Brilliant lecture; quite clearly informative about some of those difficult theoretical science "tangles" of modern day physics.  I plan to read R. P. Feynman's other published lectures.  But for now, at least I have a better, basic understanding of how one gets from point A to point B, and why it matters.  However, it is helpful to remember some Euclidean geometry and vector equations to keep from getting totally lost along the way.  Sometimes I found myself reading several sections twice or three times over, just to make certain that I was grasping the material.<br><br>Given the world's growing population and the looming climate change America's governments are especially so unwilling to deal with, I would recommend that more of earth's inhabitants acquaint themselves with Professor Feynman lecture materials, in preparation for moving to another planet, or perhaps another galaxy, even.  Astrophysicists have been quietly discovering thousands of planetary systems, outside of the Milky Way.  And they appear remarkably unique.  In some, a gas giant, like Jupiter, has it orbit closest to its sun, while planets of smaller masses are further out.  A brave new world!  No one is certain if the current acceleration of our expanding universe, as we know it, will ever slow down, for our space probes and our inhabited space ships to reach any of those alternatives "to life on earth."<br><br>So, as one prepares for the eventual colonization of other planets, we had better make certain that Plan B, "living on earth," remains viable for us to fall back on, if absolutely necessary.