Enjoy your blog a lot! A few comments below. "If the cultural and technological evolutionary processes that have enabled us to do this are characteristic of intelligent species, we should suspect intelligent civilizations to develop very quickly on galactic scales. We should also suspect them to be very loud." Maybe. Remember radio still has a speed limit. Its easy to say there's nothing out there because we can't hear it, but this only applies IF an intelligent civilization (IC) has been around longer than 100,000 years. We have to have had time to receive these signals. This line of thought also assumes that we can distinguish the signals from the normal, strange noise of the universe. Also, we have only listened to a small fraction of the radio sources in the galaxy. Not a whole lot of data to go off of. Another problem is if ICs have evolved say, only within the last 100,000 years then we SHOULDN'T expect to hear anything for many millennium. What's to say that we haven't simultaneously evolved with other civilizations, in the same galactic time frame? Since our signal has only traveled approximately 70 light years, I don't think its a reasonable assume that other civilizations are ignoring us. Only the civilizations within 70 light years would be able to detect us in the first place. To ignore us, they have to be able to hear us in the first place. The radio bubble is only a MINISCULE amount of our galaxy; an infinitesimally small portion of the potential sources that need to be sampled to provide an accurate measurement. If you haven't read it yet, Carl Sagan & Iosif Samuilovich Shklovsky wrote a book called Intelligent Life In The Universe. It's a thick and awesome read covering all of this and more. Great post!
1) With the first statement when I say "we should suspect intelligent civilizations to developed very quickly on galactic scales" I should have clarified that I meant on the scales of deep time. If a civilization like ours - that is currently experiencing a dramatic increase (over the past few centuries) in technological evolution existed for another 1 million years - I contend that we would be very loud. If you were in the Milky Way you would know about us either directly or indirectly. But your point is well taken. 2) I like your second idea. I suppose that one could best be incorporated into my first point "we are the first." It could also be that we are currently developing on the same galactic time frame. I think it would be really improbable but I guess with 100 billion earth-like planets it is completely possible. Very cool idea. 3) Well I did state in the article that I don't think it is probable that intelligent civilizations are ignoring us. I think this is one of the least likely scenarios. However, under the framework I imagine this scenario - I am talking about a type II-IV civilization ignoring us, so I think they would probably know of our existence even with a tiny radio bubble. Any civilization like this would have circumvented the speed of light barrier (if it can be) and would have a fairly good idea of what was going on in the galaxy. That is why I don't think one exists at the moment (unless they are ignoring us - which I don't think they are). Thanks for your responses. I think the way you think!