Over on the other thread we’ve had a brief discussion of the recent initiative to find extraterrestrial intelligence. In response to a couple of the comments I thought it might be instructive to look at the logic behind the privileged planet hypothesis, as it relates to the search for life beyond Earth. To that end, I pose the following:
What is the implication of the Earth being a Privileged Planet, assuming we subscribe to that view?
Does it mean:
(a) that Earth (with all of its various characteristics) is unlikely to have come about by purely natural means; and/or
(b) that Earth is unique (or nearly unique) in the galaxy or the cosmos?
The reason I pose the question is this:
Some supporters of intelligent design seem to be slightly confused about the implications of the privileged planet hypothesis.
If we take (a) above as true, then we are — by definition — asserting that we are not just dealing with purely natural causes. There was a mind, a plan, a purpose, an intelligence, a guiding force — something beyond just the natural and the material.
That is all well enough and everyone seems to be on board up to that point.
But if we then go on to assert that (b) is true, that Earth is unique, what is the basis for such a claim? Well our basis is that it is exceedingly unlikely that something like Earth would arise on its own through purely natural processes. True enough.
Yet in our prior breath we had just asserted that there is in existence something beyond the purely natural and material, something powerful, something purposeful, something capable of producing a planet like the Earth. Ergo, when considering whether another planet like Earth might exist we are not limited to purely natural and material processes. Indeed, the whole point of the privileged planet hypothesis is that something else — something capable of building a habitable world — is in play.
Looking for another habitable world is no different from looking for any other item that came about at least partly by design.
If we were to discover a beautiful temple ruin in the Amazon jungle we would rightly conclude that it could not have been produced by natural processes and that it had been built by some intelligent being or beings. In other words, the temple was built by temple builders.
Would we then pack up our bags and go home, arguing that there are no more temples to discover, because we had already discovered one that was designed and that we therefore think it is “unique”? Of course not. That would be absurd.
Indeed, we would do precisely the opposite. We would expect to find other temples and similar structures elsewhere in the jungle as we continue to search, precisely because we would now know that we are dealing with temple builders, and not purely natural processes.
The same holds true for planets. If we accept that the privileged planet hypothesis teaches us that Earth is here due, at least in part, to a planet builder, then our subsequent search for other planets (and other life) should be informed by the fact that we are not only dealing with purely natural processes, but with a planet builder.
This is pretty straight forward logically, but some individuals (all present company excluded, no doubt) seem hesitant to consider the possibility of other intelligent life beyond Earth due to religious or philosophical motivations.