The following is my opinion as a member participating in this discussion.
Good point Seagull, there are other elements that are suitable to form the kinds of chains and rings that seem to be necessary to form compound that
can carry complex information.
Could you have creatures who were made of simple Elements? Could you have 'hydrogen' creatures? Maybe, but they'd be very different than what we
know as sentient life. Under different amounts of temperature and pressure, gases like hydrogen and helium can be classed as metallic.
One could go on to speculate and even give scientific support for sentient life in an almost unlimited array of possibilities. There could be
intelligent trees or intelligent mountains. I don't mean Earth mountain, but an analogous form.
However, if the life is too different than we, then we might not be able to detect it, might not be able to communicate and we might not be able to
relate on any level.
So I think that narrows it down some and invokes an additional criteria. IOW, what good is it to detect an intelligent life form which is analogus to
a geological entity and whose life is based on a completely different time scale, perhaps measured in millions of years. We'd have to wait for
generations for them to send us one thought, I'd think. Just like the Scalosians memory-alpha.org...
who live in a blink of an
eye, we have to share a similar time-scale.
My point is that in order for any "life" form we meet to be meaningful, it has to have a fairly narrow range of characteristics and make up, because
without some common ground, we'd be unable to relate.
So add another item to the list, after 'they'd have to be alive during the time we are alive'. They'd have to be fairly similar to us.
This doesn't mean they have to look like us or think like we do. For purposes of comparison, Dolphins are within this narrow range.
When I say 'narrow' I mean in relation to the whole list of possibilities, which are probably nearly endless, from gas bags, to space-faring whales,
to sentient mountains to metallic hydrogen creatures.
In addition our living conditions would have to be fairly similar, though they could have 'encounter suits' like the Vorlons.
Again, I say narrow, but as I type this it seems there could be ways found to make things work so we never know.
We're able to imagine a lot of different possibilities. Witness the range of creatures you see in science fiction. And, we know as they say
possibilities are going to be stranger than we -can- imagine.
Alas, it's fun to speculate, but I fear that we are in too deep a quarantine, with the distances, time, vacuum, cold, radiation and other problems,
to ever meet any other sentients. And as some have said, it doesn't seem that in general evolution has any specific pressure to select for
intelligence. It's probably more slanted towards claws and teeth and stuff like that. We are a fluke.
Sorry to ramble.
As an ATS Staff Member, I will not moderate in threads such as this where I have participated as a member.