[ianburrell]

EIRP is the power as if transmitting isotropically over the whole sphere. The actual power can be a lot lower if concentrated in one direction. Arecibo EIRP was 10e13.

This means that civilization, like ours, could transmit to each star instead of all directions. But that would mean deliberately communicating.

[fnordpiglet]

In the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy lies a small unregarded yellow sun, one which I doubt anyone is sending directional signals towards.

I also wonder if we could recognize a signal from an advanced civilization. Wouldn’t compression and encryption make most signals tend towards appearing like noise?

[giantrobot]

The only signal we could possibly detect would be a deliberate one. No one sending a deliberate signal to an unknown alien civilization is going to encrypt or encode everything. Besides being unintelligible they'd literally look like noise and be discarded by the receiver.

It'd would make more sense to use a beacon with some obviously non-natural pattern. Then something like the Arecibo Message[0] on some mathematically related frequency.

The likelihood of picking up spurious stray signals from an alien civilization is vanishing small. Even our most powerful broadcasts from Earth will fade to noise before hitting Pluto. Radar (weather or military) might be detectable half way to Alpha Centauri. You'd need a very narrow beam (to focus the input power) to get a detectable signal a few light years distant.

[0] https://en.m.wikipedia.org/wiki/Arecibo_message

[genewitch]

I use kiwisdr when I want to test propagation as a receiver, and I tend to transmit carrier only or Morse, which is extremely narrow and I can get a lot of power in a narrow bandwidth. If I see a line or dashes on the receiver, I know my signal makes it through, and I can switch to a protocol that can "be heard below the noise floor" and see how good the "channel" I've made is.

If I was in charge of letting the galaxy know we existed, it would just be a carrier or a solid tone as loud as I could make it. To get fancier I'd have the transmitter tap out the Fibonacci sequence as CW, as close to 1 second on pulses as I could conceivably make it - and I can get close with the kit I have now.

[fnordpiglet]

Oh I agree if I wanted to be known I would send out some highly structured signal. That assumes a lot though, particularly a desire to be known. I could imagine quite easily a counter scenario not even based on paranoia - maybe interstellar distances are so vast and the period civilizations try to be known in is so short that they all essentially give up on being known, and the chance of two civilizations overlapping in that window is much smaller than the length of an advanced civilization. Or, without watching every where all at once all the time we just won’t see them in their space life hubris phase that I feel we are likely exiting already. Realistically Drakes equation and a non Martian search for life has only been going on for 50 years. I doubt it’ll be going on in earnest for another 50. That’s a single human life span.

[iskander]

...what happens in the next 50 years?

[fnordpiglet]

My wager is little to no SETI investment as we settle into the assumption we are either the first, the only, or are structurally isolated from intelligent life in the universe. A collective shoulder shrug and a refocus on survival in our dirty terrarium.

[gizajob]

What if your second is someone else's month?