The Fermi paradox revisited: Technosignatures and the contact era

You touch on a couple of issues.

The first is that civilizations tend to be short-lived. There are only really two ways out of this: they wipe themselves out or they somehow "transcend". "Transcending" is a trope of sci-fi (eg David Brin's Startide Rising series, the Iain M. Banks Culture series) but it's very handwavy. We really have no conception of what that might be. Living in the quantum world? Higher dimensions? This is really the sci-fi version of godhood.

As for wiping ourselves out, that's becoming increasingly harder. We are currently in the latter stages of it being possible to wipe out humanity, despite all the talk of Armageddon. If would really take a large cosmic event at this point. I'm talking the Earth being hit by a truly massive object, the kind that puts the dinosaur-killing asteroid to shame.

Things like nuclear war, biological wars, disease, etc could be truly devastating but kill every last one of us? Easier said than done. It would really take making the Earth truly uninhabitable.

Now another K2 civilization currently has the ability to wipe us out by virtue of the huge amounts of energy they have. Two talked about forms are the Nicoll-Dyson beam (quite literally, turning the energy of a star into something that would bather the target in radiation) and relativistic kill missiles.

Barring some major disaster, in 1000 years this is unlikely to be the case, particularly if we reach other stars.

Of course there's something we might not be able to conceive of but this too feels very handwavy.

The second thing is the Fermi Parai Paradox itself. You can argue that not every civilization goes the Dyson Swarm route or even continues to grow. Some might fade into irrelevance. There are a bunch of possibilities. But we're not concerned with what's likely or expected.

Imagine if there were 5 civilizations in the Milky Way. What are the odds that none of them become K2 civilizations and surviving long term? There's some nonzero possibility. But what if there were 1000 civilizations? As N gets higher the probability that zero of them become long-lived K2 civilizations starts approaching zero.

We look around us and see... nothing. That doesn't mean there's no one out there but it looks increasingly likely the galaxy isn't teeming with spacefaring life. I, for one, think it's most likely that we are the only spacefaring civilization in the Milky Way, at least within our light cone (which means much the same thing).

maybe not a planet but a mini blackhole tugged by a small ship at high velocity to crash into your sun and turn it into a proper black-hole with accretion disc and the works would do some serious damage to you as a species.

personally I'd go for something like a nanobot gray goo thing that infects & turns everything it touches in a given gravity well. then send over a bunch of ships to wipe out remaining stragglers.

Stars move relative to each other. You won't need much higher speeds than what we can already achieve, as long as you're willing to wait for another star to move nearby.

oort cloud is just a stand-in for generating enough parallax in the signal from sun. further out you go better it would be. in fact it just occurred to me that you could just launch an emitter perpendicular to galactic plane with enough velocity that it bobbles up and down say 3x over what a normal star would and it would serve as a galactic lighthouse for intelligent civilization.

Rocket propulsion benefits from directional discharge.

Project Orion lead to the investigation prospects for nuclear shaped charges, in which the blast is highly directional. The concept was developed further in the colourfully-named "Casaba-Howitzer":

https://en.wikipedia.org/wiki/Casaba-Howitzer>

Odds are reasonably good that any space-faring civilisation would create similarly directional reaction devices for space travel if they were utilising explosive nuclear fission.

... Though, thinking this through, the shaped charge would probably be directed at rather than away from the pusher-plate in an Orion design. There might of course be other directed reaction-engine designs. They'd be generating similar-magnitude energy signatures, however, and again, in a deceleration phase, would be directed toward us.

And whilst naked eye observations would of course be difficult, that's really not what we're talking about, but instead sensors which could pick up specific radiation. And I strongly suspect that sudden-onset x-ray and gamma-ray sources within the Solar System would in fact be detectable.

(It was devices that were looking for such bursts on and near Earth from Earth orbit via the Vela satellites as part of nuclear war early-warning systems which first detected astronomical gamma-ray bursts.)

Given that small meteor impacts on the Moon are quite detectable from Earth, nukes near Jupiter should be readily detectable. A 2013 lunar meteor impact from what's thought to have been a 40kg mass traveling at 25 km/s was visible to the naked eye as a 4th magnitude event. That's about 5 tons TNT equivalent.

https://science.nasa.gov/science-news/science-at-nasa/2013/1...>

The Orion concept was based on 0.15 kt (150 ton TNT) charges, or 30x larger than the meteor impact discussed here, exploding repeated at a rate of 1 Hz. That would be a pretty significant signature.