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[ Pobierz całość w formacie PDF ]
.These will again multiply, andwith the right ink and a tall cylinder you can get six generations.Larry Niven was very taken with this phenomenon, and he and Jackused it to invent a new and original alien.First, you need to know aboutthe so-called Bussard ramjet spaceship, a standard feature of Niven s known space novels, which collects hydrogen from space using amagnetic trap and fuses it at the focus, producing ample thrust energyby using the hot products for rocket propulsion.The pilot of such aship is investigating a new dust cloud, like the Horsehead Nebula inOrion, where stars are condensing all around.To his surprise, he seesanother ramjet ahead but he knows that he s the only one from hishome system.This must be an alien starship.Wow! First Contact withan extelligent alien species! He tries all his radio tricks, but can get only noise.However, he knows that sophisticated messages are alwaysencrypted, so (Lachmann s theorem) they do sound like noise so hekeeps trying to contact the other ship.Meanwhile he gets on its tail andbegins to catch it up; that doesn t work, of course, because he can t burnthe other ship s exhaust.So he runs around to ahead of the other ship which suddenly disappears. Oh my God, he thinks, the aliens haveFTL travel that ship s gone into hyperspace. Soon he finds anotherspaceship, chases that and the same thing happens.The plot gimmickis that these are not alien technology, but aliens: natural Bussardramjets, reproducing lifeforms created by an unusual but by no meansimpossible collapse of a proto-star into a torus instead of a sphere.The torus didn t disappear because it suddenly went FTL: itdisappeared because it died, unable to eat the ramjet s exhaust.These simple reproductions without heredity can just about support astory, but the problem is to imagine them evolving.We pointed outearlier that a credible alien lifeform must not only work as anorganism: there has to be a plausible route for its evolution.We saidthen that it is difficult to imagine an organism that works but does notpossess a reasonable evolutionary ancestry, but the Bussard tori are soclosely linked to specific physics that finding an evolutionary route thatcould lead to them is distinctly challenging.It is probably necessary to246 THE SENSUAL TRIBBLEhave mutable heredity in order to produce an interesting evolutionarydevelopment, but Bussard tori reproduce like flames, without heredity,and therefore they can t evolve in any very interesting ways.Earthly lifeforms do have flexible heredity, which is presumably whyvery complex organisms have been able to evolve.The chemical basis ofthat heredity is DNA and its associated molecular assistants.Themachinations of DNA and RNA are the only workable system of thiskind that humanity has observed.Are other systems available? Toapproach this question, we have to extract an underlying universal fromthe terrestrial DNA parochial; then there is a good chance that an alienspecies might realise that universal using some other parochial instance.In other words, we must generalise the hereditary system that we usebefore we try to consider alien versions of it.In the late 1940s the mathematician John von Neumann wasthinking about self-copying machines, although his ideas were notpublished until 1966.At that time, many people thought that there wasa philosophical obstacle to the existence of such machines the homunculus problem.This goes back to an old debate about humanreproduction.Sperms and eggs somehow contain , if only potentially,the complicated human being into which they grow.Including itssperms or eggs, which must also contain the complicated human beinginto which they grow.And so on.for ever.Your own body somehow contains an infinite sequence of your future descendants, like nestedRussian dolls.One theory took this image literally, and held that everysperm contains a tiny human being, called a homunculus completewith its own sub-homunculus, and so on.But atoms set a lower limitto the size of material objects, so this idea makes no sense.Livingcreatures must reproduce by some other method but what? There wasa feeling that whatever that method was, it involved special, mysticalproperties of life , and was thus impossible for a machine.Von Neumann exploded this view by devising a completely abstractmathematical system capable of making copies of itself.It was a cellularautomaton , an array of cells like a gigantic chessboard.Each cell couldbe in one of a number of internal states, and at each tick of a clock, thestate of a cell would change depending on what the states of thesurrounding cells were.He set up suitable rules for those changes, andcame up with a machine a configuration of states that could copy247 WHAT DOES A MARTIAN LOOK LIKE?itself.Its cells had twenty-nine states, and there were 50,000 200,000cells (the literature is contradictory on this point).In 1968 E.F.Coddreduced the number of states from twenty-nine to eight, at the expenseof having 100 million cells later reduced to 100,000 by J.Devore inthe 1970s, and published in 1992 by Devore and R.Hightower.Von Neumann s automaton avoided the homunculus problem in avery clever way.It came in three pieces: a blueprint which specified incoded form how to build the entire machine, a constructor that couldmake any machine given its blueprint, and a copier that could copyblueprints [ Pobierz całość w formacie PDF ]
