Wikipedia:
To further reduce uncertainty, the seventeenth CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of the second and the speed of light:

The metre is the length of the path travelled by light in vacuum during a time interval of 1  ⁄   299,792,458 of a second.[1]

The whole idea of the meter is to establish a measurement based on some physical constant, rather than the arbitrary definitions of english standards like the inch or foot.

http://en.wikipedia.org/wiki/Meter

Check out this wikipedia article for some history.

My problem with the metric system is probably not the same problem that your grandpa has with the metric system.

The definition of the meter still seems arbitrary and awkward. I agree that it should be based on some physical constant, and the speed of light seems like a great contender. But the current definition of a meter is the distance traveled by light in 1  ⁄   299,792,458 of a second in a vacume. That number, 299 million is based off a previous measurement of the wavelength of krypton, which is also a physical measurement of something which will not change, but the selection of krypton as the measure is itself ultimately arbitrary.

I propose that the standard measure of distance should be the light second. That is equal to 1Ls. A meter would then be =1Ls/100 million. So, 1 meter in this system is essentially 3 meters compared to the current system. That makes 1 centimeter = to approximately 3 current centimeters.

That is a good distance to work with and it is nicely framed in terms of "C", or the speed of light, and rooted in a cosmic constant.

So the new definition of a meter would be the distance light travels in 1/100,000,000 of a second. Much cleaner, much easier to teach, much easier to use in calculations, a nice round number that works well with our decimal system.

Any other nerds with an opinion on this? I can't get anybody i know in real life to have a reaction to this discussion, haha.

So why is 1Ls/100,000,000 not also arbitrary?

It is to an extent because we have a base ten numbering system, and there is nothing inherent about base ten either. But if we are going to use base ten then dividing 1Ls by 100 million gets us down to approximately human-scale measures. Then you could introduce the Decimeter as 1/10th of a meter and work with something not too far off from a foot that everyone can get behind. 1 Decimeter would = approximately .98 feet.

The initial division by 100,000,000 lets us express things neatly in scientific notation leaving a neat numberal 1 in the pole position.

I find it difficult to come up with a preference for why there should be a 1 instead of a 3 there, but lets call it bais and i'll accept that accusation. All the same, i can't help feel that 1 is the obviously better choice over 3, when sticking with base ten. I just don't want to chase that rabbit right now.

I always thought that the precise definition of the meter seemed arbitrary.

But yeah, I still don't care.

These are the kind of discussions I have with my mate over a morning coffee after dropping the kids off at school. The last topic was the question of whether lightning at sea kills the fish. I had to look it up in the end but it made for good discussion. I think you would fit right in.

In Australia we shifted from imperial to metric in the early 1970s when I was in primary school. So I learned feet and pounds, and then changed.

A meter was originally Napoleon's scientific estimate of one ten millionth of the distance from the equator to the north pole. But I don't think his scientists incorporated the oblation of the spheroid. The equator is about 40,000 km long.

I prefer the imperial measures because they seem to match better to measures that people relate to naturally. I suspect that is just my psychological projection, but the funny thing is that police still use feet and inches to measure people's height. An inch just seems a more practical unit than a centimeter.

Decimal counting is more practical since we use base ten, due to having ten fingers, but base twelve does have advantages of being divisible into common traditional counts such as half a dozen.

We also still use acres rather than hectares for popular measurement of land. An acre is a chain times a furlong, so is based on the old acre field of feudalism, where a peasant would use a horse to plough four furrows, each a furlong in length, and each a rod, pole or perch wide, to sow an acre field.

In England, imperial measurement has been made illegal by the European Union, so grocers who wish to sell fruit by the pound are political criminals.

Robert,

I agree that meters are a pain in the ass. We don't want to measure a person's height by fractions, for instance, or 1.6 Meters, etc..

With my formulation for a meter though, and the subsequent use of decimeters, you are back to using a distance which is basically identical to the foot. And a decimeter being comprised of 10 centimeters, then centimeters are just slightly larger than inches.

a decimeter, as i have defined it is like 98% of a foot.

Here's an interesting video on defining the kilogram, and some new efforts underway to nail it down more precisely. Turns out it's no longer tied directly to an equivalent volume of water, which i didn't know.

http://www.wimp.com/roundestobject/

All units of measurement are man-made, and thus by definition, arbitrary. The beauty of the metric system is not its accuracy, but the fact that all its units, meters, liters, kilograms, etc. are designed to interrelate to one another without a bunch of decimal places and odd number. Compare for example, the mass of a liter of water (in kilograms), with the mass one one gallon in pounds. Or the number of square meters in a hectare, compared with square feet in an acre.

I would fill in the details, but I just ran across this post, and it is late here and I am going to bed.

On this subject, I just watched a very interesting video:

www.wimp.com/roundestobject.

That's the same link i just posted above!