Hm, more controversy yesterday than with my political or religious commentary. Well, we'll cut the conflict for today: it's been a while, but it's time for more of the series on technology in Star Trek. Today: holograms.
I understand that the “holodeck” was introduced in The Next Generation, providing the crew with a means of recreation. Having not seen that series (I've seen a few episodes, but not many), I encountered the holodeck in the Voyager series, where it was far more important: they would have to travel for years to get home, and seriously needed a good schedule of “R and R”. And so it's not surprising that the holodeck played a significant part in many of the Voyager episodes.
More than that, though, the ship's doctor was killed in the pilot episode, and the doctor throughout the series was the “emergency medical hologram”, designed to assist the real doctor in emergency situations. Fitting enough: the whole series was a prolonged recovery from an emergency situation.
All that said, both the doctor and the holodeck were taken to pretty silly extremes. I'll have lots more to say about the doctor when I get to entries (yes, probably more than one) about the computer programs, so I shan't get ahead of myself here; I'll stick to the holographic aspects, specifically.
Let's start with something that's often convenient to the plot but conceptually ridiculous, owing to the nature of holograms: that they can alternately be solid and not. That someone can take a swing at the doctor, for instance, and have his fist go right through the hologram, and in the next moment be decked by a blow from the very same hologram. Yes, this is the 24th century, and lots will have been discovered 'tween now and then. But I can't accept solid holograms, much less ones that shift back and forth at will.
Then there's the issue of projecting the hologram, which requires some pretty sophisticated and specialized equipment, not available in places like the mess hall and the loo. In particular, the doctor can only appear in the holodeck, in sick bay, and on the bridge, the only places on the ship where the necessary equipment is installed. I'm guessing that that proved an annoyance to the writers, particularly as the doctor became a popular and more significant character.
They solved this with a sort of deus ex machina plot element. Someone from the 29th century came back in time, and while he was there the Voyager folks snagged from him a “mobile emitter”, a device the size of a “comm badge” that could project the doctor anywhere he
wanted needed wanted needed to be. The ridiculous part of the mobile emitter is that the doctor wore it on his own sleeve — that is, the emitter was placed (solidly; see above) on the very hologram it was projecting. Uh-huh. (Making it 29th-century technology, on the other hand, was actually clever, as it completely explained why there was only one, and why they couldn't just make (or replicate; the replicators were not without limitations) another.)
Another oddly thought out thing was that when the doctor's program had troubles, his image would flicker and fuzz (and make electric-arc sorts of noises), as if he were a failing light bulb. That seems unlikely. Maybe that would happen if the projectors were having trouble, but troubles with the program (it would often “destabilize”, but that's for later discussion) would more likely manifest themselves in other ways (which they sometimes did).
Finally, there's the holodeck itself. It's of limited size, and yet the environments projected there could be vast, and the crew would move through them as though that were so. OK, maybe the holodeck just gave the illusion that the environment was large, the crew only thought they were walking for miles, and we saw the situation through their perception. Seems like a stretch, but, hey, we have to give the writers some latitude, eh?