Ever wonder how scientists determine the exact weight of a kilogram? Or specify what exactly is an ampere of electricity? Or a mole of a chemical substance? Or agree on the kelvin, a basic measurement of temperature?
You may think these things are somehow constant and unchanging, the way nature intended. Not so. Scientists argued for decades before settling on definitions. But now these basic measurement standards — vital for science, technology and commerce — are set for a major overhaul.
Why? Because scientists now agree on better and more modern ways to measure these weights and forces. In recent weeks, delegates from governments around the globe ratified the changes, propelling the pops of champagne corks worldwide. “This is big,” metrologist Zeina Kubarych told nature.com. “It’s the best thrill ride you can get in metrology” — the study of scientific measurement. (See what you’ve learned in only three paragraphs?)
In this momentous decision, two forces have collided that are often in short supply in science and government: exemplary precision and general agreement.
Take the kilogram. The king of kilograms, the one against which all others are measured, is a palm-sized ingot of platinum known as Le Grand K. This celebrated hunk of metal is nestled in a temperature-and-humidity-controlled environment, locked away in an underground Paris vault that requires three keys to open. For generations, other scientists trekked to a Paris vault to compare the weight of their own kilograms to Le Grand K and adjust accordingly.
So why change that? Because scientists say Le Grand K has somehow become slightly — very slightly — lighter than its six official copies. Physicists aren’t sure why.
Under the new system, the kilogram’s measure will instead be based on a fundamental factor in physics known as Planck’s constant. The advantage: Planck’s constant is constant. It’s based on the behavior of photons and won’t change — ever.
The kelvin, ampere and mole also will be refined with the same goal: Define these standards not by material objects but by abstract constants in nature.
So, do these changes mark the end of the measuring overhaul? Not quite. A second of time is also due for an update. The most accurate measurements of time involve “optical clocks” that are more precise than earlier means.
Don’t worry if you can’t really wrap your mind around that. Even though scientists extol this progress, you won’t notice in your daily life. A kilogram may be measured differently, but that won’t help you get a better deal at the supermarket or receive better news when you step on the scale.
We’ve often marveled at leaps in science. In 2012, for instance, physicists finally pinned down the so-called “God particle” — aka the Higgs boson — an invisible field that fills the universe and gives elementary particles their size and mass.
That left physicists breathless — and the rest of us befuddled. Every major change in detection, in measurement, in any major field brings new possibilities for discovery, for progress. Humans have only scratched the surface. The universe has many more tricks up its sleeve. The wonder of that is, and always will be, immeasurable.
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