Doesn’t sound very convincing to me. Sufficiently advanced tech could allow things like:
build an underground civilization 50 kilometers below the surface of a rocky planet
settle in the emptiness between galaxies, too far away from anyone to bother looking for you
run your civilization of ems on extremely-low-energy computers somewhere in the Oort Cloud
hide deep in a gas giant or even in a star
run your digital mind on a carefully manipulated natural process (e.g. modify a bunch of growing salt crystals or stellar magnetic processes into doing useful computations)
go nanoscale, with entire civilizations running on swarms of nanoparticles somewhere in a small molecular cloud in the intergalactic space
In some of these scenarios, you could look right into a busy alien city using every possible sensor, but not recognize it as such, while standing one meter away from it.
As for why bother with stealth, one can view it as a question of costs and benefits:
if you don’t hide, there is some risk that your entire civilization will be killed off. Makes sense to invest at least some resources to reduce the risk.
if you hide, there is some cost of doing the hiding, which could be negligible (depending on your tech and philosophy). E.g. if your civ is already running on a swarm of nanoparticles for practical reasons, the cost of hiding is zero.
“Sufficiently advanced” tech could also plausibly identify all those hidden civilizations. For example, an underground civilization would produce unusual seismic activity, and taking up some inner portion of a gas giant or star would alter their outward behavior. Ultimately, civilizations use mass-energy in unnatural ways, and I don’t see a fundamental physical principle that could protect that from all possible sensing.
More importantly, I don’t think your suggestions address my point that hostile civilizations would get you before you even evolve.
But, let’s grant that you’re the first civilization to evolve in your galaxy, or at the least among the first before someone starts sending out probes to prevent any new civilizations from arising and threatening them. And let’s grant that they will never find you. That is a victory, in that you survive. But the costs are astronomical: you only get to use the mass-energy of a single planet, or star, or Oort Cloud, while someone else gets the entire galaxy.
To put it another way: mass-energy is required for your civilization to exist and fulfill its preferences, so far as we understand the universe. If you redirect any substantial amount of mass-energy away from its natural uses (stars, planets, asteroids), that’s going to be proportionally detectable. So, you can only hide by strangling your own civilization in its crib. Not everyone is going to do that; I seriously doubt that humanity (or any artificial descendant) will, for one.
(This comes back to my link about “no stealth in space”—the phrase is most commonly invoked when referring to starships. If your starship is at CMB temperatures and never moves, then yeah, it’d be hard to detect. But also you couldn’t live in it, and it couldn’t go anywhere! You want your starship—your civilization—to actually do something, and doing work (in a physics sense) is detectable.)
Doesn’t sound very convincing to me. Sufficiently advanced tech could allow things like:
build an underground civilization 50 kilometers below the surface of a rocky planet
settle in the emptiness between galaxies, too far away from anyone to bother looking for you
run your civilization of ems on extremely-low-energy computers somewhere in the Oort Cloud
hide deep in a gas giant or even in a star
run your digital mind on a carefully manipulated natural process (e.g. modify a bunch of growing salt crystals or stellar magnetic processes into doing useful computations)
go nanoscale, with entire civilizations running on swarms of nanoparticles somewhere in a small molecular cloud in the intergalactic space
In some of these scenarios, you could look right into a busy alien city using every possible sensor, but not recognize it as such, while standing one meter away from it.
As for why bother with stealth, one can view it as a question of costs and benefits:
if you don’t hide, there is some risk that your entire civilization will be killed off. Makes sense to invest at least some resources to reduce the risk.
if you hide, there is some cost of doing the hiding, which could be negligible (depending on your tech and philosophy). E.g. if your civ is already running on a swarm of nanoparticles for practical reasons, the cost of hiding is zero.
“Sufficiently advanced” tech could also plausibly identify all those hidden civilizations. For example, an underground civilization would produce unusual seismic activity, and taking up some inner portion of a gas giant or star would alter their outward behavior. Ultimately, civilizations use mass-energy in unnatural ways, and I don’t see a fundamental physical principle that could protect that from all possible sensing.
More importantly, I don’t think your suggestions address my point that hostile civilizations would get you before you even evolve.
But, let’s grant that you’re the first civilization to evolve in your galaxy, or at the least among the first before someone starts sending out probes to prevent any new civilizations from arising and threatening them. And let’s grant that they will never find you. That is a victory, in that you survive. But the costs are astronomical: you only get to use the mass-energy of a single planet, or star, or Oort Cloud, while someone else gets the entire galaxy.
To put it another way: mass-energy is required for your civilization to exist and fulfill its preferences, so far as we understand the universe. If you redirect any substantial amount of mass-energy away from its natural uses (stars, planets, asteroids), that’s going to be proportionally detectable. So, you can only hide by strangling your own civilization in its crib. Not everyone is going to do that; I seriously doubt that humanity (or any artificial descendant) will, for one.
(This comes back to my link about “no stealth in space”—the phrase is most commonly invoked when referring to starships. If your starship is at CMB temperatures and never moves, then yeah, it’d be hard to detect. But also you couldn’t live in it, and it couldn’t go anywhere! You want your starship—your civilization—to actually do something, and doing work (in a physics sense) is detectable.)