# SETI experiment succeeds: fails to find aliens

If there are sentient aliens on the “habitable zone” planet circling Gliese 581, they’re not calling out to us. That’s the conclusion of Western Australian astronomers, who have released the results of a targeted SETI-hunt using Very Long Baseline Interferometry (VLBI) to sniff out radio signals from the distant red dwarf. …

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1. #### Even if they were transmitting, we wouldn't likely hear them

Just so everybody is on the same page: SETI isn't looking for alien TV, or alien radio stations - we won't hear them. Imagine a transmitter of 1MW were there, transmitting a nice 6kHz wide AM signal. Imagine we used the largest area antenna we have - Mount Arecibo. Yes, the VLA is "larger" in terms of resolution, but doesn't have nearly the collection surface area, and that's what really important here.

Arecibo is 305 meters wide, or a radius of 150 meters (I'm going to keep about 2 significant digits here). So Arecibo would, under the best possible conditions, collect (pi * (150 meters)^2) / (4*pi*(20ly)^2) or about 1.5*10-31 of that 1MW - or about 1.5*10^-25 watts of signal - call it -220dBm of signal. At normal temperatures, the RF noise emitted by the antenna would be about -173dBm/Hz or about -169 dBm for our 6kHz wide AM signal, so the signal would be more than 50 dB into the noise floor.

The ONLY way SETI is going to hear anything is going to be if somebody on the other end was beaming a MASSIVE amount of power very directionally towards our solar system.

1. #### Re: Even if they were transmitting, we wouldn't likely hear them

I guess they'd have to build a 10km wide antenna so they can make up the needed 60 dB.

1. #### Re: Even if they were transmitting, we wouldn't likely hear them

60 dB would be a 1000 times increase in the antenna - or 100km wide, not 10km.

And they'd have to hold the same tolerance levels for shape over that whole 100km - keeping the antenna parabolic to better than a few centimeters over that whole distance.

And I didn't account for losses such as interstellar dust, earth's atmosphere, or anything like that - so that's likely to be another 60dB of loss or more - and now you have an antenna 100000km wide.

1. #### Re: Even if they were transmitting, we wouldn't likely hear them

60 dB would be a 1000 times increase in the antenna - or 100km wide, not 10km.

Thanks for the correction. :)

Nevertheless, I was only half kidding. Perhaps some yet to be developed technology could allow us to build such a huge surface in space and keep the shape within tolerance. /dreaming

1. #### Re: Even if they were transmitting, we wouldn't likely hear them

The problem is that unless you cool the antenna structure, bigger really doesn't help as much - you get more signal, but you have more antenna-generated thermal noise as well.

I've not run the numbers, but I suspect you'd need to keep the antenna structure below the 4K microwave background temp to get the noise levels down low enough.

I'm pretty sure that if SETI does hear something, it's not going to be an alien ball game, or an alien rag-chewing session - it's going to be a deliberate "CQ SOL SYSTEM CQ SOL SYSTEM CQ SOL SYSTEM DE GLIESE GLIESE GLIESE PLS K"

2. Any self respecting Alien would keep quiet if they knew we were looking, a bunch of war like mass murderers holding out the hand of friendship!

They have had centuries to study us.... Would you let someone know where you are if the tables were turned?

3. #### Like

those people you meet on holiday and invite to visit you, but not really expecting them to.

Then they turn up knocking on your door with a slide projector.

Keep quiet, stay away from the windows and hope they go away.

1. #### Re: Like

Am I the only one who gives wrong contact details to those people met on holiday? Unfortunately, I cannot say whether they tried to visit because the given address is not of a person I'm exactly friends with...

4. #### Re: Even if they were transmitting, we wouldn't likely hear them

The other thing SETI say they are looking for is interstellar communications. They actually think its feasible alien civilisations will be using radio to talk between star systems, despite this form of transmission taking decades even between adjacent stars. Nobody is communicating at this pace - they're using something else we don't know about.

Nice try, but it's time to think up a new method of scanning the skies.

