The outcome is these six additional lectures, drawn from the celebrated three-volume Lectures on Physics. Though slightly more challenging than the first six, these lectures are more focused, delving into the most revolutionary discovery in 20-century physics: Einstein's Theory of Relativity. No single breakthrough in 20-century physics (with the possible exception of quantum mechanics) changed our view of the world more than that of Einstein's discovery of relativity. The notions that the flow of time is not a constant, that the mass of an object depends on its velocity, and that the speed of light is a constant no matter what the motion of the observer, at first seemed shocking to scientists and laymen alike.