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Either RKVs are dangerous enough that you should expand out in space as quickly as possible to defend yourself against them because people will fire them off indiscriminately, or they aren't actually all that dangerous and so there's no rush to expand. We both seem to agree that firing off RKVs isn't actually all that great of a strategy, so it doesn't make sense to try to be grabby specifically to survive RKVs.
This sufficiently fast RKV will never arrive, because it will hit a piece of interstellar dust and vaporize. If you're worried this won't happen, you can make sure of it pretty trivially as a defensive measure by creating armor belts of small high-density particles, which is going to be considerably easier and cheaper than making an RKV kill chain.
Any RKVs that travel at a more leisurely pace to avoid obliterating itself will likely be detected by any "peer" civilization and intercepted by another RKV of some kind, or a high-energy laser or particle weapon that will ablate it and push it off course.
None of these defenses are technically hard; some of them could be probably be accomplished by civilizations below K1 on the Kardashev scale. (For reference, the interplanetary dust cloud - which is thick enough that dust strikes are routine on spacecraft - has less mass than a relatively unexceptional asteroid).
Why? If you've decided to wait until the end of the universe to crunch numbers then you might as well just wait until then to do everything.
Uhhh, here's what I in fact said:
I think you may have just skipped over my most interesting proposal for an Aestivation civilization. Sad! I thought it was neat.
Sure, and this might have already happened and we just don't happen to know it!
VNRs are considerably more complex and far-fetched than solar-sails, and, just like separatist expeditions into space, an inherently dangerous technology that a smart civilization would think twice before launching.
Not at all, my argument (which I am mostly making for the case of intellectual honesty since I too am skeptical that life elsewhere in the universe is abundant if it exists at all) is that there are a multitude of reasons why there might be aliens in the universe that we have not observed, and thus the inference from not seeing them is not especially strong.
Including, hilariously, that they've already converted most of the galaxy to Dyson swarms and we don't know that because they routinely divert a tiny fraction of their energy into masking their position from any planet with biosignatures. You say it would be pretty trivial to detect those planets via inferential telescopic means at ludicrous ranges and take seriously the idea of a Nicoll-Dyson beam; very well, I find those sorts of megastructures very far-fetched but if you're going to the trouble of making one and have the technical means to do it, you likely also have the technical means to trivially prevent planets you've detected with biosignatures from noticing via selective emissions or laser masking.
"Grabby aliens" is only one path out of thousands for a society to take, and the fact that we have not observed it being taken is not particularly strong evidence that it hasn't happened, let alone that the other thousands of options have not been pursued.
That is a very false dichotomy. RKVs are existentially threatening to a planet-bound civilization in a way they simply aren't to a K1+ one, both because the latter has its own countermeasures and deterrence, and because dispersing across enough volume makes comprehensive eradication prohibitively expensive.
RKVs are also not made equal, any more than a Stinger and an ICBM are interchangeable because they're both missiles. You can go from planet-killer to whatever the limit of your launch infrastructure allows. You can modulate speed, switch from a single projectile to a macron gun, have the projectile intentionally disintegrate, switch to MIRV mode at terminal phase, etc etc. You're also not limited to RKVs or Nicoll-Dyson beams. Ultrarelativistic electron beams are perfectly nasty in their own right.
So yes, they're dangerous enough that you'd want to grow, and a sufficiently advanced civilization can also harden itself. Both can be true.
I don't dispute that more advanced civilizations can substantially harden themselves. That's half my argument. I do dispute that a dust shield is anything close to insurmountable, because, as I mentioned, a macron gun is literally relativistic dust. Seriously. The defenses that make a "durable" interstellar craft viable apply right back: laser sweeps, sacrificial forward drones, extended Whipple shields, etc. Disintegrating an incoming RKV is also not a guaranteed solution; it depends on how far out you intercept and how massive and fast the projectile is. It's worse than trying to blow up an asteroid with a nuke, because the debris cone can do nearly as much damage as the intact projectile.
I know about black holes as propulsion mechanisms and as power plants. My point was that you don't need to make one yourself; you can just co-opt one if it's close enough. If.
The whole content of GAH is that it predicts visible, persistent signatures. "It already happened invisibly" collapses straight back into the masking argument and inherits the same thermodynamic problem, so let me deal with both at once.
I have grave reservations about this being feasible at scale, and you're getting an awful lot for free here. A Dyson swarm has to dump waste heat somewhere. To mask it, you'd need either to redirect that heat away from every potentially-observing system in real time (which fails on light-cone delay alone, since you can't react to observers you don't yet know exist), or to eat leakage that scales with swarm size. At galactic scale that gets prohibitive fast. Selective emission masking also presupposes tracking every civilization in your light-cone with biosignatures, in advance, which is strictly harder than detecting them in the first place.
