Redefinition of the kilogram and other SI units

[belligerent drunk]

In science, one of the fundamental and important tasks is to define the system of units that one measures the world in. Back in the day, base units were defined in various ways, many were based on some prototype, such as the metre. There are many problems with such a system; for instance, physical objects are impossible to manufacture in an ideal manner, they also decay with time and so on. The kilogram is the only current SI base unit that is defined based on a physical artefact. This may change in 2019. The article itself is from 2017, but it should be interesting in any case.

Additional interesting reading: Proposed redefinition of SI base units (wiki).

 

[Xorkoth]

Man I just went down a math Wikipedia hole. Thanks for that! Super interesting.

 

[Cheshire_Kat]

What's the practical ramification of this change.
Does the world need to buy new scales? Not trying to be a smart ass here.

 

[belligerent drunk]

I haven't researched it, but I don't think there will be any changes whatsoever as far as the normal everyday business goes*. Electronic scales usually work as follows: they measure the force exerted on the plate using magnets, so they don't actually measure mass, they measure force. A little physics formulae yada-yada will give you the mass of the object. Electronic scales - this includes consumer milligram scales such as those used by substance users, like myself, or analytical scales used in labs, which I've used as well, being a chemist and all - require calibration, which is done by putting an object with a known mass (say 100 g) on the scale and letting it know that it should be 100 g, then another object (say 1 g), and now with a little algorithm it can produce a calibration curve, which lets it by a way of extrapolating and interpolating measure any mass within a reasonable range. The only thing the manufacturer needs to input is the definition of "1 kg" or "1 g" in order to calibrate, using a real physical object.

The redefinition doesn't change anything within this process. It changes the definition of the original "1 kg" against which all the calibration weights and calculations are manufactured. Currently, the 1 kg is defined as the mass of a real object made of iridium-platinum alloy with a precise shape and size, and that is the exact 1.00000000(0) kg. However, since things decay and so on, the mass of this object changes, so the definition changes with time - and that's the problem, which is being addressed. If "1 kg" is going to be defined based on a constant of nature (which doesn't change/decay), then when you need to calibrate the whole metric system, you measure the constant instead of weighing a decaying lump of metal.

I hope I didn't confuse you more, lol.

*Some things will change of course, but the layman will not be affected. The changes will happen very "high up the ladder", so to speak.

 

[Cheshire_Kat]

Not at all. I understood the mechanism for measurement, I was wondering what the actual difference would be. Quite minimal I should imagine.

Some scales in everyday use such as those that dose out radioisotopes for nuclear medicine would fall under that category. There one or two in just about every modern hospital in the world.

BTW this was fascinating, it just raised some questions in my mind. I didn't expect you to have all the answers

edit for stupidity...

LOL, I don't know what I was thinking, 1 kg of radioisotopes would be a metric shit ton. 8(

Moral of the story kids ? Don't do math before your morning coffee