I’m not a big commenter, generally, but I felt motivated to leave one on this post on Charlie’s Diary. Basically it concerns the Fermi Paradox.
The Fermi Paradox is a difficult one for me. Obviously I’m interested – the fact I can’t quite shut up about it is the giveaway. But, and here is the problem, as I’ve said before, my considered opinion is that we can’t usefully speculate on it at the moment.
I was trying to wrack my brains again for anything useful that I could say. So, here is what I think we can say:
- 1: We exist, so we can reasonably conclude that civilisations are at least possible, i.e. there is nothing in the basic physics that effectively rules them out.
- 2: Our planet doesn’t appear to have been visited at any point in our fossil record. 
- 3: If higher-rated societies on the Kardashev scale exist, then they can’t be anywhere nearby. Although our galaxy has lots of elegant little structural quirks, I don’t think anyone has ever suggested that they’re down to super-civilisation infrastructure projects! 
- 4: Radio signals at interstellar distances – there is absolutely no agreement on this. I’ve seen it argued both way, with no clear sign of a consensus. So I suspect this means we can’t yet conclude anything useful here, either.
- 5: This is a bit of a cheat as it hasn’t technically happened yet, but the next round of Kepler mission data (due in February 2011) should begin to tell us something about the mass function for terrestrial-type planets. At the moment, all we can really say is that they definitely exist, and some other stars have them.
Not looking very definitive, is it? It’s looking like the paradox might stay paradoxical for some time yet.
 But is there necessarily any reason why aliens would come here? Consider – if the typical life-bearing planet is a tide-locked world around an M-dwarf, why would you send a mission to a G-class star? They’re too hot, too short-lived, emit far, far too much ionising UV and any putative planet would have to orbit so far out that it would actually still have a day-night cycle! I mean, yuck, right?
 Although you do have to wonder if the Type III equivalent of Capita was behind the Antenna Galaxies – definitely a PFI bodge if there ever was one!
 Yes, the post title is a physics pun. And not a particularly good one, no.