Cosmic archaeology approach to SETI
paradox: It is relatively
easy to move around the galaxy at one ten thousandth of the speed of
light if you are patient. Fermi
may have noticed this in the
fifties and asked why there weren't aliens on earth. A recent book by Stephen
Webb discusses the Fermi
paradox in some detail.
sphere: Dyson suggested
that all the energy from a star could be harnessed by
the planets around the star to form a loose shell. A Dyson Sphere would
be an archaeological
signal of extrasolar intelligence. There have been a number
for Dyson Spheres.
classified astronomical sources according to the potentially
available energy for SETI signaling. A Type I Kardashev civilization
could utilize all the energy available from a planet such as the
earth. A type II Kardashev would exploit all the energy from a star (a
Dyson Sphere could be one approach). A Type III civilization could
all the energy from a galaxy. Jim Annis at Fermilab has searched
for Type III civilizations using light distributions from galaxies.
Lemarchand has produced several comprehensive
reviews covering a number of cosmic archaeological signatures for SETI.
Possible signals of
(not necessarily a sign of extraterrestrial intelligence)
Meteors: Based on
their composition certain meteors found
in Antarctica can be shown to come from Mars. One analyzed by McKay, et al. has
controversial evidence for Martian life.
atmospheres: One extrasolar planetary
atmosphere has already been observed.
There is a very substantial step from a first observation to confidence
that one is observing an atmosphere generated by life or even
hospitable to it. Burrows
has recently reviewed some of the difficulties in seeing
planetary extrasolar atmospheres.
This is the idea that life may have traveled between stars perhaps as
spores carried in cosmic dust or cosmic grains. Gribbin
contains a short summary of the concept. Hoyle and Wickramasinghe
have been among the most active investigators.
one centimeter diameter sphere of DNA
would contains an amazing 1020 bytes of information. For the
relatively "slow" speeds needed to escape a star (10-4 of
speed of light) the information cost per bit are comparable to
electromagnetic signaling. The problems include the associated rockets,
shielding, guidance, etc.