Aircraft speed maxed out a long time ago. "All the aircraft which went significantly over Mach 3 are now in museums." - Scott Crossfield, former X-15 test pilot.
Well any exponential growth curve in the real world is actually a logistic growth curve in disguise. A civilization would have to go from Kardashev II to Kardashev III in about the same time as it went from I to II to maintain exponential energy growth.
As an aside, the Falcon 9 flew 30 times last year and goes significantly over Mach 3.
As an aside, the Falcon 9 flew 30 times last year and goes significantly over Mach 3.