What If Everybody Is Listening And Nobody Is Transmitting?

[tofu]

I did a forum search for this and it looks like no one else has posted it.

http://www.space.com/searchforlife/s...it_050421.html

[Lance]

As I understand it, and I could be wrong...

I believe the current various SETI projects would not find the Earth very far away. We look in "quiet" areas of the spectrum where intentional transmissions would be easier to spot. But we don't transmit there ourselves.

I should probably read the article before I click the button down ther

[Glom]

Well that's a bit self-absorbed. We tell all the aliens to transmit, and we don't transmit ourselves. How hypocritical!

[Sam5]

I did a forum search for this and it looks like no one else has posted it.

http://www.space.com/searchforlife/s...it_050421.html

We discussed this in the “wow signal” thread. I say we should be sending basic radio signals to nearby stars that might have earth-type planets.

There is no sense in sending to distant stars since our signals would take 50, 100, or more years to get out there to the stars, and any direct response would take just as long to get back.

But a signal to a star/planet 4-5 light-years away could be answered 8-10 years after we send it, if someone is listening.

[tofu]

I say we should be sending basic radio signals to nearby stars that might have earth-type planets.

I'm the owner of a local radio station. We play top 40 pop music and do the news at the top and bottom of the hour. I think I'll get rid of the non-directional antenna and have the station send only to the nearest house, for about 10 minutes, and then point it at the next nearest house. That sounds like a really good idea.

[Nick]

[quote="tofu"]

and then point it at the next nearest house. That sounds like a really good idea.

Great reception though!


I still think we are wrong about seti. Everyone always presumes intelligent life is like human life, human form, human technology (although more advanced).

I think that is wrong. It may be incorrect that life 'can' only exist in our observed and tested environment, but it cannot be presumed. This is where science fails.

Nick

[SciFi Chick]

But aren't all of our television shows and radio shows being broadcast?

[Sam5]

I say we should be sending basic radio signals to nearby stars that might have earth-type planets.

I'm the owner of a local radio station. We play top 40 pop music ...

I think the SETI people are looking for “intelligent” life.

[Sam5]

But aren't all of our television shows and radio shows being broadcast?

That is true. But with regular radio and TV transmissions, the antennas are designed only for transmission around and across the surface of the earth, i.e. for short distances. For communication with other worlds, we would need to send out a focused or beamed signal to a narrow part of the sky, so we can concentrate more power in a narrow beam. With standard broad-beam transmissions, the power of the signal falls off rapidly after a few dozen or a few thousand miles.

[SciFi Chick]

With standard broad-beam transmissions, the power of the signal falls off rapidly after a few dozen or a few thousand miles.

What does that mean exactly? Does it become muddied and turn to noise so that someone presumably listening can't get a dignal, or does it just become impossible to pick up, or something else?

[Grey]

That is true. But with regular radio and TV transmissions, the antennas are designed only for transmission around and across the surface of the earth, i.e. for short distances. For communication with other worlds, we would need to send out a focused or beamed signal to a narrow part of the sky, so we can concentrate more power in a narrow beam. With standard broad-beam transmissions, the power of the signal falls off rapidly after a few dozen or a few thousand miles.

I'd actually agree that this is a good idea. I think the likelihood that someone will respond is remarkably low, but it wouldn't be all that much effort. And if, much to our surprise, someone did respond, that would be amazing.

[Grey]

What does that mean exactly? Does it become muddied and turn to noise so that someone presumably listening can't get a dignal, or does it just become impossible to pick up, or something else?

Think about how much fainter a light bulb is if you view it from a long distance away. The power spreads out over the entire sphere centered on the source, and eventually it's impossible to make it out. But a tightly focused source, like a laser, can be seen at a much greater distance, even if the power output is the same.

[Sam5]

With standard broad-beam transmissions, the power of the signal falls off rapidly after a few dozen or a few thousand miles.

What does that mean exactly? Does it become muddied and turn to noise so that someone presumably listening can't get a dignal, or does it just become impossible to pick up, or something else?

It’s like turning on a flashlight bulb without a polished shiny reflector behind it. The light goes out in all directions and becomes weak after just a few feet of travel. But if you put a shiny reflector behind the bulb, you can send a bright beam out a long distance. This is how microwave sending and receiving antennas work. They actually work something like concaved mirrors, sending “beams” straight out, which concentrate the power into a narrow beam.

