8 ms·

For the next revision: remove the mole from the SI. It's completely pointless. A number is not a unit! Instead replace it by the bit, the fundamental unit of in

For the next revision: remove the mole from the SI. It's completely pointless. A number is not a unit! Instead replace it by the bit, the fundamental unit of information.

rimliu 7y ago
How do you imagine that? And what has the bit to do with it?
- snops 7y ago
  The SI units are supposed to be used to define all other units. The mole is just a unitless number which isn't used for many definitions, while the bit (or preferably, Shannon) has a fundamental use in information theory and the wider field of physics. The mole is a human specific number, the bit is a property of the universe. Information is a physical quantity, just like mass or length, and deserves to have a unit in the SI system. You could use other bases, like the nebit (natural log) or Hart (base 10), but bit is most elegant as it uses the smallest integer base possible, 2.
  - no_identd 7y ago
    "The smallest=the most elegant=the most desirable" seems like terrible reasoning, and similar to the reasoning behind the infamous 'Uno': https://en.wikipedia.org/wiki/Parts-per_notation#Uno https://en.wikipedia.org/wiki/Parts-per_notation#Uno However, I don't entirely disagree with where you go with this, but in my opinion, one ought to: 1. Use the nat an normalize everything else (which might seem like an odd idea at first, but think about it): https://en.wikipedia.org/wiki/Nat_%28unit%29 https://en.wikipedia.org/wiki/Nat_%28unit%29 But, if we assume you want to avoid the normalization, then it would seem more sensible, due to numerical efficiency, to use balanced ternary, which actually has, unlike what people who rather cluelessly apply the literal textbook (and terrible) metric of 'Radix efficiency'(an entirely artificial measure originally invented to account for engineering concerns related to vacuum tube spacing.) would presume, higher numeric efficiency than unsigned ternary, as shown here by a then Indian computer science student, Abhijit Bhattacharjee, whose work on this unfortunately only remains accessible via the Internet Archive Wayback Machine: https://web.archive.org/web/20090312094241/http://abhijit.info/tristate/tristate.html#Base3 https://web.archive.org/web/20090312094241/http://abhijit.in... He actually got a reply by Marvin Minsky(to an email he had sent him) at some point (also available via archive.org, but only if you do a lot of trickery which I can't do from my mobile phone, I've however previously verified the quote he provided on the bottom of the page and it does, by all things I could account for, indeed seem genuine), which I'll quote here: "Yes it is a fascinating subject, and your explorations and descriptions are extremely readable. I hope it gets the interest of more mathematicians."
pavlov 7y ago
Dear Lord no, the "mole removal" jokes in mainstream press would be too much.
- tim333 7y ago
  It happened on May 20th and I'm not finding any mole removal jokes :o The Guardian did have "The weight is over" for the Kg.
ginnungagap 7y ago
The bit is defined as the the entropy information (hence the expected value) of a random variable, which is also just a number
evanb 7y ago
As part of this SI redefinition, the Boltzmann constant is also getting an exact definition 1.380 649 e-23 J/K (thereby defining the Kelvin). If we identify the entropy formula S = kB ln W as really being about bits, we see that in natural units kB = 1/ln(2) and can eliminate all energies in favor of temperatures (or vice-versa). If you think that entropy is better measured in nats, kB = 1.
GuB-42 7y ago
The reason the mole is in the SI puzzled me too. It seems that the reason is that chemists don't care how many atoms there are in their reactions. It would be inconvenient: fractions of atoms don't make sense, and the numbers are far from human scale. They just want an agreement, so that even if they don't know the exact number of atoms in their test tube, they know they all have the same number. That's what units are for. The definition of units are done in the most convenient and precise way possible. And they are updated as science progresses. For the kg, the artifact used to be the best we had, alternative methods weren't precise enough, they changed that to the Kibble balance because now, it is better. It may change again at a later time if we find something better. Back to the mole, it used to be defined as the ratio between the kilogram and the mass of a 12C atom because it is the best we had. Now that we can count atoms with more precision, we decided to change it to just the Avogadro constant, which becomes fixed. Again it might change. What may happen (or may have happened, see Avogadro project) is that we can define the kilogram using the mole, making it fundamental.
- garmaine 7y ago
  That is what has happened, essentially. The mole is atomically precise, and will never change.
  - deleted 7y ago
    [deleted]
- hackerpacker 7y ago
  >The definition of units are done in the most convenient and precise way possible. testing my scale with a mirror that contains a kg of photons doesn't sound very convenient.
  - wongarsu 7y ago
    You were also never going to test your scale with a weight that is stored in a vault in Paris. So far you would test with a replica of a replica of that weight, in the best case (getting a copy directly from the local standards body). With the new definition in principle anybody can create an object that weighs exactly one kg and sell it to you.
garmaine 7y ago
If you think mole is redundant, the bit is just as redundant.
OscarCunningham 7y ago
> A number is not a unit! Related to this is the fact that the Avogadro constant, 6.02214076×10^23 mol^-1, is equal to 1.
anticensor 7y ago
A SI byte would comprise of 10 bits.

