On a slow Friday afternoon in a previous job I got to wondering what the next prefix would be if I ever wanted to dilute my femtomolar solution by another factor of 10-3. The answer, shown in the table below, was ‘atto’ (10-18), and if I was inclined to dilute my attomolar solution yet again, it would become zeptomolar (10-21).
Prefix | Abbr | 10n | Since | Root | Meaning |
yotta | Y | 10 +24 | 1991 | Greek | ὀκτώ: meaning eight, (10008) |
zetta | Z | 10 +21 | 1991 | Latin | septem: seven; (10007). |
exa | E | 10 +18 | 1975 | Greek | ἑξά: six; (10006) |
peta | P | 10 +15 | 1975 | Greek | πέντε: five; (10005) |
tera | T | 10 +12 | 1960 | Greek | τέρας: meaning 'monster'. |
giga | G | 10 +9 | 1960 | Greek | γίγας: meaning 'giant' |
mega | M | 10 +6 | 1960 | Greek | μέγας: meaning 'great' |
kilo | k | 10 +3 | 1795 | Greek | χίλιοι: meaning 'thousand' |
hecto | h | 10 +2 | 1795 | Greek | ἑκατόν: meaning 'hundred' |
deca | da | 10 +1 | 1795 | Greek | δέκα: meaning 'ten' |
deci | d | 10 -1 | 1795 | Latin | decimus: meaning 'tenth' |
centi | c | 10 -2 | 1795 | Latin | centum: meaning 'hundred'. |
milli | m | 10 -3 | 1795 | Latin | mille: meaning 'thousand' |
micro | μ | 10 -6 | 1960 | Greek | μικρός: meaning 'small' |
nano | n | 10 -9 | 1960 | Greek | νᾶνος: meaning 'dwarf' |
pico | p | 10 -12 | 1960 | Italian | piccolo: meaning 'small' |
femto | f | 10 -15 | 1964 | Danish | femten: meaning 'fifteen' |
atto | a | 10 -18 | 1964 | Danish | atten: meaning eighteen' |
zepto | z | 10 -21 | 1991 | Latin | septem: meaning 'seven' |
yocto | y | 10 -24 | 1991 | Greek | οκτώ, meaning 'eight' |
At this point I chuckled to myself because I thought that Zepto was one of the Marx brothers, and therefore we should designate the next lower prefixes as grouchomolar (10-24), chicomolar (10-27) and harpomolar (10-30). As it turns out the 10-24 prefix was already assigned to yoctomolar – though I don’t recall any Yocto Marx brother.
It turns out I wasn’t the only one who ever had a slow day in the lab and started wondering about SI prefixes. In 2010, Austin Sendek, a physics student at UC Davis, wondered about the highest prefix currently assigned to 10+24: 'yotta'; where do you go after that? He proposed that the 10+27 prefix should be assigned to ‘hella’ at the uppermost end of the list, ‘hella’ being North Californian slang for "very" or "a lot of". Examples in daily local use are “Those Dodger fans are hella late to the game (as usual)” or “There's hella chocolate in that cake”. As far as I can tell he is serious in his quest, with a blog and the obligatory Facebook petition. At the time of writing the petition has reached 63,681 votes (which is 63.7 kilovotes, or 0.06 megavotes but only 6x10-23 hellavotes). So far the only implementation of ‘hella’ appears to be at Google (always the paradigm for early adopter) who have included the ‘hella’ prefix in its calculator: 1 light year is 9.4 x 10-12 hellameters.
The official adoption of ‘hella’ as an SI prefix would require ratification by the Bureau international des poids et mesures. The task of the BIPM is to ensure world-wide uniformity of measurements, and was set up under a diplomatic treaty between fifty-five nations; its members are the national metrology laboratories of the signatory states (thank you Wikipedia!). In 1960, BIPM adopted the name Système International d'Unités (hence SI units) for the “recommended practical system of units of measurement”, and defined the rules for their prefixes. The original SI prefixes were originally assigned in 1795 and were based on Greek and Latin – the languages of science in that period; there were subsequent additions in 1960, 1964, 1975 and 1991.
While SI prefix updates have generally stuck with Greek and Latin based etymology, in 1964 the Danish language made a fleeting appearance – I have yet to discover why. Le BIPM assigned ‘femto’ to 10-15 ('femten' is Danish for fifteen) and ‘atto’ to 10-18 ('atten' is Danish for eighteen). I wonder how the discussion started: “Hey guys, we’ve already used the Greek and Latin words for small, teensy and itsy bitsy – anyone got any ideas?” At this point in the proceedings the Danish delegate seized the moment and piped up with ‘femto’ and ‘atto’. Perhaps he preemptively averted any resistance by bringing a hectoliter of Danish pilsner beer to the lunchtime recess - just a hypothesis.
The next SI meeting is scheduled in October of 2011 - I will send a DVD of “A Night at the Opera”, a box of cigars and joke spectacles/moustaches for each delegate to lobby for ‘groucho’ as the prefix for 10-27 – though it's hella unlikely to be ratified either.
Finally, a bit of SI prefix humor stolen from the BBC (nerd page):
Finally, a bit of SI prefix humor stolen from the BBC (nerd page):
10 cards = one decacards
One trillion pins = one terrapin
1,000 whales = one killer whale
One trillion microphones = one megaphone
1021 piccolos = one gigolo
2,000 mockingbirds = two kilomockingbirds
