Forget Moore’s Law. Forget quantum computing. The real limits to computational growth may be the “foaminess” (noise) of spacetime itself at the level of 10^-35 meters, says Jack Ng of the University of North Carolina, as reported in Physics News 532, March 28, 2001.

“The foaminess of spacetime leads to an uncertainty in timekeeping (the more accurate the clock, the shorter its lifetime), which in turn leads to a bound on information processing (speed and memory simultaneously) analogous to the Heisenberg bound on simultaneous measurement of momentum and position.”

Of course, long before that limit kicks in, we would have to deal with little annoyances like seismic disturbances, thermal noise, and (maybe) gravity waves.

Seth Lloyd of MIT has calculated the conceivable limits of computing power of a black hole computer (Nature, 31 August 2000): a maximum processing speed of about 10⁵¹ operations/sec (equivalent to 10³³ IBM Blue Gene supercomputers) for a 1-kg black hole. But if Ng is right, future inhabitants of a Type III civilization may have to scale back their expectations a bit.