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> I do not understand the consistent assumption that life on other planets must take a chemical and physical form similar to our own. I always pondered about t

> I do not understand the consistent assumption that life on other planets must take a chemical and physical form similar to our own. I always pondered about this as well. I came to the conclusion that, given the sheer number of celestial bodies (e.g. planets) in the universe, restricting our gaze to only the ones that can sustain life as we know it (i.e. carbon-based bags-of-mostly-water) restricts the search space considerably. I don't know whether that actually increases our likelihood of finding extraterrestrial life; I certainly do hope so.

simonh 9y ago
There are two spaces to consider. One is the range of habitats available, the other is the range of chemistry complex and rich enough to form viable metabolic pathways. The problem is the OPs comment about restricting ourselves to a narrow range of chemistries is a bit naive. Carbon chemistries are so rich and so complex it's a whole field of study alongside all other forms of chemistry put together. That's not just because it happens to be interesting because we are made of it, it's just a fact of chemistry and physics that carbon chemistry is fantastically diverse and scalable compared to all other known and theoretical chemistries. A lot of somewhat simplistic conjecture starts from the idea that the universe is vast and unknown and could contain 'anything'. But the fact is we can see the universe through our telescopes and other instruments. We know what all the elements are and what their properties are so it seems rational to use that information to optimise our search. After all, if there are unknown elements and unknown chemistries or structural paradigms out there that might also be viable, since we don't know what they are, we also don't know what to look for to find them, so that avenue of speculation doesn't actually take us anywhere useful.

simonh 9y ago

There are two spaces to consider. One is the range of habitats available, the other is the range of chemistry complex and rich enough to form viable metabolic pathways. The problem is the OPs comment about restricting ourselves to a narrow range of chemistries is a bit naive. Carbon chemistries are so rich and so complex it's a whole field of study alongside all other forms of chemistry put together. That's not just because it happens to be interesting because we are made of it, it's just a fact of chemistry and physics that carbon chemistry is fantastically diverse and scalable compared to all other known and theoretical chemistries. A lot of somewhat simplistic conjecture starts from the idea that the universe is vast and unknown and could contain 'anything'. But the fact is we can see the universe through our telescopes and other instruments. We know what all the elements are and what their properties are so it seems rational to use that information to optimise our search. After all, if there are unknown elements and unknown chemistries or structural paradigms out there that might also be viable, since we don't know what they are, we also don't know what to look for to find them, so that avenue of speculation doesn't actually take us anywhere useful.