Fermi Paradox

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?

mike3 wrote:

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?

How do sonars hear a submarine miles away in the midst of all the noise in
the ocean?

You listen for a particular frequency while filtering out _all_ the other
frequencies. If the signal is greater than the noise in that very narrow band
you hear it. Further, you can integrate that frequency over time. Noise in
that band will average out to zero while the frequency will increase with time.

Using your example how do you hear your friend sitting next to you in a
stadium in the midst of all the noise in a stadium? You can also talk in a
loud factory and there the trick is not to shout but to speak normally and
distinctly. The ear is very good at picking out the frequencies of interest.

The only requirement is to have frequencies of interest louder than the noise
at those same frequencies. The broadband noise level (stadium noise) is not
important. The entire radio/TV spectrum has a huge noise level broadband. But
by tuning to just a narrow range of frequencies you can pick one station out
of all the stations and all the noise.

In practice, SETI is looking at the "water hole" frequency which is
particularly quiet over very long distances. It is assumed anyone sending
knows that also and chooses that frequency so as to be heard. That assumption
does not apply unless there is a deliberate attempt to communicate. I am not
aware of any reasoning which can lead to a second frequency to monitor so
after that one frequency it is a crap shoot.

"Matt Giwer" wrote in message
g.com...
mike3 wrote:

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?

How do sonars hear a submarine miles away in the midst of all the
noise in the ocean?

You listen for a particular frequency while filtering out _all_ the
other frequencies. If the signal is greater than the noise in that
very narrow band you hear it. Further, you can integrate that
frequency over time. Noise in that band will average out to zero while
the frequency will increase with time.

Using your example how do you hear your friend sitting next to you in
a stadium in the midst of all the noise in a stadium? You can also
talk in a loud factory and there the trick is not to shout but to
speak normally and distinctly. The ear is very good at picking out the
frequencies of interest.

The only requirement is to have frequencies of interest louder than
the noise at those same frequencies. The broadband noise level
(stadium noise) is not important. The entire radio/TV spectrum has a
huge noise level broadband. But by tuning to just a narrow range of
frequencies you can pick one station out of all the stations and all
the noise.

In practice, SETI is looking at the "water hole" frequency which is
particularly quiet over very long distances. It is assumed anyone
sending knows that also and chooses that frequency so as to be heard.
That assumption does not apply unless there is a deliberate attempt to
communicate. I am not aware of any reasoning which can lead to a
second frequency to monitor so after that one frequency it is a crap
shoot.

That's the long answer. The short answer is the question relies upon
total
ignorance concerning its topic. There used to be rational and informed
people posting here, but mostly rubbish lately. How come?

Titeotwawki -- mha [sci.astro.seti 2008 Sep 20]

Martha Adams wrote:

There used to be rational and informed
people posting here, but mostly rubbish lately. How come?

Because a group of kooks likes to cross post here and several other sci.*
groups. Their purpose in life is to count how many posts they can make and how
much reaction they can get. They are like an itch. If you scratch it, it gets
worse.

Martha Adams wrote:

"Matt Giwer" wrote in message
g.com...
mike3 wrote:
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?
How do sonars hear a submarine miles away in the midst of all the
noise in the ocean?
You listen for a particular frequency while filtering out _all_ the
other frequencies. If the signal is greater than the noise in that
very narrow band you hear it. Further, you can integrate that
frequency over time. Noise in that band will average out to zero while
the frequency will increase with time.
Using your example how do you hear your friend sitting next to you in
a stadium in the midst of all the noise in a stadium? You can also
talk in a loud factory and there the trick is not to shout but to
speak normally and distinctly. The ear is very good at picking out the
frequencies of interest.
The only requirement is to have frequencies of interest louder than
the noise at those same frequencies. The broadband noise level
(stadium noise) is not important. The entire radio/TV spectrum has a
huge noise level broadband. But by tuning to just a narrow range of
frequencies you can pick one station out of all the stations and all
the noise.
In practice, SETI is looking at the "water hole" frequency which is
particularly quiet over very long distances. It is assumed anyone
sending knows that also and chooses that frequency so as to be heard.
That assumption does not apply unless there is a deliberate attempt to
communicate. I am not aware of any reasoning which can lead to a
second frequency to monitor so after that one frequency it is a crap
shoot.

