Sunday, January 06, 2019

When is a kilogram not a kilogram?

A long long time ago the standards for meter's, kilograms, etc was an actual physical object.

Those days are long gone of course. For example, the meter is defined is the length of the path traveled by light in 1/299,792,458 th of a second. Why such an odd number (can fractions be odd?)? Because they retrofitted it to what that the meter is.  Rather than go to France and compare my stick to the one under a glass case I can just measure the speed of light. Oh. That sounds hard!

It matters a bit since the weight of what was the standard kilogram did increase over time, though of course not by much. When did the measurements for stuff STOP being based on physical objects and was all done based on constants of the universe?

The answer surprised me:

On Nov 16, 2018 (yes, you read that light) they decided that by May 20, 2019, the Kilogram will be defined in terms of Plank's constant. I have not been able to find out how they will use Plank, maybe they don't know yet (they do and its known -- see the first comment) .With that, there are no more standards based on physical objects. Read about it here.

Why did it take so long? I honestly don't know and I am tossing that question out to my readers. You can leave serious or funny answers, and best if I can't tell which is which!


  1. "the weight of what was the standard kilogram did increase over time": No, it always weighed one kilogram, by definition. The new standard uses a Kibble balance to measure the Planck constant. Since the units of the Planck constant are kg m^2 s^-1, this gives you the kilogram in terms of the second and meter. See

    1. Thanks! I have pointed to your comment in the post.

  2. Here is Veritasium's video on the topic:

  3. ------
    GASARCH requests "You can leave serious or funny answers, and best if I can't tell which is which!"
    Plainly the time has come — hasn't it? — for the world's quantum researchers to acknowledge publicly the radical technological potentialities, and the concomitantly radical progressive agendas, that are associated to the capacities that political theorists call omnitemporal quantum editing (OQE).

    The everyday reality of OQE is evident in works like "LEGO watt balance" (arXiv:1412.1699, video here), "Quantum metrology triangle experiments: a status review" (arXiv:1204.6500), "Advanced LIGO" (arXiv:1411.4547), and Carlton Caves' essay "Realizing squeezing" (LIGO Magazine, 2013). In these works we discern, for example, that topology-based, quantum dynamical, scalable error-correction technologies are practical present-day realities, not abstract future possibilities.

    Caves' maxim that "physicists are really obliged to give every explanation they can think of" applies — retrocausally of course! — to every quantum information technology roadmap that has ever been seriously proposed, from the QIST roadmaps of 2002-4, to the National Quantum Initiative (NQI) roadmaps of today. An arxiv-style "tar.gz" roadmap archive is downloadable here (some of these roadmaps aren't easy to find); the recently released National Academies Consensus Study Report Quantum Computing: Progress and Prospects (2018) especially is commended.

    When Michael Nielsen asks "In what sense is quantum computing a science?" in his recent essay of the same title (Cognitive Medium, December 2018), he suggests that part of an answer is "Up to now, physics has for the most part not been a design science, but my guess is that’s going to change in the coming decades." Needless to say, as quantum designs for the future evolve, our narrative conception of the quantum past changes concomitantly … humanity's retrocausal cognition thus ensures that "quantum editing", regarded as an undending process of narrative design and construction, inherently is "omnitemporal."

    Suppose, for example, that an infallible oracle were to proclaim that "the Extended Church-Turing Thesis is true" (or alternatively, "Quantum Supremacy is infeasible", or even "Gil Kalai is right"). In what respects would the National Quantum Initiative (NQI) require alteration? Thanks to the fabulous quantum capabilities that already are being demonstrated by projects like LIGO, and like the Quantum SI — and thanks also to retrocausally omnitemporal readings of quantum roadmaps — the happy answer is that the NQI is entirely good-to-go, as it stands, for any-and-all foreseeable quantum eventualities.

    In a nutshell — a nutshell that borrows a concluding phrase from Jordan, Lee, and Preskill (arXiv:1112.4833v2) — the NQI as-it-stands provides reasonable and reliable guidance for the development of practical technologies that "suffice to capture completely the computational power of our universe" … even (or especially!) in the event that our universe is ECT-governed.

  4. I do recall a time when a kilogram was not a kilogram (nearly 10% less in fact):

    In the early 1980s Canada was finishing the transition to the metric system which forced businesses to label and advertise items only in nice round metric quantities. To ease the transition there was a period of one or two years during which they could use their old packaging equipment and sizes of packages but could round up and label them with the nearest nice metric quantity: In particular, 2 lbs could be sold as 1 kg.

  5. If only we had made this switch sooner, pirates wouldn't have been able to stop the U.S. from adopting the metric system!

    1. Great story! Darn those pirate!

      Early on yes, America could have gone metric since the system we use now was not so entrenched.

      I've heard (jokingly?) that the main reason we don't switch to metric is that football gets all screwed up. Its build on yards!