On Friday, scientists will have an appointment with a "heavy" finish when representatives of more than 60 countries meet in Versailles, France, to agree on a new definition of a kilogram.
Since the 19th century, scientists have based their definition of the basic unit of mass on a physical body, a solid cylinder made of platinum and iridium, placed in a closed vault at the International Bureau of Weights and Measures (BIPM) in Sevres, France.
For scientists, this standard kilogram weight scale, which is 39 mm in diameter and also 39 mm in height, may lose weight after losing atoms over time or may be shattered by accident or for any reason.
By Friday's vote, scientists will redefine the kilogram of the 21st century by linking it to a fundamental property of the universe, a small and precise value of quantum physics known as arithmetic or Planck constant, which describes the smallest possible unit of energy.
With Albert Einstein's discovery of energy and mass bonding, precisely how much energy in this unit can allow scientists to define the mass in terms of Planck's constant - a value that must withstand space and time - rather than relying on an unstable metal cylinder.
The redefinition is the result of a decades-long global endeavor to measure Planck's constant with sufficient accuracy to withstand the value of scientific scrutiny.
Although the newly defined kilogram will not affect the balance we use to measure our weight or the things we buy, it will have practical applications in research and industries that rely on accurate measurement.
Friday's vote is mostly a formality, where there is international scientific consensus, but for John Pratt, one of the leaders of this global effort, the event revolves around more than mere symbolism, bigger business and even post-physics.
Pratt says the redefinition is a fine thing in this age of conflict and violence, when there seems to be too little to agree on.
"It is a recognition of the firm truth - that nature has laws that are subordinated to all of them, another step towards a noble dream, in our understanding of the laws of nature, scientists can help build a better world."
For decades, scientists in the field of metrology have been trying to shift the solid cylindrical mass made of platinum and iridium, known as the "grand grandpa," to retirement.
The "Big Thousand" is a solid cylindrical block defined and known as the kilogram 126 years ago and is kept in a high-security vault outside the French capital Paris. Other copies are in other international cities, but all rely on the international kilogram.
The kilogram is the only standard international unit of measurement that is defined materially, other than the meter, the second, the amps, and the other units of measurement that are determined on the basis of computational constants that constitute physical facts rather than physical objects.
