Brian Greene's latest (equation-less) book "The Fabric of The Cosmos", addresses why spacetime is not simply a metric but a real "something", and the overarching question, "Just what is reality?" My take is that everyone should read this book!!Part I contains a magnificent overview of the development of Relativity and Quantum Mechanics. This is both fully understandable to the layman and has fascinating new angles - new insights - that are spellbinding to this professional physicist (new views/descriptions of acceleration and gravity, Bell/Aspect vs. EPR, possible conflicts between Relativity and QM on large scales [not just quantum fluctuations at the Plank length], etc.).Part II (what's time?) is absolutely fascinating! Greene's whole discussion of what time might be, its apparent "flow" as experienced by us, and his discussion of statistical mechanics and entropy and their insufficiency to define a classical "arrow of time" ("flowing" from past to future), absent something like the Big Bang, are super -AND CLEAR TO THE GENERAL READERSHIP. I loved his review of the whole business of quantum theory and reality, e.g., the so-called "delayed choice" and "quantum eraser" experiments, the various attempts to come up with some glimmer of understanding of "the measurement problem" (technically, the unpredictable collapse of the wavefunction by another system, e,g., a macroscopic instrument still composed of underlying quantum states) and progress on the proposition of "decoherence".For non-cosmologists, Part III ain't for sissies but does have some wonderful word pictures, mainly towards the beginning and end, which are extremely worthwhile if one doesn't get too bogged down in the middle with unified quantum field theories and elementary particle physics. Towards the beginning of Part III is a terrific discussion of the curvature(s) of space, and towards the end are many fresh insights on repulsive gravity, the inflation field, dark matter and energy, wrinkles in the cosmic-ray background, etc. The real gem is Greene's description of the inflationary (vs. "standard") Big Bang model, with a great summary of our current understanding - and the potential limitation of our further understanding - of how this universe could have started in the first place. (For the serious student, I would note that Greene's enthusiastic description of how inflation impacts the problem of "fine tuning" is perhaps overstated. One important aspect of fine tuning is greatly relaxed, but there are many others that are not affected.)I found Part IV (superstring theory) of Greene's book surprisingly easy going, especially re. the extra space dimensions, M-Theory, and Branes. It provides a far superior view of the "big picture" than is found in his earlier, more detailed and technical book on superstrings, "The Elegant Universe" (1999). I should add a note here for those who have not yet read books like The Elegant Universe. While string/M-theory provides a conceptual framework for reconciling quantum mechanics and general relativity (each being, individually, solidly proven theories but which don't work together), and therefore affords in principle some way to mathematically describe the origin and elemental constituents of spacetime, it is still a long, long way from being subject to experimental verification, due both to current inadequacies of the theory and to the lack of experimental equipment to conduct relevant experiments.Part V, the final chapters, includes a summary of some future experiments that might confirm some of the stranger aspects of the theoretical constructs, some quantum teleportation phenomena (and their unlikelihood of being extended to macroscopic objects), time travel (including Kip Thorne's version of wormholes, which are also unlikely), and a final chapter described next. I particularly enjoyed Greene's introductory discussion of time travel where he explains a resolution of the common apparent paradoxes in a person's traveling backwards in time (e.g. to kill his parents before he was born) using only classical spacetime, i.e., without resorting to any quantum phenomena (pp. 451-455). The final chapter is titled "The Future of an Allusion" and deals with probable future changes to our ideas about spacetime. These concepts are very exotic and pertain to both the macroscopic and microscopic properties of spacetime. An example of the former and, of those presented, Greene's favorite, is one in which our everyday universe is a holographic projection of some surface around us upon which the "real" events are happening. The final pages of the book contain this comment: "...regardless of future discoveries, space and time will continue to frame our individual experience; space and time, as far as everyday life goes, are here to stay. What will continue to change, and likely change drastically, is our understanding of the framework they provide - the arena, that is, of experimental reality. After centuries of thought, we still can only portray space and time as the most familiar of strangers. They unabashedly wend their way through our lives, but adroitly conceal their fundamental makeup from the very perceptions they so fully inform and influence."I would grade the drawings/illustrations in "The Fabric of The Universe" as top-notch aids to understanding. (I once complained that the drawings in a related general readership book by Stephen Hawking, "The Universe in A Nutshell" (2001), appearing after his best-selling "A Brief History of Time" (1998), were the greatest obstacles to understanding the book!)Finally, I would note that an interesting step upwards in generalizing Greene's question, "what is reality?", can be found in the three physics chapters (Chapters 4-6) of another excellent (and easier) book, "The Case for a Creator" by Lee Strobel (2004). There, the interpretation of many of the phenomena described by Greene is extended to metaphysics - metaphysics no longer being a stranger to science (a major paradigm shift sparked by scientific advances in the last two decades). A critical question in theism, "did the universe have a beginning?", is examined vis-à-vis concepts including Hawking's imaginary-time (no-boundary) proposal, Guth's inflation theory, and oscillating universes. Superb examples are given of "fine tuning" (for which hard data have been produced since the 1980s) and its arguments for "Intelligent Design" vs. multiple universes. (As atheist Nobel Laureate in Physics Stephen Weinberg said at one conference, these are the only two choices.) Instead of simply hypothesizing enough alternate universes (essentially infinite) to offset fine tuning, the dependence of a multiverse on superstring theory and inflationary cosmology is examined, including cyclical universes with Brane collisions.Martin Fricke, Ph.D.Del Mar, CA1/17/2005