When we think about our Universe at a fundamental level, we think about all the particles in it and all the forces and interactions that occur between them. If you can describe those forces, ...

Is a meter a meter and a second a second? Yes, but they will be defined differently from May 20th on. This marks the beginning of a new era for science. New rules have been in force since May 20th: ...

A new definition of the kilogram is required, an international team of scientists contends. The current one is imprecise, they say, because it is not linked to an unvarying property of nature. The ...