We have subsonic and supersonic for speeds below or above the speed of sound. What is the equivalent for the speed of light?
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5Superluminal or FTL for the positive, but nothing special for ordinary velocities, even relativistic ones. Sublight or sub-lightspeed are some of the terms that appear in science fiction stories, but they're guessing at future usages rather than reporting them. Since nothing moves faster than light that we know of, there's little non-SF usage.– John LawlerCommented Mar 15, 2014 at 18:12
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7Sci-fi writers sometimes use FTL for "Faster Than Light", but obviously so far as the boffins are concerned no such thing is possible anyway. And we don't really need "sub-light speed" since that's basically everything except light. But there are several thousand written usages to show that people do use it.– FumbleFingersCommented Mar 15, 2014 at 18:14
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@FumbleFingers I was just typing the same about the lack of necessity for sub-lightspeed.– David MCommented Mar 15, 2014 at 18:14
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1@David: Oh, my sainted aunt! Who would have to buy the Cokes in a three-way Jinx?– FumbleFingersCommented Mar 15, 2014 at 18:19
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1@David: Not at all - they're jinks, as in Philip Roth has a scene in Portnoy's Complaint wherein Alexander Portnoy and his girlfriend festively hire a prostitute for some three-way high jinks. As ever, context (and spelling) is all.– FumbleFingersCommented Mar 15, 2014 at 18:36
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4 Answers
I've seen superluminal and subluminal. Sometimes sub-lightspeed
answered Mar 15, 2014 at 18:11
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2I would point out that the linked Wikipedia article, "Superluminal motion", concerns a phenomenon where something merely appears to be moving faster than light despite not actually doing so. Nevertheless, physicists do use "superluminal" and "subluminal" to refer to true faster- and slower-than-light motion respectively, and most physicists would recognize these words as the closest equivalents to "supersonic" and "subsonic". (The phenomenon in the article probably shouldn't be called superluminal motion at all; it's just a misleading name we're stuck with due to tradition.)– David ZCommented Mar 15, 2014 at 21:31
Particularly if you are referring to particles, you could use tachyonic for faster-than-light and bradyonic for slower-than-light.
answered Mar 15, 2014 at 18:19
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"bradyonic" ..and that makes me think of the Brady Bunch. Commented Mar 16, 2014 at 3:01
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@Jim: Presumably tardyonic refers to the speed of a TARDIS? ;-) Commented Mar 16, 2014 at 16:39
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For speeds below the speed of light, you can consider the word sublight http://stargate.wikia.com/wiki/Sublight_engine
For speeds above the speed of light, you can consider F.T.L., meaning faster-than-light. See here
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6any discussion of speeds equal to or greater than c is by definition science fiction.– DougMCommented Mar 15, 2014 at 22:13
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1@DougM There are plenty of ideas involving FTL event propagation which are more than science fiction even if not established fact either. Tachyons, wormholes, and Alcubierre drive are all more than science fiction. Even if none of them turn out to be true, or at least practical for communication/travel, they are still reasonable hypothesis to be considered given our current understanding. The idea of FTL travel/communication is a useful one to have, even if it really is impossible.– smithkmCommented Mar 16, 2014 at 3:10
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2@DougM Equal to or greater? The speed c appears quite frequently in works of science fact. :) Some things (e.g., light in vacuum) even go at that speed. Commented Mar 16, 2014 at 4:12
Faster than light has to be Warp speed. Everything else is just normal, impulse power.
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Notwithstanding the existence of some real-world theoretical analogues, warp speed is a fictional technology. Nor is "everything else" impulse power, unless you are generously inviting real technologies like solar sails under that umbrella. NASA Sunjammer, launching later this year! Commented Mar 16, 2014 at 7:52
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1This might be a reasonable answer on Science Fiction & Fantasy.SE: on ELU it is unhelpful. Commented Mar 16, 2014 at 19:00