Amazon.com description: Product Description: This textbook, designed for senior undergraduates, or first year graduates in Theoretical Physics, introduces, in an extremely pedagogical way, Einstein's General Relativity and Tensor Calculus, and important developments: Black-Holes were some time ago considered just a matter of imagination, devoid of reality--but now we are quite sure that they exist, and not far from us, in the center of galaxies like ours, for instance: Mach's Principle was a name given by Einstein to the idea that inertia "here", is caused by the distant matter "there", in the whole Universe. Berman explores the subject, and includes a more or less known idea, that the Universe has zero-total-energy; from this fact, the author extracted, for the first time, a series of conditions that need to be obeyed by the "Machian Universe" (read, "our" Universe). Variational methods are explored, including superpotentials, which provide simple energy calculations in General Relativity. Many of the topics presented in this book never did appear in books directed to beginners, like the present one.