For the next revision: remove the mole from the SI. It's completely pointless. A number is not a unit! Instead replace it by the bit, the fundamental unit of information.

rimliu 7y ago

How do you imagine that? And what has the bit to do with it?

snops 7y ago
The SI units are supposed to be used to define all other units. The mole is just a unitless number which isn't used for many definitions, while the bit (or preferably, Shannon) has a fundamental use in information theory and the wider field of physics. The mole is a human specific number, the bit is a property of the universe. Information is a physical quantity, just like mass or length, and deserves to have a unit in the SI system. You could use other bases, like the nebit (natural log) or Hart (base 10), but bit is most elegant as it uses the smallest integer base possible, 2.
- no_identd 7y ago
  "The smallest=the most elegant=the most desirable" seems like terrible reasoning, and similar to the reasoning behind the infamous 'Uno': https://en.wikipedia.org/wiki/Parts-per_notation#Uno https://en.wikipedia.org/wiki/Parts-per_notation#Uno However, I don't entirely disagree with where you go with this, but in my opinion, one ought to: 1. Use the nat an normalize everything else (which might seem like an odd idea at first, but think about it): https://en.wikipedia.org/wiki/Nat_%28unit%29 https://en.wikipedia.org/wiki/Nat_%28unit%29 But, if we assume you want to avoid the normalization, then it would seem more sensible, due to numerical efficiency, to use balanced ternary, which actually has, unlike what people who rather cluelessly apply the literal textbook (and terrible) metric of 'Radix efficiency'(an entirely artificial measure originally invented to account for engineering concerns related to vacuum tube spacing.) would presume, higher numeric efficiency than unsigned ternary, as shown here by a then Indian computer science student, Abhijit Bhattacharjee, whose work on this unfortunately only remains accessible via the Internet Archive Wayback Machine: https://web.archive.org/web/20090312094241/http://abhijit.info/tristate/tristate.html#Base3 https://web.archive.org/web/20090312094241/http://abhijit.in... He actually got a reply by Marvin Minsky(to an email he had sent him) at some point (also available via archive.org, but only if you do a lot of trickery which I can't do from my mobile phone, I've however previously verified the quote he provided on the bottom of the page and it does, by all things I could account for, indeed seem genuine), which I'll quote here: "Yes it is a fascinating subject, and your explorations and descriptions are extremely readable. I hope it gets the interest of more mathematicians."

pavlov 7y ago

Dear Lord no, the "mole removal" jokes in mainstream press would be too much.

tim333 7y ago
It happened on May 20th and I'm not finding any mole removal jokes :o The Guardian did have "The weight is over" for the Kg.

ginnungagap 7y ago

The bit is defined as the the entropy information (hence the expected value) of a random variable, which is also just a number

evanb 7y ago

As part of this SI redefinition, the Boltzmann constant is also getting an exact definition 1.380 649 e-23 J/K (thereby defining the Kelvin). If we identify the entropy formula S = kB ln W as really being about bits, we see that in natural units kB = 1/ln(2) and can eliminate all energies in favor of temperatures (or vice-versa). If you think that entropy is better measured in nats, kB = 1.

GuB-42 7y ago

The reason the mole is in the SI puzzled me too. It seems that the reason is that chemists don't care how many atoms there are in their reactions. It would be inconvenient: fractions of atoms don't make sense, and the numbers are far from human scale. They just want an agreement, so that even if they don't know the exact number of atoms in their test tube, they know they all have the same number. That's what units are for. The definition of units are done in the most convenient and precise way possible. And they are updated as science progresses. For the kg, the artifact used to be the best we had, alternative methods weren't precise enough, they changed that to the Kibble balance because now, it is better. It may change again at a later time if we find something better. Back to the mole, it used to be defined as the ratio between the kilogram and the mass of a 12C atom because it is the best we had. Now that we can count atoms with more precision, we decided to change it to just the Avogadro constant, which becomes fixed. Again it might change. What may happen (or may have happened, see Avogadro project) is that we can define the kilogram using the mole, making it fundamental.

garmaine 7y ago
That is what has happened, essentially. The mole is atomically precise, and will never change.
- deleted 7y ago
  [deleted]
hackerpacker 7y ago
>The definition of units are done in the most convenient and precise way possible. testing my scale with a mirror that contains a kg of photons doesn't sound very convenient.
- wongarsu 7y ago
  You were also never going to test your scale with a weight that is stored in a vault in Paris. So far you would test with a replica of a replica of that weight, in the best case (getting a copy directly from the local standards body). With the new definition in principle anybody can create an object that weighs exactly one kg and sell it to you.

garmaine 7y ago

If you think mole is redundant, the bit is just as redundant.

OscarCunningham 7y ago

> A number is not a unit! Related to this is the fact that the Avogadro constant, 6.02214076×10^23 mol^-1, is equal to 1.

anticensor 7y ago

A SI byte would comprise of 10 bits.