1. #### Re: Even if they were transmitting, we wouldn't likely hear them

How do the parties supposedly communicating from light decades apart even know about each other in the first place ?? Either they randomly found each other with random decades-apart radio signals (in which case surely we could also pick up same), or else one of the parties traveled to the other location tens of light-years distant (implying close-to-light-speed travel)

5. #### Re: Even if they were transmitting, we wouldn't likely hear them

They would also need to send the signal at the right time. We've only been broadcasting for about a century, which is insignificant relative to the age of the universe. For us to intercept an alien broadcast we would have to come across a civilization that achieved broadcast capabilities at the right time for their signals to reach earth while we are capable of receiving such signals.

6. #### FIXED!: Even if they were transmitting, we wouldn't likely hear them

"The ONLY way SETI is going to hear anything is going to be if somebody is actually there - which there isn't, sorry - and if that somebody on the other end was beaming a MASSIVE amount of power very directionally towards our solar system."

Fixed it for ya! : )

2. #### They'll just have to wait a few billion years...

I'm sure when Andromeda has come a little closer there will be whole new opportunities again to search for aliens.

3. #### Knowing humanity's rotten luck...

They will have sent us a message something along the lines of, we're coming, and you're toast, using a star powered transmitter, indicative of the vast amounts energy they have harnessed.

When we receive their message, it should then be obvious that they pack a punch, which will then be confirmed the following day when their battle fleet folds space into the solar system.

All because they found a Voyager plaque which read to them as a declaration of war, or a gigantic insult mocking of their historic figures.

1. #### Re: Knowing humanity's rotten luck...

If they have run into Voyager, they are very close to us already.

2. #### Re: Knowing humanity's rotten luck...

I think it's more likely that the message would be notification that the plans for the new hyperspace bypass are available for viewing at our local library.

Mine's the one with the towel.

3. #### Re: Knowing humanity's rotten luck...

"They will have sent us a message something along the lines of, we're coming, and you're toast, "

Bloody galactic trolls, they'll be strutting up and down in front of some creationist wearing silly antennae

on their head and making beep beep noises next.

4. #### I hope they don't call

While we are out!

5. #### So...

MarsOne, anyOne?

6. #### Andy Capp

SETI stories always remind me of an old Andy Capp cartoon. Flo looks at the moon and says "I wonder if there's intelligent life out there." Andy replies, "There must be - you don't catch them spending billions to find out if there's intelligent life down here."

(The pint's for Andy....)

7. #### Here we are

Its highly unlikely that they would send a high powered direct signal at us in the first place.

8. #### Of course they keep shtumm

They would not communicate with cricket-playing nations, would they

Held in very bad taste out there in the galaxy.

9. #### "...the ParselTongue scripting language."

Surely that's eminently unsuitable for analysing weak radio signals as it'll introduce a lot of hiss?

Er, yes please. The snakeskin one.

10. #### Poor choice...

... to include the Parkes radiotelescope in that system. It's known to pick up terrestrial, umm, "interference"... for example, from handheld radios - as shown in the movie "The Dish".

11. The problem is you will have a short period of time when a species will be radiating tons of radio waves out into space, a few decades I guess, before they start focusing their transmissions to save power...

Then they would do like us, satellites pointing down, and lower power transmitters.

After that I am sure they will find way to talk over interstellar distances, like using wormholes or something similar...

12. #### They did in fact transmit

A long time ago, and they burnt their entire star up to send us this massive message with so much power in a highly energetic ray which basically said 'Hi' in mathemeatical formula, they realised that by the time we would receive it we would have the knowledge to decode it, and thus allow us to transcend to the next level of our evolution and the realisation we are not alone, however the slight flaw is, by the time it gets here, it is still so powerfull and focused it sorches all life off the planet.

The really sad part is this species of alien keep doing this because they know the signal will get there, and have not heard of any bad consequences from doing it, and are now wondering why every time the fire their hello message at a planet they never hear a response, they think they are the only intelligent life in the universe

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