Inside the Quest to Redefine the Kilogram

We need a new kind of kilogram, here's how we're making it.

Jennifer Lauren Lee/NIST PML

When we measure the world, we measure it using base units like 'foot,' 'mile,' 'meter,' and 'second.' But who decides how big those units of measurement are? In the United States, those units are maintained by an agency called the National Institute of Standards and Technology (NIST), and it's their job to make sure all the yardsticks—both literal and metaphorical—are the same length.

Until recently, that was done by defining those units of measurement using physical objects. The kilogram is now the only unit of measurement still defined by an object (a chunk of metal sitting in a building in France). But a few years ago, scientists discovered the mass of the chunk of metal was changing slightly, which isn't good. Technically, this means that one kilogram measured today might be different than one kilogram measured 20 years ago.

We need a different constant, and YouTuber Veritasium explains this redefinition process in his latest video.

Scientists have been trying to define the kilogram in terms of some unchanging physical constant, but that turns out to be very difficult. One of the most successful approaches was done by a team of scientists at NIST, where they built an extremely sensitive scale designed to tie the kilogram to a number called Planck's constant.

The kilogram still hasn't been completely redefined just yet, even though the NIST experiment has been completed. They're still waiting on results from other experiments to make sure they agree. If they do, the kilogram will be officially redefined sometime next year.

And then we can retire the old kilogram standard and put it where it belongs: in a museum.

Source: Veritasium

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