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发信人: by (春天的小懒虫), 信区: SFworld
标  题: 2010 (49)
发信站: 哈工大紫丁香 (Wed Oct  6 15:25:28 1999), 转信

                        49
                 Devourer of Worlds

They  saw  it  again  the  next  morning, ship's time, as it came
around  to  the  dayside  of  Jupiter.  The  area of darkness had
now  spread  until  it  covered  an  appreciable  fraction of the
planet, and at last they were able to study it at leisure, and in
detail.
  `Do  you  know  what  it  reminds  me  of  ?'  said  Katerina. `A
virus  attacking  a  cell.  The  way a phage injects its DNA into
a bacterium, and then multiplies until it takes over.'
  `Are   you   suggesting,'   asked  Tanya  incredulously,  `that
Zagadka is eating Jupiter?'
  `It certainly looks like it.'
  `No   wonder  Jupiter  is  beginning  to  look  sick.  But  hy-
drogen and helium won't make a very nourishing diet, and
there's not much else in that atmosphere. Only a few per
cent of other elements.'
  `Which adds up to some quintillions of tons of sulphur
and carbon and phosphorus and everything else at the lower
end of the periodic table,' Sasha pointed out. `In any case,
we're talking about a technology that can probably do
anything that doesn't defy the laws of physics. If you have
hydrogen, what more do you need? With the right know-
how, you can synthesize all the ether elements from it.'
  `They're sweeping up Jupiter - that's for sure,' said Vasili.
`Look at this.'
  An extreme close-up of one of the myriad identical rec-
tangles was now displayed on the telescope monitor. Even
to the naked eye, it was obvious that streams of gas were
flowing into the two smaller faces; the patterns of tur-
bulence looked very much like the lines of force revealed by
iron filings, clustered around the ends of a bar magnet.
  `A million vacuum cleaners,' said Curnow, 'sucking up
Jupiter's atmosphere. But why? And what are they doing
with it?'
  `And how do they reproduce?' asked Max. `Have you
caught any of them in the act?'
  'Yes and no,' answered Vasili. `We're too far away to see
details, but it's a kind of fission - like an amoeba.'
  `You mean - they split in two, and the halves grow back
to the original size?'
  `Nyet. There aren't any little Zagadki-they seem to grow
until they've doubled in thickness, then split down the
middle to produce identical twins, exactly the same size as
the original. And the cycle repeats itself in approximately
two hours.'
  `Two hours!' exclaimed Floyd. `No wonder that they've
spread over half the planet. It's a textbook case of exponen-
tial growth.'
  `I  know  what  they  are!' said  Ternovsky  in sudden excite-
ment. `They're von Neumann machines!'
  `I believe you're right,' said Vasili. `But that still doesn't
explain  what they're doing. Giving them a label isn't all that
much help.'
  `And   what,'   asked   Katerina   plaintively,   `is  a  von
Neumann machine? Explain, please.'
  Orlov   and   Floyd  started  speaking  simultaneously.  They
stopped  in  some  confusion,  then  Vasili  laughed  and waved
to the American.
  `Suppose   you   had  a  very  big  engineering  job  to  do,
Katerina - and I mean big, like strip-mining the entire face of
the  Moon.  You  could  build  millions  of  machines to do it,
but  that  might  take  centuries.  If  you were clever enough,
you'd  make  just  one  machine  -  but  with  the  ability  to
reproduce  itself from  the  raw  materials  around it. So you'd
start  a  chain  reaction, and in a very short time, you'd have
...  bred  enough  machines  to  do  the  job  in  decades, in-
stead  of  millennia.  With  a  sufficiently  high rate of repro-
duction,  you  could do virtually anything in as short a period
of   time  as  you  wished.  The  Space  Agency's  been  toying
with  the  idea  for  years  -  and  I  know  you have as well,
Tanya.'
  `Yes:   exponentiating   machines.   One   idea   that   even
Tsiolkovski didn't think of.'
  `I  wouldn't care to bet on that,' said Vasili. `So it looks,
Katerina,  as  if  your  analogy  was pretty close. A bacterio-
phage is a von Neumann machine.'
  `Aren't  we  all?' asked  Sasha.  `I'm  sure Chandra would say
so.'
  Chandra nodded his agreement.
  `That's  obvious.  in  fact,  von  Neumann  got  the original
idea, from studying living systems.'
  `And these living machines are eating Jupiter!'
  `It  certainly  looks like it,' said Vasili. `I've been doing
some calculations, and I can't quite believe the answers -
even though it's simple arithmetic.'
  `It may be simple to you, 'said Katerina. `Try to let us have
it without tensors and differential equations.'
  `No - I mean simple,' insisted Vasili. `In fact, it's a perfect
example of the old population explosion you doctors were
always screaming about in the last century. Zagadka repro-
duces every two hours. So in only twenty hours there will be
ten doublings. One Zagadka will have become a thousand.'
  `One thousand and twenty-four, said Chandra.
  `I know, but let's keep it simple. After forty hours there
will be a million - after eighty, a million million. That's
about where we are now, and obviously, the increase can't
continue indefinitely. In a couple more days, at this rate,
they'll weigh more than Jupiter!'
  `So they'll soon begin to starve,' said Zenia. `And what
will happen then?'
  `Saturn had better look out, answered Brailovsky. `Then
Uranus and Neptune. Let's hope they don't notice little
Earth.'
  `What a hope! Zagadka's been spying on us for three
million years!'
  Walter Curnow suddenly started to laugh.
  `What's so funny?' demanded Tanya.
  `We're talking about these things as if they're persons -
intelligent entities. They're not - they're tools. But general-
purpose tools-able to do anything they have to. The one on
the Moon was a signalling device-or a spy, if you like. The
one that Bowman met - our original Zagadka - was some
kind of transportation system. Now it's doing something
else, though God knows what. And there may be others all
over the Universe.
  `I had just such a gadget when I was a kid. Do you know
what Zagadka really is? Just the cosmic equivalent of the
good old Swiss Army knife!'

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