NIST to redefine the kilogram based on a fundamental universal constant
washingtonpost.com
NIST to redefine the kilogram based on a fundamental universal constant
1–10 of 90 posts
Re: NIST to redefine the kilogram based on a fundamental universal constant
#2That's also a dreadful pun.
Re: NIST to redefine the kilogram based on a fundamental universal constant
#3> Scientists don't know whether the BIPM prototype is losing mass, perhaps because of loss of impurities in the metals, or if the witnesses are gaining mass by accumulating contaminants.
Can we stop this nonsense? It would be a big problem if it were true, but it isn't. It's the later (contamination weight gain) and we have fairly good understanding of what's going on. For example, see https://phys.org/news/2013-01-kilogram-weight.html
Re: NIST to redefine the kilogram based on a fundamental universal constant
#4>When the International Committee for Weights and Measures announced that it would reconsider the kilogram definition, it said it would require three measurements with uncertainties below 50 parts per billion, and one below 20 ppb. But with the new NIST measurement, the world now has at least three experiments below 20 ppb — another was conducted by a Canadian team using a Kibble balance, the third by an international group that calculates the Planck constant based on the number of atoms in a sphere of pure silicon.
>The weights and measures committee will meet this month to establish a global value for Planck's constant by averaging the values calculated at NIST and other labs. And in 2018, at the next General Conference on Weights and Measures, the scientific community will draft a resolution to redefine kilogram based on this constant.
Looks like the current title "NIST to redefine the kilogram based on a fundamental universal constant" is confusing because it implies that NIST defines kilogram but it's International Committee's for Weights and Measures job.
Re: NIST to redefine the kilogram based on a fundamental universal constant
#5They define it based on Planck's constant, so the results also depends on the definition of meter and seconds if I understand it correctly.
Would it have been possible to define it as the weight of N amount of electrons (assuming all electrons have the exact same weight under all circumstances) or another fundamental particle?
EDIT: it would be the weight of 9.10938356e31 electrons at rest
Re: NIST to redefine the kilogram based on a fundamental universal constant
#6They define it based on Planck's constant, so the results also depends on the definition of meter and seconds if I understand it correctly. Would it have been possible to define it as the weight of N amount of electrons (assuming all electrons have the exact same weight under all circumstances) or another fundamental particle? EDIT: it would be the weight of 9.10938356e31 electrons at rest
How to define fundamental units has always been a matter of precision measurements, not theoretical purity. If the standards body decides to base the definition on Planck's constant, instead of a certain amount of electrons, the rationale will be higher accuracy in measurements of Planck's constant than of the mass of electrons.
Re: NIST to redefine the kilogram based on a fundamental universal constant
#7They define it based on Planck's constant, so the results also depends on the definition of meter and seconds if I understand it correctly. Would it have been possible to define it as the weight of N amount of electrons (assuming all electrons have the exact same weight under all circumstances) or another fundamental particle? EDIT: it would be the weight of 9.10938356e31 electrons at rest
One way has been by counting silicon atoms in a nearly-perfect spherical crystal.
Re: NIST to redefine the kilogram based on a fundamental universal constant
#8They define it based on Planck's constant, so the results also depends on the definition of meter and seconds if I understand it correctly. Would it have been possible to define it as the weight of N amount of electrons (assuming all electrons have the exact same weight under all circumstances) or another fundamental particle? EDIT: it would be the weight of 9.10938356e31 electrons at rest
It's OK though, because the metre and second are already based on physical constants: the second is "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and the metre is defined from the second by fixing the speed of light at 299 792 458 m/s.
Re: NIST to redefine the kilogram based on a fundamental universal constant
#9That's also a dreadful pun.
For those who missed it, the original submission title (from the article) was "Scientists are about to change what a kilogram is. That’s massive."