Wow, excellent replies gents, thanks :)
Fraggle: Excellent points, and I was kidding about the Scottish :P
Maes: While the basic diagnostic criteria work fine with humanity's current experience, I have a couple of questions. When/if we create artificial intelligence which is self-aware, is capable of thinking for itself and has the same or higher IQ than a genius-level human, would they then be considered alive - or would they never be considered alive as they are not biological and/or were not "made by God" or do not have "souls"?
If such beings were restricted so they couldn't reproduce themselves, but regarded themselves as alive, what would be the difference between them and us? Can we measure the "spark of life", and can we say that machines don't have souls when we can't prove we have them?
By reproducing, wouldn't that simply mean building another machine? We are provided the natural tools to create new human lives, I suppose the difference is machines would have to make the tools themselves - it would be artificial conception. If we gave them those tools, would we be God?
This is just one aspect of a super-science that we don't need yet -- I just wonder what will happen to contemporary science if the universe does provide us with something new. (There are other complications too. What if a machine knowingly sacrificed itself to save a human, or dedicated itself to exploring the mysteries of the universe to try to find God, or loved the philosophy of meaning, or wanted to become a doctor but lacked the software/hardware...)
Eris: Nice, thanks. Imagine if something like this was discovered in our lifetime. I sometimes wonder if life on earth will grind to a halt for a couple of weeks when/if we discover alien life - then after those weeks, life would go back to normal, the papers would be full of sleazy celebrities and scandalous politicians again and basically nobody would care. Humanity's "who cares if it doesn't directly affect me" attitude would come to the rescue.
Enjay: That was very relevant. Does anyone else wonder at the accuracy of these equations? They seem to be based on finding life like ours on worlds like ours. I have heard lots of theories about black holes and supervoids leading to different dimensions or realities. Wonder what would happen with the equation if they could take that lot into account. Just think, in at least one reality, humanity never went through the dark ages and we probably sent our first manned ship outside the solar system.
Fredrik: I can't find the reference either, I read it on the net so it probably isn't canon. I suppose my view of scientists is tainted; I love sci-fi and watch a lot of documentaries about weird and wonderful things, and no reputable scientist will come on the shows except to debunk things. It's a bit of "don't mess with the fantasy" I think.
HP Lovecraft takes a refreshing approach. He wondered what would happen if the rules of physics etc only applied here, in a limited region of the universe. The creatures of his mythos are beings who belong to the "true" universe. Their magic is actually the galaxy's underlying science. It seems nightmarish and chaotic to humans as our brains are evolved to work here, not out there, and we cannot interpret or safely use mythos science. That explains why some of our weapons and technology won't work against some of them: it's designed to work against us, and we're fundamentally different. The only way to defend ourselves is to hide from the universe or turn mythos technology against its creators, sacrificing our sanity and physical health in the process.