Original URL: http://www.theregister.co.uk/2012/11/20/live_chat_kilogram/

Register boffinry confab: Mass debate on the Perfect Kilogram

Readers have their say (but don't weigh in)

By Gavin Clarke

Posted in Science, 20th November 2012 16:00 GMT

Live Chat For more than a century the world has relied upon a lump of metal protected under high security in a location outside Paris to accurately measure the kilogram.

Problem is, the metal lump's mass might not actually amount to one kilogram - meaning the kilogram as you know it is wrong.

Now, more than 30 years since they began theorising about a new, more reliable way to measure the kilogram - boffins are discussing the rollout of a new standard based on current and magnetism and the principles of quantum mechanics.

It’ll be the first time you can’t touch or feel the kilogram; the kilogram will be the last of the seven fundamental units to make the leap from being based on a physical object to being based on a stable property of the universe (for example, the metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second).

But there’s a problem: although the boffins have agreed to use Planck's constant - an atomic-scale constant - to calculate the kilo's mass, nobody knows the constant's precise value. Two key instruments, called watt balances, used by scientists to calculate the quantum constant don't agree and can't as yet produce sufficiently reliable results.

The gap is tiny, yet huge: the equivalent of specks of dust or a parts of a grain of sugar.

Those working to crack the problem include the National Institute of Standards and Technology (NIST) and Canada's Institute for National Measurement Standards.

The Reg recently spoke to Ian Robinson, a fellow with the UK's National Physical Laboratory, as part of our article here on the quantum kilogram. You can hear more about his work and ask Ian any questions on the quantum kilogram during our half-hour Live Chat on 23 November at 14.00 GMT, 9.00 Eastern and 6.00 Pacific.

We’ll chat about:

Sign up for our quantum kilogram revolution Live Chat in the window below.