How We're Redefining the kg

In 2018 the kg will be defined by Planck's constant, not a hunk of metal.
Special thanks to the staff at NIST who made this possible: Darine Haddad, Jon Pratt, Stephan Schlamminger, and Ben Stein.

Additional footage and animations by Sean Kelley, Jennifer Lauren Lee, and Frank Seifert.

I have been obsessed with measurement for a long time and I'm not sure quite how it happened. The world's roundest object played a role in this. I guess I'm just fascinated by how difficult it is to pin down a quantity like a kilogram. A physical object seemed like a good idea until the mass of the international prototype kilogram wasn't as constant as expected. These methods of the Kibble balance and silicon sphere have shown better precision than 20 parts per billion, making them superior to the old method. The agreement between Avogadro approaches

Special thanks to Patreon Supporters:
Tony Fadell, Donal Botkin, Jeff Straathof, Zach Mueller, Ron Neal, Nathan Hansen

Studio filming by Raquel Nuno

[lamafarmer]

It's a good thing they went with the Plank's Constant in the end. I've weighed loads of avocados and none of them were close to a kilogram.

[smartereveryday]

I appreciated the giggle at the end. The guy basically said "solve this simple algebra equation and redefine the two fundamental units of ALL OF PHYSICS".

[Zorgongola]

Hey Veritasium
I was part of the team working with Bryan Kibble on the NPL mkII Kibble Balance (aka Watt Balance, aka Moving Coil experiment) between 1991 and 2000. Firstly I'd like to congratulate you on a great video. It's not easy explaining this elegant but complex method of redefining the kg and you guys did a good job.

One thing to possibly add is the importance of keeping the magnetic field constant. Both weighing and velocity measurements are not quick and are conducted over a long time period. Back then it lasted over an hour, and the field strength is highly susceptible to temperature changes, so keeping the large magnet at a constant temperature is imperative. I worked on the NPL system and we managed to keep the temperature drift down to a millikelvin or two over the duration of measurement, usually overnight.

[yuvneesh]

Watching this on May 20, 2019.
SI units have been officially redefined today, kg is defined by Planck’s constant.

[smartereveryday]

Another thing.. I thought the fact that you've locally mapped g in the room was FASCINATING.

[trun_k]

One Balance to rule them all, one balance to define them.
One balance to standardise them all, and into light forever bind them.

[fizizy]

5:00 Yes, I can definitely see why they call it the "Watt", because that's what everyone says after you explain it to them.

[smortboi]

No one:
Bryan Kibble: “I want to weigh myself with *electricity”*

[conure]

R.I.P. the 1-kg mass in France. You'll be remembered.

[James__]

4 years of my physics degree later and I'm still like "ah yes I know some of those words"

[Kraigon]

This kind of thing is what restores my faith in humanity.

[makc]

The official day has come....
Today kilogram definition is changed

[Hatch]

I will not lie, and tell you that I understood everything that you just said, but enough to understand that an amazing amount of work happens behind the scenes to provide the folks like me that use these standards daily to be able to rely on them being constant. I enjoy your channel.

[hassanallama]

drugs dealers are going back to school because of this

[Toolx]

The kg is dead, long live the kg! All hail the kg!

[LonDiffenderfer]

Although I understand the need to change the method of defining the kilogram (thanks to you), I still have no idea how it is done. Those calculations are still currently beyond my abilities to comprehend. I often have difficulty grasping all of what is said in your videos, but I still appreciate that you produce them for our benefit. Thank you for your time, effort, and desire to educate us. :) Very best to you and yours!

[harshachoudhary]

''Derek changing the world, one kilogram at a time''

[kcwidman]

The kilogram is being redefined in the United States? How ironic.

[observingrogue]

I couldn't stop smiling through this whole thing. My face hurts.

As an amateur Electrical, Mechanical, and Structural Engineer. Just seeing what it takes to maintain the consistency of measurements, is really interesting & exciting to me.

Thank you, this channel, for showing me this. And I thank the scientists doing that.

[JOELwindows]

R.I.P., Elder Kg, 1799-2017 You'll be missed.