Lex I'm a big fan of your show, but I can't give you a sycophant's response of "great job." I'm figuring that your calculation went something like: 100 Billion Stars * 100% * 0.2 * 0.01 * 0.02 * 0.2 = 800,000 civilizations through the lifetime of the galaxy. The 10,000 year communication period means that if you just lined them up end-to-end then you'd get 8 billion years of communicating civilization, which if you divide by the age of the universe  gets to around the 0.6-&gt;0.7 you're talking about. The problem I have is that, despite your asterisk, you seem to put an arbitrary limit on communicating with us because of your implication that technological species just disappear or lose interest in doing anything that we could recognize. Your constraints are too tight to even fit humanity: The Voyager spacecraft is already an interstellar probe and will continue on its merry way for far longer than 10,000 years. One of the things I love about your show is your willingness to ask the big questions - I only hope you keep looking at this topic and realize that there are a lot of advancements that have been made in the field since Frank Drake and Carl Sagan - I'd suggest looking into the work of Professor Jason Wright - he would also be an amazing interview guest - he will give you the lowdown on the state-of-the-art SETI and is a fair and balanced thinker.