3 ms·

The metric "interface" has nice "round" numbers, but the implementation idk: "In the SI, the standard metre is defined as exactly 1/299,792,458 of the distance

The metric "interface" has nice "round" numbers, but the implementation idk: "In the SI, the standard metre is defined as exactly 1/299,792,458 of the distance that light travels in a second." "The kilogram was originally defined as the mass of one cubic decimetre of water at 4 °C, standardized as the mass of a man-made artefact of platinum-iridium held in a laboratory in France, which was used until a new definition was introduced in May 2019. Replicas made in 1879 at the time of the artefact's fabrication and distributed to signatories of the Metre Convention serve as de facto standards of mass in those countries. Additional replicas have been fabricated since as additional countries have joined the convention. The replicas were subject to periodic validation by comparison to the original, called the IPK. It became apparent that either the IPK or the replicas or both were deteriorating, and are no longer comparable: they had diverged by 50 μg since fabrication, so figuratively, the accuracy of the kilogram was no better than 5 parts in a hundred million or a proportion of 5x10−8:1. The accepted redefinition of SI base units replaced the IPK with an exact definition of the Planck constant, which defines the kilogram in terms of the second and metre."

Ekaros 4y ago
So what are the "imperial" Volts and Amperes?
- function_seven 4y ago
  As an unashamed imperial units enthusiast, now I’m sad we don’t have different ones for current and potential. But at least we still have horsepower! My PSU is a 3/4-horse unit. My toaster oven is a full horsepower. I like it.
  - mrguyorama 4y ago
    Your battery-electric vehicle has a capacity of 70 thousand horsepower-hours
    - function_seven 4y ago
      Oh boy I wish. I'd only have to recharge like once a year! That's just nuts. My 70kWh battery holds only 95 horsepower-hours. But I use the British Thermal Unit when talking about energy. My BEV has 240 kilo-BTUs stored in it.
russellbeattie 4y ago
We should start first be redefining the second: 9,192,631,770 oscillations of a cesium atom. It's too long anyways, we can easily perceive time down to at least 1/60th of that. So let's call it 150 million oscillations, and refer to it simply as "time", since the word second only makes sense in context of an analog clock anyways. Then we can start rounding the other weights and measures accordingly until everything is nice and clean. It appeals to the OCD in me, despite the societal chaos that would ensure. But then the universe will undoubtedly throw random numbers at us like π or the fine-structure constant and mess it all up.
12baad4db82 4y ago
Not sure what you are trying to say with your quoted phrases. There was an issue with the standard for the Kilogram, which was recognised then corrected by introducing a definition which is based on physically measurable phenomenon. The new approach allows independent experiments to derive the value of the Kilogram. That seems to me like a process that works, and I struggle to think of a better outcome.
- chungy 4y ago
  > Not sure what you are trying to say with your quoted phrases. That the metric system is just as arbitrary as the customary units. Things like the meter and (kilo)gram were based on arbitrary objects rather than anything objective. They've since been redefined using physical constants to come close enough to the old reference objects. (And the US customary units are officially defined as exact fractions from the SI units -- making the whole world happy to have exact measurements regardless of the system you use.) At least the customary units have nice divisors. Just saying.
  - dkbrk 4y ago
    > That the metric system is just as arbitrary as the customary units No-one claims it isn't arbitrary. Any choice of units is arbitrary. "Not being arbitrary" just isn't a desideratum when considering what makes a good system of units. The main desirable property is coherence [0], which SI has. But I don't think anyone would claim SI is perfect. It's not; it's got at least a couple of warts. One is that "kg" is a base unit and is prefixed. But that's about the worst of it. CGS is also coherent, but has a similar problem with a prefixed base unit (in this case, cm). US Customary units is not only incoherent, but does things like conflate mass and force (lb is a technically a measure of force, so is the long/short ton, and slug is the proper unit for mass) and has far too many derived units that measure the same thing (e.g. ft lb/s, hp and BTU/h, vs just W). [0]: https://en.wikipedia.org/wiki/Coherence_(units_of_measurement) https://en.wikipedia.org/wiki/Coherence_(units_of_measuremen...
  - fanf2 4y ago
    The metric system was based on the existing unit of time and the dimensions of the earth. The metre was originally defined as 1/40,000,000 of the circumference of the earth (through the poles and Paris). From the metre they derived units of weight and volume. There was some debate at the time about using a pendulum with a 1s period to define the metre, but it was known to be less accurately reproducible than the geodetic version. Their aim was to define a system that could in principle be recreated from scratch anywhere on Earth without necessarily relying on access to the physical prototypes. In practice the relative imprecision of the original measurements compared to the later demands of science and engineering meant that the prototypes became the definition. It’s interesting to compare with the British Imperial units reform in the 1820s. Part of that act specifies how to recreate the prototypes from physical properties of the units. When the Palace of Westminster burned down in the 1830s the ancient prototypes were destroyed. But the replacements were recreated from copies, not from the specification in the act. And not much later, the official definition was based on the metric system because the metric standards were manufactured to much greater quality.

