As noted earlier, life on Earth is rather diverse, especially if you include past eras. Diverse conditions produced diverse life. When conditions change, some life forms disappear (become extinct), others evolve to adapt to the changing conditions, others retreat to narrow niches, while others who were once were restricted to niches find the changed conditions so much to their liking that they flourish and become widespread. This can be helpful in speculating upon universal biologies and what kinds of alien life could exist.
For example, in the History channel documentary "How the Earth was Made" (2007 - shown 10 Nov 2007), it was discussed how life changed the Earth, but also how the Earth changed life: one reason dinosaurs were able to flourish and grow to such gargantuan sizes is that because of the warm temperatures which created lush forests and jungles that covered the Earth (even Greenland was a lush forest) and the heavily oxygenated atmosphere, there was plenty of food and air to sustain such creatures. At the time of the dinosaur demise, there was a species of dinosaur that had what was believed to be opposable "thumbs" (I need to track down the source for this information, I recall watching a documentary on the demise of the dinosaurs on the Discovery channel several years ago, but, alas, I do not recall the title. If anyone can produce a citation for this, I would greatly appreciate it). Had the Earth been more "boring" and was not struck by a large meteor, and did not enter such a harsh ice age, the dominant life form today sitting at computers and contemplating the universe may have been a species of lukewarm blooded dinosaur. Again, sentient life requires time to develop - the more boring the solar/celestial environment, the better.
So, when contemplating alien life, we need to keep in mind, I believe, that chemical and physical logic needs to apply - the universal physical laws place restraints on biological laws.
Though, I wonder, can biological laws be separate, and not merely subsets of interactions between chemistry and physics? For instance, in quantum physics, the observer affects reality by merely observing. Now I know many pseudo-scientists take that and run like crazy with it, but it does give one pause - if my mere observation affects reality, then that means sentience is a force of some kind. Maybe it is still "just" the result of physics, chemistry, and biology. Maybe it is an aspect of physics we just don't understand yet - our sentience is just another physical force, like muons, quarks, gravity, and gamma rays.
But if so, then that means sentience might be a part of the universe - it's not just a local, Earth bound phenomenon.
So is sentience a physical particle like a muon, or a physical force, like gravity that takes a set of chemical and physical reactions to cause it to be "emitted" or released? Or is sentience something that arises as a result of the set of chemical and physical reactions? If so, could sentience then arise from an artificial mind - if we, in creating that mind, set up the right conditions, such that a "sentience" field is emitted?
OK, this is more of an aside, as the purpose of this blog is to discuss what would the result of alien sentience be - speculations of what kind of alternative extrasolar biological, psychological, theological and societal realities that could exist.