Many years ago I discovered a British TV movie about nuclear war called “Threads.” I was reading the Web site Metafilter, and people were talking about how they’d seen “Threads” as kids, in 1985, and been traumatized. The movie was available on YouTube—in twelve parts—so of course I dropped what I was doing and watched it immediately.

“Threads” follows a small group of ordinary people who live in Sheffield, a city in Yorkshire; it’s shot as a docudrama, with occasional intertitles offering up horrifying factoids about megatonnage and rads. In the first half of the movie, the United States and the Soviet Union are marching steadily toward a nuclear confrontation, which has something to do with a coup in Iran. The protagonists go on living their nineteen-eighties lives, as one would, while the geopolitical situation leers and murmurs from televisions and radios. Soon, they are advised by the government to start making preparations for nuclear war—they begin somewhat farcically: taping up their windows, building shelters out of mattresses and sofa cushions, stockpiling water, and so on. About halfway through the movie, the war begins.

I’ve seen pretty much every nuclear-apocalypse movie, and I feel confident in saying that “Threads” is the most unsparing. Many movies look away from the bombing itself—often, it’s happened before the story even begins—but “Threads” shows it all in documentary detail. The characters are in the middle of their day when Sheffield’s early-warning sirens go off; needless to say, the warning is “early” by only a few minutes. (I think of these sirens every time I hear the closing guitar chords of Portishead’s song “Threads,” which, I’m convinced, was inspired by the movie.) Optimistic men hide under their cars; families start helping grandparents down the basement stairs—what else could you do in such a situation? People in a great crowd are shopping for groceries and supplies, and, when the sirens sound, they can only rush, pointlessly, amongst the stores, with their deadly plate-glass windows.

When a mushroom cloud appears over the nearby R.A.F. airbase, the director, Mick Jackson, shows a woman’s horrified face, and cuts quickly to her soaked trouser leg. But this is only the initial stage of the attack: “Nuclear exchanges escalate,” an intertitle warns. A minute later, there’s a direct hit, a flash of light, and Sheffield is engulfed in a howling firestorm. “Two-thirds of houses in Britain are within possible fire zones,” the intertitles note. Human beings, and, in one shot, a cat, writhe and crawl atop piles of flaming rubble. I thought about these scenes for months afterward while walking down the street in Boston, where I lived at the time.

“Threads” continues, for a while, in a post-apocalyptic vein: the survivors gather at burned-out hospitals, scrounge for water, and, eventually try to farm despite the nuclear winter. Ultimately, though, this is a feint: the movie doesn’t really believe there’s a “post-” to the nuclear apocalypse. The metaphorical threads that tie civilization together have snapped. At the end of the film, many years after the war, one of the characters becomes pregnant, and, after desperate labor in a filthy hospital, gives birth to a stillborn baby. She sees its face, which we don’t see, and is horrified—presumably, the baby has been deformed by the radiation. The film cuts to the credits just as she’s about to scream. It’s cheesy, I admit—but I’ve never forgotten it and never will.

As an apocalypse aficionado, I’ve thought a lot about “Threads.” It was horrifying, as I knew it would be, so why did I watch it in the first place? The truth is that I will watch and read (almost) anything about the apocalypse. It’s not that I enjoy contemplating death and destruction. I can’t bring myself to watch horror movies, for example. Still, I enjoy thinking about the sorts of things that apocalyptic stories push me to think about. I keep reading and watching because I’m searching for the ideal apocalypse—the most illuminating one. “Threads” isn’t the ideal apocalypse, but it’s at least part of the way there.

As a public-service announcement about nuclear war, of course, “Threads” is supremely effective; part of me thinks that everyone should see it. And considered purely as a prompt for apocalyptic thought, it’s ideal in some respects. Its greatest strength, I think, is that its apocalypse is final. There are, broadly speaking, two kinds of apocalypse stories: post-apocalyptic ones, in which life goes on after the apocalypse, and finally apocalyptic stories, in which nothing else goes on ever again. The finally apocalyptic ones—Lars von Trier’s “Melancholia” is one of my recent favorites—tend to be better. The word “apocalypse” comes from Greek roots which mean something like “uncovering” or “revealing,” but in most post-apocalyptic stories, the only things that get revealed are familiar tales about brawny men leading women and children to safety—nothing, in other words, that we don’t already know. What you really want is the end of everything, full stop, because that reveals something more challenging and strange: nothingness. That’s what “Threads” forces you think about. Someday, it might all blow up, and then what? The mind goes blank, as the world will go blank. And yet that nothingness draws you in.

“Threads” also has weaknesses which keep it from being an ideal apocalypse. Its main weakness has to do with the reality it represents: the apocalypse it describes is avoidable. That’s the whole point; you’re supposed to watch “Threads” and think, “I’d rather not.” The best apocalyptic stories, I’ve come to feel, have a doubleness to them. Outwardly, they may be lurid and arbitrary fantasies—how could they be otherwise?—but, inwardly, they burn with accurate certainty. The stories seem to say that, though this scenario isn’t quite right, something very much like this will happen eventually. “Threads” doesn’t want to say that; its whole purpose is to convince us to change our ways.

Put together, I’m convinced, these two conditions—finality and inevitability—make for the most ideal apocalypse stories. They mirror the way the universe really works, at least as far as secular, scientific people such as myself are concerned. Someday, for whatever reason—entropy, a meteor, that giant volcano under Yellowstone—life on earth will end, and when it ends, it will end for good. Eventually, the human world will simply vanish, leaving behind only the affectless emptiness of space, which will continue on, unconsciously, without us. It’s not just that we’ll die, but that our values, and value, will end. There will be no one left to admire the nebulae through the Hubble; no one left to look at human life and consider it beautiful. No one will care about the things we care about—not even us.

An apocalypse of this kind doesn’t even have to be an event. It can—will?—simply happen as part of the natural aging of the world. A movie like “Threads” is committed to the human reality of the end of the world, and, like the Bible, or, for that matter, like “Dawn of the Dead,” it offers us a moral vision of the apocalypse as a day of judgment: on some level, we deserve the terrible ending. But apocalypses just as readily emerge out of the naturalist tradition, which is basically modern; they can be vast, abstract, and scientific. In “The Time Machine,” H. G. Wells sends his time traveller far into the future to witness such an apocalypse. He parks his time machine on a beach, and, as he moves into the future, he sees the waves slow, then stop. A line of salt builds up on the shore. The sky grows dark; the sun grows large, red, and dim. The world, Wells writes, “was silent…. It would be hard to convey the stillness of it. All the sounds of man, the bleating of sheep, the cries of birds, the hum of insects, the stir that makes the background of our lives—all that was over.” In its place, there is only an “awful twilight.” Softly, on the shadowy beach, some dark, tentacled thing flops about. The world itself has wound down and died of old age, probably long after some now-unknown, human-scale apocalypse. There is no stopping this kind of ending, Wells seems to say, and there is no life after it. It is final and inevitable, waiting there in the future, visible to anyone who wants to look for it.