Welcome to ronnagrams and quettameters: the General Conference on Weights and Measures (CGPM) adopted on Friday, November 18 new prefixes to express tiny or immense orders of magnitude, which have become ever more common in modern science. This is the first time in more than three decades that the International System (SI), established in 1960 and more commonly known as the metric system, has adopted new prefixes.
If everyone knows the kilo, which expresses for example a number of meters or grams in thousand, with three zeros behind the unit, only scientists use the zetta or the yotta, which express a quantity with respectively 21 and 24 zeros behind. They were introduced in 1991, when the chemical community needed to express quantities of molecules of this order of magnitude.
The infinitely small
But even yotta can’t satisfy the need to express ever-increasing orders of magnitude because of the explosion of digital technologies, says Richard Brown, head of metrology, the science of measurements, at Britain’s National Physical Laboratory.$
“We are very close to the limit for expressing data in yottabytes, which is the highest prefix available”, notes this scientist, who is at the initiative of this change. This change does not only concern the infinitely large: it also applies to the infinitely small, when we study “quantum science, particle physics, where you measure very, very small things”adds Richard Brown.
Baptism at Versailles
The new prefixes ronna (R) and quetta (Q) express quantities with respectively 27 and 30 zeros behind the unit. Symmetrically, the ronto (r) and the quecto (q) express quantities whose unit is respectively the 27th and the 30th behind the comma.
With these prefixes, “the Earth weighs about six ronnagrammes”, a six followed by 27 zeros, notes Dr. Brown. Conversely, something weighing six rontograms would be equivalent to a decimal number with the six placed 27th to the right of the decimal point. These changes were adopted Friday at the Palace of Versailles (west of Paris) by scientists gathered at the CGPM, which is held every four years.
Brontobytes et hellabytes
The British scientist wanted to create new prefixes by noting the appearance of whimsical denominations used for data storage, such as “brontobytes” or even “hellabytes”.
But the International System requirement to use single-letter prefixes had to be satisfied. “The only letters not to be used for other units or symbols are R and Q”, he says. A convention also dictates that prefixes of large orders of magnitude end with the letter « a »and those of very small quantities by a « o ». Ronna and ronto, quetta and quecto, should meet the needs of measuring very large numbers for at least the next 20 to 25 years, says the metrology specialist.