by Paul Davies
vol 183 issue 2459
07 August 2004, page 30
ConTACTinG humAns musT be
frusTrATinG if They miss The messAGe ThAt's stArinG Them
in The fACe,
says Paul Davies
Paul Davies is at
The Australian Centre for Astrobiology at Macquarie
University, Sydney, and author of The Origin of Life
SEARCHING for alien messages is a wild and speculative idea. For
more than 40 years, a heroic band of astronomers has been sweeping
the skies with radio telescopes in the hope of stumbling across a
signal. Though the silence so far has been deafening, this search is
buoyed by the belief that the truth is out there somewhere.
Now may be the time to try a radically
Even if it turns out to be a hopeless or completely misconceived
quest, the search for extraterrestrial intelligence, or
SETI, is worth carrying out because it forces us to think deeply
about the nature of life and intelligence, and the place of humanity
in the universe.
The use of radio telescopes in this
endeavour is predicated on several questionable assumptions. Even if
we take for granted that there are intelligent aliens who use radio
technology, and that they are trying to contact us - already a big
leap of faith - the problem of timing remains acute. By common
consent and simple statistics, any alien civilization in our corner
of the galaxy is likely to be millions - possibly tens or even
hundreds of millions - of years ahead of us technologically.
They will have been waiting a very long
time for earthlings to come on air. It is inconceivable that ET
would beam signals at our planet continuously for untold aeons
merely in the hope that one day intelligent beings might evolve and
decide to turn a radio telescope in their direction. But if ET
transmits messages only sporadically, the chances of us tuning in at
the right time are infinitesimal.
It would be more credible if the aliens could somehow spot the
emergence of terrestrial radio technology, so that they begin
blasting the airwaves at a time when they have a reasonable
expectation that we might be listening. But our own radio signals,
traveling across the galaxy at the speed of light, are unlikely to
have reached any alien civilizations yet, even using the most
optimistic estimates of SETI enthusiasts. So at this time, ET has no
idea that Earth hosts radio astronomers and so no reason to begin
An altogether more attractive strategy from ET's viewpoint would be
to plant artifacts containing messages in the vicinity of any
planets that have the potential to evolve intelligent life at some
unknown stage in the future. Then, if and when a technological
community emerged on that planet, it would encounter the cosmic
calling card on its doorstep. This is a favorite science fiction
theme: remember the obelisk in
2001: A space odyssey?
The problem with this "set-and-forget" technique of communication is
that the information content of the message may have to survive for
hundreds of millions of years. A conventional artifact placed on the
Earth's surface might be overlooked, and would be subject to the
vagaries of tectonic activity, glaciation and other turmoil. In
near-Earth orbit it would be even less conspicuous and at the mercy
of cosmic radiation, meteorites and solar flares. Obviating these
problems by making the artifact physically large would enormously
increase the cost of sending it here.
A better solution would be a legion of small, cheap,
self-repairing and self-replicating machines that can
keep editing and copying information and perpetuate themselves over
immense durations in the face of unforeseen environmental hazards.
Fortunately, such machines already exist. They are called living
cells. The cells in our bodies, for example, contain messages
written by Mother Nature billions of years ago.
So might ET have inserted a message into the genomes of terrestrial
organisms, perhaps by delivering carefully crafted viruses in tiny
space probes to infect host cells with message-laden DNA? It's an
idea that has been swirling around for a few years, and has recently
been championed by the Apollo astronaut Rusty Schweickart.
But on the face of it, there is a
serious problem. Living cells are not completely immune to
change. Mutations introduce random errors into the stored
information, and over a long enough time span they would inexorably
transform ET's message into molecular gobbledygook.
To minimize the effects of mutations, it would make sense to
incorporate the message into a highly conserved segment of DNA.
Such segments are normally associated with key coding regions of the
genome that control the most vital
functions of the organism. They tend to be unchanged between
species, suggesting an ancient origin. Mutations in such regions are
invariably fatal. But unfortunately tinkering with them by inserting
alien DNA would likely prove as lethal as any random
Conversely "junk" DNA - sections of the genome that seem
to serve no useful purpose - can be loaded with all manner of
genetic oddments without affecting the performance of the cells.
Inserting a message here would almost certainly be harmless. The
trouble is, junk DNA is famous for accumulating lots of
mutations. So the choice seems to be between killing
the messenger and compromising the message. What is needed is a
region of junk DNA that is also highly conserved.
Until recently, this would have been regarded as an oxymoron.
But no more. Genomics researchers at the Lawrence Berkeley
National Laboratory in California who compared human and mouse
DNA have reported the discovery of
vast, highly conserved sequences of junk DNA (New Scientist,
5 June, p 18).
These segments are apparently surplus
to requirements. When the researchers deleted them from the mouse
DNA, the animals seemed to be perfectly normal. If ET has put a
message into terrestrial organisms, this is surely where to look.
Looking for messages in living cells has the virtue that
DNA is being sequenced anyway. All it needs is a computer to
search for suspicious-looking patterns. Long strings of the same
nucleotides are an obvious attention-grabber. Peculiar numerical
sequences like prime numbers would be a clincher and patterns that
stand out even when partially degraded by mutational noise would
make the most sense.
A great example was given by cosmologist
Carl Sagan at the end of his
Contact, in which the supposedly
random digits of pi, when displayed as a two-dimensional
array, unexpectedly contained the figure of a circle. In the same
way, if a sequence of junk DNA bases were displayed as an
array of pixels on a screen (with the colour depending on the base:
blue for A, green for G, and so on), and a simple image like a
ragged circle resulted, the presumption of tampering would be
Such a feature would merely serve the purpose of flagging the
information. What might the message contain? One segment of DNA
excised by the Lawrence Berkeley team contained more than a
million base pairs - enough for a decent-sized novel or a potted
history of the rise and fall of an alien civilization. But the
message need not be the last word from ET. Rather, it could
tell us how to download the entire contents of Encyclopaedia
Galactica by conventional radio or optical techniques.
I am not suggesting that radio SETI be abandoned just yet.
The commissioning of the long-awaited Allen Telescope Array
in northern California will bring a much larger volume of the galaxy
within the scope of current search techniques. Trying to
second-guess alien communication strategies is fraught with
uncertainty, so we should try everything we can afford.
The truth may be out there somewhere. Or
it could be a lot closer to home.