Because it's been a little while since I've done an alien post.
Bryan Caplan is convinced of the existence of alien life. Very good to see. He has an interesting twist on the recent announcement of hundreds of billions of planets in our galaxy. I haven't read the studies but I imagine the point is that as we collect information on more and more exoplanets it becomes easier to extrapolate exactly what sort of galaxy it is that we live in. Caplan's point is that if planets are so hard to detect life is going to be particularly hard too. This is especially true of intelligent life which itself hasn't developed space-faring or advanced communication technology.
This is a good time for me to bring up Annie Jacobsen's history of Area 51, which I'm almost done with. It's an excellent book based on a surprising amount of first-hand interviews from personnel, and recently declassified material. Most of it is about the U-2 and A-12 spy planes and the nuclear testing that went on there, but of course substantial sections of the book also cover the Roswell incident. I think Jacobsen's Roswell chapters offer a good example of how people can let bias slip in when talking about aliens. What concerned me most was Jacobsen's tendency to cite Occam's Razor. My initial reaction when reading these passages of the book was "Jacobsen doesn't seem to understand the concept of Occam's Razor", but of course a more charitable interpretation is that she brings certain assumptions to the evidence that I think are completely unjustified, and as a result all manner of claims can be justified by Occam's Razor.
There shouldn't be anything particularly shocking about noting that intelligent (and unintelligent) life outside of the Earth exists If you accept that life on Earth evolved over millions of years. I'd go as far as saying that the default assumption should be that there is life elsewhere, although certainly there are a couple more hurdles for intelligent life. Extraordinary claims require extraordinary evidence, but it doesn't seem to me that "extraterrestrial life exists" is an extraordinary claim at all. The extraordinary claim would seem to me to be that phsyical and chemical processes here on Earth happen in the rest of the universe but for some reason biological processes don't happen anywhere in the whole universe except here. That seems like a quite extraordinary claim that I can't personally justify.
Jacobsen clearly doesn't agree, and as a result that influences her use of Occam's Razor. Her explanation - which she contends is the simplest explanation of the evidence about the 1947 Roswell crash - is that Joseph Stalin sought out Nazis associated with two research efforts: Mengele's biological experimentation and the Horton brothers' experiments with hover technology and flying discs. Stalin got Mengele to produce surgically altered children who were made to look like aliens and the Hortons to produce a flying saucer so that he could send the children in the saucers to crash at Roswell so that it would create a public panic about aliens. Why? As revenge for Truman's lies to Stalin at the Potsdam Conference about the U.S.'s nuclear capabilities.
To me, the explanation comes off as highly contrived and unnecessarily complicated, which is why I was surprised to see that she cited Occam's Razor - a principle that I would have thought would lead her to reject the explanation.
This isn't to say I'm 100% convinced that the Roswell crash was an alien ship. The eye-witness accounts suggest to me that the whole weather-balloon story is easily rejected as an explanation, but we of course don't only have aliens and weather balloons to choose from. I'm quite willing to accept that it was either a U.S. or a Soviet (or hell, even a rogue Nazi) test flight. The Horton brothers were working on hovering discs in Nazi Germany, and it's entirely plausible that either the U.S. government or the Soviets continued to work on this after the war.
What's striking about Jacobsen's explanation is that she clearly accepts the testimony of several eye-witnesses who assert that several small grey humanoids with large heads and large black eyes were recovered from the wreck, and that some had not yet died. She just explains it with Mengele. I don't know if the testimony about the pilots is true or not, but if it were true, the Mengele story seems at least as contrived and overcomplicated as the claim that it was aliens.
But I guess the point I'm trying to make is that I say all this because the existence of intelligent aliens doesn't strike me as absurd, where it does seem to strike Jacobsen as absurd. That can really influence how you think about these things.
For the record I accept it as almost certainly true that intelligent life exists elsewhere in the universe. I do have a harder time accepting that they've visited us. That is an extraordinary claim, and the evidence is not decisive enough to be convincing. The Roswell incident is by far one of the most compelling cases, and I attach a small but non-trivial (single digits to teens) probability that it was an actual alien crash. I also find the consistency of a lot of the abduction stories at least something to take seriously. They may all be crazy, but it seems silly to just assume that they are. I find a lot of the UFO reports interesting, but less convincing. I think everybody, on all sides of the issue accept that the lion's share of reports are quite easily explained. As for the cases that are harder to explain, I think that what we don't know about military technology rules out jumping to conclusions about aliens. Of the "unexplained" UFOs, I bet they're mostly military tech. That's what's so compelling about Roswell - there's lots and lots of eye-witness evidence that this was more than just a military test flight that got out of control...
...maybe. But then aside from the obvious importance of extraterrestrial life, it's precisely the "maybe" that makes all this so interesting.
UPDATE: One more point on this. Two more recent sci-fi shows reject intelligent alien life as an important part of humanity's space-faring future: Firefly, and Battlestar Gallactica. There are strange creatures in the universe in each of these cases, to be sure - but they are entirely man-made. I think this is probably the most likely vision of our future. We will be an interplanetary species, hopefully in my lifetime. We will eventually be an inter-stellar species. But if it turns out that intelligent aliens haven't visited us yet (something that - as I note above - I consider the most likely but certainly not the only possibility), then it's doubtful we'll meet them in any sojourns in the near future. As for unintelligent aliens, I think that's far more likely. I'm still optimistic about finding life in the soil of Mars.