Calculating The Cosmos is a book about the history and current practice of physics, astronomy, and cosmology by British mathematics professor Ian Stewart. The book gives the reader an overview of many topics, including gravitation, the solar system, spacetime, extraterrestrial life, and quantum mechanics. The book is divided into nineteen chapters, as well as a short prologue and epilogue.

The prologue begins with the mission to comet 67P/Churyumov-Gerasimenko, then gives a brief recounting of previous space missions. The role of mathematics in astronomy is discussed, followed by its role in cosmology. The first chapter takes us through the history of gravitational theories, from the ancient Greeks to Galileo, Kepler, and Newton, and onward to general relativity and quantum mechanics. More detail in the path toward relativity would have improved the book here. With the second chapter, Stewart begins discussing the solar system, starting with its formation. The nebular hypothesis of a collapsing gas cloud that forms stars and planets is the main focus, along with previous theories and why they were rejected. These are used to illustrate the importance of physics concepts like momentum and angular momentum. The chapter ends with a discussion of possible futures for the solar system, some of which involve planetary collisions and ejections.

The third chapter is devoted to the theories for the formation of the Moon. These include the giant impact hypothesis, as well as several other ideas that fail to explain the Moon’s composition, tidal locking with Earth, and angular momentum. Much of the chapter concerns the nature of constructing simulations for events like an impact between Earth and a Mars-sized object, or the formation of a solar system. In the fourth chapter, Stewart examines the Titius-Bode law, then expands to power laws in general. Their use in discovering Uranus comes next, followed by the use of perturbation techniques to find Neptune. The chapter ends with the accidental correctness of perturbation techniques concerning Pluto and their failed prediction of Vulcan, a hypothetical planet closer to the Sun than Mercury. Oddly, no mention is made here of the hypothetical Planet Nine, and Stewart does not note that Neptune is out of place by the Titius-Bode law.

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