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One common response in these discussions is "but there are so many assumptions". This annoys me. As I see it, the whole *point* is to make those assumptions explicit and facilitate talking about them. And then people cycle through various objections as if they're refuting the paradox, rather than proposing various solutions.
Semi-formal statement:
Given the fact of a huge and old universe,
and assuming that we are "normal" and thus life, intelligence, and spacefaring industry are common,
and [assuming that such would be detectable
OR assuming that interstellar transport of something that can propagate is possible, with even more detectable results]
then where the hell is everyone?
"Paradox" isn't a particularly good name for it, but it's traditional. But the conclusion of some natural (to many) assumptions is a result at odds with observation, hence sort of "paradox", and discussion. Which of course consists of give and take dispute over various assumptions. "Why do you assume detection is possible?" "Because..." And more assumptions, on *both*, or *all*, sides. It's not clear to me who has to make the strongest assumptions; after all, someone saying travel isn't possible is ruling out *every* combination of propulsion, AI, stasis, mini-tech, longevity, etc., and every form of replication (including bio-heavy ones), while the pro-propagation view just needs one viable way to spread. Life (or replicators) is like water, and the universe prone to leakiness.
Similarly if we posit stealthy civilizations, we ultimately need all of them to be stealthy, in all modalities, including radio deliberate and leaky, thermal emissions, artificial lights, gamma or neutrino emissions, stellar occlusions, probe debris, etc. (Not that we've looked thoroughly at all of these; everything could change tomorrow with some new signal discovery.)
I guess I'm complaining about tone. If you dispute some assumption, you're not proving Fermi was bunk, you're participating in the discussion as intended.
Semi-formal statement:
Given the fact of a huge and old universe,
and assuming that we are "normal" and thus life, intelligence, and spacefaring industry are common,
and [assuming that such would be detectable
OR assuming that interstellar transport of something that can propagate is possible, with even more detectable results]
then where the hell is everyone?
"Paradox" isn't a particularly good name for it, but it's traditional. But the conclusion of some natural (to many) assumptions is a result at odds with observation, hence sort of "paradox", and discussion. Which of course consists of give and take dispute over various assumptions. "Why do you assume detection is possible?" "Because..." And more assumptions, on *both*, or *all*, sides. It's not clear to me who has to make the strongest assumptions; after all, someone saying travel isn't possible is ruling out *every* combination of propulsion, AI, stasis, mini-tech, longevity, etc., and every form of replication (including bio-heavy ones), while the pro-propagation view just needs one viable way to spread. Life (or replicators) is like water, and the universe prone to leakiness.
Similarly if we posit stealthy civilizations, we ultimately need all of them to be stealthy, in all modalities, including radio deliberate and leaky, thermal emissions, artificial lights, gamma or neutrino emissions, stellar occlusions, probe debris, etc. (Not that we've looked thoroughly at all of these; everything could change tomorrow with some new signal discovery.)
I guess I'm complaining about tone. If you dispute some assumption, you're not proving Fermi was bunk, you're participating in the discussion as intended.
Maybe they're like us
Date: 2012-02-21 20:09 (UTC)From: (Anonymous)What if they're technologically on the same level as us. Or, what if they are at a stage we were in the 18th century, or earlier?
And yet another possibility: our assumption about their technology and knowledge being far superior to ours is correct, but they have encountered a logistical problem to far-space exploration, one that is so fundamentally detrimental that they would rather not risk it? E.g. stray alpha particles, the monumental task of getting back home in a universe where everything is still moving at very high speeds.
Maybe there are aliens, maybe there aren't. I'm just saying it's a little bit unrealistic for us to expect aliens to always be technologically superior to us.
Re: Maybe they're like us
Date: 2012-02-22 01:56 (UTC)From:On evolutionary time scales, we had a long Stone Age hunter-gatherer period and a rather short agricultural and even shorter industrial periods. The chance of another intelligent species being right at the 17th century, say, seems low. Stable states seem likely to be primitive or highly advanced.
Alpha particles aren't that dangerous. No idea what "monumental task of getting back home in a universe where everything is still moving at very high speeds." means.