This quantity is raised to the negative fourth power in the definition of Einstein’s gravitational constant. The slope of a 45 degree line on a Minkowski diagram equals (10[1])this quantity because Minkowski time is scaled (10[1])by this quantity. The ratio of velocity to this quantity is denoted (-5[1])by beta. By comparing interference patterns, this quantity was found not to depend on the direction of measurement in the Michelson-Morley experiment. (10[1])The mass-energy equivalence states (read slowly) rest energy equals mass times (10[1])this (-5[1])quantity squared. For 10 points, name this universal speed limit equal to about three times ten to the eight meters per (10[2])second. ■END■