Stairway to the heavens in search for ET

ON October 12 last year Nasa celebrated the 500th anniversary of

Columbus' discovery of America by starting the biggest search for ET in

history.

The world's largest radio telescope, the 1000ft dish at Arecibo in

Puerto Rico, and the Goldstone Tracking Station, in the Mojave Desert,

Southern California, began scanning the heavens for evidence of

non-human civilisations at 7pm GMT.

This 10-year $100m programme, aimed at establishing whether we are

alone in the galaxy, has been proceeding for six months. In that time

deep space has been examined hundreds of times more thoroughly than all

preceding Search for Extraterrestrial Intelligence projects combined, so

far without significant result.

SETI has roots going back to the last century when it was suggested

that pine trees be planted in the shape of right-angle triangles over a

vast area of Siberia so that we may contact the inhabitants of the moon.

Another suggestion was to dig a 20-mile-wide ditch across the Sahara,

fill it with paraffin and light it! In 1983 the wealthy Percival Lowell

had an observatory built at Flagstaff, Arizona, with the specific

intention of studying the ''advanced civilisation'' on the planet Mars.

Today we listen for ET's radio signals from other stars.

Each era uses the means available to it. The problem with radio being

that ET may communicate with some other at present unknown technology.

Back in the days when scientists were first experimenting with ''Hertz

waves'' no-one thought of them as a means of communication. Astronomers

actually said then that there might be some unknown way for

civilisations in space to confer. Even when radio technology was

developed it was initially dismissed as being useful for this purpose.

Now SETI scientists discuss endlessly which radio wave bands are best

for making searches. Of course there may be some other method adopted in

future which they regard today as unlikely. An example could be the

curious quantum effect that seems to make particles influence each other

instantaneously over vast distances. Perhaps in 100 years this will be

the main thrust of SETI and a century later something else, and so on.

There is a philosophy behind their attitude. They believe that

although it would take decades or centuries for messages to pass back

and forth across the immense reaches of space, the ''conversations''

would be between individual civilisations rather than individual people.

The likelihood of there being civilisations similar to ours, in as

much as they want to chat on the phone, is all part of a formula at the

heart of this thinking. It is called the Drake Equation.

Frank Drake, an astronomer at the University of California, has been

pushing SETI for more than 30 years and set up the SETI Institute in the

mid-eighties. He made the first modern radio search for ET back in 1960.

His analysis of the problem boiled down to this: first take the number

of stars in the Milky Way Galaxy, which is currently believed to be

about four hundred billion.

Determine how many of these are stars like our sun -- the proportion

turns out to be around 10%, so we have 40 billion.

Recent observations by astronomical satellites indicate that possibly

10% of these if not more have planets. Now we are down to four billion.

From here on the assumptions pile up thick and fast. How many planets

are abodes of life? The number usually drawn out of the hat is one per

thousand stars or four million planets bearing life in our galaxy.

Of these it is assumed another one in a thousand produces a

civilisation roughly like our own.

If this guesswork is anywhere near accurate there should be a few

thousand civilisations out there. If only a handful of these are

interested in radio messaging one another we should be able to tune in

to them with Nasa's current programme.

There are two programmes under the one umbrella. The Targeted Search

concentrates on carefully examining the nearest 800 sun-like stars over

the next 10 years. The All Sky Survey will, as its name suggests,

investigate every part of the heavens over the same period, dissecting

the radio spectrum by examining more than a million channels

simultaneously. In previous attempts the problem was that whenever

something interesting was picked up, no-one realised it until the

results were analysed. By the time the radio telescopes were realigned

to go back and examine the source, it was gone. The computers being used

now are faster and programmed to be much smarter. They can recognise

what a scientist would find interesting and there and then concentrate

on that alone.

There are dozens of objections to the thinking behind the project.

Drake's equation contains too many unknown quantities. Even the

supposedly hard astronomical data is still greatly guesswork.

Another stumbling block is that we do not know enough about these

civilisations supposedly like our own. Here is the biggest question mark

of all.

Although we are acquainted well enough with the problems associated

with the immensity of space, consideration has to be afforded to the

immensity of time.

Human civilisation has evolved explosively in terms of cosmic time. A

million years ago we were bright pack animals. A hundred thousand years

ago the packs were evolving into family based tribal units. What we call

civilisation is fewer than 10,000 years old and even that has changed

dramatically in nature and complexity over the past 1000, and

particularly the past 100 years. The rate of change is accelerating. In

all probability we would be lost in the world of a century hence. The

world of a thousand years in the future is unimaginable, but it is safe

to say that the changes in nature and complexity will continue.

The problem is then that what we regard as civilisation might merely

be a brief transitory phase in the evolution of intelligent species such

as our own. Whether we destroy ourselves or use technology to change

ourselves, in 1000 years' time the curtain could well have come down on

human civilisation as we know it.

In our 10 billion-year-old galaxy, civilisations could wink in and out

of existence. The 4000 ET phone calls may have rung once briefly before

anyone picked up the phone.

* Lost messages? Some interesting signals picked up by SETI

investigators in the past 20 years:

* August 17, 1977: Ohio State's receiver picks up a signal from

Sagittarius. The scientist who examines the printout scribbles ''Wow!''

beside it.

* October 10, 1986: Again from the region of Sagittarius, this was one

of around 40 interesting signals detected by the Harvard META project.

* August 14, 1989: Another META pickup this time from Virgo.

* August 16, 1989: Like the rest; when the META people at Harvard came

to examine this signal from Pisces it had stopped.

* May 9, 1990: Parkes radio telescope in Australia detected an

artificial-looking signal from Ophiuchus.