- The kilogram is the only SI unit still based on a physical object. Although experiments that could define it in terms of fundamental constants were described in the 1970s, only in the past year have teams using two completely different methods achieved results that are both precise enough, and in sufficient agreement, to topple the physical definition.
That's cool, although it makes me ponder what would happen in the event of a societal collapse. Imagine the technology necessary to derive these definitions, compared to just having a platinum brick. I'm not saying that means we shouldn't do this, I just think it's an interesting thought how advanced and impenetrable science has become. It's literally impossible to be up to date on every subject in any meaningful way. It boggles the mind.
I'm kinda perplexed why they're trying to do it this way when I'd expect that it'd be easier to measure fundamental constants using optics and detectors, to constrain the speed of light and Planck's constant. Cosmology and satellite network data seem like they could yield better resolution than using a mechanical balance to match two weights, and then counting the number of atoms to convert to Avogadro's number. Edit: Pretty sure I'm wrong though. Also: Given sufficient technology (and $'s, and sometimes foolishness), there is technically no limit to the number of unique experiments that could yield relative values of "one" kilogram, and they should all converge, or you're science'ing wrong. Maybe our eventual robot overlords will design CPU-chip-scale experiments that they can run programs and actions with (iteratively and/or divergently) to further refine fundamental constants. Juuuust the type of bullshit you'd see on /r/fyoochur, so much fun to make that up, but I guess it's possible. Can you imagine dropping that reference kg though? All, Please immediately report to the hallway outside of YWT381 with any spare scanning/tunneling electron microscopes, and comb the floor for Pt and Ir atoms while hoisted on the new pulley system currently undergoing installment. Thank you! - Dr. Phil""FWD: ALL GRAD STUDENTS>