Speed of light fibre optic signals which travel 30–40% slower at the speed of light through glass. There are different ways to determine the value of "c". One way is to measure the actual speed at which light waves propagate, which can be done in various astronomical and earth-based setups. However, it is also possible to determine "c" from other physical laws where it appears, for example, by determining the values of the electromagnetic constants "ε" and "μ" and using their relation to "c". Historically, the most accurate results have been obtained by separately determining the frequency and wavelength of a light beam,
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",