[time-nuts] Re: NPR: Researchers Are One Step Closer To Redefining The Second

[Attila Kinali]

On Tue, 30 Mar 2021 08:15:30 +0000
"Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:

> In one of his lectures Feynmann mentions that the energy levels of
> hydrogen have been calculated to 15 or 16 digits "from first
> principles".
> 
> As far as I can figure out, that must have happened in the 1970'ies,
> which means it was probably done on one of Seymour Cray's designs.
> 
> Hydrogen is obviously "the easy one", but even if the calculation
> scales to the power of four on the number of particles in the atom,
> we should still be well inside current super-computing capacities.
> 
> Do you know if anybody has considered that as way to nail the frequencies ?

The Hydrogen atom is much easier to calculate than any of the
Hydrogen-like atoms that we use for atomic clocks these days.
As far as I am aware of, the complexity of doing a full from
first principles calculation of even Ca+ is beyond what current
computers can do. So people are still using approximations to
calculate the energy levels for these. Sorry, I can't point you
at papers at the moment. I know I have them somewhere on my
harddrive, but I cannot figure out where I put them.


			Attila Kinali
-- 
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always 
wonder about. And that's why we do research.
		-- Kobayashi Makoto