I notice they restrict themselves to the surface of the earth. Out of curiosity, is it feasible to use modulated neutrino beams to communicate straight through the center of the earth? You could theoretically shave up to 24.3 ms in latency this way.
Not really, it's only about 40 meters in diameter. With trillions of dollars at stake, I imagine they'd find a way to bury one under lower Manhattan.
I've found some figures here -- this is an experiment which creates a focused neutrino beam with an accelerator, and sends it through 810 kilometers of earth to a distant target:
If I'm reading Table IV correctly (page 26, and I doubt it), their expected signal rates are up to 10^3 counts per [(megawatt beam power) * (10^7 seconds time) * (kiloton detector mass), for μ-neutrinos. Some reasonable parameters (skimming in the article) are on the order of 1 MW beam power and 10^2 kilotons detector mass, for a theoretical maximum of 10^-2 counts per second. (But I'm not sure if the accelerator can run continuously, or just in pulses). For a 10,000 km beam the signal rate would up to 100 times lower, because of quadratic beam divergence (though attenuation is negligible). So that's 10^-4 counts per second. To send 10 bits (as on/off pulses) in 10 ms, you'd need a lower bound of 10^3 counts/second. That's 10^7 times more than this experiment. So basically feasible, if you have the resources of a hedge fund: scale the total beam power to ~3 gigawatts (by linear extrapolation ~$300B, but probably much less), and the detector mass to ~300 megatons (of liquid argon?) (also ~$300B by extrapolation. This about 6,000 times Super-K, or a cryogenic sphere ~3 km wide. Or an array of smaller spheres).
Besides, I'm certain my numbers are large overestimates. I extrapolated numbers from a completely different scale; surely optimizing for this problem would yield very different designs. Like more focused neutrino beams. They have a large fraction of their neutrino beam going out >6 km off-axis (at 810 km distance); at 8,100 km, this would be >60 km off axis. So there's maybe 6-7 orders of magnitude potential in designing a lower-divergence beam.
