Hidden universal expansion: stopping runaways

Speculation about why alien civilizations are concealing themselves is approximately as reasonable as speculation about why angels and demons apparently are concealing themselves.

The main question is why they don't wage visible wars with each other? Because in the case of war for the territory the earlier you start, the more you gain (for the future computations).

One possible sign of such war would be sending messages addressed to naive civilizations as our, in order to enslave it by powerful AI - I called it SETI-attack. But we don't see such messages.

However, we still could find them, if medium distance between civilization is in order 100 mln -1 bln light years, and physical travel is below 0.5 c I explore these limitations on the civilization density here: https://www.academia.edu/30029491/The_Risks_Connected_with_Possibility_of_Finding_Alien_AI_Code_During_SETI

S. Jay Olson's work on expanding civilizations is very relevant here, e.g. https://arxiv.org/abs/1608.07522 and https://arxiv.org/abs/1512.01521 That work suggests that even non-hidden civilizations will be fairly close to their light front.

Now, the METI application: if this scenario is true, then sending messages so that the expanding civilization notices us might be risky if they can quieten down and silently englobe or surprise us. (Surprise is likely more effective than englobement, since spamming the sky with quiet relativistic probes is hard to stop)

When does this matter? If we happen to be far away from the civilization, then they will notice the message late and we could have done all sorts of things in the meantime - escape, becoming an equivalently powerful civilization, gone extinct etc. We would have done the same even if they had not been there. So there is no change.

If they are already here there is only an effect if they react to the attempt at messaging ("Only talk to civs that want to talk to you"/"Only wipe out civs that might pollute the ether with deliberate messages"), so there is no change.

[ In fact, a civilization that deliberately tries to conceal itself may be particularly concerned with signalling civilizations since they might act as beacons: if they get cut off, that might tell other listeners where something is going on. Keeping them signalling even when well inside their englobement might be good camouflage. Until they are discreetly replaced with decoy young civilizations...]

So the only case that leads to nontrivial effects is the nearby but not here case. Friendly civilizations react by doing something friendly, but that would have happened anyway when they came here. Unfriendly civilizations use the information to be more efficiently unfriendly (like quiet englobement). The main thing that changes is that the opportunity for running away (or other reactive responses) decreases.

So the overall utility change is U(METI)-U(no METI) = -Pr[nearby but not here] * U(running away).

Now, Pr[nearby but not here] seems to be small for rapidly expanding civilizations. If they spread at speed v, then it is (v/c)^3. For v=0.9c, it is only 27.5%, and for 0.99c it is 2.97%. So it is a small net negative, assuming U(running away) is positive.

All of the above is conditioned on that interstellar/intergalactic expansion is doable. If it isn't, we get informational game theory instead.

What are your scenarios for interstellar warfare? The question obviously depends on whatever turns out to be the technically mature way of violent conflict resolution.

Let me propose a naive default guess:

Small technically mature von-neumann probe meets primitive civilization or unsettled system: probe wins.

Small technically mature von-neumann probe meets system with technically almost-mature inhabitants: probe cannot even make problems.

System with dyson swarm + AI: Unassailable on short timescales. Impossible to profitably invade. Maybe sling another star at it if you control the stellar neighbourhood.

In this scenario, interstellar warfare is a matter of land-grabbing: Spam the entire sky with probes, moving as fast as possible, dyson a fraction of stars to keep up the expansion front, and fortify all other systems. "Fortify" might just mean "build and maintain a couple thousand tons of observatories & industrial base", i.e. almost nothing: One just needs enough headstart to win any inner-system race against later von-neumann probes. This is relevant if the colonizer has reasons to keep most systems mostly virgin, and is compatible with the silent sky.

In this scenario, if we saw an expansion front, we would rush to move from category (1) to (2); this is slightly bad for the big colonizer.

What does "flee" mean in this context? It would mean rushing to grab a bigger slice of the pie. Do I understand you correctly there?

On the other hand, the game-theory appears to suggest that colonization speed dominates stealth, all the time: The only reaction move we have is to do what we should do anyway, if we care about colonizing the universe (if we don't care then we don't need to react at all, just keep our system).

So, in summary, I do not understand how the red civilization intends to influence our decision processes by staying stealthy.

Why would they want to stop us from fleeing? It doesn't reduce their expansion rate, and we already established that we don't pose any serious threat to them. We would essentially be giving a perfectly good planet and star to them, undamaged by war (we would probably have enough time to launch at least some nuclear missiles, probably not harming them much but wrecking the ecosystem and making the planet ill-suited for colonization by biological life). Unless they're just sadistic and value the destruction of life as a final goal, I see no reason for them to care. Any planets and star systems that would be colonized by the escaping humans would be taken just as easily as Earth, with only a minor delay.

First of all, the Earth has been around for a very very long time. Even slowly expanding aliens should have hit us by now. The galaxy isn't that big relative to the vast amounts of time they have probably been around. I don't feel like this explains the fermi paradox.

If aliens wanted to prevent us from fleeing, this is a terribly convoluted way of doing it. Just shoot a self replicating nanobot at us near the speed of light, and we would be dealt with. We would never see it coming. They could have done this thousands of years ago, if not millions. And it would be vastly more effective at snuffing out competition than this weird strategy. No need to even figure out which planets might evolve intelligent life. Just shoot all of them, it's cheap.

You could time them so they all hit their targets at the same time and give no warning. Or have them just do the minimal amount of destruction necessary so they aren't visible from space.

I think it's a lot more likely that an expanding civilization will want to conceal themselves after they have surrounded any given point, with that point being far away from their frontier of expansion. Because that's precisely when such advanced civilizations will gain the most simply from being as resilient as possible to the threat of other expanding entities. By contrast the frontier will see intense competition to simply expand into unpopulated space as fast as they can, so hiding is unlikely to be a priority. Even if their expansion might be checked by some hostile entity, this is not a big deal in expectation; it might just be what those farther back from the frontier were waiting for, a chance to try again and leap-frog the earlier colonists.