Enrico Fermi |
In their famous book of hard scientific popularization, The Anthropic Cosmological Principle,
published in 1986, the cosmologists John Barrow and Frank Tipler offer a proof that we are alone in the galaxy by
means of a variant of the Fermi paradox (if
there are any extraterrestrial intelligences in the Galaxy, why aren’t they
here?) which can be summarized as follows:
1.
In 100 years we will have succeeded in creating life
in the laboratory. Not just life, we will also be able to build a complete
human being from its chemical components and information about the human genome,
which can be stored in a digital memory.
2.
In 100 years we will have managed to build
artificial intelligences as intelligent as human beings, able to replace us in
any place and circumstance.
3.
Our current space technology allows us to reach a
speed of 0.0003 c (where c is the speed of light). At that speed, a spaceship
would take about 50,000 years to reach the nearest stars.
4.
The ship in question (let’s call it a von Neumann probe) may carry one or
more artificial intelligences, along with the information necessary to
synthesize human beings as soon as they reach their target. The ship does not
need to carry expensive equipment to keep the crew alive. Consequently, the
cost of the expedition would be little more than the cost of the Apollo
project. The star that is reached does not need to have planets suitable for
life. The synthesized human beings could be installed in space stations (O'Neill colonies) built after
arriving there from raw materials in the planets or asteroids in the target planetary
system.
5.
The artificial intelligences making the trip would build,
from the same raw materials, new von Neumann probes that would be sent to
neighboring stars.
6.
It would be enough that two von Neumann probes from each
starting point would be successful, in average, in the colonization of nearby
stars. The colonization of the galaxy would then take place exponentially.
Barrow and Tipler estimate that 300 million years would suffice to colonize the
whole galaxy (the authors claim that this upper limit is actually exaggerated).
7.
If we can do this (or rather, if we could do this by 2085, according to points 1 and 2), other extraterrestrial intelligences would
have been able to do it too. Any of them with a lead of 300 million years over
us (a little over 2% of the age of the universe) would already be here. Since they
are not, they do not exist.
This argument depends on two initial hypotheses: points 1 and 2. If it were
impossible to artificially synthesize living human beings from inert matter, or
if it were not possible to build artificial intelligences equivalent to us, the
whole argument would fall to the ground. It is true that the results do not
depend on whether it would take us precisely 100 years to achieve these
objectives. If 1000, 2000 10,000 years, or even more were required, the results
would be the same. The problem is that at least one of those points, 1 and 2,
may be unattainable.
In their book, Barrow and Tipler predicted that the first complete living
cell would be synthesized in the laboratory in about 30 years, i.e. by 2015. This prediction has not been fulfilled. As for artificial
intelligence, since 1958 it has been considered imminent several times, but all
these predictions have failed. As a result, 30 years after the publication of the
book by Barrow and Tipler, we still cannot confirm their assumptions.
Manuel Alfonseca
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