After a third read of this book (late 2024), I had a few more observations on this book. I put these at the bottom of this review.
The first run through on this book was hard. Technical, detailed, dry. Second run through was better - started to absorb more, though, as before, the writing was largely over my head. A few highlights, and comments and questions:
From the preface, Weinberg, reflecting on whether or not to write this book, says: "What could be more interesting than the problem of Genesis? Also, it is in the early universe, especially the first hundredth of a second, that the problems of the theory of elementary particles come together with the problems of cosmology." The book spends a good amount of time on this conversion of energy to matter and matter to energy, and I feel I made some headway in understanding this after my second review.
Weinberg writes that "In the beginning there was an explosion. Not an explosion like those familiar on earth, starting from a definite center and spreading out to engulf more and more of the circumambient air, but an explosion which occurred simultaneously everywhere, filling all space from the beginning, with every particle of matter rushing apart from every other particle. "'All space,' in this context may mean either all of an infinite universe, or all of a finite universe which curves back on itself like the surface of a sphere. Neither possibility is easy to comprehend, but this will not get in our way; it matters hardly at all in the early universe whether space is finite or infinite." I am not sure what "all space," "infinite," or "finite" means here. Is it pre-existing (infinite?) or is it created (finite?)? If not a definite center, what then is a singularity (a term Weinberg does not use in this book)?
The first particles of mass/matter "were continually being created out of pure energy," he writes. This age of "pure radiation" began at the end of the "first few minutes," but this was preceded by mass/matter that created energy (the "real beginning" as "a state of infinite temperature and density, which occurred at o.o108 seconds'). But that matter was a "kind very different from that of which our present universe is composed," and when the then universe approached "a moment of infinite density." Was that moment pure energy, pure matter, or pure energy-matter? To these sorts of questions Weinberg says that "this leaves us unsatisfied. We naturally want to know what there was before this moment, before the universe began to expand and cool."
Regarding a "common misconception about the expanding universe," Weinberg says that "the galaxies are not rushing apart because of some mysterious force that is pushing them apart....Rather, the galaxies are moving apart because they were thrown apart by some sort of explosion in the past." What does this statement mean regarding a repelling, repulsive dark energy force? Weinberg also discusses "escape velocities" for galaxies (per Hubble's observation), suggesting the possibility of an infinite universe where galaxies escape the effects of gravitation and continue outward forever (as opposed to a finite universe where gravitational contraction brings these galaxies back into the corral).
Of gravitational waves, Weinberg writes that "if some ill-advised giant were to wiggle the sun back and forth, we on earth would not feel the effect for eight minutes, the time required for a [gravitational] wave to travel at the speed of light from the sun to the earth."
I like Weinberg's definition of "rest energy," which is "the energy that would be released if all the mass of the particle were converted into energy." In his glossary, he writes that "material particles approach the speed of light when their energies are very large compared to the rest energy mc squared in their mass." Particles of zero mass "such as photons, neutrinos, or gravitons, travel at the speed of light."
Weinberg closes with this, a nice bookend complement to his beginning: "The more the universe seems comprehensively, the more it also seems pointless....The effort to understand the universe is one of the very few things that lifts human life a little above the level of farce, and gives it some of the grace of tragedy." I thought this was a solid observation, eloquently written, surprisingly, given how thick the rest of the book was.
Third Review (2024)
Weinberg says that the big bang was not an explosion into space, but was the creator of space. This begs the question of what surrounded the big bang before space was created?
He states that elementary particles (electrons, positrons, neutrons, protons) and light were all created by “pure energy.” What is “pure energy?” He doesn’t say, but this implies that energy is primary as matter originates from “pure energy.”
The big bang hypothesis comes, theoretically, from the reversing of receding galaxies so that time and space collapses to a big bang initiating point. Does the inverse square law play a role here? The closer to the cosmic gravitational center, speed, and time and space, would be less as it would be bound by gravity. Similarly, the further out from the gravitational center, would inertial motion from the big bang be freer of gravitational effects, thus allowing for more speed without gravitational drag? Might this have a role to play in the speed of cosmic phenomena (galaxies, light)? Weinberg says nothing about the inverse square law or inertial motion in this context (and neither is in the glossary).
Surprisingly for cosmology, Weinberg states that Einstein’s theory of general relativity is “less important than was at first thought.” As that theory is about non-Euclidean geometry, it is about curvature, not straight lines in space and straight motion. And isn’t curvature the balance point between the outward (inertial) motion from a big bang (or supernova) event and the movement of energy and matter, backward, toward high density masses (the gravitational center)?
Regarding open and closed scenarios for the universe, Weinberg discusses the role of “critical density” (greater than 1 is open; lesser than 1 is closed). How does one know critical density if cosmologists have no idea of what dark energy or dark matter is - other than an amount that is said to be (theoretically) necessary to explain the missing mass question (dark matter) and the repulsive force (dark energy) that accounts for the fast receding galaxies? Might there not be alternative (non-paradigmatic) explanations, such as the role of the inverse square law (as related to dark matter) and inertial movement per Newton’s first law (as related to dark energy) in which energy-matter’s natural state is straight-line motion?
Weinberg states that expansion occurs from the big bang (“the effect of velocities left over from “past explosions”), which suggests that it is the big bang that creates inertial motion (per Newton’s first law of motion) that creates the expansion, but he does not connect this to the dark energy mystery (which is said to be repulsive).
Weinberg and others diagram the cosmic expansion from the big bang in a linear way, whereas for an explosion, the outward movement is from a center point into all directions (straight lines emanate from a curvature origin). If this is the case, would that mean that under cosmic curvature, all straight-line inertial motion returns back to its starting point (not go out and back as in a contraction scenario, depicted as linear, straight line motion, but to continue to go around the curvature to its beginning point, i.e. the cosmic gravitational center)?
Weinberg on galactic formation: “The theory of formation of galaxies is one of the great outstanding problems of astrophysics, a problem that seems far from a solution.” Might Einstein be relevant: If matter-energy flows inward toward a gravitational center, are the inward spiraling motions of gas and dust a way of seeing Einstein’s theory in “real time” so to say? Does Hubble's near 100 year old classification scheme hamper attempts to see the various galactic forms as different aspects of Einstein's theory?