Well, bacteria can certainly survive hard vaccuum. The only problem is that bacteria can’t grow in hard vaccuum, and they can’t evolve in hard vaccuum, and to the extent that we understand the origin of life, they certainly can’t originate in vaccuum.
All living organisms that we know are actually very closely related on a biochemical level. We’re all the same sort of life…we use DNA which makes RNA, which makes proteins using ribosomes, we have phosolipid cell membranes, all DNA codes for the same amino acids in the same way, we all use water as a solvent and on and on. Even bacteria that can live in boiling water use the same biochemistry, they just use it in different ways.
So imagining silicon life, or life in an ammonia or methane ocean is kind of difficult, because all earth life is pretty much alike, and all clearly related to each other. And we don’t know if radically different life is possible. There are pretty good reasons to believe that your classic science fiction-style silicon life form is impossible. But we just don’t know, and the discovery of the first non-earth life will answer a lot of questions about what sorts of things are possible.
Some broad possibilities:
Non-earth life is discovered, and it’s almost identical biochemically to earth life. Which means that it probably shares a common ancestor with earth life, which means that panspermia is confirmed. Maybe earth life arose on Mars rather than earth, and traveled from Mars to Earth on a meteor. Or vice versa. Or life arose in comets.
Non-earth life is discovered, and it’s pretty similar biochemically in broad strokes to earth life, but with fundamental differences. This indicates that life can arise independently in different environments but converges to a few optimum solutions. It uses a molecule very similar to DNA with a few slightly different functional groups, it has different codons, it uses proteins but a different suite of amino acids, it uses molecules with an opposite chirality, and so on.
Then we get into the weird cases. Ammonia life, silicon life, clay life, non-DNA life, life with radically different organization. Life that exists in gas giants, in stars, in hard vacuum, in liquid helium, life on a radically different scale than Life As We Know It.
As for the philosophical speculation in the OP, the best we can do is realize that we’re human beings, and realize that our brains evolved because they helped our ancestors survive and reproduce as social primates on the African savanna, they didn’t evolve to allow us to understand the mysteries of the universe. In a certain sense we know that human beings are finite creatures, and so we’ll never understand everything.
But we can also understand that a species that didn’t have eyes could still understand light as a phenomemon, even if they couldn’t percieve it directly. We can’t percieve x-rays, gamma rays, radio waves, or any other portion of the electromagnetic spectrum except a tiny slice that just happens to correspond to the peak output of our sun. A species that lived in water can still understand air, and could understand that organisms flew in the air and lived on land, because they could percieve them directly, as Blake points out. We humans have no intuitive understanding of how matter and energy and time and space behave at very high speeds and at very small scales, but we’re able to write equations that describe that behavior, even if that behavior goes against every common sense notion we have.
So we can imagine a species that uses sonar instead of vision, and then see that species would have difficulty understanding stars, because they wouldn’t have seen tiny dots in the night sky since the dawn of their civilization. But they could eventually develop a theory of the electromagnetic spectrum, and they could build optical telescopes and discover a weird result…millions of point sources emitting o-radiation, their name for the mysterious phenomemon of “light”. And this is exactly what happened to us when we started scanning the universe at wavelengths other than visual…x-ray emitters, radio wave emitters, gamma ray emitters, UV emitters, IR emitters, and so forth, all completely new, all completely mysterious and unexpected, because the human eye can’t directly percieve these emissions. So we might have had a head start in getting the idea to scan the sky for emitters, because we wanted to figure out what those tiny dots called “stars” were, but even if we were blind we would have discovered them at the same time we started doing non-optical astronomy, because optical astronomy would be just one more slice of the spectrum to us.
And we can then speculate about the opposite, what sorts of phenomeon are we not understanding because we don’t have sonar? Well, we’ve just invented ultrasound imaging, but that would be a commonplace for a sonar-using species, from the very beginnings of their civilization they’d be able to use their natural senses to see below the surfaces of objects. But as far as I can see there’s nothing fundamental that we, as non-sonar-users would be totally incapable of understanding, ever. Just as I don’t think there would be phenomenon that non-visual species would be incapable of understanding, ever. They might not understand them on an intuitive common sense everyday level, but their scientists could easily explain how light works, and how these strange creatures have organs with nerves that are stimulated in the presence of radiation of a particular wavelength, and this allows the creatures to construct a three dimensional model of their surroundings. And those scientists would theorize that because EM radiation can travel very long distances in certain circumstances that the creatures might be able to image objects that are very far away, and so on.