In the above article, Dex states “There’s no such thing as absolute precision” as he warns of the dangers of compounding errors.
The point of the article is valid, but isn’t this additional statement a bit too broad?
I agree that “All measurements in the real world … are estimates”, but what is the connection to precision?
By definition, light travels (in a vaccum) precisely 299 792 458 m in 1 second.
This is a definition, not a measurement per se, but its the only constant in physics with 0 error, and hence absolutely precise.
It’s the difference between a metaphysical and epistemic modality. Metaphysically, it is not possible that 2 + 2 = 5. But epistemically, 2 + 2 = 5 for all we know. If you don’t think so, let my wife put the sugar in your coffee sometime.
Welcome to the Boards ThinkQuick. As you say, that’s how a metre is defined. But if we adopted an official metre piece of metal made by our best endeavours and held it under ideal conditions it would not quite scale up to the distance travelled by light in a vacuum. We could only approximate the definition.
Well, that’s pretty accurate, but it’s not precise. My point: when you measure the speed of light in an experiment, are you sure that you can’t get 299,792,458.2 m in a 1 second?
I’m not denying accuracy in measurement, I’m denying precision in measurement. Except in pure theoretic mathematics, where an answer can be some abstract concept like pi. In real life, you cannot draw me a line exactly pi cm long, because there’s no way to measure to that degree of precision.
If you’re saying that a meter is nowadays defined related to the speed of light, there’s an easier example: you can say that there are precisely 100 cm in a meter. But that’s a matter of definition, not of measurement. You cannot measure off for me a precise meter, nor a precise centimeter.
My statement about precision was related to the prior sentence, that there is always an element of estimation in measurement. There can certainly be precision outside of measurements, like in definitions.
In any case, welcome to the Straight Dope Message Boards, ThinkQuick, we’re glad to have you with us!
I really appreciate your replying to me Dex, thanks.
However, I’m a bit confused about your repeated references to accuracy. I thought I was careful to avoid confusing the issue in my original post, but I guess not and now I’m confused.
As I’m sure you know (I think you know everything), accuracy and precision have different scientific definitions - accuracy is how close a measurement is to the true value, and precision is how reproducible a measurement is - or how near it is to being exactly replicable. A set of measurements can be precise but innacurate or vice versa.
Anyways my point is that you stated “Well, that’s pretty accurate, but it’s not precise” in reference to my stated definition for the speed of light in a vacuum. But the definition is exactly precise and is accurate by its own definition - so I guess you meant “well that’s pretty accurate, but you could never measure it precisely” <-- ?
