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Originally Posted by 3rdvogon
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Originally Posted by hhEb09'1
That's the big mistake that Bostrom makes. There is no such thing as a Great Filter that exists only at a single critical juncture.
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I totally agree. I think he is in error to talk about a single Great Filter. |
Well, in the last page of the article he does say:
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Nothing in the preceding reasoning precludes there being steps in the Great Filter both behind us and ahead of us. It might be extremely improbable both that intelligent life should arise on any given planet and that intelligent life, once evolved, should succeed in becoming advanced enough to colonize space.
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I see other flaws in his reasoning, though. One is what
eburacum said above:
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Originally Posted by eburacum45
Bostrom is a profound thinker, but I think that his suggestion that finding dead vertebrates on Mars would be Bad News is going a little too far. The fact that Mars might have supported complex life that then died out has no real relevance for the Earth- that planet is entirely different in many characteristics to our own, so may be intrinsically more likely to become a dead planet.
A dead Mars with fossils doesn't imply anything about the existence of a Great Filter that eliminates intelligent life on Earth-like worlds.
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Mars is a good example, because it shows that Bostrom neglected a little hastily the differences between planets. Some life-bearing planets may well be more hospitable to life than others.
On page 5 of the article there is another assumption which seem questionable.
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Consider the implications of discovering that life had evolved independently on Mars (or some other planet in our solar system). That discovery would suggest that the emergence of life is not very improbable. If it happened independently twice here in our own backyard, it must surely have happened millions of times across the galaxy.
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Or it might mean that the chemical composition, or some other characteristic of our solar system (such as the low eccentricity of all major planets), are especially favorable to life. It seems a mistake to me to treat Earth and Mars as two independent data points. More likely, they are correlated. There's even the possibility of panspermia: that life could have arisen first in only one of these planets, and then migrated to the other.
And on page 4 there's something else I'd question:
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[...] even if most advanced civilizations chose to remain nonexpansionist forever, it wouldn't make any difference as long as there was one other civilization that opted to launch the colonization process: that expansionary civilization would be the one whose probes, colonies, or descendants would fill the galaxy. It takes but one match to start a fire, only one expansionist civilization to begin colonizing the universe.
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He's assuming that the more expansionist civilisation will always triumph. But perhaps the opposite is what tends to occur: when one civilisation tries to colonise other solar systems, the colonised ally themselves to neutralise the coloniser, and stop the expansion.
Food for thought, nonetheless...