Ekaros 4y ago

So what are the "imperial" Volts and Amperes?

function_seven 4y ago
As an unashamed imperial units enthusiast, now I’m sad we don’t have different ones for current and potential. But at least we still have horsepower! My PSU is a 3/4-horse unit. My toaster oven is a full horsepower. I like it.
- mrguyorama 4y ago
  Your battery-electric vehicle has a capacity of 70 thousand horsepower-hours
  - function_seven 4y ago
    Oh boy I wish. I'd only have to recharge like once a year! That's just nuts. My 70kWh battery holds only 95 horsepower-hours. But I use the British Thermal Unit when talking about energy. My BEV has 240 kilo-BTUs stored in it.

russellbeattie 4y ago

We should start first be redefining the second: 9,192,631,770 oscillations of a cesium atom. It's too long anyways, we can easily perceive time down to at least 1/60th of that. So let's call it 150 million oscillations, and refer to it simply as "time", since the word second only makes sense in context of an analog clock anyways. Then we can start rounding the other weights and measures accordingly until everything is nice and clean. It appeals to the OCD in me, despite the societal chaos that would ensure. But then the universe will undoubtedly throw random numbers at us like π or the fine-structure constant and mess it all up.

12baad4db82 4y ago

Not sure what you are trying to say with your quoted phrases. There was an issue with the standard for the Kilogram, which was recognised then corrected by introducing a definition which is based on physically measurable phenomenon. The new approach allows independent experiments to derive the value of the Kilogram. That seems to me like a process that works, and I struggle to think of a better outcome.

chungy 4y ago
> Not sure what you are trying to say with your quoted phrases. That the metric system is just as arbitrary as the customary units. Things like the meter and (kilo)gram were based on arbitrary objects rather than anything objective. They've since been redefined using physical constants to come close enough to the old reference objects. (And the US customary units are officially defined as exact fractions from the SI units -- making the whole world happy to have exact measurements regardless of the system you use.) At least the customary units have nice divisors. Just saying.
- dkbrk 4y ago
  > That the metric system is just as arbitrary as the customary units No-one claims it isn't arbitrary. Any choice of units is arbitrary. "Not being arbitrary" just isn't a desideratum when considering what makes a good system of units. The main desirable property is coherence [0], which SI has. But I don't think anyone would claim SI is perfect. It's not; it's got at least a couple of warts. One is that "kg" is a base unit and is prefixed. But that's about the worst of it. CGS is also coherent, but has a similar problem with a prefixed base unit (in this case, cm). US Customary units is not only incoherent, but does things like conflate mass and force (lb is a technically a measure of force, so is the long/short ton, and slug is the proper unit for mass) and has far too many derived units that measure the same thing (e.g. ft lb/s, hp and BTU/h, vs just W). [0]: https://en.wikipedia.org/wiki/Coherence_(units_of_measurement) https://en.wikipedia.org/wiki/Coherence_(units_of_measuremen...
- fanf2 4y ago
  The metric system was based on the existing unit of time and the dimensions of the earth. The metre was originally defined as 1/40,000,000 of the circumference of the earth (through the poles and Paris). From the metre they derived units of weight and volume. There was some debate at the time about using a pendulum with a 1s period to define the metre, but it was known to be less accurately reproducible than the geodetic version. Their aim was to define a system that could in principle be recreated from scratch anywhere on Earth without necessarily relying on access to the physical prototypes. In practice the relative imprecision of the original measurements compared to the later demands of science and engineering meant that the prototypes became the definition. It’s interesting to compare with the British Imperial units reform in the 1820s. Part of that act specifies how to recreate the prototypes from physical properties of the units. When the Palace of Westminster burned down in the 1830s the ancient prototypes were destroyed. But the replacements were recreated from copies, not from the specification in the act. And not much later, the official definition was based on the metric system because the metric standards were manufactured to much greater quality.