this post was submitted on 29 Sep 2024
342 points (97.5% liked)

Mildly Interesting

17469 readers
629 users here now

This is for strictly mildly interesting material. If it's too interesting, it doesn't belong. If it's not interesting, it doesn't belong.

This is obviously an objective criteria, so the mods are always right. Or maybe mildly right? Ahh.. what do we know?

Just post some stuff and don't spam.

founded 1 year ago
MODERATORS
marcar
[email protected]
WhatsHerBucket
[email protected]
342
A tagliatelle made from gold that defines the official size of a tagliatelle, at the Palazzo della Mercanzia in Bologna (sh.itjust.works)
submitted 1 month ago by [email protected] to c/mildlyinteresting
46 comments fedilink hide all child comments
 

Image source: https://facciamoungiroincentro.blogspot.com/2016/07/palazzo-della-mercanzia.html

you are viewing a single comment's thread
view the rest of the comments
[–] [email protected] 83 points 1 month ago (2 children)

Gold makes for an awful standard due to thermal expansion, but I feel this is more a historical artefact than an actual standard.

[–] NegativeInf 55 points 1 month ago* (last edited 1 month ago) (3 children)

Right? Didn't they define the kilogram, make identical copies of the standard, sent them to different countries, then after years, reunited them and found they all diverged in mass?

And now they have made a perfect silicon sphere with the same mass as the standard kilogram, then counted all the atoms. So now we know the exact mass in silicon atoms of a kilo.

Let's just define tagliatelle in light nanoseconds and be done with it.

[–] subtext 19 points 1 month ago (1 children)

Since 2019, the kg is just defined in terms of the Plank constant and some math with the resonant frequency of cesium as well as the speed of light. There was too much variability in anything physical so they decided to just fix some constants at whatever value they were close to.

https://en.wikipedia.org/wiki/2019_revision_of_the_SI

[–] NegativeInf 7 points 1 month ago (1 children)

It's part of the attempt to more accurately define Avogadro's number and the kilo.

https://www.nist.gov/si-redefinition/kilogram-silicon-spheres-and-international-avogadro-project

[–] subtext 5 points 1 month ago* (last edited 1 month ago)

The redefinition of the mole in 2019, as being the amount of substance containing exactly 6.02214076×10^23 particles

Since the 2019 SI redefinition, avogadro’s number is a constant.

https://en.wikipedia.org/wiki/Avogadro_constant

Edit: looks like we were both right! I was reading through your link and it seems the work reported by the NIST led to the exact definitions for Avogadro’s number and the Planck constant.

[–] [email protected] 5 points 1 month ago (2 children)

They counted the atoms?
Didn't they just took the mol mass and calculated it? (Not sure if mol mass is the right term... School chemistry is a long time ago...)
And I don't see how we even should be able to count them.
Would be really interested, if it happened that way, how they did it.

[–] TunaLobster 2 points 1 month ago

They gave up on that plan. Defining Plank's constant happened first. It could still be done as a secondary confirmation, but it's less of a race now to get away from K

[–] Buffalox 7 points 1 month ago

This is Italy, it's got have style.