Gravitation proved to be far more than its jumble of equations, nonlinear structure, and famous text-boxes. Though several newer textbooks have displaced the book from graduate students' syllabi, none has rivaled the book's cross-over appeal.

This month marks the 100th anniversary of Albert Einstein's theory of general relativity. Amid all the celebrations and conferences, it is easy to forget about the real human being who actually did it. But if you live in Princeton, and his piano is in your living room, he is always present.

For someone who is determined to get propellantless propulsion off the ground, I worry that there isn't enough experimental research to make propellantless propulsion a reality sooner rather than later.

On November 25, 1915, Albert Einstein finally announced the complete mathematical details of his General Relativity Theory in the last of a series of four papers, but gravity and the nature of space itself, remain as mysterious today as they were back then.