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My favorite theory: the von Neumann probes are already in the solar system. They've been continuously monitoring this system for a billion years. They could jus

My favorite theory: the von Neumann probes are already in the solar system. They've been continuously monitoring this system for a billion years. They could just be unwilling to make the first move toward contact with humans -- maybe we'll notice them, eventually, once we have better monitoring of small in-system objects. They could even be deliberately avoiding detection, like wildlife researchers who don't want animals to notice them. They haven't turned moons into copies of themselves for, basically, the same reason they haven't turned everything into paperclips -- that sort of unbounded-growth directive is useless and/or dangerous. Note that I don't really believe this, but it does seem to be a resolution of the paradox that (like many others) we don't yet have enough evidence to reject.

red75prime 8y ago
So we are another kind of special to deserve observation and galaxy wide bubble of silence.
- philipkglass 8y ago
  No, I'm assuming that probes are widely distributed. Laser communication is better than radio communication over long distances. Shorter wavelengths make for tighter beams. The whole galaxy could be mesh-networked with ultraviolet laser links and repeaters, and it would still take a rare stroke of luck for any of our telescopes to notice, even if the links aren't operated for deliberate stealthiness.
  - red75prime 8y ago
    Tight laser beams are limited by diffraction. Kilometer wide laser beam on wave length 308mn will have diameter around 15 millions meters on 4 light year distance. Meter wide beam will have diameter 15 billions meters, all other things being equal. I can't, right now, estimate probability of breaking the silence, though.
    - philipkglass 8y ago
      Right, a 15 billion meter wide beam aimed at e.g. a solar gravitational lens relay station some 542 AU out, or even aimed at much closer receiving stations around Jupiter, would not intersect Earth most of the time. At 308 nm it wouldn't be visible to ground based telescope since the atmosphere would mostly absorb it. If using gravitational lensing to set up system-to-system communication is the norm, the beam might not be bright enough to be observable by current space based UV telescopes. All of this could just be driven by ordinary post-biological-alien good engineering practices. It would seem extremely stealthy to humans, but that doesn't need to be intentional, any more than ham radio communications are intentionally stealthy against observation by whales.
roywiggins 8y ago
I'd object on the basis that it is hard to imagine everyone cooperating on that sort of project. It implies everyone has about the same incentives and motivations, which suggests a remarkable uniformity... so if it's true, there's probably only one civilization in our galaxy, and it's spread uniformly everywhere.
- philipkglass 8y ago
  Or that one civilization (more likely: a tiny number of decision makers within one civilization) got the capability first, and had outposts waiting everywhere before any other species could reach the same galaxy-spanning capabilities. Or that a handful of civilizations spread out before there was one galaxy-wide winner. But all faced similar incentives against paperclip maximizers and toward peacefulness upon contact with other interstellar civilizations. World powers here on Earth recognized that thermonuclear war is a terribly bad idea even though a thermonuclear weapon has never been used in anger. Multiple alien civilizations could perhaps foresee that deploying Nicoll-Dyson Laser weapons would end badly without a single proof-of-concept firing. If a civilization does expand via von Neumann replicator machine life, it becomes a lot more plausible that every machine has similar incentives. It also becomes a lot harder to fully exterminate all machines. There may be no winnable wars between interstellar-capable machine civilizations, assuming that more than one exists in the first place. I know, I'm invoking a lot of speculation. But answering the "where are they?" question of the original Paradox with "lots of places, but we've failed to notice" feels more satisfying to me than guessing that Earth is extraordinarily special. Also more satisfying than guessing that technologically developed species inevitably self-destruct before developing interstellar capabilities.
mordant 8y ago
My favorite theory is that there's been at least one Bracewell probe in our solar system since the 1920s. https://en.wikipedia.org/wiki/Bracewell_probe https://en.wikipedia.org/wiki/Bracewell_probe https://en.wikipedia.org/wiki/Long_delayed_echo https://en.wikipedia.org/wiki/Long_delayed_echo http://folk.uio.no/sverre/LDE/ http://folk.uio.no/sverre/LDE/

red75prime 8y ago

So we are another kind of special to deserve observation and galaxy wide bubble of silence.

philipkglass 8y ago
No, I'm assuming that probes are widely distributed. Laser communication is better than radio communication over long distances. Shorter wavelengths make for tighter beams. The whole galaxy could be mesh-networked with ultraviolet laser links and repeaters, and it would still take a rare stroke of luck for any of our telescopes to notice, even if the links aren't operated for deliberate stealthiness.
- red75prime 8y ago
  Tight laser beams are limited by diffraction. Kilometer wide laser beam on wave length 308mn will have diameter around 15 millions meters on 4 light year distance. Meter wide beam will have diameter 15 billions meters, all other things being equal. I can't, right now, estimate probability of breaking the silence, though.
  - philipkglass 8y ago
    Right, a 15 billion meter wide beam aimed at e.g. a solar gravitational lens relay station some 542 AU out, or even aimed at much closer receiving stations around Jupiter, would not intersect Earth most of the time. At 308 nm it wouldn't be visible to ground based telescope since the atmosphere would mostly absorb it. If using gravitational lensing to set up system-to-system communication is the norm, the beam might not be bright enough to be observable by current space based UV telescopes. All of this could just be driven by ordinary post-biological-alien good engineering practices. It would seem extremely stealthy to humans, but that doesn't need to be intentional, any more than ham radio communications are intentionally stealthy against observation by whales.

roywiggins 8y ago

I'd object on the basis that it is hard to imagine everyone cooperating on that sort of project. It implies everyone has about the same incentives and motivations, which suggests a remarkable uniformity... so if it's true, there's probably only one civilization in our galaxy, and it's spread uniformly everywhere.

philipkglass 8y ago
Or that one civilization (more likely: a tiny number of decision makers within one civilization) got the capability first, and had outposts waiting everywhere before any other species could reach the same galaxy-spanning capabilities. Or that a handful of civilizations spread out before there was one galaxy-wide winner. But all faced similar incentives against paperclip maximizers and toward peacefulness upon contact with other interstellar civilizations. World powers here on Earth recognized that thermonuclear war is a terribly bad idea even though a thermonuclear weapon has never been used in anger. Multiple alien civilizations could perhaps foresee that deploying Nicoll-Dyson Laser weapons would end badly without a single proof-of-concept firing. If a civilization does expand via von Neumann replicator machine life, it becomes a lot more plausible that every machine has similar incentives. It also becomes a lot harder to fully exterminate all machines. There may be no winnable wars between interstellar-capable machine civilizations, assuming that more than one exists in the first place. I know, I'm invoking a lot of speculation. But answering the "where are they?" question of the original Paradox with "lots of places, but we've failed to notice" feels more satisfying to me than guessing that Earth is extraordinarily special. Also more satisfying than guessing that technologically developed species inevitably self-destruct before developing interstellar capabilities.

mordant 8y ago

My favorite theory is that there's been at least one Bracewell probe in our solar system since the 1920s. https://en.wikipedia.org/wiki/Bracewell_probe https://en.wikipedia.org/wiki/Bracewell_probe https://en.wikipedia.org/wiki/Long_delayed_echo https://en.wikipedia.org/wiki/Long_delayed_echo http://folk.uio.no/sverre/LDE/ http://folk.uio.no/sverre/LDE/