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The grandparent of my comment was a suggestion that ETs should be an explanation of last resort for any unexplained phenomenon, which seems highly sensible to m

The grandparent of my comment was a suggestion that ETs should be an explanation of last resort for any unexplained phenomenon, which seems highly sensible to me and worthy of support. If you enjoy probabilistic arguments, then you'll appreciate why I think that B-vN probes are inevitable. P(probes) = 1 - P(no probes) = 1 - (1 - P(civ launches one probe))**Nciv If you believe that Nciv is large (and it's the number of tech civilizations up to now, not just at the moment), then you have to argue that P(civ launches one probe) is tiny if you agree that we haven't observed a probe here yet.

Udo 10y ago
> If you enjoy probabilistic arguments, then you'll appreciate why I think that B-vN probes are inevitable. You seem to be under the impression that I wasn't familiar with that argument, even though I explicitly described it as "the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected". I don't think there is a person in this thread who doesn't understand the basic assumption. Your claim of inevitability only applies to an infinite amount of time, so in our universe at this point in time the number can still be (and probably is) zero. So I'm trying to talk about a more refined model instead, namely one that tries to at least reserve room for factors such as the overall number of active civilizations, and the likelihood that we actually discover a drone. To start off with, we have no idea what the probability of a single civilization colonizing the galaxy with drones even is, and we're also making a lot of implicit assumptions about the nature of these drones. The argument that "one case is enough" is valid, but still the overall likelihood of that one very specific case may be too low. There is also the possibility of drones going by undetected. We don't know what the drones' navigation algorithm would look like, but it's at least conceivable that some solar systems might have been left out altogether. Finally, I'm not sure if we could necessarily detect moderate drone activity in the outer solar system at all.
mrow84 10y ago
Shouldn't the expression be more like P(probes) = 1 - P(no probes) = 1 - (1 - (P(civ launches one probe)*P(probe reaches Earth)))**Nciv You can then simply argue that P(probe reaches Earth) is small, because you don't believe that Bracewell-von Neumann probes are effective.

Udo 10y ago

> If you enjoy probabilistic arguments, then you'll appreciate why I think that B-vN probes are inevitable. You seem to be under the impression that I wasn't familiar with that argument, even though I explicitly described it as "the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected". I don't think there is a person in this thread who doesn't understand the basic assumption. Your claim of inevitability only applies to an infinite amount of time, so in our universe at this point in time the number can still be (and probably is) zero. So I'm trying to talk about a more refined model instead, namely one that tries to at least reserve room for factors such as the overall number of active civilizations, and the likelihood that we actually discover a drone. To start off with, we have no idea what the probability of a single civilization colonizing the galaxy with drones even is, and we're also making a lot of implicit assumptions about the nature of these drones. The argument that "one case is enough" is valid, but still the overall likelihood of that one very specific case may be too low. There is also the possibility of drones going by undetected. We don't know what the drones' navigation algorithm would look like, but it's at least conceivable that some solar systems might have been left out altogether. Finally, I'm not sure if we could necessarily detect moderate drone activity in the outer solar system at all.

mrow84 10y ago

Shouldn't the expression be more like P(probes) = 1 - P(no probes) = 1 - (1 - (P(civ launches one probe)*P(probe reaches Earth)))**Nciv You can then simply argue that P(probe reaches Earth) is small, because you don't believe that Bracewell-von Neumann probes are effective.