4 ms·

Confused, so how do they measure 1 kilo of something now when they need to calibrate the most precise instruments? They count 10^40 photons? How? And how does t

Confused, so how do they measure 1 kilo of something now when they need to calibrate the most precise instruments? They count 10^40 photons? How? And how does that translate into a physical mass they want to carry around? Edit: Seems I completely missed a paragraph somehow. Thanks!

sanxiyn 7y ago
The term of art is "realisation". The article mentions two realisations but does not elaborate: "In practice, there are currently two known methods for measuring such masses with great precision. These are known as the Kibble balance and the single-crystal silicon sphere". You should be able to google from that.
- deleted 7y ago
  [deleted]
- crankylinuxuser 7y ago
  I never understood why a sphere was even in the discussion of a standardized atomic count. Any rational fractions using pi = pi atoms or molecules. And that's absurd to have r=(3V/4pi)^1/3 . No matter how you mess with it, it's irrational to the extreme! Now.. Face-centered or ody-centered cubic follows a nice quadratic expansion for integer based counting. We don't need no steenkin pi's!
  - protonfish 7y ago
    It's not difficult to round to the nearest atom.
  - fl0wenol 7y ago
    Because it's easiest to polish perfectly and verify the diameter of if there's no preferrer orientation. Edges of any kind are liable to wear.
tty2300 7y ago
For most intents and purposes its OK if you are a bit inaccurate. The important thing is that we will never drift further and further away. In 1000 years time we will still have exactly the same kg as we have now.
- nraynaud 7y ago
  Transitioning is quite interesting, you have to measure your old unit with the new system at a resolution never reached before so that you know you don’t invalidate a large collection of numbers everywhere in the world. Then, depending on your definition, you might choose a special number, Avogadro’s number has to be a perfect cube, number of transitions have to be integer, etc.

sanxiyn 7y ago

The term of art is "realisation". The article mentions two realisations but does not elaborate: "In practice, there are currently two known methods for measuring such masses with great precision. These are known as the Kibble balance and the single-crystal silicon sphere". You should be able to google from that.

deleted 7y ago
[deleted]
crankylinuxuser 7y ago
I never understood why a sphere was even in the discussion of a standardized atomic count. Any rational fractions using pi = pi atoms or molecules. And that's absurd to have r=(3V/4pi)^1/3 . No matter how you mess with it, it's irrational to the extreme! Now.. Face-centered or ody-centered cubic follows a nice quadratic expansion for integer based counting. We don't need no steenkin pi's!
- protonfish 7y ago
  It's not difficult to round to the nearest atom.
- fl0wenol 7y ago
  Because it's easiest to polish perfectly and verify the diameter of if there's no preferrer orientation. Edges of any kind are liable to wear.

tty2300 7y ago

For most intents and purposes its OK if you are a bit inaccurate. The important thing is that we will never drift further and further away. In 1000 years time we will still have exactly the same kg as we have now.

nraynaud 7y ago
Transitioning is quite interesting, you have to measure your old unit with the new system at a resolution never reached before so that you know you don’t invalidate a large collection of numbers everywhere in the world. Then, depending on your definition, you might choose a special number, Avogadro’s number has to be a perfect cube, number of transitions have to be integer, etc.