Exactly One Kilogram Of Silicon

Ed Pegg Jr writes "You may know of the importance of 299792458 for length, and 9192631770 for time. However, the official standard for weight is still a block of platinum/iridium made a hundred years ago. A group of scientists from the Avogadro Project are hoping to change that, though, by producing a perfect sphere of ultrapure silicon."

Comments

why kilogram?

[Anonymous Coward]

the SI unit for length is the metre - not the kilometre

why is the unit for mass the kilogram when it should more logically be the gram?

using the gram might be easier to accurately measure too.

that won't help much

[u19925]

the problem of mass standard is not that it was made 100 years ago. the problem is that there is no way to describe it so that it can be reproduced independently. as one of the famous scientist said, "we can communicate our definition of length and time to aliens 1000 light years away (if they are listening us), but we can't tell them what we mean by 1 kilo".

Secondly, it doesn't matter either what exactly is 1 kilogram. what matters is some reference atomic mass and then pick up Avogadro number (based on existing 1 kilo mass) and then get rid of the existing standard. this would allow independent reproduction (e.g. 1 kg is equivalent of 6.02...... x 10^23 atoms of Oxygen 16 in certain energy state. this scheme too has problem. there is no practical way of verifying that you have met the standard definition. so, two scientists can argue that each is possesing exact 1 kg and this cannot be arbitrated.