wrote:
snipsnipsnip

On the lack of observed alien civilization, we need to remember that
the universe is still pretty young. Sure, 13 billion years sounds a
real lot, but remember if we subtract 3 billion years that leaves 10
billion. The point is, it´s taken life here about that time to evolve
intelligent life. While that might take shorter time ellsewhere, one
has to remember that evolution of life from bacteria is not simple and
unlikelly to take a short time. In addition, we need to consider the
age of stars, and evolution of matter inside the galaxy. The fact is
that heavyer elements than hydrogen have to be manufactured by stars.
Basigly, generations of stars have to live and dye for enough material
to be available for rocky planets of the sort we live on. Remember,
stars aren´t shortlived. Now, subtract another billion years and half,
and 8.5 billion is the time we have before the Solar System began to
form. That is the time that the Milky Way has for succeeding
generations of stars to live and dye, and to result in increasingly
higher concentrations of heavy materials. Apparently the Sun is a
third generation stars of its type, i.e. the universe has had enough
time to produce three generations of yellow stars of that particular
type. There is though one litle bit, I´ve heard somewhere that the Sun
is a billion years younger than is the average age of third generation
yellow stars.

So, if the third generation is the first generation with enough heavy
materials present for rocky planets to be likelly enough, and the Sun
is relativelly young among that groups of stars, that leaves perhaps a
chance that if life has evolved on theyr planets that it has had a
longer time to evolve. Even so, there are so many uncertainties about
evolution of life, that the age difference could easilly be eaten up
by that.

Cheers, Einar