"mike3" wrote in message
...
Hi.

I was wondering: How do we know it would even be possible to receive
the signals from aliens even if they did exist and did send out radio?
Considering we have a galaxy full of stars blasting out far more
intense radio signals than any ground-based transmitter could.
Wouldn't it be like trying to listen for a fly buzzing on the other
end of a stadium, with 50,000 screaming fans in between you and it?

The stars are actually surprisingly silent in the (microwave) radio
spectrum.

Stars radiate what is called 'blackbody' radiation, which is very strong in
the visible spectrum (visible light), but almost nonexisting for radio
frequencies. Even a fairly feable transmitter will be able to 'outshine' its
own star in the background.

Also note that a good (large) radio telescope does not have more than a few
stars in it's 'aparture' (its field of view).
The noise from all the other stars in the Galaxy is thus not so important.

Below 1GHz there is actually a lot of noise coming from the center of the
Galaxy (called cyclotron radiation). Besides that, it's difficult to make
narrow beams below 1GHz (need increadibly large antenna's) and Earth radio
So below 1GHz is not a good place to look for ET.

On the high end, our atmosphere absorbs most of the radiation (oxygen and
water have strong absorption lines that really start to count above 10 or 20
GHz.

But between 1GHz and 10GHz it's very nice and quiet in the Galaxy, so that
(after terminating human-created radiation and natural phenomenon (like
pulsars)) we can hear the soft hum of the cosmic background radiation as the
most notable 'noise'.

Rob