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Will the first extraterrestrial life-forms we encounter be carbon-based?
As of question writing, all known life is carbon-based, in the sense that it needs to contain carbon atoms to survive.
But life could take many forms:
- Wikipedia has a handy list of hypothetical types of biochemistry, notably silicon biochemistry.
- Life could be based on non-organic chemistry (e.g. inorganic chemistry, or nuclear chemistry in the degenerate crust on the surface of a neutron star*).
- Life could also not be chemistry based at all. It could be electrical (e.g. Ems) or mechanical (e.g. clockwork).
- Life could operate on vastly different time / space scales from us (e.g. a cloud of interstellar stuff somehow consistently implementing a sentient computation).
These examples are not necessarily mutually exclusive, and I obviously make no claim regarding their respective feasibility/likelihood. They are rather meant to suggest the vastness of design-space.
Question: If we encounter a phenomenon that is widely considered by the scientific community to be an alien life-form, will all simple life-forms we discover be carbon-based?
- The life-form has to have originated independently from earth life. That is: earth life can be a consequence of the alien life-form, they can share a cause, but earth life cannot have caused the alien life.
- The life-forms that count for this question are ones on the complexity level of our single-celled organisms or lower (as determined by a poll of xeno-biologists if there is any ambiguity). If there are none, then the simplest life-forms we have found are taken for resolution.
- The life-form has to need less than 1% of its atoms to be carbon atoms in order to keep being alive. It can incidentally contain carbon atoms, as long as they could theoretically be absent and the life-form still be alive.
- The scientific community has to have reached a consensus as judged by Metaculus admins.
- This resolves positive if any life-form we encounter satisfies points 1. 2. and 3.
- This resolves negative if all the life-forms we encounter that satisfy points 1. and 2. do not satisfiy point 3.
- This resolves ambiguous if no life-form that satisfies point 1. is found before 2500, or if before then we have conclusive evidence that none exists in the observable universe.
- This resolves 50 years after we first discover an alien life-form that satisfies condition 1., to give time for consensus forming.
* My thanks to @(Uncle Jeff) for this example.
Note that in this sense Humans are only "based" on hydrogen (60%), oxygen (25%), carbon (10%) and nitrogen (1.5%).
Metaculus help: Predicting
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The basics of predicting are very simple: move the slider to best match the likelihood of the outcome, and click predict. You can predict as often as you want, and you're encouraged to change your mind when new information becomes available.
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Metaculus help: Community Stats
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When you make a prediction, check the community stats to see where you land. If your prediction is an outlier, might there be something you're overlooking that others have seen? Or do you have special insight that others are lacking? Either way, it might be a good idea to join the discussion in the comments.