The Fabric of the Cosmos the book, such as discussions revolving around classical physics, quantum mechanics, and cosmological physics. Chapter 2, "The Universe and the Bucket", features space as its key point. The question posed by Greene is this: "Is space a human abstraction, or is it a physical entity?" The key thought experiment is a spinning bucket of water, designed to make one think about what creates the force felt inside the bucket when it is spinning. The ideas of Isaac Newton, Ernst Mach, and Gottfried Leibniz on this thought experiment are discussed in detail. Chapter 3, "Relativity and the Absolute", focuses on spacetime.
Non-physical entity many minds each person can have, which is not an issue for physicalism which can simply declare one-mind-per-person almost by definition; and whether non-physical entities such as minds and souls are simple or compound, and if the latter, what "stuff" the compounds are made from. Describing in philosophical terms what a non-physical entity actually is (or would be) can prove problematic. A convenient example of what constitutes a non-physical entity is a ghost. Gilbert Ryle once labelled Cartesian Dualism as positing the "ghost in the machine". However, it is hard to define in philosophical terms what it is, precisely, about