[ Pobierz całość w formacie PDF ]
.The data might be misleading, because  living processescould have been parasitic on, for example, the inflation phase of theuniverse.Or the remnants of such  lifeforms have led us to assume thatthere had to have been such an inflation phase.We used both of theseideas, semi-seriously, in Wheelers  because they were a good way topersuade our readers that life will appear anywhere it can.and alsoanywhere it can t.Several fictional aliens have been used to make the same point.InFred Hoyle s Black Cloud, particles interconnected into a complexsystem by radio form a sentient network.Stanislaw Lem s Solarisenvisages a sentient ocean with mystical and mystifying properties.Robert L.Forward s Dragon s Egg is a neutron star inhabited by thequasi-crystalline cheela, believable alien lifeforms of exotic provenance.In many ways the cheela show the complete puzzle laid out, theexistence of genuine lifeforms with a wholly different basis fromorganic chemistry.They do not even share our kind of matter.Yet theyinhabit a world that is entirely consistent with our currentunderstanding of physics, they exhibit biology and sociology that arereasonable, and finally they evolve  believably  far beyond ourcapabilities.We have learned so much about Earthly life, so quickly, and with suchamazing results, that we forget how special it all might be.Ask abiologist what life is, and ten to one you ll get an answer containing DNA.On this world, that s a good answer, in that it states a crucialfeature of all (well, most) life here.However, it is an answer thataddresses a parochial realisation of a process that is probably far moreuniversal. Life is a more general phenomenon, capable of manydistinct realisations, employing many different types of organisedmatter  and even non-matter.236NOT AS WE KNOW ITPart of the evidence for this proposition, which forms a keydistinction between astrobiology and xenoscience, is the rapidlygrowing area of research known as  artificial life.This is not aboutmaking Earthlike lifeforms in the laboratory, but about hypotheticalcomplex systems whose properties resemble those that make lifeformsinteresting.The scientists who study artificial life, usually throughcomputer simulations, have constructed systems that by all the usualcriteria, except that of being based in organic chemistry, conform to ourideas of  living.Computer viruses are an all too familiar example.Several computerscientists have invented little evolutionary ecologies in computersystems.We are not very impressed by the ones, like Dawkins s biomorphs in The Blind Watchmaker, that are refined using artificialselection by a human.We do see that more sophisticated programmingcould eliminate the human element, but this has to be done, not justasserted.We are much more impressed by Tom Ray s Tierra system.Tierra plays out its evolutionary drama in the memory of a computer,and its  organisms are strings of binary digits.Ray discovered that itsevolutionary lineages diverged into parasites, symbionts, efficientorganisms that did well in the short-term, and more robust systems thatoutlasted them.A form of sexual reproduction evolved surprisinglyquickly, as did rudimentary social behaviour.None of these possibilitieswas  built in explicitly, or even cryptically, beforehand.They emergednaturally as high-level patterns of the system, unpredictableconsequences of the simple bit-level rules.If there are advanced aliens out there, they will surely have theequivalents of our computer viruses, and probably of our computergames.(Play is probably a universal.) They may well have made,invented, initiated self-replicating machines for mining andmanufacture.Our nearly-automated factories are not far from that imagine an automated factory set up to make basic programmableautomated factories.Come to that, there could well be somethinglike that working on Earth now, given the speed with which roboticsand nanotechnology are advancing.Many thinkers, following this road, have argued (in some ways likethe anthropist we ve been so unkind to) that there are no extelligenttechnological aliens out there because, if there had been:237WHAT DOES A MARTIAN LOOK LIKE?1.The aliens would have built automated mining machines andsuchlike.2.Improvement of these would have led to their becoming self-constructing and self-repairing.3.The aliens would doubtless have seeded them on to the otherbodies of their solar system.4.Some of these self-replicating machines would have escaped thatsolar system  they would have spread.5.Even at very slow spread speeds  say a walking-pace  they wouldhave spread throughout the galaxy by now.However, we haven t found any such machines in our solar system.Ergo, there aren t any aliens out there.We don t buy this as a reverse-explanation of the Fermi Paradox,  Ifintelligent aliens exist, why aren t they here? The whole argument isincredibly fragile, and assumes that the aliens will be like us in allimportant ways.But we should not be surprised to find that aliens  orhumans  with a level of technology very little above ours have madeself-replicating and self-modifying machines.We re close that doingthat ourselves.There are many arguments for supposing that any  aliens that wemeet will not be the organic beings themselves  who like us will not bewell-adapted for lengthy interstellar travels  but their sophisticatedmachines [ Pobierz całość w formacie PDF ]