Project Cyclops, A Design... - Department of Earth and Planetary ...

acquisitionphasefor otherraces.Suppose thatEarth
doesindeedbecomelectromagnetically quietasour
technology becomesmoreadvanced. Mightwenotthen,
realizinghowundetectable wehadbecome, construct a
beaconto helpotherracesf'mdus?Wewouldconclude
thatourownradiativehistorymightbetypicalandthat
it wouldbe prettysilly for everyoneto listenwith
nobodytransmitting.
There is a somewhat more speculative reason to
expect beacons. Population I stars, which condensed
from gas clouds enriched in heavy elements from earlier
supernovae explosions, began to form in large numbers
early in the history of the galaxy and were very
numerous 9 billion years ago. If we take the 4 billion
year gestation time for advanced life on Earth as typical,
then as long ago as 5 billion years advanced cultures
appeared in the galaxy in large numbers. If we assume
that most of these attempted interstellar communication
during their advanced lifetimes, then many of them may
have been successful. One of the consequences of this
success would be the accumulation of a large common
body of knowledge that would include, in addition to all
the biological knowledge of all races in contact, a rather
complete picture of our galaxy, our neighboring galaxies,
and of the universe as these appeared 5 billion years ago.
As new races came of age and made contact with the
galactic community they would inherit this body of
knowledge, add to it, and in turn pass it on to still
younger races when they made contact. In fact, the
transmission down through the aeons of this accumulated
heritage of galactic knowledge could become one
of the principal raisons d Ttre for interstellar communication.
In this event beacons would very likely be used
to ensure the survival of the "galactic heritage" by
attracting the attention of young races.
Directivity of Beacons
In the search phase we very quickly conclude that we
need a large receiving antenna with its high gain and
directivity to (!) collect enough signal energy, (2) exclude
local interference, and (3) tell us where the signal
came from. In fact. the collecting area we will need is
probably so large that. even at the lowest usable frequencies
in the microwave window, we will be only able
to search one star at a time, as we have seen.
Suppose now that a similar system were used as a
beacon: that is, a single transmitter with a highly
directive antenna is used to irradiate sequentially m stars
over and over again. This beacon would be detectable by
beings around any one star only 1/mth of the time. In
effect this replaces p in equation { ! _by p/m to give
Pc = 1 - e -np/m (20)
Assuming an equal search effort rn _ n and, since
p