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[MaximumZero]

I cannot wrap my hands around my neck. Sorry, Vector, no choking me out for you.

[Leafsnail]

I recently realised that my internal definitions for Sine and Cosine were weirdly circular.  I then got the same thing for my definitions of units of electricity, and decided to find out exactly what an amp really is.

It was like looking into the void.

The constant current which will produce an attractive force of 2 × 10–7 newtons per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum

[Aqizzar]

The constant current which will produce an attractive force of 2 × 10–7 newtons per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum

Okay, I know amps have been around longer than some of those concepts.  How the fuck is that garglemesh a definition of anything?  And how do make a meter to represent them?

[Vector]

This is why I hate physics.  They don't seem to be able to just sit down and define things, or say "Look, we don't actually understand.  We're just rolling with what's convenient.  Let's call it an axiomatic system and be done with it."

Bah.  I used to get in the craziest arguments with physicists.

[Leafsnail]

It's about being fundamental, I suppose.  That definition holds true regardless of all other factors, and, well, they feel silly if they can't have something like that.  I mean, metres were originally defined by the distance between two lines on a bar in Paris.  Now it's

the length of the path travelled by light in vacuum during a time interval of 1⁄299 792 458 of a second.

The thing is, there is a potentially logical definition for an amp... just make it x electrons per second (although second isn't exactly any better - "The time needed for a caesium-133 atom to perform 9,192,631,770 complete oscillations").

[dragnar]

The constant current which will produce an attractive force of 2 × 10–7 newtons per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum

Okay, I know amps have been around longer than some of those concepts.  How the fuck is that garglemesh a definition of anything?  And how do make a meter to represent them?

A meter is defined as the distance light travels in 10^1(some big number) seconds. A second is the amount of time it takes some molecule to vibrate some number of times. Most units have been redefined to use measurable constants, since the universe doesn't HAVE base units, and so things have to be defined in a precise way. Otherwise precise measurements are impossible.

...ninja.

[Aqizzar]

Actually, when I said "meter", I meant like a gauge.  How do you build an accurate gauge to check and display the value of something whose definition is that bubblefuck sentence about newtons and vacuum?

[Leafsnail]

I would think it's theoretical, really.  Or someone was messing around with such a meter.

Incidentally, the definition for kilogram is actually

it is equal to the mass of the international prototype of the kilogram

Yep, there's a Platinum-Iridium prototype that weighs exactly one kilogram at the International Bureau of Weights and Measures.

[Duke 2.0]

I would think it's theoretical, really.  Or someone was messing around with such a meter.

Incidentally, the definition for kilogram is actually

it is equal to the mass of the international prototype of the kilogram

Yep, there's a Platinum-Iridium prototype that weighs exactly one kilogram at the International Bureau of Weights and Measures.

Which due to decay is slowly losing mass.

[dragnar]

I would think it's theoretical, really.  Or someone was messing around with such a meter.

Incidentally, the definition for kilogram is actually

it is equal to the mass of the international prototype of the kilogram

Yep, there's a Platinum-Iridium prototype that weighs exactly one kilogram at the International Bureau of Weights and Measures.

Yes, as far as I know it's the only scientific unit that remains tied to a real-world object. Meters used to have a similar prototype.

[Virex]

They're working on a replacement for that though, but they haven't really decided what method would be best.

[Urist Imiknorris]

EDIT: Ignore my rantings.

[MaximumZero]

If anyone needs me, I'll be over here feeling like a moron.

[Virex]

You're going to count some 6*10^23-odd carbon atoms? How are you going to get any accuracy out of that?


One of the plans is actually to try and make a perfectly round sphere of a silicon single-crystal, with a radius so that it would be precisely a kilogram, and then measure it's deviation from a perfect sphere (in picometers) and grind off some more so it becomes exactly a kilogram.

[Urist Imiknorris]

One mole of carbon = 12.01 grams.