by Paul Davies
New Scientist

vol 183 issue 2459

07 August 2004, page 30
from WolframScience Website
 

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.

• But what if the truth isn't out there at all?

• What if it lies somewhere else?

Now may be the time to try a radically different approach.

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 signaling us.

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 mutation.

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 novel 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 inescapable.

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.