On June 27th, 2017 NIST released an important article about the progress towards redefining the Kilogram with a fundamental constant of nature rather than a physical artifact.

The Kilogram is currently the only SI unit that is still traced back to a physical artifact.  The salt shaker sized hunk of iridium and platinum currently lives outside Paris in a secured vault, exactly where it has lived since 1889.  At the time of its creation, the standard had several copies of it made, which all weighed exactly the same.  Nested inside three bell jars, the kilogram standard has been pulled out only three times, all for comparison against its copies.  Over the course of 100 years, the kilogram standard appears to be losing weight.  Yes, this means 100 years ago if you bought a kilo of meat from the butcher, you got more than you would today.  However, along with most of the world, you would never know the difference because the loss is relatively small (about 0.000050 grams).  This is assuming that the standard lost mass and its copies didn’t (it could just as well be that the copies are gaining particulates).  We know that something has changed, the main issue is that we cannot precisely identify what it is.  This is a major issue in the scientific community; and this is where the Planck Constant and the Kibble balance come into play.

The scientific community has pushed forward in their efforts to standardize mass by using a Kibble balance to determine the Planck Constant.  This was done by measuring masses with nominal values from 500 grams to 2 kilograms on NIST’s Kibble balance, NIST-4.  The Kibble balance (formerly known as a watt balance) measures the mass of an object by utilizing coils of wire, rare earth magnets, and electromagnets to relate mass to amps, another SI unit.  This principle is demonstrated in this video by NIST:

Operating Principals of the NIST-4 Watt Balance

Through over 10,000 tests the Planck Constant was determined to be  6.62669934(89)x10-34  Joules.  The Planck Constant is an important constant when dealing with quantum physics, and a is probably best explained in another video from NIST:

Measuring Planck’s Constant

So what does this mean to you?  For most of the world this means nothing.  For most metrologists, quality personnel and technicians this is a forecast of changes in the industry and something to keep an eye on as the kilogram is due to be redefined in 2019.  But for the few metrologists that work in world class labs this will change the definition of mass and quantum physics! Not only is this big news for the SI Units, some might even say its massive!

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