Dave Typinski wrote:

jc <cirejcon@yahoo.com> wrote:

On Mar 24, 12:53 am, "K_h" <KHol...@SX729.com> wrote:

Fermi's paradox suggests that there are little or no other intelligent
civilizations within the Milky Way galaxy.  On the other hand, intelligent
life should exist on a substantial fraction of planets with life because
natural selection broadly increases intelligence with time.
 Here on the
Earth, for example, numerous mammals have a high degree of intelligence and
I suspect many of them could reach human intelligence with a few more
million years of evolution.

The galaxy could be full of intelligent life that we just don't
see.  SETI makes the assumption that the more advanced
a civilization is, the more EM radiation they emit, but this
is arguably untrue.  SETI would not find our civilization
even in the nearest solar system, and more and more of
our communications are being broadcast in forms
that radiate less, not more.

Or, given a more advanced understanding of mathematics and better
technology for communications via electromagnetic radiation, what EM
they do radiate may be impossible for us to distinguish from noise. 

Assuming they still use EM radiation to communicate, they might
encrypt it - in which case it looks like noise, which is what we
observe.  If they don't encrypt it, but use spread spectrum emission
and/or some other fancy modulation scheme, it looks like noise, which
is what we observe.

All that radio noise coming from the sky could be the encrypted
traffic of a galaxy-spanning civilization and we'd never know it.

http://setiathome.berkeley.edu/ap_faq.php