Keith Henson, of whom I’ve long been a fan, has a new article where he imagines our descendants as fragmenting Roman-Empire-like into distinct cultures, each ~300 meter spheres holding ~30 million ems each ~1 million times faster than a human, using ~1TW of power, in the ocean for cooling. The 300m radius comes from a max two subjective seconds of communication delay, and the 30 million number comes from assuming a shell of ~10cm cubes, each an em. (Quotes below)

The 10cm size could be way off, but the rest is reasonable, at least given Henson’s key assumptions that 1) competition to seem sexy would push ems to run as fast as feasible, and 2) the scale of em “population centers” and culture is set by the distance at which talk suffers a two subjective seconds delay.

Alas those are pretty unreasonable assumptions. Ems don’t reproduce via sex, and would be selected for not devoting lots of energy to sex. Yes, sex is buried deep in us, so ems would still devote some energy to it. But not so much as to make sex the overwhelming factor that sets em speeds. Not given em econ competitive pressures and the huge selection factors possible. I’m sure it is sexy today to spend money like a billionaire, but most people don’t because they can’t afford to. Since running a million times faster should cost a million times more, ems might not be able to afford that either.

Also, the scale at which we can talk without delay has just not been that important historically in setting our city and culture scales. We had integrated cultures even when talking suffered weeks of delay, we now have many cultures even though we can all talk without much delay, and city scales have been set more by how far we can commute in an hour than by communication delays. So while ems might well have a unit of organization corresponding to their easy-talk scale, important interactions should also exist at larger scales.

Those promised quotes from Henson’s article:

I have long had misgivings about large aggregations of computing nodes forming a mind because of speed-of-light delays. That will reduce “thinking speed,” since a mind cannot “be of one mind” if much it is not aware of the current situation due to speed-of-light delays. There is an analogous problem within a culture. We have a world culture today headed toward a monoculture because electronic communications on fiber optics has cut the delay to getting. …

How much communication delay can a society tolerate before it breaks up into smaller units? There are historical examples; the Roman Empire broke up partly because their communications failed. …

Human brains are asynchronous, but, given reaction times, we can impute an equivalent clock rate of ~200 Hz. Which means a human brain (or brain equivalent) running in moderately fast hardware could run a million times faster. (200 MHz is not fast hardware.) You might ask, “Why would humans do such a silly thing?” Because intelligence is a large factor in sexual attraction. … Of course, intelligence is valuable outside of sexual attraction, being correlated with many other personality and life-history traits … One aspect of being smart is thinking fast, or at least thinking faster than the person you are trying to impress. That leads at once to a runaway “Red Queen” situation where, when we can run our thinking faster, we would rapidly push the computational speed to the limit, whatever it is.

… The faster you run your brain, the more the world around you seems to slow down. With only a modest speedup, movement would seem like wading through molasses. If you desire serious speedup, it probably has to be in a simulation of the environment to match your faster perception. … A million-to-one speed up would impose a subjective round-trip delay of three days from one side of the earth to the other. … The speed-up limit may be 100 times as high. … I suspect population centers will shrink to sizes in the few hundred-meter range and sunk in the deep oceans for cooling.

Taking two subjective seconds as the upper limit round-trip delay for telephone-like communication, … for a million-to-one speedup, that means that all the communicating nodes can be no more than 300 meters apart. … [Assuming] a 10-cm cube, or 100 minds to the square meter arranged one layer deep, … the population of fast uploaded humans per communicating fast culture could be as high as 28 million. If each drew 20 kW (1,000 times the 20 W our biological brains use), the total power draw would be 540 GW. …  A water flow of one liter per second through each person (10 square cm) would carry off 20 kW with a temperature rise of about 5° C. …

With each order of magnitude speed up, the maximum community size falls by a factor of 100. … Talk about a physics-enforced oligarchy! Would you want to move from a slum where there was only a 100,000-to-one speed up to one of these “elite” places with a million-to-one speed up? …  If humanity takes the speed-up route, then I don’t see a future for M brains, S brains or even Luna-sized brains, and the maximum size of a communicating civilization becomes a good deal smaller than the Earth.