Indeed.
Not quite.
The biggest problem would be: How did they
evolve so far that the question of movement even has to be considered ...?
In space, there is simply no possibility to initiate life.
Even if not carbon based, you would need some molecules to meet and match. Therefore you'll need a solvent. There is no solvent in the cold vacuum.
Well, then why not let them form on a planet and then let them "somehow" immigrant into the void?
Unfortunately, such a species would have adopted to the conditions of their planet. Evolution can take us so and so far. But it has to work with what is based on the passed. There is still a fish in us (our bone structures, for example). Even single cell organisms (certain enzymes haven't changed much since their very first days - incidentally enzymes that enable us to deal with oxygen, which is highly toxic for organisms if not properly dealt with).
One simply can't take a creature that has evolved on a planet and make it space-dwelling. (Only a tiny part of it is indeed locomotion. How to leave the gravity sink in the first place? I want to see the bird that is able to reach hyperbolic excess velocity ...)
Okay, not planet-born then. What about species composed out of pure energy? We see it in science fantasy all the time, so ...
Unfortunately, energy has the nasty tendency to disperse. Ask the physicists who try to keep those fusion plasmas in check. Or laser engineers who try to keep the focus of a laser beam.
One of the major attributes of life is the separation of 'inner' and 'outer'. Cell membranes were the first thing "invented" to make life possible at all. What physical, spontaneous process do you guys know that assures this regarding pure energy? (Magnetism, I hear? Again, tell it those fusion researchers; they might be interested to learn about it.)
Speaking of cell membranes and solving agents.
There are theoretical possibilities that life might be able to form in different solutions than water. H
2S, for example.
The thing is, water is almost a magic molecule. My chemistry professor had an encyclopedia of 1 1/2 meter just about this "element".
The main reason for its properties lies in its high dipole momentum. Life, if not in vacuum then somewhere else, might be possible without water - theoretically.
But as water is such a common feature in the galaxy, it's much, much less likely.
Oh ... and liquid water and vacuum doesn't match well ...
Then there is the issue of energy turnover, which is another basic characteristic of life. Where to get this energy from?
Photosynthesis? Maybe. But you'll need something to deoxidize in order to store all the gathered energy. maybe water again? Oh, I forgot... vacuum!
Regarding "dense" space nebulae to feed on ... well, yes, they look impressive and dense from a distance. And oh my, distances we have, in space!
From closer within, things change a bit. Those "dense" nebulae feature approximately
one atom
per cubic meter. Which makes it harder to breath than on the top of the Mount Everest, but is still way more than in other regions of space.
I could go on and on and on.
Sorry for the long, meaningless post. You guys know all this already, of course.
It's just hot outside and I can not play ED in my Rift and I am bored.
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TLDR:
Scientifically, living space creatures are utter nonsense. Doesn't matter, how big space is. Sorry.
But as I mentioned already in a post above: As a player and science fiction/fantasy reader, I
still would love to see those creatures in Elite Dangerous!
And I don't care, if they are space dragons propelled by rainbow farts ...