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Comment by amerine | Hacker News Reader

“All detections were either automatically rejected or visually inspected and confirmed to be of anthropogenic nature.”

From the paper.

> Based on our observations, we found that there is a high probability (94.0-98.7%) that fewer than ~0.014% of stars earlier than M8 within 100 pc host a transmitter that is detectable in our search (EIRP > 10e12 W).

A terawatt transmitter is one hell of a transmitter. That's about 10% of the power our entire civilization consumes, IIRC. The civilizations detectable in this search would have to be much more advanced than our own, to be able to dedicate such a large amount of power to a single transmitter.

The assumption being "advanced" means "radiate prodigious amounts of RF in spectral ways we can detect, and see as information-rich".

Because a truly advanced society probably doesn't needlessly pollute space with RF nobody else needs to see.

On the other hand "yea, they're probably as dumb as we are"

A truly advanced society might be investing significant effort into making itself detectable to other civilizations though. Any civilization experiencing a substantial post-scarcity phase would be likely to have at least some off-shoot groups which use their substantial resources to engage in this activity.

i.e. if energy was functionally free for the average man (because we had the Dyson swarm up and running or something), then what are the odds that some group wouldn't have used their time to build a transmitter to act as a beacon? Could we even stop them if they wanted to (i.e. even if we didn't want to broadcast locally, sending probes to Alpha Centauri and broadcasting from there would be a good way to conduct intelligence gathering on potential interstellar threats).

We've been broadcasting at quite detectable volume for "contact" (sagan) 100 light- years in a radiating spherical radius. We didn't even have to argue about it.

Beaconing, assumes random dice throw (of who to beacon at) pays off. I'd say the odds are worse than lotto winning: Higher input costs, lower chance of success.

You don't need to though: directed radio can be switched to point at different targets. In fact this would be preferable: i.e. blinking prime numbers out into the universe could be by switching radio targets to create the message.

Again, you assume that point-source RF which beacons to many places by switching aligns with when they're looking. You have to do a LOT Of hand waving around "better wiser Aliens can listen everywhere all the time" for this to pay off, and I would observe if this is such a brilliant technique, how come we haven't received the beams sent to us?

It’s EIRP, not actual radiated power. If the beam is narrow this is achievable with moderate total power. The DSN transmitter in Canberra is capable of this EIRP on about 100 kW total power.

Thank you for the clarification. I was mistaken.

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.

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?

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.

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.

...what happens in the next 50 years?

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.

What if your second is someone else's month?

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

I would say it is a safe bet that if the authors had found something, the publication would be titled something significantly different.

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