Gro-Tsen Profile picture
Dec 3 14 tweets 3 min read
I'm being asked to summarize my position on the decision taken by the CGPM, a few weeks ago, to get rid of leap seconds. Here are my main takes on this: 🧵⤵️ •1/14
‣ Maybe it does make sense to stop synchronizing legal time with the sun, or to find a system other than leap seconds (e.g., “smoothing” as Google proposed) to do it, BUT this should require a society-wide debate, not just a vote among metrologists. •2/14
(OTOH, it makes sense to decide to technically abolish NEGATIVE leap seconds, by waiting, if one should happen, until it cancels with the inevitable next positive leap second. First I thought the CGPM wanted to do just that — but it seems they plan to scrap it all.) •3/14
‣ The argument that leap secs cause computer problems is nuts. It's trivial to implement UTC with leap seconds in a perfectly unambiguous way, the only problem is one of standardization, and it's insane that we should prefer to disagree with the sun than fix computers. •4/14
‣ For the CGPM to claim that they're just relaxing the bound on |UT1−UTC| and pretend UTC is not being disconnected from the sun, but they'll come up with a way to resync later, is hypocritical bullshit: the difficulty of resyncing will only get worse → won't happen. •5/14
‣ What will happen (if mankind survives this long…) is that as UTC drifts apart from the sun, a correction will be incorporated in the local time zone offset: so UTC will remain stuck at TAI−37s but countries will start having minute level differences in time zones. •6/14
(So we'll have even more time zone chaos, with offsets like UTC+00:59 decided at the national level. This is not necessarily worse than leap seconds, as there is already the sw infrastructure to handle this, but it's a capitulation of the international agencies' mandate.) •7/14
‣ The claim that GNSS's are coming up with their own leap-second-less version of UTC makes NO SENSE AT ALL. They're just using TAI−T₀ for some epoch T₀ which happens to be a fairly round moment (midnight) in UTC, but really, THEY'RE JUST USING TAI. •8/14
(So “GPS time” and “Galileo time” are simply TAI counted from a certain epoch T₀, and they are no more a threat to UTC than TAI, which has existed for quite some time, ever was. This whole part of the argument makes NO SENSE.) •9/14
‣ Google's proposed method of smoothing leap seconds, admittedly, represents a more significant departure from UTC. I think the correct answer here would be to have standardized it, under a different name, for computer purposes. But I agree it's a less trivial problem. •10/14
‣ Legally speaking, I believe it is ultra vires for the CGPM to take the decision to abolish leap seconds. It is simply not under the remit they got after the abolishing of the Bureau International de l'Heure (which was the uncontested authority here). •11/14
The CGPM has authority over the units, not over timekeeping. The ITU has even less authority here. Authority over timekeeping is unclear (who controls the Gregorian calendar?) but at the very least this decision needs approval from the IAU (overseeing the IERS). •12/14
‣ At the very least, there's a serious transparency issue, because when you read the resolution that the CGPM ACTUALLY passed, it does NOT say anywhere they intend to scrap leap seconds. Deciding to abolish leap seconds without even SAYING it is totally unacceptable. •13/14
More details about my position on this blog post of mine (in French, mostly overlapping what's been said above, but not completely):… •14/14

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More from @gro_tsen

Dec 5
J'ai produit différents graphiques que je trouve intéressants pour illustrer la distribution de la consommation et de la production électrique en France: 🧵⤵️ •1/11
Tous sont produits selon le même schéma général: en ordonnée je représente une certaine puissance P consommée ou produite (exprimée en GW), et en ordonnée la proportion du temps que la quantité considérée est ≥P. •2/11
Ce sont donc, si on veut, des courbes de la distribution de probabilité de la puissance considérée dans le temps (sauf que la puissance est mise en ordonnée, parce que c'est plus lisible comme ça). Il paraît qu'on appelle ça une «monotone de puissance». •3/11
Read 11 tweets
Dec 4
This clip from a BBC documentary (whose name I don't know) is one of the most fascinating I've seen in the “electricity porn” department. It shows how the British national power grid deals with millions of people turning their kettle on simultaneously …
… at the end of a TV show, a phenomenon known as a “TV pickup” which apparently is mostly pronounced in the UK because of Britons' fondness for tea (and drinking it after watching TV, I guess).
Apparently these TV pickups can reach magnitudes of about 3GW in the UK. And for once, a unit like “GW/h” makes sense (the guy in the clip mentions “100MW/min” of variation in power, which you can express as “6GW/h”).
Read 4 tweets
Dec 3
Précisions sur les modalités des coupures électriques probablement à venir en France: 🧵🔽
«Différentes raisons» doing some heavy lifting here: 😐
L'affirmation sur les lignes fixes me semble suspecte: pour une écrasante majorité, la «ligne fixe» n'est plus une vraie ligne RTC sur fil de cuivre mais reliée à une «box» Internet (fibre ou ADSL) qui ne marchera pas sans courant. Donc, pas de téléphone.
Read 4 tweets
Dec 3
La seule technique de stockage de l'électricité d'échelle utilisable et vraiment utilisée actuellement, c'est sous forme d'hydroélectricité (centrales «STEP» = «pompage-turbinage»). Mais double limitation: ①sur la puissance et ②sur l'énergie. Les deux importent! •1/9
C'est-à-dire que ①on ne peut pas libérer (ni stocker) de l'eau trop vite (les turbines ont leurs limites), donc ceci limite la puissance disponible ainsi, et ②le réservoir amont a aussi ses limites. Toujours la différence entre flux et stock. •2/9
Qu'en est-il en France? Je ne trouve pas de chiffres très à jour sur la capacité des STEP français en puissance et en énergie stockable, mais l'article… est très intéressant, … •3/9
Read 9 tweets
Dec 3
Mon collègue a bien raison d'insister🔽 sur ce point: avoir un problème de manque d'ÉNERGIE ou un problème de manque de PUISSANCE (de pointe), ce n'est pas pareil.

Le manque de compréhension de ce concept scientifique ultra-basique est vraiment problématique.

J'ai entendu plusieurs personnes me faire des remarques équivalentes à ça: «pourquoi ne fait-on pas ces coupures d'électricité la nuit?» ou «on pourrait commencer par économiser le courant la nuit» ou (ici) évoquant le gâchis de l'éclairage ou de la pub nocturnes. •2/7
Alors certes, ces personnes comprennent vite l'erreur quand on leur signale: c'est au moment des pointes qu'on manque d'électricité, pas la nuit.

Mais ça traduit quand même un manque de compréhension de la différence entre ÉNERGIE et PUISSANCE, entre un STOCK et un FLUX.

Read 7 tweets
Dec 2
I feel a bit stupid for not knowing this: if (x_n) is a real sequence such that x_n → 0 (mod A) for every A>0, does it follow that x_n → 0?
How to get a sequence which tends to 0 mod 1 and mod √2 but which doesn't tend to 0 (see also the next tweet after the quoted one):
Read 6 tweets

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