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From: Michael S <already5chosen@yahoo.com>
Newsgroups: comp.lang.c
Subject: Re: "A diagram of C23 basic types"
Date: Sat, 19 Apr 2025 23:15:46 +0300
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On Sat, 19 Apr 2025 17:15:42 +0200
David Brown <david.brown@hesbynett.no> wrote:

> On 19/04/2025 09:46, Janis Papanagnou wrote:
> > On 17.04.2025 17:56, David Brown wrote:  
> >> On 16/04/2025 02:53, James Kuyper wrote:  
> >>> On 4/15/25 18:56, Keith Thompson wrote:
> >>> ...  
> >>>> The uncertainty in the timing of January 1, 1970, where 1970 is a
> >>>> year number in the current almost universally accepted Gregorian
> >>>> calendar, is essentially zero.  
> >>>
> >>> Modern Cesium clock are accurate to about 1 ns/day.That's an
> >>> effect large enough that we can measure it, but cannot correct
> >>> for it. We know that the clocks disagree with each other, but the
> >>> closest we can do to correcting for that instability is to
> >>> average over 450 different clock; the average is 10 times more
> >>> stable than the individual clocks.
> >>>
> >>> Note: the precision of cesium clocks has improved log-linearly
> >>> since the 1950s. They're 6 orders of magnitude better in 2008
> >>> than they were in 1950. Who knows how much longer that will
> >>> continue to be true? 
> >>
> >> I don't think cesium is still the current standard for the highest
> >> precision atomic clocks.  
> > 
> > Well, the "Cesium _fountain_" atomic clocks are still amongst
> > the most precise and they are in use in the world wide net of
> > atomic clocks that are interconnected to measure TAI.[*]  And
> > the standard second is _defined_ on Caesium based transitions.
> >   
> 
> Caesium fountain clocks are old school, but still used.  Rubidium is 
> popular because it is cheaper, and very high stability atomic clocks
> use aluminium or strontium.  Caesium is still the basis for the
> current definition of the second, but that will change in the next
> decade or so as accuracy of timekeeping has moved well beyond the
> original caesium standard.
> 
> >> But anyway, the newest breakthrough is thorium
> >> nuclear clocks, which IIRC are 5 orders of magnitude more stable
> >> than cesium clocks.  (And probably 5 orders of magnitude more
> >> expensive...)  
> > 
> > I've not heard of Thorium based clocks. But I've heard of
> > "optical clocks" that are developed to get more precise and
> > more stable versions of atomic clock times.
> >   
> 
> It was only last year that a good measurement of the resonant 
> frequencies of the Thorium 229 nucleus was achieved - the science bit
> is done, now the engineering bit needs to be finished to get a
> practical nuclear clock.
> 
> 


Record my prediction: it's not going to happen.