why people can be so evangelistic about it.

My favourite example of this is.. Robocop!

https://dejareviewer.com/2014/04/29/cinematic-chiasmus-roboc...

Is this the Wayne Holder of Dungeon Master fame?

I remember the Snow Crash MOO! I spent a while there around 1996-1997: it was (despite the name) sort of William Gibson themed - I vaguely remember it being distributed across multiple hosts, and being impressed at the time that it was running on an SGI box. I think the language was standard MOO.

Err, no it doesn't - the viscosity in LB is a function purely of the relaxation time (for LBGK anyway). Nor do you need to do any simulation repeats to average out the noise. The main weakness of LB is that it's not as numerically stable as a lattice gas method.

Off the top of my head (it's quite a while..), lattice gas models wind up giving you a velocity-dependent viscosity, i.e. the viscosity of the fluid is a function of how fast it is travelling relative to the lattice. This is unphysical to say the least: while I think you can apply some sort of rescaling to alleviate it, it doesn't make it any easier to get to high Reynolds number flows: that and the huge amount of averaging make lattice gas rather impractical compared to later methods.

> Also, which continuum are you referring to here? Number of particles? Lattice spacing?

By continuum I mean you write down the continuum Boltzmann equation, i.e. a partial differential equation for the evolution of the single particle distribution function. You can then discretize this onto a lattice to recover the lattice Boltzmann method.

They might not be strictly Navier-Stokes but the way in which real fluids deviate from N-S is completely unlike the way in which lattice gas fluids deviate from N-S. Absolutely, you can discretize time and space and get a useful fluid model, and (as Wolfram showed in a very good paper in 1986) you don't even have to worry too much about isotropy, as long as your lattice obeys certain constraints. You do need Galilean invariance, though.

Look, I do get your point about lattice gas fluids being interesting conceptually, and I do think they make an interesting point about how little you can get away with and still yield a useful fluid model at the macro scale, but I don't think they're a good example of a trend towards NKS-style methods. If anything the trend in that field since the late 90s has been away from NKS and towards seeing the lattice Boltzmann method as a solver for continuum treatments at the Boltzmann (rather than N-S) level.

You can see it as continuum-ing up from a CA, or you can see it as a discretization of the continuum Boltzmann equation.

What do you mean you don't need Galilean invariance? In the real world, fluid motion is Galilean invariant (unless you're talking relativistic motion, which is a whole other class of thing that lattice gases have trouble with). You might be simulating something but it sure ain't a Navier-Stokes fluid.

I was under the impression that lattice gas methods in CFD were more or less obsolete. They're nice in that they're unconditionally stable and only use bitwise operations, but the amount of CPU time you save from this is massively outweighed by the number of simulation runs you need to do to average out the noise. They're also not Galilean invariant (at least not without messing around with rescaling factors). Lattice Boltzmann is much more practical.