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Figure 2- Peak side lobe levels of radiation patterns for large antennae

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View of Arecibo Observatory in Puerto Rico with its 300 m dish

its observation time is devoted to ETI searches.

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SECTION I

CONSENSUS

INTRODUCTION

THE IMPACT OF SETI

CONCLUSIONS

1. IT IS BOTH TIMELY AND FEASIBLE TO BEGIN A SERIOUS SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

2.

3.

A SIGNIFICANT SETI PROGRAM WITH SUBSTANTIAL POTENTIAL
SECONDARY BENEFITS CAN BE UNDERTAKEN WITH ONLY MODEST
RESOURCES

LARGE SYSTEMS OF GREAT CAPABILITY CAN BE BUILT IF NEEDED

4.

SETI IS INTRINSICALLY AN INTERNATIONAL ENDEAVOR IN WHICH
THE UNITED STATES CAN TAKE A LEAD

....

INTRODUCTION

Heaven and earth are large, yet in the whole of space they are but as a small grain of rice ........ It is as if the whole of empty space were a tree, and heaven and earth were one of its fruits. Empty space is like a kingdom, and heaven and earth no more than a single individual person in that kingdom. Upon one tree there are many fruits, and in one kingdom many people. How unreasonable it would be to suppose that besides the heaven and earth which we can see there are no other heavens and no other carths?

Teng Mu, 13th Century philosopher
(translated by Joseph Needham)

In the enormous emptiness of space we can now recognize so many stars that we could count one hundred billion of them for each human being alive. Yet we know of only one inhabited planet, our Earth. The Earth has supported the development of life nurtured by one commonplace star, the nearby five-billion-year old Sun. We look out into the starry Universe quite unable to see within its compass any sign that we are not alone. The other planets near our Sun offer some hope to a search for other life, and indeed for many months Viking on the surface of Mars has been reporting the enigmatic chemical activity of the Martian soil. We remain uncertain, at the time of writing, whether the chemical changes are biological or inorganic in nature.

The web of life here on Earth is the consequence of a long complex sequence of natural selection by which life increased its scope and its variety, always exploiting the flood of energy bestowed directly or indirectly by the Sun. The Earth has seen fire and ice, yet it has provided steadily, for three billion years without a break, some environments to which life could adapt. Changes were never so drastic or so rapid that all survival became impossible, though particular species have arisen and died by the millions. Indeed, life has spread from its origins, probably near the seashore, to alpine peaks and ocean troughs, and has diversified almost beyond description. Our species and a few of our forebears have achieved considerable technological abilities and some degree of self-knowledge. Nor do we foresee any natural catastrophe ending this fabric of life until in due course the Sun itself runs out of nuclear fuel, some five billion years in the future.

We all know the starry sky at night, and on our deep photographs of the sky we see everywhere a dusting of small dots. Analysis of the light which caused those images, using its intensity and the details of its spectrum, has made it certain that such dots represent suns resembling our own, about which we know only that they are suns. Our own Sun with its cortege of planets would be just such another single dot, quite indistinguishable from a hundred million others at the distances we scan.

We have been able to understand in a general way how stars are born out of dense clouds of gas and dust in the interstellar spaces; we can see other stars in the transient stages of birth, as once was the Sun and its planets. Are planets always born in the spinning disk of gas out of which the

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