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A tagliatelle made from gold that defines the official size of a tagliatelle, at the Palazzo della Mercanzia in Bologna (sh.itjust.works)
submitted 2 weeks ago by jxk@sh.itjust.works to c/mildlyinteresting@lemmy.world
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Image source: https://facciamoungiroincentro.blogspot.com/2016/07/palazzo-della-mercanzia.html

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[-] Tar_alcaran@sh.itjust.works 83 points 2 weeks ago

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

[-] NegativeInf@lemmy.world 55 points 2 weeks ago* (last edited 2 weeks ago)

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@lemmy.world 19 points 2 weeks ago

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@lemmy.world 7 points 2 weeks ago

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@lemmy.world 5 points 2 weeks ago* (last edited 2 weeks 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.

[-] naeap@sopuli.xyz 5 points 2 weeks ago

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@lemmy.world 2 points 2 weeks 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@lemmy.world 7 points 2 weeks ago

This is Italy, it's got have style.

this post was submitted on 29 Sep 2024
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