Speed Of Light

More flippantly, perhaps less usefully, it's: So there you are.


"What do you mean? A European speed of light or a Bose-Einstein condensate speed of light?" (with apologies to Monty Python)

:-) But since you bring it up: there's only one speed of light. When people talk about the speed of light varying in different media, that's a shorthand/euphemism for rather complex phenomenon, and a reasonably descriptive euphemism -- but not literally true.


Why does this page exist? Can we have c in units people are likely to understand please?

What units would you like? If you're a programmer, or a scientist, how is it that you are not capable of converting units for yourself?


as a physicist I'd usually use 3*10^8 m/s (or 1 and convert other quantities e.g. energy in eV )


Well the problem is that most of the world does metric and a small portion of the world does more archaic units. Therefore it wouldn't be fair to enumerate the speed in units "we" would understand because some people will not understand it. I therefore submit that the speed of light is 1799884800000 furlongs per fortnight.

Oh fine. 299337984 meters per second

-- BruceIde

Do people really find 300,000,000 metres/sec easier to grasp than 1 foot/nanosecond? Just how far is 3*10^8 metres? Can you truly grasp that? Yes, but only because we want to calculate another quantity in SI units. approx 9*10^8 feet. Just how quick is a nanosecond, can you truly grasp that? The speed of light doesn't really make sense in a human way, SI units are a nice consistent way of dealing with dimensions when plugging constants like this into equations, which is the only time numbers like the speed of light are useful, it just isn't a number that is useful on a human scale. -- JamesKeogh

Sampling at 50 MHz, the speed of light corresponds to a 3 metres intersample distance for radar. And no, there isn't a factor of two error here, that's left as an exercise for TheInterestedReader.

If you're dealing with the speed of light on a regular basis, you probably want to use PlanckUnits?, where c = 1. This is the appeal of 1 foot/nanosecond; it's only a power of 10 from the appropriate Planck unit, so you don't need to carry around numeric constants. SI is just as arbitrary as any other unit system when you're using ScientificNotation?; PlanckUnits? are sometimes described as "God's own units" because they let you drop the constants from most of the laws of physics. -- JonathanTang Yes - all unit systems are arbitrary, hence 1 foot/nanosecond is not universally easier to understand than 3*10^8 m/s. I don't consider having a numeric constant that is close to a power of ten an advantage over one which is close to 3 times a power of ten, but then I've been brought up with the metric system alongside imperial units. I would use PlanckUnits? normally but that is because I normally don't mind getting an energy in MeV, it's all about the units you want to end up in (which is an arbitrary choice until a 3rd party supplies one of the numbers in particular units, if you don't use their units you will need a numerical constant to convert units anyway). -- JamesKeogh
JulyZeroFive

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