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  1. Embed this notice
    John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Saturday, 22-Jun-2024 08:48:09 JST John Carlos Baez John Carlos Baez

    Why do we call electrons 'negative' and protons 'positive'? It's an arbitrary convention but it's annoying: it means that when electrons flow through wires, the current is defined to flow in the OTHER DIRECTION.

    If you ask people why electrons got called 'negative', you get a bunch of crap answers:

    "Electrons are referred to as negative because of their behavior in an electric field. In an electric field, an electron will move from the negative pole to the positive pole, giving it a negative charge by convention."

    Yes, but why THAT convention?

    "If we re-designate all positive electric charges as negative and vice versa, while keeping their absolute value, the resulting physics would be the same. So exact choice is merely a matter of convention."

    Yeah, it's a convention - but why THAT convention?

    "In quantum theory of elementary particles (in a sense of irreducible representation of Poincare group with mass m and spin (helicity) s) if some operator Q of internal symmetry commutes (like electric charge charge) with Hamiltonian H...."

    Irrelevant crap which never leads up to an answer.

    The answer is that Benjamin Franklin chose this convention and nobody knows why.

    In Franklin's day there was a 'two-fluid' theory of electricity saying electricity comes in two kinds. Around 1750 he developed a 'one-fluid' theory after showing that a rubbed glass receives an equal but opposite charge as the cloth used to rub the glass. He decided that electrical fluid was going into the glass. So he said the charge of the glass was 'positive' and the cloth was 'negative'.

    Unfortunately it turns out that that electrons are going into the cloth.

    The whole history is interesting:

    https://en.wikipedia.org/wiki/Electric_charge#History

    In conversation about a year ago from mathstodon.xyz permalink

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    1. https://media.mathstodon.xyz/media_attachments/files/112/654/420/323/434/029/original/7696ba4c8b5ae3a9.png
    • clacke likes this.
    • Embed this notice
      Mans R (mansr@society.oftrolls.com)'s status on Saturday, 22-Jun-2024 08:48:15 JST Mans R Mans R
      in reply to
      • j_bertolotti
      • groff
      • Arcaik

      @Arcaik @geoffl @j_bertolotti @johncarlosbaez It probably varies between languages, but at least in Swedish, decimetres are quite often used in casual speech when giving an approximate size of something, e.g. "I guess it was a few decimetres, maybe half a metre."

      In conversation about a year ago permalink
      clacke likes this.
    • Embed this notice
      Arcaik (arcaik@hachyderm.io)'s status on Saturday, 22-Jun-2024 08:48:16 JST Arcaik Arcaik
      in reply to
      • Mans R
      • j_bertolotti
      • groff

      @geoffl @j_bertolotti @mansr @johncarlosbaez Wait what? Nobody I know uses decimeters in real life, and we use grams for small quantities (e.g. when cooking). Plus, decimeters and kilograms *are* standard units.

      In conversation about a year ago permalink
    • Embed this notice
      groff (geoffl@mastodon.me.uk)'s status on Saturday, 22-Jun-2024 08:48:17 JST groff groff
      in reply to
      • Mans R
      • j_bertolotti

      @j_bertolotti @mansr @johncarlosbaez
      The French also use a crazy system. The base unit of distance is metres (Earth's circumference/40,000 to make it roughly equivalent to a yard) but don't lead directly to volume in litres, you have to remember to do your measurements in decimetres. The unit of weight isn't the gramme but the thousand-gramme (kilogramme). Instead of a cube of sides 1 metre containing one litre and that volume of water weighing 1 gramme, it weighs 1 thousand thousand-grammes. ;)

      In conversation about a year ago permalink
    • Embed this notice
      j_bertolotti (j_bertolotti@mathstodon.xyz)'s status on Saturday, 22-Jun-2024 08:48:18 JST j_bertolotti j_bertolotti
      in reply to
      • Mans R

      @mansr
      The ones stubbornly using weird units are the people in the US, not the French 😉
      @johncarlosbaez

      In conversation about a year ago permalink
    • Embed this notice
      Mans R (mansr@society.oftrolls.com)'s status on Saturday, 22-Jun-2024 08:48:19 JST Mans R Mans R
      in reply to

      @johncarlosbaez It could have been worse. Imagine if a Frenchman, say, had been working on the same things at the same time, only with the opposite convention, and French physicists then stubbornly stuck with it to this day while everybody else followed Franklin.

      In conversation about a year ago permalink
    • Embed this notice
      clacke (clacke@libranet.de)'s status on Saturday, 22-Jun-2024 08:48:24 JST clacke clacke
      in reply to
      • Mans R
      • j_bertolotti
      • groff
      • Arcaik

      @johncarlosbaez The decimeter is pretty neat, because it's about the distance between the tips of your lightly outstretched index finger and thumb.

      @mansr @j_bertolotti @geoffl @Arcaik

      In conversation about a year ago permalink
    • Embed this notice
      John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Saturday, 22-Jun-2024 08:48:25 JST John Carlos Baez John Carlos Baez
      in reply to
      • Mans R
      • j_bertolotti
      • groff
      • Arcaik

      @mansr - yet another example of how civilized the Swedes are.

      @Arcaik @geoffl @j_bertolotti

      In conversation about a year ago permalink
      clacke likes this.
    • Embed this notice
      Mans R (mansr@society.oftrolls.com)'s status on Sunday, 23-Jun-2024 02:46:23 JST Mans R Mans R
      in reply to
      • clacke
      • j_bertolotti
      • groff
      • Arcaik

      @geoffl @clacke @johncarlosbaez @j_bertolotti @Arcaik I'm going to start confusing people by using unusual units like decigram and hectometre. Or deka- anything (except decadence).

      In conversation about a year ago permalink
      clacke likes this.
    • Embed this notice
      groff (geoffl@mastodon.me.uk)'s status on Sunday, 23-Jun-2024 02:46:25 JST groff groff
      in reply to
      • clacke
      • Mans R
      • j_bertolotti
      • Arcaik

      @clacke

      The decimeter is almost exactly the same measurement as a "hand" (equal to 4 inches) which is the unit most often used to measure the height of a horse.

      @mansr @johncarlosbaez @j_bertolotti @Arcaik

      In conversation about a year ago permalink
    • Embed this notice
      Mans R (mansr@society.oftrolls.com)'s status on Sunday, 23-Jun-2024 02:46:33 JST Mans R Mans R
      in reply to
      • j_bertolotti
      • groff
      • Arcaik

      @geoffl @Arcaik @j_bertolotti @johncarlosbaez I think it's fine to use a power of 10 (or whatever radix your number system has) scaling factor for convenience, at least in casual situations.

      In conversation about a year ago permalink
      clacke likes this.
    • Embed this notice
      groff (geoffl@mastodon.me.uk)'s status on Sunday, 23-Jun-2024 02:46:34 JST groff groff
      in reply to
      • Mans R
      • j_bertolotti
      • Arcaik

      @Arcaik @j_bertolotti @mansr @johncarlosbaez
      That's kind of the point; the current variant of metric system, MKS, and the units people use, like litres, are not coherent (other metric variants include CMS and MTS). And while gramme is a unit of weight it is not a "base unit" so can't be used in other calculations, such as force = mass * acceleration.

      "A coherent derived unit, for a chosen set of base units, is a product of powers of base units, with the proportionality factor being one."

      In conversation about a year ago permalink

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