A massive change: Nations will vote to redefine the kilogram

Though the new formula will not affect your bathroom scale, it will have practical applications in research and industries that depend on meticulous measurement.

Friday's vote is mostly a formality; everyone involved says the resolution will pass. But to Jon Pratt, one of the leaders of this global effort, the event is more than symbolism, bigger than business and beyond even physics.

In this era of violence and vitriol, Pratt said, the redefinition represents something sublime.

It is an acknowledgment of an immutable truth. And it's a step towards a lofty dream – that, understanding nature's laws, can help build a better world.

The scientist grinned, sheepish. "It's an emotional moment," he said. "I'm just really proud of our species."

Leaving behind 'The Big K'

At the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., Where Pratt works, measurement is often described as the "invisible infrastructure" of the modern world. Everything about a weather, cooking a meal, building a rocket, signing a contract, waging a war.

The International System of Units, or SI, is what allows us to communicate measurements around the globe. This system, which has its origins in the headline of the Enlightenment, was meant to brew the language of the English language. was based on the amount of fish that could be used in a ship's hold, and sold them in France, where weight was tied to the heft of a wheat grain.

The motto of one of the system's creators, "for all times and for all people," is among Pratt's favorite phrases.

"It's such an optimistic view," Pratt said. "He just imagined this business of science. . . was going to be a great force for freedom and a great force for moving the world forward. "

In 1875, the signing of the Treaty of the Meter made the official system. Two platinum and iridium prototypes – a meter-length bar and a kilogram-mass cylinder – were forged to serve as standard units for the whole world. The BIPM distributed copies of each prototype to the signatory nations; the century-old U.S. national kilogram still sits in a glass case in a locked room down the hall from Pratt's lab.

As science and commerce advanced, the SI has been revised to allow for greater accuracy and greater accuracy. The meter prototype was published in a 299,792,458th of a second light. The length of a radioactive decay of the cesium element. The candela, used to measure luminous intensity, was related to the brightness of a particular wavelength of green light.

These values – the speed of light, the behavior of atoms, the nature of electromagnetism – They are fundamental features of nature that do not change whether the observer is on Earth or March, whether it is the 1875 or 2018 year.

But the kilogram prototype, known as "The Big K," was made by humans and is subject to all our limitations. It is inaccessible – the safe container can be opened up by three custodians carrying three separate keys, an event that has less than a dozen times in the object's 139-year history. And it is inconsistent – when the Great K was examined in the 1980s, it weighed several micrograms less than it was supposed to. This meant that anyone who made products based on the standards had to reissue their weights. Manufacturers were furious. Lawmakers were called. Metrologists, people who have studied measurements, were accused of incompetence.

So, in a meeting at the BIPM, the metrology community resolved to redefine the kilogram. But the value of Planck's constant was still uncertain, and the scientists could not redefine the kilogram without it.

'Chasing perfection'

It has been more than 100 years since the quantum physicist Max Planck discovered that energy is expressed in discrete units – that is, it's "quantized." But his constant – a figure that describes the size of these energy packets down.

There are only two experimental setups that allow scientists to calculate this number, and both require rare and expensive tools.

One technique involves counting all the atoms in a perfectly round silicon sphere.

The second option uses an exquisitely accurate weighing machine. This is no ordinary scale; it took a pair of British scientists Several decades to invent and refine the instrument, and there are only two in the world powerful enough to meet the BIPM's high standards for precision.

One is in Canada. The other sits inside Pratt's lab in the NIST basement.

"It really is a beautiful instrument," Pratt said during a visit to the steel-encased room where the balance is stored. "I like it just here and stare at it."

The enormous metal machine, which is a professional ball player and a disc player with a tungsten carbide fulcrum. While experiments are run, the entire balance is placed inside a vacuum chamber. Anyone who operates the instrument must wear a hairnet, a lab coat and bootees. Pratt and his colleagues measure each factor that could possibly affect their results, from the temperature of the room to the strength of Earth's gravity.

"In a physics sense, we're really chasing perfection here," Pratt said. "We really need things to behave just as their idealized versions."

Planck's constant to an uncertainty of just 20 parts per trillion – or within 0.000002 percent of what is thought to be the correct number.

On June 30, 2017, the day before the deadline to submit a report to the BIPM 's weights and measures committee, Pratt and his team finally published this standard.

Planck's constant is equal to 6.626069934 x 10-34 kg ∙ m2 / s, they said. And their uncertainty was just 13 parts per billion.

That number may be barely intelligible to the casual observer. But to Pratt, measuring it felt like a cosmic curtain had been lifted, revealing the innermost workings of the universe.

Here in the echoing basement of an obscure federal agency, he and his crew of hair-netted nerds had gotten as far as perfection. They had transcended their human biases and earthly flaws to make an observation so precise it will work for all times and for all people "- or at least, until the day when scientists are able to pull back another fold of the curtain, eliminating one more degree of uncertainty about this fundamental fact of physics.

Pratt and his colleagues are not the only scientists who have had the best part of the past decade in pursuit of Planck's constant. Researchers using the watt balance in Canada have achieved a measurement with even less uncertainty than NIST's. Teams in Germany and Japan produced similarly accurate measurements using the technical silicon-sphere.

But not all the measurements agreed. In the metrology community, where careers can be staked on quibble over decimal points, this discrepancy could have been catastrophic. "There was a lot of hemming and hawing, and there were some questions about whether [the vote] would even happen, "Pratt said.

But that debate, too, was an important part of the process. Only through repeated observations, refutations and confirmations does an idea become a globally accepted fact. It's what makes science bigger than scientists; it's how we establish that something is true.

Still, Pratt did not wait for the debate to end to get NIST "s value for Planck's constant tattooed on his forearm – the 10-digit number and an illustration of a statue clutching a meter bar and a kilogram cylinder. And above it, in French, were the words that have guided metrologists since the beginning: At all times, to all peoples.

For all times, for all people.