In fact, the SETI antennas are parabolic concaved antennas, which are actually reflectors. The “big dish” collects a narrow beam of the light or radio waves, and focuses it into a small radio antenna. To beam a signal out with the most power in a narrow beam, a transmitting antenna is placed in the prime focusing spot of a dish antenna.

The signals of the old “I Love Lucy” TV shows of 50 years ago are probably still out there in space, 50 light-years away from the earth, but without the old signals being “beamed” out with a dish antenna, the old signals are probably too weak to distinguish from normal space background noise and signals, which are emitted by stars, galaxies, etc.

[SciFi Chick]

So, how do you decide where to focus the beam?

[Sam5]

So, how do you decide where to focus the beam?

I would start by focusing the beam at the nearest stars, for a few weeks at a time, since they are are only about 4 light years away. Then we should work our way out to more distant stars, up to maybe 10 or 20 light years away. If there is an earth type planet circling one of the stars, and if it contains “people”, and if they have developed basic radio, then they might receive our signal and send us a response.

I think it’s very unlikely, but remember that for 5,000 years the Europeans and others thought it was unlikely for there to be any land or people across the big ocean.

[SciFi Chick]

I would start by focusing the beam at the nearest stars, for a few weeks at a time, since they are are only about 4 light years away. Then we should work our way out to more distant stars, up to maybe 10 or 20 light years away. If there is an earth type planet circling one of the stars, and if it contains “people”, and if they have developed basic radio, then they might receive our signal and send us a response.

I think it’s very unlikely, but remember that for 5,000 years the Europeans and others thought it was unlikely for there to be any land or people across the big ocean.

Are we certain we want to find others? Especially if we're going to do what the Europeans did - or worse, have it done to us?

[Lycus]

Are we certain we want to find others? Especially if we're going to do what the Europeans did - or worse, have it done to us?

Well, we're certainly in no position to do that ourselves for the time being. Whether we should be afraid of that happening to us? I've often wondered if it's nothing more than wishful thinking when we expect a hypothetical spacefaring race to look upon us as equals. Oh well, I figure that whether we do the SETI thing or not, if they're out there and more advanced, then they're going to find us sooner or later anyway.

[umop ap!sdn]

The nearest star system is a multiple; multiple systems are thought to be not terribly favorable to life as we know it.

The next closest sunlike stars are out around 10-11 ly but even these are not necessarily good candidates: Epsilon Eridani is very young so life hasn't had much time to evolve there whereas Tau Ceti may have too many asteroids to maintain an earthlike planet.

Farther out approaching 20 ly is where the sunlike stars begin to get less scarce - Sigma Draconis, 36 Ophiuchi (but even out that far away, 82 Eridani might be too old and Delta Pavonis is entering its subgiant stage) anyway stopping at 20 ly could leave out many possibilities for life.

I say we send signals out to stars 100 ly away and let our descendants head out there in starships and intercept any replies halfway.

[Grey]

Are we certain we want to find others? Especially if we're going to do what the Europeans did - or worse, have it done to us?

I'd certainly like to know if someone else is out there. As far as risks of invasion go, remember that we're nowhere near mounting an expedition to even the nearest star, and they probably aren't either (if they were able to travel between stars with relative ease, and they're close by, they'd already be here). So, for a long time, probably all we could do is talk, and even that would have a multiple year delay between messages. The colonization of the New World might have gone very differently (hopefully, for the better) if for the first hundred years or so the only contact possible was writing letters back and forth.

[Lycus]

The nearest star system is a multiple; multiple systems are thought to be not terribly favorable to life as we know it.

How exactly would an Earth-size planet that's about 1 AU away from one of the Alpha Centauri stars fare?

[Crazieman]

Its possible for an earth size planet to orbit the habitable zones of Alpha Centauri A or B - but it is viewed as extremely unlikely.

Better odds at winning powerball.

[Van Rijn]

The nearest star system is a multiple; multiple systems are thought to be not terribly favorable to life as we know it.

How exactly would an Earth-size planet that's about 1 AU away from one of the Alpha Centauri stars fare?