Project Hephaistos is actually informative here, and you're the one who mentioned it as a technosignature candidate in the first place. The fact that we can flag mid-IR excess candidates around individual M-dwarfs at galactic distances, and that the follow-up work suggests background Hot DOGs explain the contamination rather than masking failures, all of which tells you the detection floor is low. Hiding swarm-scale waste heat isn't a free lunch you can hand-wave. That is a ridiculous amount of engineering effort, for not very good reason. We don't hide the ISS from uncontacted tribes in the Amazon, even though we are actively trying not to contact them.
GAH only needs one civilization, anywhere, in the entire history of the observable universe, to launch them. If 99.9% of species are too cautious or too sensible or too risk-averse, the remaining 0.1% fills the lightcone. That was my "all it takes is one defector" point earlier, and it applies equally hard here. You're implicitly demanding universal restraint without admitting that you are, and "every species coordinates on the same restraint forever" is the part of your argument that I or anyone else familiar with Hanson would strenuously object to.
Pointing out that it's "one path out of thousands" is sloppy reasoning. There are an unbounded number of paths from my bed to the living room. I could climb out the window. I could head out the front door, catch a flight to Singapore, then another to Djibouti, come back in a bus and grab lunch on the way. But what would I actually do? Walk there. It's 10 seconds away.
The strength of GAH is that the absence of the signatures it predicts genuinely is strong evidence, because the assumption set is minimal. All you need is: STL interstellar travel is possible, and at least some civilizations will use available resources over geological timescales. That's it. Non-trivial amounts of time have passed since metallicity was sufficient for life to form. So either nobody is out there, or every single civilization in the lightcone independently converged on some elaborate restraint or hiding strategy.
The speed of light allows for cross-temporal sampling. We know what's happened in our galaxy in the last few tens of thousands of years, and we can see billions of years back. That's a lot of data.
The alternatives all require multiple, often jointly held assumptions about alien psychology, technology, or coordination. Aestivation needs everyone to also forgo currently available resources while they wait. Dark Forest needs a workable hiding strategy plus universal adoption. Fodor's intraterrestrials need every civilization to virtualize and also forgo probes. Masking needs a thermodynamic miracle plus universal adoption plus advance detection of every observer. The fewer joint assumptions, the better the explanation, and "no one is here yet" is just the cheapest fit.
But there's no evidence that hardening against RKVs requires K2 levels of energy. If the Sierra Club's lawsuit against the Dyson sphere succeeds, we're not doomed to be struck by RKVs. Furthermore, as discussed previously (and also below) a Dyson sphere isn't even the best method of energy collection.
If you are really worried about this, you can use a laser or similar system to ablate them so you can move them off-course in a predictable way.
Yes, and from what I understand, it is also unstable if sufficiently dense.
This also describes a Dyson swarm to begin with. If you're going to go to a ridiculous amount of engineering effort, for not very good reason, you may as well keep going!
No it doesn't. Self-replicating devices with short doubling times already exist, but they have not eaten the observable universe despite trying. In addition, plenty of things with (probably) much lower floors for "happening" haven't happened.
Notice that you employ this argument selectively: civilizations will build Dyson swarms because it's the best idea, but launch VNRs even though it's a TERRIBLE idea. But maybe we live in a universe where the opposite happens: civilization don't launch VNRs because it's a bad idea but they don't make Dyson swarms, either, even though it's a good one.
For the GAH to tell us anything about the universe, it specifically requires assuming that technological progress will arrive at "can build Dyson swarms" and stop there. If it turns out that the most efficient way to harvest energy is by the care and feeding of your own black hole then we'd never notice the stars being blotted out.
And yeah, I'd bet that the black hole is actually preferred by truly advanced civilizations:
So yeah, if we just assume advanced aliens prefer to use more efficient energy gathering methods then we won't observe them (or at least not by looking for stars being eaten). Waste heat isn't hard to move around (or put to work) so I am not sure we'd see that, or even know if we did see it (my understanding is that there are plenty of odd IR signatures in space.)
Now, maybe it turns out that artificial black holes are ~impossible to create (right now our estimates are that creating one artificially would be extremely difficult) but if it's doable then you would expect that to be preferred.
I tend to agree that it's the cheapest fit, I just don't find the GAH very persuasive, because it seems to me there is a lot of uncertainty around it, and from what I can tell about our own future trajectory as a species, we are not on the path to creating the technosignatures in question.
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