That's the long answer. The short answer is the question relies upon total
ignorance concerning its topic. There used to be rational and informed
people posting here, but mostly rubbish lately. How come?

At one time there were also people here who answered the questions of
novices. I waited a day and then replied. As expected my reply generated
responses to me rather than different style answers to the questioner. Why is
that?

Whether or not we choose to remember it, we were all novices at one time. As
the questioner did not hint at his background a response touching on several
different factors was given in hopes of finding common ground upon which to
build a more useful answer.

When there was regular discussion on the problems of the S@H follies there
were technical discussions. Now that S@H has had its lunch eaten by a more
general program and that program works smoothly there is little to discuss and
thus very few technical discussions get started.

--
Charon only takes Euros.
-- The Iron Webmaster, 4044
http://www.haaretz.com What is Israel really like? http://www.jpost.com a7

Golden California Girls wrote:
Martha Adams wrote:
There used to be rational and informed
people posting here, but mostly rubbish lately. How come?

Because a group of kooks likes to cross post here and several other sci.*
groups. Their purpose in life is to count how many posts they can make and how
much reaction they can get. They are like an itch. If you scratch it, it gets
worse.

That does not fit the person asking this basic question. It is just to this
newsgroup and it is a quite common question for newbies. The answer to it is a
start to understanding the rationale for the project.

The Brad Guths of this world are another matter.

--
The US economy is in such bad shape Bush had to hold a press
conference to assure us it is in great shape.
-- The Iron Webmaster, 4045
http://www.giwersworld.org a1

Matt Giwer wrote:
Golden California Girls wrote:
Martha Adams wrote:
There used to be rational and informed
people posting here, but mostly rubbish lately. How come?

Because a group of kooks likes to cross post here and several other sci.*
groups. Their purpose in life is to count how many posts they can
make and how
much reaction they can get. They are like an itch. If you scratch
it, it gets
worse.

That does not fit the person asking this basic question. It is just
to this newsgroup and it is a quite common question for newbies. The
answer to it is a start to understanding the rationale for the project.

The Brad Guths of this world are another matter.

At one time there were also people here who answered the questions
of novices. I waited a day and then replied. As expected my reply
generated responses to me rather than different style answers to the
questioner. Why is that?

Whether or not we choose to remember it, we were all novices at one
time. As the questioner did not hint at his background a response
touching on several different factors was given in hopes of finding
common ground upon which to build a more useful answer.

When there was regular discussion on the problems of the S@H follies
there were technical discussions. Now that S@H has had its lunch eaten
by a more general program and that program works smoothly there is
little to discuss and thus very few technical discussions get started.


Funny. My post quoted Martha and answered her question. Maybe I didn't tag the
subject [meta]. That must be it. Otherwise I can't figure out how Matt thinks
I was in any way responding to him.

In any case to answer Matt's [meta] question of why Martha sent her post, he
might ask her directly. My guess it is for the very same reason Matt posted his
most recent two posts here. The long answer is the signal to noise ratio got to
the point there is more noise than signal and at that point people stop
listening because it isn't fun any more.


S@H isn't the only program looking. It isn't the program with the most funding.

Now if you want to actually answer the OP, S@H is looking for two very different
but specific kinds of signals. The first is the very intentional broadcast
using a carrier wave, like AM or FM radio. The second is looking for a
broadband signal, more like a cellphone. It is rather easy to use math to pick
either signal out of noise. Neither is looking to find intelligence on the
signal, just its presence.

As for the frequency being searched, it happens to be near a frequency that is
scientifically interesting and where the universe is otherwise quiet. The
thinking is that other civilizations that want contact would be expecting us to
be looking there because it is scientifically interesting so if they transmit
there they would stand a better chance of being heard.

"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