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added- would an observer in the dark measure the speed of light to be zero?
Haven't heard of the 30cm method.This is one of the things Wiki is good at, explaining basics so have a look there.Also look at http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.htmlQuote from: Thebox on 01/03/2016 11:19:13added- would an observer in the dark measure the speed of light to be zero?Of course not.Either you are being silly and suggesting a situation where there is no light (that would be like asking what is the speed of a car if there is no car), or you are thinking of someone in a dark room with a beam of light to measure. Obviously you need light to be able to measure it.
I was being a bit silly, but just considering the strict definition of ALL observers in an inertial reference frame. Not quite all observers.
Quote from: Thebox on 01/03/2016 12:57:30I was being a bit silly, but just considering the strict definition of ALL observers in an inertial reference frame. Not quite all observers.Yes, all observers. Think what observer means.If a car didn't pass you, you can't measure its speed because you didn't observe one!
Haven't heard of the 30cm method.This is one of the things Wiki is good at, explaining basics so have a look there.Also look at http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.html
One method is by chopping the light with a toothed wheel, look up Armand Fizeau. Other methods have used rotating mirrors to cause breaks in the light, try Foucault or Michelson (of Morley fame).There will be a lot of articles on line that can describe how it was done in far greater detail than we can here.Come back with (sensible) questions if you have any.
Is the speed of light infinite
Quote from: Thebox on 01/03/2016 21:40:16Is the speed of light infinite No. It's quite easy to measure and is about 300,000,000 m/s in vacuo.
In this vacuum, do you measure the tip of the light ''stream'' or a flash of light?
In this vacuum...
Large vacuum tubes are expensive, so the first experiments were conducted in air.This gave a cheap (but pretty accurate) measure of the speed of light. The refractive index of air is 1.000277, so the measurement will be low by 0.0277%.If you are planning to repeat this experiment at home, I suggest that you measure it in air, and then subtract 0.0277%.
I think the rational way would be the Galileo method and a flash/flashes of light
if we had a vacuum of exactly 299 792 458 m in length between emitter and sensor