Is the speed of light in a vacuum an assumption, not a certainty ?

@Convivial yes the measured speed of light

@Messi I'm saying it's not hypothetical, it is a measured quantity

@Convivial Unfortunately , the measurement are not exact because of a few discrepancies. One of these is the Isometric (one way) measurement has never been achieved or attempted yet. It has been measured on Earth under a round trip measurement so far which is very accurate but not precise

@Messi there's always an uncertainty in every measurement... That's why the error of uncertainty exists... Like π, we'll get closer and closer, but never knew exactly, i don't think... But for different usage, 186,000 mps will do me!

Fun fact..i read with the Apollo missions they only ever used pi to 3 decimal places as it was good enough

@Convivial you now have the knowledge to answer my question..lol

@Messi definitely not an assumption ;)
And as the question stands it's a certainty as you place no value upon it except it's own

@Convivial So you still have no idea ? that's ok

@Messi not quite true...i knife the speed of light is the speed of light. It's measurable speed varies with its environment, but it's always the speed of light

@Convivial So is it the speed as we measured it ?

@Messi as previously discussed, that's a good approximation only... It goes at the speed off light..

@Convivial Great, you arrived at the right answer, well done. A good approximation can be a kin to an assumption.

@Messi no... An assumption is something you assume without any foreknowledge...

@Convivial it is also "the act of taking possession or asserting a claim". To assume anything is to state something as exact without knowing if it is exact or not