drthmik said:
talideon said:
drthmik said:
so what?
You carve up the distance light travels into a certain number of chunks
We cave it up into a different number of chunks
that is the definition of arbitrary
Eh... it's less arbitrary than that. In fact, the definition of the metre has always been an attempt to find a non-arbitrary measurement based off of natural constants.
The
real original proposal for the metre came from John Wilkins in the mid-1600s, and was defined as the length of a pendulum with a half-period of one second. The only truly arbitrary thing (at the time) there is the length of a second. However, it was found that due to gravity varying slightly over the surface of the Earth, that wasn't ultimately workable, so
after the French Revolution, it was defined as 1/10,000,000th the distance from the North Pole to the Equator along the meridian line passing through Paris. This was pretty damned close to Wilkins' original proposal and had the benefit of being more absolute. However, we later found that measurement to be less stable and more mathematically complex than would be convenient, so other standards were used, until we settled on using the speed of light, which is, best as we can tell, a fundamental constant.
And thus it turns out that the only thing that makes a metre arbitrary is the length of a second, and I'm OK with that.
ar·bi·trar·y
ˈärbiˌtrerē/
adjective
adjective: arbitrary
1.
based on random choice or personal whim, rather than any reason or system.
Why the length of a pendulum swing?
Answer: Some guy in the 1600s thought it would be a good length
It wasn't arbitrary. There was a reason behind it: the idea behind using the pendulum was
reproducibility. Nobody chose a metre as a good length, it was simply a measurement that could be easily and repeatedly derived from physical phenomena using a simple apparatus.
drthmik said:
Why 1/10,000,000th the distance from the North Pole to the Equator along the meridian line passing through Paris?
why not London or New York?
Why not the circumference of the earth at the 22nd parallel? Or at the equator?
Why not 1/100,000,000th or 1/50,000,000?
Answer: Some guy though it would be a good length
[/quote]
Several reasons, but the main one being that it was as close as they could get to the original metre. The idea was to preserve the measurement using a more accurate mechanism.
drthmik said:
Why the length of the path travelled by light in vacuum during a time interval of 1 / 299,792,458 of a second?
Why not 1/300,000,000 of a second?
or even 1/299,792,450 of a second?
WHY!?!
Because then you'd be changing the physical length of a metre from existing standard measurement.
drthmik said:
I'll tell you why
Some
guy
thought
it
would
be
a
good
length
Could you please be a little less obnoxious?
drthmik said:
And a lot of other people agreed
And for a good reason: the idea was to find a universal measurement that wouldn't change over time. All these seemingly odd mechanism were chosen for that specific reason, and each one was a refinement on the previous one as far as universality went. The lack of a consistent, reproducible basis for measurement was a
huge issue: the introduction and subsequent refinement of a universal unit of measurement was a huge boon. There's a good reason why the US customary measurement system is defined in terms of SI units.
Nobody
chose the metre to be the length it is: it simply fell out of the mechanism originally used to derive a universal measurement.
drthmik said:
some guy thought a foot would be a good length
Except nobody actually
agreed on what a foot was. Equivalent customary units varied quite a bit across Europe and even within countries. A foot
seems like a good basis for measurement, but how do you consistently derive the length of a foot? The thing is that nobody had a consistent way to derive the length of a foot. But the metre started with the derivation mechanism first, which was
critical to solving the problem of finding a universal measurement.
drthmik said:
Standardized Measurements are not universal truths no matter how you come up with them
they are practical language and culture
they exist to service understanding
and changing them all for no better reason than a bunch of guys in lab coats(who use the other system ANYWAY) find it EASIER is not a reason to confuse the language of a people for decades
I think what you're missing is that until the metre was derived, there was
no universal and standardised measurement mechanism. The whole
point of the SI units was to develop standardised measurements.