Who ordered that? I.I. Rabi (1936)



(Click the image for a pdf version.)

Two different scientific views on the atoms that we are made of and move in.

The left half of the figure displays the relative beauty and mathematical simplicity of the electronic structure of atoms that govern almost all that is important in our world.

The right half of the figure illustrates the complete mess needed to describe the nuclei of atoms. To add insult to injury, nuclei are only important for various special applications in the first place.

The quote by Rabi at the top of this page, Who ordered that?, was on learning of the discovery of the "muon," a particle that does exactly the same thing as the electron is already doing, and is just heavier. But Rabi did not know half of it. At the time they had electrons, protons, and neutrons, besides the new muon. Now we have also the still heavier "tau" version of the electron, and for each of the three versions a corresponding "neutrino." We now also have "up quarks" and "down quarks" that make up our protons and neutrons, and two heavier versions of each of those quarks. Then there is also an "antiparticle" version of each of these twelve particles. Besides our good old electromagnetic and gravity force fields, we now have two fundamentally different force fields, the "strong force" and the "weak force," various particles to carry these forces, and of course, the Higgs particle to give the other particles mass. The theory of in particular the strong force is prohibitively difficult. And because of astronomical observations, we are sure we are not done, but that a lot more of this stuff will be coming our way. None of it affects our understanding of the electronic structure in the good old periodic table significantly. But pretty much all of it affects nuclear physics nontrivially in some way or the other. And that mess reflects in the right half of the figure.

The two plots in the figure come from my book "Quantum Mechanics for Engineers." See there for detailed explanations. However, in the periodic table to the left, elements in the same column tend to behave similarly. Color indicates ionization energy. The length of the bar below the element number in the top left of the cells indicates electronegativity in chemical reactions. Wavy lines in the top right corner indicate a liquid under normal conditions, and dots a gas. Daggers and exclamation marks indicate radioactivity of the nucleus. Boxes below the name show filling of available quantum states by electrons.

In the "chart of the nuclei" to the left in the figure, nuclei are indicated by little squares. Nuclei on the same horizontal line have the same element number (number of protons) Z. That means that each horizontal line corresponds to exactly one square in the periodic table to the left. Nuclei on the same 45 degree line going down have the same number of neutrons N. The size of the squares indicate how long these nuclei survive on average, the biggest green squares being nuclei that live forever if left alone. For the other nuclei, the colors and any markings inside indicate the mechanism through which they get lost. Nuclei that do not manage to survive for at least a nanosecond are not shown. That includes beryllium-8, ₄⁸Be, which only survives a median 80 attoseconds (10^-18 seconds). Despite that, beryllium-8 is still the reason that the carbon and oxygen of which we are made exists in the first place. Needless to say, none of the properties of the nuclei while they still exist is shown. You would need a microscope. But my book has separate graphs for key properties.

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