Galactic Civilizations

Dr. Michio Kaku, a theoretical physicist often interviewed on shows such as NOVA, has a good overview of the limitations on civilizations imposed by the basic laws of physics.  He discusses the classic three types of civilizations based on energy consumption and control, the potential use of Von Neumann machines, and he covers some of the reasons why SETI isn't detecting anything beyond static.  I hope that the reason we don't hear anything when we turn to the stars is simply that we're not listening the right way, and not that nobody is out there.

This might be a little basic for my readers, but I found it to be a pretty good overview.  Some days, I have no hope that we will ever have meaningful contact with interstellar sentient life.  An invasion would almost be preferable to nothing.

(Cross-posted to Futurismic)