Great Shift - The Gram to Be Redefined

[XB-70A]

Great news! 

On 2018-11-13/16, the I.S.U. will redefine the gram (and also the A and the K) by switching from its actual material base, the famous International Prototype Kilogram, but whose mass has slowly varied along the years, to an immaterial one related to the Planck constant (J*s)

More available on this page: https://news.cnrs.fr/articles/measures-the-great-shift

[Green Baron]

Wow. That was about time. I knew that the prototypes had problems holding their weight mass.

Glad to read that a kg is still a kg :-)

[Racescort666]

Relevant Veritasium video (also very interesting if you’ve got 10 minutes to watch): 

 

[YNM]

3 hours ago, XB-70A said:

The Gram to Be Redefined

*Kilogram

I'm glad they finally went somewhere with both the kibble balance and the spherical silicone monocrystal atom measurement.

Finally the title of this video can be put to rest.

 

Edited October 20, 2018 by YNM

[wumpus]

7 minutes ago, YNM said:

*Kilogram

I'm glad they finally went somewhere with both the kibble balance and the spherical silicone monocrystal atom measurement.

Finally the title of this video can be put to rest.

Looks like Avagadro's number will require measurement of that sphere and comparison to the Planck constant and not the other way around.  Makes sense, the Planck constant is certainly seen as more fundamental, but I always liked the Avagdro number.  In other news, we should be adding a few decimal places to Avagardo's number, even if it won't be exact.

[Nightside]

So can I trade in all my old kilograms for the new ones, or are they just junk?

[Green Baron]

No no, keep them ! They automagically adopt the new flavour.

Don't be fooled by somebody telling you "Hey, pssst, I can trade all your old kg into new ones. Special price."

Edited October 20, 2018 by Green Baron

[DerekL1963]

50 minutes ago, Nightside said:

So can I trade in all my old kilograms for the new ones, or are they just junk?

Unless you're doing lab or reference standard grade measurement, you can keep and continue to use your old kilograms.  If you are doing precision measurement using laboratory or reference grade kilograms, then your metrology people will have some thinking to do on how to handle the changeover.

Or, to put it more simply, unless you're currently using a managed standard, you probably won't have to do anything.

[lajoswinkler]

1 hour ago, Green Baron said:

Don't be fooled by somebody telling you "Hey, pssst, I can trade all your old kg into new ones. Special price."

God damn it. Thwarted again!

[satnet]

I would also like to add Practical Engineering's video. It doesn't go quite as deep into the subject as Veritasium, but he actually builds one himself. This is why I always preferred the Kibble balance approach. Basically it can be replicated by anyone with reasonable effort (though for extreme precision/accuracy you still need the resources of a nation-state or at least a large corporation).

 

[Superfluous J]

Finally. What a stupid way to define something so critical.

[YNM]

7 hours ago, wumpus said:

Avagadro's number will require measurement of that sphere and comparison to the Planck constant and not the other way around.

From what I've heard from Derek Muller (Veritasium) they'll compare their results. I think the kibble balance is ultimately chosen because of the ease of actually doing it in other places (so rather than needing national kilogram copies they can just calibrate their environment and build their own balance, much like atomic clocks), but they had to crosscheck with the result from the atom lattice measurement. As the two results agree strongly, the whole replacement is given the go-ahead.

I mean, if they had locked the Planck's Constant and the value for speed of light, it's not too surprising that Avogadro's number will also be locked down.

Here's his video with the silicone crystal sphere.

 

Edited October 20, 2018 by YNM

[magnemoe]

Its a bit fun, one meter was defined by the distance from pole to equator. Yes it was selected as the length was decent for everyday use. it was also inaccurate
So they made an standard bar, that is also easier to replicate. 
Later they defined it on light eliminating the need for an unique bar.

One liter is 0.1 meter  cubed.

One Kg is one liter of water, that is at 4 centigrade an also has inaccuracies so they made an new unique weight, its now replaced by physical constants.