Dr. Stephen Hawking argues that alien life almost surely exists & warns that human encounters with aliens could well end badly for us. In the absence of actual evidence for the presence of extraterrestrial life, much less for its intentions, I would say that Dr. S. Hawking’s guesses are as good as anyone else’s. I guess that it is equally likely that extraterrestrial life does not exist either because it never arose or, if it did arise, was soon eliminated. Another possibility is that some sort of primitive photosynthetic or chemosynthetic organisms exist elsewhere in the Universe. If, as on Earth, the primary form of energy available on other planets is radiation from a nearby star, it seems likely that, as on Earth, photosynthetic organisms must predominate. It follows that consumers of these producers may well have also evolved. However, life that exists away from Earth will not necessarily use the same chemistry rules. If, as we generally assume, water is required for life, then the range of possible chemistries is constrained but there is absolutely no reason to assume that anything remotely close to plants or animals, much less humans, exists elsewhere. Although dissimilarities in chemistry could limit our ability to analyze or even detect extraterrestrials, it could also protect us from harm. An alien organism without proteins, for example, may have a difficult time digesting us. If, on the other hand, we were to encounter alien life forms that ravenously consume all of the energy containing chemical compounds that they can get their ”hands” on, it would indeed be tragic for us, but a good meal for them!
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