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I've long thought the starseeder hypothesis was a good bet from purely statistical grounds. What are the odds of intelligent life arising ex nihilo? We'd assume

I've long thought the starseeder hypothesis was a good bet from purely statistical grounds. What are the odds of intelligent life arising ex nihilo? We'd assume infinitesimal. Given that it happened once, what are the odds that life will successfully expand to other planets? I at least would assume better than it happening independently again, we've never seen autogenesis but we have sent tardigrades to the moon.

cgriswald 6y ago
I'm imagining two paths for life to spread between star systems. The first is via intelligent life actively exploring those systems—the purpose or mechanism of that exploration doesn't really matter; life could get there either way. So now you're comparing the statistical probability of abiogenesis against the product of the probabilities of a half dozen unlikely events (roughly, first abiogensis -> cells -> animals -> intelligence -> civilization -> technological civilization -> society stable enough to spread life amongst the stars). This isn't clear cut, but my best guess is that abiogenesis happening twice is rather more likely. The second is via some form of microbial life leaving the star system and spreading to other stars by accident (whether evolutionary accident or 'act of God'). I think it's possible life could leave the star system by some mechanism and with a ridiculous number of individuals and time could hit other star systems rather than floating in between systems forever. Then it has to land on a planet that not only doesn't kill it, but allows it to thrive. (Tardigrades aren't going to populate the moon.) I'm not sure how possible or likely this would be, but I'm guessing it requires a ton of time (that the universe may not have experienced yet) and, if it were likely, we'd have already found evidence of life on Mars.
mrec 6y ago
> What are the odds of intelligent life arising ex nihilo? We'd assume infinitesimal. Why would we assume that? We've been seeing biologically interesting chemicals appear from much simpler ones for well over a century. https://en.wikipedia.org/wiki/Abiogenesis#Chemical_synthesis_in_the_laboratory https://en.wikipedia.org/wiki/Abiogenesis#Chemical_synthesis... Also, your "starseeder hypothesis" sounds a lot more deliberate than panspermia theories, but correct me if I'm misunderstanding you there.
- SuoDuanDao 6y ago
  Why wouldn't we assume that? Even with the ability to synthesize full DNA molecules, we haven't yet figured out how to make a living cell from scratch. If our best synthetic biologists still find it impossible to assemble a viable cell while having all the tools to do so in theory, I wouldn't expect it to be likely to happen by accident, barring some quantum weirdness that makes the starseeder hypothesis seem positively banal. As to deliberateness... I see the difference between starseeder and panspermia hypotheses that in the former; life happened once in a gravity well, became multicellular, figured out a means to escape the gravity well, and then spread throughout the galaxy while in the latter; life happened once in space, drifted a while, got stuck in a gravity well and then figured out how to be multicellular. I suppose - particularly given the vastness of the places with no gravity wells compared to places with gravity wells - that it's my own gravity-well bias that makes me reach for 'starseeder' hypotheses before panspermia ones. But I think whether life was multicellular before or after the bulk of the interstellar spreading, the instinct of life to spread would be the motive force whatever its problem solving capabilities.
  - mrec 6y ago
    > in the latter; life happened once in space AIUI most panspermia theories don't posit either of those - definitely not that life originated in space, and not necessarily that it only originated once. The most common variants seem to be that life originates in gravity wells, is ejected by major impact events, drifts through space and eventually re-enters other gravity wells. Simulations suggest that bacteria can potentially survive all of these.

cgriswald 6y ago

I'm imagining two paths for life to spread between star systems. The first is via intelligent life actively exploring those systems—the purpose or mechanism of that exploration doesn't really matter; life could get there either way. So now you're comparing the statistical probability of abiogenesis against the product of the probabilities of a half dozen unlikely events (roughly, first abiogensis -> cells -> animals -> intelligence -> civilization -> technological civilization -> society stable enough to spread life amongst the stars). This isn't clear cut, but my best guess is that abiogenesis happening twice is rather more likely. The second is via some form of microbial life leaving the star system and spreading to other stars by accident (whether evolutionary accident or 'act of God'). I think it's possible life could leave the star system by some mechanism and with a ridiculous number of individuals and time could hit other star systems rather than floating in between systems forever. Then it has to land on a planet that not only doesn't kill it, but allows it to thrive. (Tardigrades aren't going to populate the moon.) I'm not sure how possible or likely this would be, but I'm guessing it requires a ton of time (that the universe may not have experienced yet) and, if it were likely, we'd have already found evidence of life on Mars.

mrec 6y ago

> What are the odds of intelligent life arising ex nihilo? We'd assume infinitesimal. Why would we assume that? We've been seeing biologically interesting chemicals appear from much simpler ones for well over a century. https://en.wikipedia.org/wiki/Abiogenesis#Chemical_synthesis_in_the_laboratory https://en.wikipedia.org/wiki/Abiogenesis#Chemical_synthesis... Also, your "starseeder hypothesis" sounds a lot more deliberate than panspermia theories, but correct me if I'm misunderstanding you there.

SuoDuanDao 6y ago
Why wouldn't we assume that? Even with the ability to synthesize full DNA molecules, we haven't yet figured out how to make a living cell from scratch. If our best synthetic biologists still find it impossible to assemble a viable cell while having all the tools to do so in theory, I wouldn't expect it to be likely to happen by accident, barring some quantum weirdness that makes the starseeder hypothesis seem positively banal. As to deliberateness... I see the difference between starseeder and panspermia hypotheses that in the former; life happened once in a gravity well, became multicellular, figured out a means to escape the gravity well, and then spread throughout the galaxy while in the latter; life happened once in space, drifted a while, got stuck in a gravity well and then figured out how to be multicellular. I suppose - particularly given the vastness of the places with no gravity wells compared to places with gravity wells - that it's my own gravity-well bias that makes me reach for 'starseeder' hypotheses before panspermia ones. But I think whether life was multicellular before or after the bulk of the interstellar spreading, the instinct of life to spread would be the motive force whatever its problem solving capabilities.
- mrec 6y ago
  > in the latter; life happened once in space AIUI most panspermia theories don't posit either of those - definitely not that life originated in space, and not necessarily that it only originated once. The most common variants seem to be that life originates in gravity wells, is ejected by major impact events, drifts through space and eventually re-enters other gravity wells. Simulations suggest that bacteria can potentially survive all of these.