SETI - when could we expect a result?

When can we expect a result from SETI? This was the question I was asked this morning by email. After some thought I came on the idea that the best place to look for life are similar stars to our own. G type stars - G-type stars are are main sequence stars of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 of our suns mass and a surface temperature between 5,300 and 6,000.

So I have compiled a list, sorted by year of all the 'local' G type candidates and especially those with known planets. I then took the distance away in light years and doubled it - this being the time taken for our radio waves to get to them, and theirs to travel back. Starting in 1953 when hugely powerful radio transmitters were used for TV and American AM stations this gives a range of dates for possible contact back. Here is my table below.

Contact Distance Star Name Star In  Known
 (Lt Yrs)    Class       Facts
1961.8  4.4  Alpha Centauri AG2 V  Centaurus  
1976.8  11.9  Tau Ceti  G8 Vp  Cetus  
1991.8  19.4  Eta Cassiopeiae G3 V  Cassiopeia  
1992.6  19.8  82 Eridani  G5 V  Eridanus  
1992.8  19.9  Delta Pavonis  G5-8V  Pavo  
1996.6  21.8  Xi Boötis A  G8 Ve  Boötes  
2001.8  24.4  Beta Hydri  G2 IV  Hydrus  
2002.2  24.6  Mu Cassiopeiae AG5 VIp  Cassiopeia  
2007.6  27.3  Alula Australis G0-5 Ve Ursa Major  
2007.6  27.3  Chara   G0 V  Canes Venatici  
2007.8  27.4  Mu Herculis Aa  G5 IV  Hercules  
2008.6  27.8  61 Virginis  G5-6 V  Virgo   Planets
2009.6  28.3  Chi1 Orionis A  G0 V  Orion  
2010.4  28.7  41 Arae A  G8-K0 V Ara  
2012.8  29.9  Groombridge 1830G8 VIp  Ursa Major  Unstable
2012.8  29.9  Kappa Ceti  G5 Ve  Cetus   Unstable
2013.2  30.1  HR 4523 A  G3-5 Ve Centaurus  
2015.2  31.1  61 Ursae MajorisG8 Ve  Ursa Major  
2019.2  33.1  Alpha Mensae  G5-6 V  Mensa  
2021.8  34.4  Iota Persei  G0 V  Perseus  
2023.4  35.2  Zeta Herculis B G7-K0 V Hercules  
2023.8  35.4  Delta Trianguli G0.5 Ve Triangulum  
2026  36.5  11 Leonis MinoriG8 V  Leo Minor  
2027  37.0  Muphrid A  G0 IV  Boötes  
2029.6  38.3  Lambda SerpentisG0 V  Serpens Caput  
2029.8  38.4  Iota Pegasi B  G8 V  Pegasus  
2032.8  39.9  Zeta2 Reticuli  G1-2 V  Reticulum  
2032.8  39.9  Zeta1 Reticuli  G2.5-5V Reticulum  
2033.8  40.4  85 Pegasi Aa  G5 Vb  Pegasus  
2034.8  40.9  55 (Rho1) CancriG8 V  Cancer   Planets
2035  41.0  HR 3259  G7.5-K0VPuppis   Planets
2035.4  41.2  HR 483 A  G1.5 V  Andromeda 

So for example in 2008 we could have got a reply from 61 Virginis, our next strong candidate would be in 2034.

As to why we cannot see anybody else broadcasting the answer is simple, as communications move on less and less brute force is needed. The planet becomes quieter and quieter until with the advent of satellite and cable communications we cannot be detected easily, if at all, beyond a few light years away. So our best bet for somebody to find us is the 15 light year thick 'shell' of radio communications when TV and Radio were in their infancy in 1953-1978. Similarly we would probably only have a ten to twenty year period to listen to broadcasts from elsewhere.

Consider this. If a civilisation has a lifespan of 10,000 years and is only detectable at a distance for 20 of them then our chances of spotting emissions from a particlular civilisation is one in 500. In other words we would have to study on average 500 stars that did have intelligent life like us before we found a single one by radio.

This being said SETI did intercept what they called the WOW signal which may well have been a tight band starship to base type radio communication which just happened to beam our way. It was too short to be regarded as proof but it had all the right characteristics.

So the best answer is that if another civilisation is looking and if they spot the thin shell of radio waves then they may send us a tight beamed signal directly which we would easily pick up in the years indicated above. Preferably that than the 4000 ship invasion fleet eh?