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.These will again multiply, andwith the right ink and a tall cylinder you can get six generations.Larry Niven was very taken with this phenomenon, and he and Jackused it to invent a new and original alien.First, you need to know aboutthe so-called Bussard ramjet spaceship, a standard feature of Niven s known space novels, which collects hydrogen from space using amagnetic trap and fuses it at the focus, producing ample thrust energyby using the hot products for rocket propulsion.The pilot of such aship is investigating a new dust cloud, like the Horsehead Nebula inOrion, where stars are condensing all around.To his surprise, he seesanother ramjet ahead but he knows that he s the only one from hishome system.This must be an alien starship.Wow! First Contact withan extelligent alien species! He tries all his radio tricks, but can get only noise.However, he knows that sophisticated messages are alwaysencrypted, so (Lachmann s theorem) they do sound like noise so hekeeps trying to contact the other ship.Meanwhile he gets on its tail andbegins to catch it up; that doesn t work, of course, because he can t burnthe other ship s exhaust.So he runs around to ahead of the other ship which suddenly disappears. Oh my God, he thinks, the aliens haveFTL travel that ship s gone into hyperspace. Soon he finds anotherspaceship, chases that and the same thing happens.The plot gimmickis that these are not alien technology, but aliens: natural Bussardramjets, reproducing lifeforms created by an unusual but by no meansimpossible collapse of a proto-star into a torus instead of a sphere.The torus didn t disappear because it suddenly went FTL: itdisappeared because it died, unable to eat the ramjet s exhaust.These simple reproductions without heredity can just about support astory, but the problem is to imagine them evolving.We pointed outearlier that a credible alien lifeform must not only work as anorganism: there has to be a plausible route for its evolution.We saidthen that it is difficult to imagine an organism that works but does notpossess a reasonable evolutionary ancestry, but the Bussard tori are soclosely linked to specific physics that finding an evolutionary route thatcould lead to them is distinctly challenging.It is probably necessary to246 THE SENSUAL TRIBBLEhave mutable heredity in order to produce an interesting evolutionarydevelopment, but Bussard tori reproduce like flames, without heredity,and therefore they can t evolve in any very interesting ways.Earthly lifeforms do have flexible heredity, which is presumably whyvery complex organisms have been able to evolve.The chemical basis ofthat heredity is DNA and its associated molecular assistants.Themachinations of DNA and RNA are the only workable system of thiskind that humanity has observed.Are other systems available? Toapproach this question, we have to extract an underlying universal fromthe terrestrial DNA parochial; then there is a good chance that an alienspecies might realise that universal using some other parochial instance.In other words, we must generalise the hereditary system that we usebefore we try to consider alien versions of it.In the late 1940s the mathematician John von Neumann wasthinking about self-copying machines, although his ideas were notpublished until 1966.At that time, many people thought that there wasa philosophical obstacle to the existence of such machines the homunculus problem.This goes back to an old debate about humanreproduction.Sperms and eggs somehow contain , if only potentially,the complicated human being into which they grow.Including itssperms or eggs, which must also contain the complicated human beinginto which they grow.And so on.for ever.Your own body somehow contains an infinite sequence of your future descendants, like nestedRussian dolls.One theory took this image literally, and held that everysperm contains a tiny human being, called a homunculus completewith its own sub-homunculus, and so on.But atoms set a lower limitto the size of material objects, so this idea makes no sense.Livingcreatures must reproduce by some other method but what? There wasa feeling that whatever that method was, it involved special, mysticalproperties of life , and was thus impossible for a machine.Von Neumann exploded this view by devising a completely abstractmathematical system capable of making copies of itself.It was a cellularautomaton , an array of cells like a gigantic chessboard.Each cell couldbe in one of a number of internal states, and at each tick of a clock, thestate of a cell would change depending on what the states of thesurrounding cells were.He set up suitable rules for those changes, andcame up with a machine a configuration of states that could copy247 WHAT DOES A MARTIAN LOOK LIKE?itself.Its cells had twenty-nine states, and there were 50,000 200,000cells (the literature is contradictory on this point).In 1968 E.F.Coddreduced the number of states from twenty-nine to eight, at the expenseof having 100 million cells later reduced to 100,000 by J.Devore inthe 1970s, and published in 1992 by Devore and R.Hightower.Von Neumann s automaton avoided the homunculus problem in avery clever way.It came in three pieces: a blueprint which specified incoded form how to build the entire machine, a constructor that couldmake any machine given its blueprint, and a copier that could copyblueprints [ Pobierz całość w formacie PDF ]