Speed of light special theory of relativity, in which the speed of light in vacuum "c" featured as a fundamental constant, also appearing in contexts unrelated to light. This made the concept of the stationary aether (to which Lorentz and Poincaré still adhered) useless and revolutionized the concepts of space and time. In the second half of the 20th century much progress was made in increasing the accuracy of measurements of the speed of light, first by cavity resonance techniques and later by laser interferometer techniques. These were aided by new, more precise, definitions of the metre and second. In 1950, Louis Essen
Speed of light (cellular automaton) is because it's impossible to build a spaceship that can move every generation. (This is not true, though, for cellular automata in general; for instance many light-speed spaceships exist in Seeds.) It is, however, possible for objects to travel at the speed of light if they move through a medium other than empty space. Such media include trails of hives, and alternating stripes of live and dead cells. Certain patterns can appear to move at a speed greater than one cell per generation, but like faster than light phenomena in physics this is illusory. An example is the "Star Gate",