My 9 year old self was being introduced for the VERY first time here (in the briefing room scene in AF) to the idea of another reality somehow existing in the SAME SPACE, at the same time. Starting with Mirror Mirror, mainstream audiences have been presented with parallel universes ad nauseum, and it's a standard tired-out entertainment cliché by now. It's trotted out to get another episode made. Back then though, unless you were a reader of SF novels, it was new, at least in a show purporting to be based on possible science, not fantasy. Viewers probably don't think about WHERE parallel universe stories take place, any more than they wonder where heaven is. "Somewhere else" is enough for them. AF, though, talked about overlapping realities in the exact same space, in the same room you're sitting in. This stuff is happening right now, right here, and it's as real as this table, or me..... A later generation viewer is obviously just going to think "just another parallel universe story", but timing matters. An overlapping reality in the same space was mind bending to me, never ever having heard it before, and then the idea of the other being anti-matter, making contact between the two disastrous, that grabbed me. I knew what anti-matter was.
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I'm trying to think of when I learned what anti-matter is. This may be the only TOS episode where it's explained that m and anti-m particles annihilate each other, and putting that together with references to the m/anti-m engines, I got it. Maybe. So this supposedly worthless scene may have explained a key part of Star Trek for me, as well as a key part of physics, which I was able to flesh out further on my own.
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I'm trying to think of when I learned what anti-matter is. This may be the only TOS episode where it's explained that m and anti-m particles annihilate each other, and putting that together with references to the m/anti-m engines, I got it. Maybe. So this supposedly worthless scene may have explained a key part of Star Trek for me, as well as a key part of physics, which I was able to flesh out further on my own.