The last time I read something on this, the argument was that an earthlike world could be in a stable orbit at that distance, or even in a substantially larger orbit about Alpha Centauri A (which, by the way, is a bit more massive/brighter than the sun). The question seems to be if a planet could form in the first place. Given how little we know about planet formation, I'm waiting until we can confirm this in practice.

Over the next few decades we will be getting a better idea of where there are earthsized worlds, and eventually will be able to detect their atmospheres. If we find something promising, that is where we would focus SETI efforts.

[edited for minor text changes]

[Sam5]

I would start by focusing the beam at the nearest stars, for a few weeks at a time, since they are are only about 4 light years away. Then we should work our way out to more distant stars, up to maybe 10 or 20 light years away. If there is an earth type planet circling one of the stars, and if it contains “people”, and if they have developed basic radio, then they might receive our signal and send us a response.

I think it’s very unlikely, but remember that for 5,000 years the Europeans and others thought it was unlikely for there to be any land or people across the big ocean.

Are we certain we want to find others?

Why of course! Just think of all the GOLD they might have!!! And we can use them for free labor in our fields!!!

Of course I hope they are not really big and hungry and don’t want to gobble us up.

[Evan]

Each time this comes up I point this out. We have been transmitting strong signals since the development of radar in WWII and short wavelength signals that easily penetrate the ionosphere since the 1950s.

The most detectable signals are from Pave-Paws radars that have been operational since April, 1980. These radars conduct space surveillance and ballistic missile warning tasks. Due to the extreme high power, narrow beam width, wide scan coverage (3 to 85 degrees vertically and 120 degrees horizontally for each radar) they are covering nearly the entire sky 24/7 with a signal that is unmistakably unnatural. Because their job is in part characterizing junk in LEO they won't be turned off until we no longer care about going into space, regardless of the world political/military situation.

[tofu]

Each time this comes up I point this out. We have been transmitting strong signals since the development of radar in WWII and short wavelength signals that easily penetrate the ionosphere since the 1950s.

The most detectable signals are from Pave-Paws radars that have been operational since April, 1980. These radars conduct space surveillance and ballistic missile warning tasks. Due to the extreme high power, narrow beam width, wide scan coverage (3 to 85 degrees vertically and 120 degrees horizontally for each radar) they are covering nearly the entire sky 24/7 with a signal that is unmistakably unnatural. Because their job is in part characterizing junk in LEO they won't be turned off until we no longer care about going into space, regardless of the world political/military situation.

So the question is, how far away could a civilization like our own, running a seti program like ours, detect pave-paws? If no one knows I'll send an email to a seti scientist.

[Evan]

The ERP (effective radiated power) is in the multi gigawatts because of the very narrow beamwidth. I seem to recall that it would appear brighter than the sun in terms of electromagnetic energy. That beam is sweeping every part of the sky multiple times per second. This place is like a lighthouse.

[Grey]

The ERP (effective radiated power) is in the multi gigawatts because of the very narrow beamwidth. I seem to recall that it would appear brighter than the sun in terms of electromagnetic energy. That beam is sweeping every part of the sky multiple times per second. This place is like a lighthouse.

Cool. Though if it's a narrow beam, it can't really be sweeping every part of the sky multiple times per second, I would think.

[Evan]

Pave Paws is a phased array radar with no moving parts. The beam can be shifted in nanoseconds. The only constraint is the time delay required for a pulse to be received in the range gate chosen vs the beam width. Beam width IIRC is about two degrees.

The range gate is determined by the time required for a round trip signal from the radar to object and return. Pave Paws is designed to detect objects of baseball (or smaller, they don't tell all) size at several hundred km. Assuming a 500 Km range gate then the dwell time is 3 microseconds per 2 degree square of sky. Each Pave Paws installation has three such radars operating independently for 120 degrees of sky.

There are three such radars in the US for a total of nine such transmitters. That easily amounts to about 70% sky coverage several times per second.

[dvb]

If we were to send out deliberate transmissions, it might be a good idea to time stamp them with information on when we'll be listening in that area next. That way if our signal does get picked up, the aliens will know when we're listening.

[SciFi Chick]

Thanks Evan. I knew there was some reason I thought our part of space was noisy.