Really enjoyed reading up on this during a train from work to Gloucester last night and back to work this morning. Science (and this borders on the geeky no-go area of Sci-Fi in parts) isn't really my thing but I loved this.
The Fermi Paradox is the apparent contradiction between the high statistical probability of the existence of extraterrestrial civilizations and the lack of evidence for (or contact with) them.
What I found interesting is the number of assumptions that scientists have made and the mind-boggling amount of possibilities that this rules out. I am perfectly happy with the high statistical probability of existence- though this in itself is an assumption which rules out the Rare Earth hypothesis (the billions of enormous coincidences which created human life would almost certainly not happen again) in favour of the mediocrity principle (Earth is not special, but merely a typical planet). I'm happy to go with this; partly because of my natural bias toward humility but also because the Rare Earth scenario requires us to assume that only human-like species can exist. There are 70 sextillion stars in the visible universe (that's 70,000,000,000,000,000,000,000!) and so I am happy to presume that there is a high statistical probability that other civilizations exist or have existed or will exist somewhere amongst them. To deny this would cause me to rule out the infinite monkeys with infinite typewriters scenario which I genuinely can't. It's a leap of faith but one I'm comfortable making.
The other side of the paradox is the one I struggle with. I read a great deal about the search for evidence and found that the way in which we are looking and the expectations that this is built upon seem deeply limited and unimaginitive. This is not to say that I have a better alternative, my criticism is from the 'I know this is wrong but I don't know what is right' school.
Evidence is expected (or hoped for) in one of two ways; either by seeing them through one of our super-duper telescopes or by having them come and find us. Both of them are deeply flawed.
"Radio technology and the ability to construct a radio telescope are presumed to be a natural advance for a technological species" apparently. And I have a real problem with this as a starting point since it rules out infinite possibilities in favour of the one we're comfortable with from our limited human experience. What it means is that we are looking for evidence of radio technology (meaningfully repetitive signals, unusually intense radio waves, brighter than expected signals) which are either deliberate attempts to communicate or the by-product of normal activity. Assuming all of the little green men watch analogue TV we should be laughing. And this leads me onto another problem with the expectation of evidence we could find by scanning the sky: Earth would have become visible in this way in 1901 and as we switch from analogue to digital our visibility will cease. Let's say that we have 150 years of visibility, that's a very small window on a planet that is billions of years old for a species that is 200,000 years old. As I read "a civilization may well have been visible from 1325 to 1483, but we were just not listening at the time". In addition to this we have only had the capability of seeing this activity in others since the radio telescope was invented in 1937 and that even our most sensitive radio telescope (the Arecibo Observatory) could only detect signals at distances up to 0.3 light years. And in the direction that we point it.
And so we're expecting to see human-type activity that occurs for a relative blink of an eye and that we're only able to detect for a relative blink of an eye in a tiny fragment of the universe. It isn't a wonder that we haven't seen any evidence, the wonder is that we expect to.
The less clearly-defined type of evidence that we're looking for is proof in the form of aliens coming to visit or deliberately communicating with us. There are a number of assumptions here; that they would want to (the Zoo hypothesis supposes that we're being watched without interference, as does Bowie's Life On Mars for that matter), that they are sufficiently advanced to (and we aren't and won't be for the realistically foreseeable future even if the Arecibo Observatory miraculously stumbles across a civilization that we might like to visit), that they are sufficiently human-like for us too recognise (imagine a species made up of clouds who communicated telepathically- is this more outlandish than the theoretical existence of humanoids?) and that they haven't already arrived and we simply didn't recognise them (could historical myths or religious figures have been alien species? Could they be sufficiently advanced to be able to cloak themselves?).
It's a bit of a brain-fuck but I'm content with my own assumptions; that there could be alien civilizations, that we could conceivably never know and that some brainiac scientists can be really dumb when they want to be.
