Definition of the Kilogram to be changed

[#1]

Is the prototype kilogram in Paris the last physical standard to be redefined? 

https://www.bbc.co.uk/news/science-environment-46143399

[#2]

Yes, it was yesterday. Not that you would notice. It's now totally based on quantum measurement which takes away all the variables associated with keeping a lump of it in a jar! 

https://www.wired.com/story/new-kilogram-definition-based-on-planck-constant/

[#3]

It's hard to get excited about some artificial made up measurement system.

[#4]

Of course you have to ask how they know it weighs a Kilogram in the first place with out having something to measure it by!

[#5]

Is 1 kilogram the weight or the mass as one is relative, the other isn't.

[#6]

@Strat

It can be either...  if it's measured and includes the effect of the force of gravity, it's 1Kg weight. In absolute terms (without gravity) it is 1Kg mass. 1Kg of sprouts on the moon would give you many more sprouts because the force of gravity is much lower.

This new system doesn't rely on actually measuring the weight or mass to be compared with anything else. It relies on the effect of the 1Kg thingy on the current produced by the measuring device, which is proportional to Planck's constant, which is invariable. That's why it's absolute so you don't need to have 1Kg in the first place to compare it with!

Or so it says in the link above. I think. 

[#7]

@Strat

So, if you get more sprouts in 1Kg weight on the Moon because of lower gravity, if you bought 1Kg of sprouts in a gravity-free place like deep space, would you get an infinite number of sprouts? Juts think of the effect that that would have! Parp. 

[#8]

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@billnotben wrote:

It's hard to get excited about some artificial made up measurement system.

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Aren't all measurement systems artificial and made up? The only one I can think of that could be described as "natural" is the day. And even then, as soon as you start to divide a day into smaller parts, you're introducing an artificial construct.

[#9]

They know it's a kilogram, because people sat down and agreed, that "This lump of platinum iridium alloy is one kilogram."  In the same way as someone decided that a "yard" was the distance from their nose to their outstretched hand. Then sensible people said, "OK, but we'll just describe that in terms that are consistent across populations".

[#10]

You're right of course, the international prototype kilogram has a mass of 1kg, it's weight will vary depending on where in the world you are standing,(among other things)

[#11]

A "Quite Interesting" factoid is that the basement in the Louvre where the International Prototype 1kg is kept (in its hermetically sealed jar), is international territory; it legally belongs to no country.

[#12]

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@John_Hull wrote:

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@billnotben wrote:

It's hard to get excited about some artificial made up measurement system.

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Aren't all measurement systems artificial and made up? The only one I can think of that could be described as "natural" is the day. And even then, as soon as you start to divide a day into smaller parts, you're introducing an artificial construct.

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@John_Hull

The new definition is absolute, not artificial, because it uses the Planck number, which is a natural universal number that doesn't depend on anything else.

[#13]

But why did we ever need this piece of metal in the first place if the Planck number was known ?

[#14]

I don't disagree, but the concept of a "kilogram" or a "pound" or a "shekel" are artificial constructs, designed to make society work, in the same way as every other measurement system. The metre used to be defined in relation to the distance from the north pole to the equator on the longitude line going through Paris, (although there was a physical artefact that was "the metre").  but was redefined in terms of wavelengths of a specified light, in a vacuum around 40 years ago. Over time natural phenomena have been used to redefine measurement terms, in order to make the measurements more accurate and repeatable.

(You'll gather, I'm a metrologist by profession - in my case an inspector of weights and measures - and could bore for Essex on the subject :-))

[#15]

Because all measurement standards started out as physical artefacts. So the National Physical Laboratory in Teddington had official copies of all of the internationally recognised standards, including the UK copy of the kg. Gradually, as technology and metrology has progressed, physical measurement standards have been surpassed by using "natural" measure - wavelengths of light for length, and now Planck's constant for mass. Capacity is defined by length (so a litre is 1000 cubic centimetres).

Second "quite interesting" fact; when weighing machines are approved for trade use, they have to be tested in the geographical region where are intended to be used, because gravity varies very slightly in different parts of the world, enough to make modern scales accurate in one region, but inaccurate in another.