We are, of course, talking FarScape.
FarScape had a core cast through its four seasons, plus the miniseries that completed a story that extended over some 65 hours of TV (ignoring ads). There also was a semi-core cast that drifted in and out and out and in. The story was episodic for a couple of seasons, with several threads holding it together. Then it raised the stakes and picked up the pace; becoming less episodic, and finally, toward the end of the final season, it was the longest and strongest sustained thread I've come across in a TV series. The Peacekeeper Wars miniseries at the end was basically a major feature film in HD format; and, on several levels, more powerful than Serenity, which is kind of a benchmark for me.
FarScape is superb story-telling. It poses endless serious questions, and you kind of know it is asking them, but at the same time you are really gripped by the story; so it isn't in-your-face.
The most serious issue it brought up for me, in the sense of making me say "hmm, now what's this really all about?", was that of what constitutes personal identity, and it is this I want to talk about here. The matter came up during the latter half of S3, when John Crichton, astronaut stranded in a distant place because of a worhole transition, suffered what you might call 'duplication'.
I'll paraphrase the FarScape scenario into a suitable thought experiment; and, no, it isn't a new one, but FarScape sustained it far beyond the superficial silly-level common to most other variations on the theme, both literary and cinematographic.
So, here's the scenario:
Two adjacent rooms, connected by a door. Well, two doors actually—or maybe not. You exit Room A through one door and two of 'you' enter Room B through two side-by-side doors at exactly the same time.
You look left and see...you. You also look right and see...you. That you and you seeing you and you.
You and you are astonished at seeing you and you; understandably so, I guess.
Anybody capable of performing a complete scan of either one of 'you' would find no difference in the physical configuration or physical and mental states of you and you. Either of you reacts exactly as the other would in response to finding you in this situation. The two John Crichtons played paper-scissor-rock until the cows came home; yet they always came up with the same thing at the same time. The game became the symbol of their desire to differentiate between themselves, but it never succeeded.
So, who are you? The one looking left or the one looking right?
Thing is, there's no 'original' and no 'copy', as in the usual scenarios. None of this cloning stuff I talked about some time back. None of the two 'you' can claim to know who is the original, since there isn't any. Both of you will be convinced, for all the usual reasons, that you are you and the other one can't be—because our uniqueness is a basic cognitive axiom, if you will.
In FarScape, the 'real' John Crichton thinks he knows who he is, but the other knows it, too: that he is just as 'real'. The theme is pursued through several episodes as the two John Crichtons follow their diverging paths, until one of them is killed.
I found the thoughts resulting from this story-thread troubling. I know that there isn't going to be any 100% instant duplicator available anytime soon—at least I think not—but thoguth experiments have a venerable tradition in science. The Special Theory of Relativity for example is the result of a bunch of thought experiments whose results weren't verified until decades after the theory was proposed by Einstein. Stories are, in many ways, like thought experiments about all kinds of things, and FarScape had a lot of those.
The Two-Crichtons thread made me at least question the whole notion of 'personal identity' and whatever definitions we have for it. Certainly, there is nothing in the philosophy of 'mind' or 'the self' that accommodates two identical 'you's. But in principle it is not physically impossible to construe such a double-entity; and since we're physical creatures we must ask ourselves what that actually means for our understanding of ourselves.
Some will argue—and this is a standard device to demolish the thought experiment—that, all right, at the very first instant of duplication you and you were the same, but everything after that serves to make you into different people, since you're subjected at every level, to differing 'experienes' that will guarantee that the 'identity' is destroyed.
But the device is questionable, and tries to skirt the issue by avoiding answering the original question by re-defining 'you' as whatever comes out of the duplicated identity. But that doesn't deal with the issue of what you and you actually think, and how you understand what you are. It's easy to look at it from the outside and say "this is so", but that's from a point of view that isn't yours and yours. Meaning the device fails because of its inherent incompleteness and the reliance on the assumption that 'identity' can be defined objectively from the outside of the object in question.
If you're wanting to investigate the issue further, treat yourself to this test, which will invariably raise more questions than it answers; but also will reveal things about your own notions about what constitutes 'you'. As you may have gathered I consider these at least as if not more weighty than those looking at the issue from without.