First Contact With E.T.

[magnemoe]

However, those broadcast signals diffuse according to the inverse square law, so at any meaningful distance they'll be indistinguishable from the background noise. SETI are looking for messages specifically targeted at Earth.

Then finding something is pretty much like jackpot. We sent one deep space message 30 years ago, we might send another in 20. Yes you could fist scan for life signals on planet and transmit to the relevant ones. However you could transmitted to earth some hundred millions years before anybody had an chance of detecting it. Sending an interstellar flyby probe sounds far more cost effective.

[Monkeh]

Don't forget as well that the creatures on this planet considered the most intelligent are all predators. Makes perfect sense of course, having to work out how to catch something for dinner is a going to select for inteligence a lot more than being good at running away.

So I feel any sentient species out there will have a bloody bistory of war and murder. We do after all. Would they have passified with time or will they be intergalatic hunters, only caring about the chase and the kill?

The lengths of time we need to consider make it so much less likely to happen as well. Sentient beings may evolve close spatially but within the few decades we've been able to look for them? Vanishingly small probabilities appear. Mars may have had a bustling ecology and civilisation in the past, maybe we're all that's left of it, but there's no trace now we can find.

If a space faring species existed close enough to us we would have seen some evidence by now I feel. A Dyson sphere or something. Were all alone people. The Rare Earth.

[magnemoe]

Don't forget as well that the creatures on this planet considered the most intelligent are all predators. Makes perfect sense of course, having to work out how to catch something for dinner is a going to select for inteligence a lot more than being good at running away.

So I feel any sentient species out there will have a bloody bistory of war and murder. We do after all. Would they have passified with time or will they be intergalatic hunters, only caring about the chase and the kill?

The lengths of time we need to consider make it so much less likely to happen as well. Sentient beings may evolve close spatially but within the few decades we've been able to look for them? Vanishingly small probabilities appear. Mars may have had a bustling ecology and civilisation in the past, maybe we're all that's left of it, but there's no trace now we can find.

If a space faring species existed close enough to us we would have seen some evidence by now I feel. A Dyson sphere or something. Were all alone people. The Rare Earth.

One exception to the smart=predator must be the elephant. However they are a bit special, very large, this makes an huge brain an trivial expense and probably an good idea as they live long time.

Pigs and apes are omnivorous.

As for war an murder, decent chance for it, however I think other factors than diet has more impact, look at the differences between human cultures. You want to run into Switzerland rather than Djengis Khan, other groups are far more warlike like some tribes on New Guinea. One feature that animals who are dangerous to each other usually has an well developed surrender reflex.

[Seret]

Sending an interstellar flyby probe sounds far more cost effective.

Er, not really. A single large telescope can survey millions of stars. A big array of them can do so with very fine resolution and high speed. Sending probes to every exoplanet you though capable of harbouring life would get hugely expensive and take take hundreds or thousands of years to get results.

Electrons and photons are cheap and fast, lumps of metal are expensive and slow. Radio and optical astronomy is the right toolbox for SETI.

As you point out, there's a high risk of missing a signal, due to their intermittent nature. We still don't know what the Wow! signal really was, it may well have been artificial, but since it never repeated we'll probably never know what it was. However, sending probes really isn't a more practical option. The distances and the number of stars are just too large.

[magnemoe]

Er, not really. A single large telescope can survey millions of stars. A big array of them can do so with very fine resolution and high speed. Sending probes to every exoplanet you though capable of harbouring life would get hugely expensive and take take hundreds or thousands of years to get results.

Electrons and photons are cheap and fast, lumps of metal are expensive and slow. Radio and optical astronomy is the right toolbox for SETI.

As you point out, there's a high risk of missing a signal, due to their intermittent nature. We still don't know what the Wow! signal really was, it may well have been artificial, but since it never repeated we'll probably never know what it was. However, sending probes really isn't a more practical option. The distances and the number of stars are just too large.

To listen is cheap however to have any chance of receiving anything sent towards us they has to send in our direction at an time we listen, as we don't listen for long on each star they have to transmit all the time, shifting between 25 targets during a day and we have a roughly 95% chance of missing it.

And you don't know then we start listening, if you stopped 100 millions years ago it was pretty pointless. Same if they start in 50 million years. The mass use and geological time-span you had to do this project over would make it costly.

Far better to build some kilometer sized receivers in deep space and search for broadcasts. Polling each planet with life every 50 years is easy.

[Seret]

Far better to build some kilometer sized receivers in deep space and search for broadcasts. Polling each planet with life every 50 years is easy.

Any big receiver you build in space you can build a lot cheaper on Earth.

Having said that, one of the better ideas for long-range long-term space exploration is IMO a large, low mass antenna-based von Neumann machine with an AI on-board. If it could sail through space for thousands of years and replicate itself whenever it bumped into the right resources then the problems of large distances and long timespans become much less of an issue. We'd still need a direction to initially point them in though, and that means some kind of prior radio reconnaissance.