Talk:Speed

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Superluminal velocities

Stargate may be an optical illusion, so why not just say so rather than deleting its mention? Superluminal velocities can occur in agars; this is analogous to group velocity vs. phase velocity in optics. The effect is real enough, so the only thing required is a careful description.

I've added "in a vacuum" to the end of that sentence to hopefully make it precise enough. We could probably use a note saying something along the lines of "the speed of light does not apply if the object is travelling through an agar" and then list some fun examples. Nathaniel 19:42, 14 March 2010 (UTC)
No, effects can propagate faster than the vacuum speed limit (c/2) through agars, but cannot travel faster than c. This is easy enough to prove; each cell can only affect its direct neighbours in one generation, so no effect whatsoever can propagate faster than one cell per generation (c). 2c/3 signals, which are faster than any possible spaceships, are still slower than the speed of light. Regards, Calcyman 15:43, 15 March 2010 (UTC)
This is still not quite right; the problem has been with us ever since Maxwell wrote the equations for electromagnetic wave propagation and Lorentz, Poincaré and Einstein fiddled with light propagation. Maybe even earlier. As for fun examples, note that the vacuum can propagate at any (integral) velocity you choose. Silly, but true. As for Life, the phenomon was already discussed in Lifeline; now that we have copies the reference could probably be found.
True that Life (nor electromagnetism) doesn't have "action at a distance," but the quibble consists in whether a pattern can repeat at another location after a time lapse. Or in other words, propagation of "information" as contrasted with "waves." As for shift periodicity, automata exhibit this in abundance. Its being useful for some application seems to be dependent on its being localized, hence the desire to discount agars, and the remark concerning finite patterns.
Surely this phenomonon could be described adequately, even if it meant opening up a new page titled "Superluminal."

Maximum speed

Oblique spaceship currently contains a table with two columns related to speed: One labeled "Maximum speed", which apparently lists what is simply called "speed" here, and the other one called "Absolute maximum". That second label is particularly unsuitable: Firstly, because the basic meaning "speed" doesn't even occur in it, and secondly, because the distinguishing word "absolute" is not distinctive, but has many meanings, including that of absolute value, which is already part of the definition of the speed of a spaceship. Presumably, what was meant by "absolute" was that it's independent from any particular spaceship, and only depends on the direction. But for precisely that reason, I believe this information should not be presented there, but right here in this article. Micromegas (talk) 09:00, 12 March 2018 (UTC)