Talk:Physical constant

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Correction for molar mass constant

The molar mass constant is listed as 0.99999999965(30) kg⋅mol−1 but I believe the correct value should be 0.99999999965(30)×10−3 kg⋅mol−1.

I'm new here, so I couldn't figure out how to make the edit myself.

Ericman314 (talk) 22:43, 22 May 2019 (UTC)[reply]

Thank you, Ericman314, for bringing this to my attention. I have corrected it. It is a value hidden in the innards of the template {{Physical constants}}. —Quondum 23:56, 22 May 2019 (UTC)[reply]

Time to move the tables into List of physical constants?

As the tables of listed constants grows, this article has taken on the nature of a list-class article. It seems appropriate to move these tables to List of physical constants (currently a redirect), leaving behind a short section with a hatnote linking to it, and a short table of frequently used physical constants. Opinions? —Quondum 23:01, 21 June 2019 (UTC)[reply]

Done

SI time vs Uzan?

The SI system uses Δν_Cs for its time definition. The second on "Number of fundamental constants" is based on Uzan's long paper, but it does not call out a time or frequency definition. I think we should have some comment about how these two compare. Johnjbarton (talk) 17:26, 10 January 2024 (UTC)[reply]

I'm afraid I'm having difficulty following what you are trying to say. Δν_Cs is an emergent quantity, that is directly determined by all the fundamental constants (in a hypothetical correct model), but is used experimentally as a time reference. Notice that ε₀ does not occur in the list either, but is also considered fundamental (as would be any function of fundamental constants). That there are a few constants in common should not be taken as that there is anything special about their status as fundamental constants. All that we could say is that the SI constants are in principle fully determined by whatever list of constants one chooses as the "base" fundamental constants, but I'm not sure we should even do that. —Quondum 17:44, 10 January 2024 (UTC)[reply]

The article current mentions kilogram based two values, h and c, listed among the ones on Uzan's list and one not listed. I think a legitimate question by readers would be: "Why isn't it listed?" I'm saying that if "ΔνCs is an emergent quantity, that is directly determined by all the fundamental constants", it is not evident to readers. Johnjbarton (talk) 18:15, 10 January 2024 (UTC)[reply]

Okay, so the narrative you might be looking for is that since 2019, the SI is in principle wholly determined by fundamental constants. Three of the SI dimensions (temperature, amount of substance, and luminous intensity) are technically determined by the other four, and can be ignored. Two are directly from the list (c and h), one is directly determined (e, directly determined by the coupling constants of the gauge groups or may even be one of them, or so I guess), and the fourth is an emergent property of a complex system, namely a caesium atom, whose properties are in principle determined by the fundamental constants but which is beyond us to derive. We realize those units by using physical properties that are directly related to these constants, aside from the experimentally determined property of the caesium atom. —Quondum 20:22, 10 January 2024 (UTC)[reply]

LOL, probably not something we want in the article ;-) Johnjbarton (talk) 01:50, 11 January 2024 (UTC)[reply]

Yes, it is quite a mouthful just to put in anticipation of the reaction to the SI happening to have moved in this direction – and kinda off-topic. Maybe we should actually trim down what is said on the SI to, in effect, that the SI has moved towards using fundamental constants in preference to artefacts for defining units? —Quondum 01:57, 11 January 2024 (UTC)[reply]