So perhaps there are some star systems that are outside of the Great Barrier. Maybe some the are right in the middle of it. If it is a constructed phenomenon then whoever built it would have arbitrarily defined it during construction.
The problem is that the dialogue in "Where No Man Has Gone Before" is full of references to the galaxy having a clearly defined edge, even before the crew encounters the barrier. Their whole mission is to probe beyond the edge of the galaxy. Kelso says "Approaching galaxy edge, sir." Spock mentions the
Valiant getting "about half a light year out of the galaxy," implying that the edge is so clearly defined that it can be narrowed to a fraction of a light year.
(Not to mention, what was the point of probing beyond the "edge" anyway? If there actually were a point where the stars stopped, anything beyond it would be too far to reach.)
I do not understand why Memory Alpha assumes that the swirling phenomenon seen in the "unknown void" during the extragalactic scenes in "Is There in Truth No Beauty?" is the same phenomenon as the negative-energy barrier seen in "Where No Man Has Gone Before" and "By Any Other Name".
It wasn't meant to be, but viewers have always interpreted it that way in an attempt to create a sense of continuity. Memory Alpha is just following the lead established by the
Star Trek Concordance back in the '70s.
Besides, the alternative is to take the episode's bizarre cosmology literally. The writer didn't seem to understand the difference between a galaxy and a universe, assuming that the region beyond the galaxy was some bizarre alien dimension with no recognizable points of reference, rather than just empty space. You wouldn't need a Medusan to find your way back into the galaxy -- just turn around 180 degrees and point yourself back toward the big swirly clump of stars.
Actually we can't define the edge of the Earth's atmosphere. By international convention, we arbitrarily define "space" as beginning at 100 kilometers' altitude because 99 percent of the atmosphere's mass is below that height -- and also because it's a round number and we like those -- but that other 1 percent tapers off gradually between roughly 100 and 10,000 kilometers -- making the "edge" 100 times wider than the "atmosphere" itself.
In what way is that not a definition of the edge of Earth's atmosphere? I mean, you say it right there: we define the boundary of the atmosphere as this particular altitude. There's points obviously inside the atmosphere; there's points obviously outside it; somewhere in-between, the status changes.
As I said, the
Kármán line is an arbitrary convention agreed upon internationally to represent the beginning of "outer space" for the purposes of record-keeping. The only physical significance it has is that it's the approximate altitude at which the atmosphere becomes too thin to support aeronautic flight, so anything that can fly above that height is considered a spacecraft rather than an aircraft. (Or rather, it's the altitude at which the velocity needed to keep a plane aloft in the thinning atmosphere equals orbital velocity -- so beyond that point it's orbiting rather than flying.) So it's a functional definition as far as aviation is concerned. But it's not a physical definition of the edge of the atmosphere, since there are layers of the atmosphere that extend far higher. The Kármán line, as you can see in the image at the Wikipedia link, is actually in the lower part of the thermosphere, which is the second-highest layer of the atmosphere.
Nor is the Kármán line even universally agreed upon as a boundary. It's used to represent the "edge of space" by the Fédération Aéronautique Internationale, but not by NASA, not by the United States, and not by international law. It's a convenient fiction, nothing more.
And even beyond that, as I said, it's a matter of scale. It's not as if the atmospheric density instantaneously drops by a huge amount at the Kármán line. The actual point of transition from aeronautic to orbital flight is not at exactly 100 km, but we arbitrarily set the boundary at 100 km because, as I said, we like round numbers. The actual dropoff is gradual enough that the difference of a few kilometers doesn't matter. And when it comes to the edge of the galaxy, we're talking about a scale millions of times larger, with a margin of error of dozens of parsecs rather than kilometers. It would be meaningless for something as proportionately tiny as a starship to define anything remotely resembling a clear boundary.
That we could define the boundary as being somewhere else without it making a huge difference in what we use the boundary for --- and we do; the United States Air Force puts the boundary at 60 miles above sea level (and sea level itself is not an easy thing to define!) rather than 100 kilometers --- doesn't change the fact that we can and do define the boundary.
But human definition doesn't alter physical reality. You can draw an arbitrary line anywhere, but it doesn't actually cause the galaxy to behave the way Peeples portrays it in "Where No Man," with the stars suddenly stopping beyond a certain point that can be demarcated to within a fraction of a light year.
And saying "The aliens who created the barrier put it in such-and-such a place" doesn't work, because the characters in "Where No Man" were aware of the "edge of the galaxy" well before they discovered the barrier.
Incidentally, how many of us thought of this barrier when Kirk mentioned 'the great barrier' in Star Trek V?
