[FRIAM] sum of atomic spectra == 9000K black body?

[David Eric Smith]

Frank, 

> On May 13, 2020, at 7:31 AM, Frank Wimberly <wimberly3 at gmail.com> wrote:
> 
> When I worked at the PIttsburgh Supercomputing Center, a division of CMU, we had a user who produced a visualization of the first few milliseconds after the big bang.  How can they do that?
> 
> Didn't Penzias and Wilson win the Nobel Prize for showing that the background radiation caused by that event is what radio telescopes hear/see that they can't otherwise account for?

Yes, this is correct.  There is a big time difference, though.  The microwave radiation we see as the CMB is the last image of a matter-radiation equilibrium just before a plasma of free electrons and nuclei (which couples actively and continuously to the radiation field in which it is embedded, and is thus “opaque") condensed into the first neutral atoms, which are mostly transparent to that radiation.  The event is called “recombination”, even though there had been no combination before that, and it is reconstructed to have happened at about 370k years after the Big Bang.  The non-uniformity of the CMB reflects fluctuations in the density of matter and radiation, which probably were mainly maintained through the inertia of matter, since just electromagnetic radiation would have smoothed faster.  (Although, exactly how much of this was imposed at distances larger than the causal horizon at that time, by inflationary initial conditions, is not something I know off the top of my head.).  All that to say, the CMB as we see it today is the image of what was even, at the time, a relatively low-energy transition, on the order of ten thousand degrees.

A 1ms simulation requires going through several much earlier transitions, but they are all still within physics that we can characterize in accelerators.  The number I find on google is 10^12K, which is around 10^8eV, so less than 1GeV, which is the characteristic energy scale for condensation of nucleons from strong interactions, and a factor of nearly 10^5 lower than the highest energies now characterized at the Large Hadron Collider.  That simulation could have been done within Enrico Fermi’s very earliest-generation representation for the interaction of pi mesons with nucleons, before even tackling the hard problems of predicting nucleon masses correctly from QCD, which dragged on for a few more decades.

A thing that is so strange is that, although these were very indirect to discover and technically difficult to reach, and hard to simulate well, they are still “simple” phenomena, in the sense of having few new organizational motifs required to be understood.  So a simulation of them is less of a problem in principle than a simulation of how the changes in a regulatory law should be expected to change the long-range possibilities for the trajectory of an economy.  

It’s all very strange, how these things fit together.

Eric




> 
> On Tue, May 12, 2020 at 3:59 PM Roger Critchlow <rec at elf.org <mailto:rec at elf.org>> wrote:
> Jon --
> 
> It's a mystery to me.  I believe they are simply counting the number of spectral lines at each wave number and plotting the histogram.  And the link is between the now and the very long ago.  And I believe there's no reason to expect this histogram to have any particular distribution at all?  It's just a weird result.
> 
> -- rec --
> 
> On Tue, May 12, 2020 at 1:10 PM Jon Zingale <jonzingale at gmail.com <mailto:jonzingale at gmail.com>> wrote:
> Roger,
> 
> I get the sense that this is a link between the very small
> and the very large, but I am far from being a physicist.
> Could you say more about this result?
> 
> Jon
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> -- 
> Frank Wimberly
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