The book's table of contents is nicely organized. This made the topic - the atom, sub-atom; quantum world - a more tempting one to tackle. Digging into this, Asimov outlines the fundamental particles (those that cannot be broken up into anything smaller) into a table of particles: There are the matter particles of electrons and quarks (I've seen a variable number for these but 12 is in the ballpark, not counting anti-particles) that make up the atom, and there are the four force carriers that tie energy and matter together on micro scale and macro (gravity) scales, along with the Higgs boson (which seems to be categorized separately) that gives matter its mass. These are the foundation for all that is seen and understood to be material reality. It is for the lay person a subject that lies on the astounding end of the spectrum. Most of us, I suppose, understand the Newtonian world of classic physics, at least in some vague sense. The stuff that Asimov talks about is that whole new world of atomic and nuclear physics that largely opened up, mainly, just in the last century.
The names for these specific particles - those words that end in "...on" - are, on the other hand, not easy to understand. "What is what, and why are they categorized that way" is not super clear.* At least, that's my reaction to the way Asimov presented these concepts. I found it maddening to sort through how he used this terminology and how the various terms for this and that related to each other. Just as I thought I understood, I got some Asimov description or comment that didn't match up with what I thought he had said before. Even Asimov here and there took issue with the naming conventions, as applied to some of the things he wrote about.
The four forces that tie everything together via pushing (movement away) and pulling (a movement toward), flowing one way or another as a result of some energy differential. Gravity, operating at the macro scale, seems to be an exception as it is talked about as an attractive force, that pull two bodies together. Yet if two bodies are put on a teeter totter, a point of equilibrium is reached where the relative power differential is negated. The relationship is One, or Zero, between the two. Occasionally, relative bodies of mass are said to resist the pull of larger masses. Is "resist" the same as "inertia?" And isn't the flip side of "attraction" a "resistance to attraction?"
At the end, Asimov discusses some of his ideas that would connect the quantum world with the macro world of cosmology. He focuses on the Big Bang (or, rather, Time Zero that preceded the big explosion) and suggests that all matter and energy condensed into a singularity (the unstable "cosmic egg" of Lemaitre [1894-1966]).** The sorting through of what happens immediately, post Big Bang (BB), is, the way Asimov describes it, a bit of a nightmare to follow. First there's a "sea of quarks" followed a millionth of a second later by quarks (forming baryons and mesons) and leptons and the interacting forces (gravity, electro-magnetic-weak and strong forces). One second post BB free neutrinos make their appearance. At the three second mark, atomic nuclei form, and then at the 100 thousand year mark, electrons and atomic nuclei form. From there on out, atoms and collections of atoms form, followed by stars and galaxies. Asimov presents this more or less as a stream of consciousness and doesn't tie down a few loose ends as a result. For example, if an electron is a lepton what happened from a millionth of a second when leptons popped into existence and when electrons combined with the nucleus at the 100 thousand year mark? There's a similar question with the four forces forming also at one millionth of a second, yet apparently the electro-magnetic and strong forces did not kick into applied existence until the 100 thousand year mark. Given that Time Zero was condensed beyond imagination, could it be that this is where quantum gravity kicks in - matter-energy quanta pulled together into a singularity of some sort? Of course, if even at that point there is "movement" among the minutest of whatever is there or not there at the point, and inevitable instability because gravity pulls together push and pull forces beyond what can be tolerated? Who knows or, rather, can it ever be known?
*Baryons, leptons, pions, hadrons, mesons, bosons, fermions, muons and a few others that I can't remember.
**As one moves backward toward the time of the Big Bang, Asimov writes that "the temperature grows higher and higher and the energy density is more and more enormous. Scientists feel that they cannot talk of times less than 10 -45 second (one billion of a trillionth of a trillionth of a trillionth of a second after the big bang. Less time than that brings about conditions so extreme that space and time have no meaning." This statement is impossible for me to wrap my mind around, and I have no idea what he means by saying that space-time before 10 -45 has "no meaning." Even so, I like this statement. It promotes humility.