National Physical Laboratory

Why do you not use a stabilised laser to define the metre? (FAQ - Quantum)

If we did, we would have to change the definition of the metre each time we were able to make a more precise laser. The present definition allows us to maintain a metre in terms of a number of laser transitions of specified accuracy and these can be amended as better lasers are found without the need to change the definition.

Last Updated: 25 Mar 2010
Created: 9 Aug 2007