Calculate the speed of light.

[mar_zim]

If an object traveling 75% of the speed of light and head on to a light travel towards to the object (and we all know that speed of light is constant(300 km/s)). What is the calculation that make the speed of light(300 km/s) constant? I mean how to derive in mathematical way that made the speed of light constant?

[BlindSniper]

I don't think there is a mathematical way of deriving the speed of light.(You could rearrange e=mc^2 but i'm not sure where you would get your values from then)
I think scientists simply used equipment to mesure how long it takes for white light travel distance x and did a simple calculation to figure out it's value.

[Niya]

Actually you guys have it backwards. Speed is a measurement based on distance and time and the metric of distance itself is derived from this. Distance when expressed in a denomination of metres is actually in terms of the speed of light itself. Make sense ?

To clarify, you don't measure how fast light travels and then say its x metres per second. You measure it and say a metre is how far light travels in a second(Actually its how far it travels in approximately 1/3 of a second in a vacuum).

EDIT

In a perfectly logical world, if by some magic the speed of light were to double then logically a metre would now be equal to twice what it was before of course we wouldn't accept this because it would probably break a lot of things. More realistically, we would probably redefine it in terms of something else.

EDIT

Thing you need to realize about measurements is that it doesn't correspond with anything absolute. It is simply used to express how a property of one thing relates to the same property of another.

I could make up a unit of measurement and say today that the speed of light is 100 Niyans. Would I be wrong ? Not really. If I were to measure the speed of a comet or something and discovered that it is traveling at 10 % the speed of light, measured in my fictional "Niyans" it would be traveling at 10 Niyans. If I were decided to declare the speed of light to be 1500 Niyans then our comet would be traveling at a speed of 150 Niyans. Did the comet start traveling faster ? No, I just changed the units used to measure the relationship between the speed of the comet and the speed of light. The speed of light serves as a sort of reference point and since nothing is known to go faster, it makes the perfect reference from which we can derive units of measure.

I hope that makes sense.

[Hack]

I don't think there is a mathematical way of deriving the speed of light

There is something faster than the speed of light and that is the speed at which my wife finds out I've received a bonus at work.

[InvisibleDuncan]

You measure it and say a metre is how far light travels in a second(Actually its how far it travels in approximately 1/3 of a second in a vacuum).

So light travels at 3 metres per second? Marvellous - I could outrun it!

[namrekka]

I could outrun it!

Wonder who is faster, Hack's wife or you.

[Niya]

Oh s**t. Was kinda sleepy when I wrote that. I was stupidly thinking in terms of decimal fractions. Its actually 1/299,792,458 of a second which I rounded to 1/3 something I admit is super retarded. Can't believe I made such a huge mistake.