Sentient Developments has a guest blog from Milan M. Cirkovic which looks at what he calls "solipsistic" solutions to the Fermi Paradox (you know: if the aliens aren't here why not? I made enough potato salad for everyone!!), although I'll just go with "alternative". And so some solutions are more "alternative" than others.

Of course this veers heavily into science fictional territory and is much more fun than trying to figure out the probability of there being aliens somewhere out there as we cut out all that chin-stroking and work from the idea that they are already here (or nearby):

• The ETH i.e., they are here, flying around in (apparently unreliable) saucers, kidnapping folk and mutilating cattle. This is a tricky one. UFOs, in their broad meaning, clearly comprise a number of phenomena from fakes to misperceived mundane items to as yet poorly understood natural phenomena to black project/secret vehicles (all of which, it is worth noting, are interesting and some are very much worthy of further study). Is there something else once you've separated out these causes? Even if we discount hypnotically recovered memories (as I think we have to do at this stage) there seem to be too many people reporting strange encounters to dismiss them all as liars or mistaken. That said when you look a the data it seems far too strange and much too varied (including variations across time and between regions) to be as literal as the ETH (in the strict, commonly expressed form) would have us believe. What is interesting, looking at it in this context, is that the strangeness of the data might suggest one of the other theories is at work but it could be something far stranger or outside the purview of this piece.
• The Ancient Astronaut Theory, is another difficult one to tackle head on. As commonly expressed (by people like von Daniken) it tends to trade on gaps in our knowledge about how the ancients did things and often does them a disservice for their ingenuity. For example, I dealt with an example Graham Hancock used in FotG, where the making of stone vases was presented as being so amazing that complex technology had to be used, when experiments show you can do it with copper tubes, a bow and some figure of eight shaped stones. Just because we don't know how the pyramids were built doesn't mean that aliens or Atlanteans did it. The big problem is that there is little direct evidence of ancient alien visitations and accounts from the time could just be us reading too much into sufficiently vague texts. It is an intriguing idea and I can't clearly rule this out  but would need better evidence to rule it in. However, that said, I do think that whatever is currently largely being interpreted by the ETH is something that has a long history definitely going back a few hundred years but quite probably stretching back for millennia. However, as explained above, this needn't imply "aliens" which puts us back to square one really.
• The Prime Directive, which is the simplest way to express it to most people. Essentially, we, as struggling up and coming species, are fenced off on our own reservation until we can make the leap to bieng a fully space-capable civilisation (presumably around Kardeshev 1.0). The big problem for me is that there is no proof for this and if we do make the transition and nothing happens, someone can just move the goalposts, saying we need to gain... faster-than-light travel or some other esoteric piece of technology and even something more spiritual, recognising the true nature of the Universe on a philosophical level. If this theory does properly reflect the state of affairs then I don't think we should concern ourselves with it, if it happens it happens. There also seems to be a flaw here - if aliens are interested in us and presumably in the general area then this actually makes the ETH more likely and if they are aliens who are visiting us then there are an awful lot of "blockade runners" (presumably from all over the galaxy) suggesting the Prime Directive plus the evidence for the ETH cancels out the Prime Directive.
• Directed panspermia, this is an interesting one, a civilisation that arises early in the life of the universe seed galaxies with genetic material. The aliens are here, and they are us (in my best Twilight Zone-style voice). It might seem a bit odd way to colonise space, after all you could throw out a few von Neumann-style seeder ships, packed with the encoded genetic information of your species and enough kit to terraform any planet they stumble across. However, perhaps the idea of colonising known space is the kind of silly idea that young and thrusting civilisations come up with just before some older, larger and nastier species turns up to inform you they don't appreciate you pissing on their doorstep and that voluntary self-extinction would save one a whole world of hurt. It would also reduce diversity and make for a much duller universe, why bother exploring if all you find is yourself looking back at you? Of course, perhaps you have other ideas. Spread a little of starseed around to make things interesting. Follow it up with Bracewell probes to seek out developing life and keep an eye on it, perhaps throw a few giant rocks in if the animals are growing big but stupid, nurse them along with some gods and myths and bingo half a billion years later you have some uppity apes you can do whatever you want with (like turn them into components in your war machines). A recent report may ad another angle to this, some aspects of culture may be encoded in DNA. This clearly comes about due to natural selection but could genetic tinkering leave little cultural time bombs hidden in our cellular structure? Perhaps giving us a questing curiosity or a compliance to the orders of sky gods or a liking for potato salad?
• The Planetarium Hypothesis, not one I was aware of but a variation of the simulation hypothesis, it is just the simulation is out there, presenting us with fake information of the rest of the Universe. This seems like another dead end because until you reach the very walls of the universe (which is possibly impossible) because the you'd just shift the limits of the simulation (or someone could come up with some work-around, like the planetarium keepers kidnapping explorers/hijacking satellites and messing with their memories/sensor readings - after all, whoever is doing it has gone to a lot of time and effort to maintain the illusion).
• The Simulation Hypothesis, beloved of David Icke and other fans of The Matrix, there are some formulations of this that suggest it is not only possibly but actually likely. The idea being that a simulated reality would reach the point where they'd develop one or more simulated realities, who would do the same in turn, creating a near infinity of simulated realities. Power might be a limiting factor, but such a civilisation would also have harnessed black holes for power. However, this doesn't necessarily explain the Fermi Paradox (unless the aliens are the simulators rather than our future selves or even a real selves, even if they can never be sure they aren't real) because surely the simulation could contain aliens. This is also a theory not worth bothering with because we'd still have to live our lives as if they are real.

Cirkovic concludes:

It is difficult to objectively assess the value of solipsist hypotheses as solutions to FP. Most of them are either untestable in principle, or testable only in consideration of very long temporal and spatial scales; they do not belong to the realm of science as it is conventionally understood.

However, this is probably not strictly true. While I suggest the Prime Directive cancels itself out and it and the simulation/planetarium hypothesis are impossible/difficult to test for and/or don't make any difference even if we knew, we could test the others. There is the burgeoning field of xenoarchaeology (and SETA, the Search for Extraterrestrial Artefacts) which could find the bits and bobs aliens might have scattered through the Solar System. Of course, this just leads into the debate about Faces on Mars and odd objects on the Moon (in fact what we are looking for might be the Moon). Equally we might be able to tell we are in a simulation by looking out for glitches in the Matrix, and this isn't just black cats it could be any synchronicity. So this turns out to be less black and white and instead we get mired down in the age-old, ongoing debate(s) about how strong the evidence is. It all adds to the fun though!!

Equally, he forget the Subanthropic Principle (and similar Stanislav Lem-style scenarios). These bring up an interesting extra problem - we are limited by our imagination, experience and world views. What if the answer is beyond our ability to imagine it?) The eventual solution might not only be impossible to test for (at this stage in our development) it might be we aren't even capable of coming up with the theory to test. How do you like them apples? What if we are really twelfth dimensional entities on an incarnation holiday to experience what it is like to be a meandering meatbag for a while, just to see what it is like restricted to three dimensions? Except I was easily able to come up with that theory, so it doesn't count.

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