Important day for SI nerds, the meeting to formally redefine the kilogram, the kelvin, the ampere and the mole is happening today! Watch a livestream of the vote here: bipm.org/en/the-si/
If the resolution is approved, the SI will be based on fundamental physical constants, instead of physical objects. Timetable and resolutions being decided today is available here: For the first time bipm.org/utils/en/pdf/C… 
Why is #SIredefinition happening? Because physical objects can change over time. By fixing the kilogram in terms of the Planck constant, it can never change. There's a good explainer all about it by @B_resnick here: vox.com/science-and-he…
look at these absolute units #SIredefinition
Jean-Philippe Uzan @CNRS is now speaking about fundamental constants and their role in physics, quotes Maxwell: "If a structure is truly fundamental it is imperishable" #SIredefinition
