Decades of “Twilight Zone” episodes and movies from “Primer”” and “Timecrimes” to “Safety Not Guaranteed” have demonstrated that you don’t need a huge budget to tell a time travel story.

The best films of the genre are intellectual exercises, and for all the laughs and “cool” parts of the blockbuster “Back to the Future” franchise, the mental math required to keep timelines straight is at least half the fun.

Time travel tales make us face choices, dilemmas and unforseen “Butterfly Effect” repercussions that are theoretically probable if anyone masters the machinery of giving a life or a historical period a temporal “do over.”

“Aporia” brings a fretful melancholia to the genre by taking away the “travel” from time travel, and letting characters impact the past and future by pushing a button that kills someone. So it’s a little like like a laugh-free “Safety Not Guaranteed,” a less moral version of the Frank Langella/Cameron Diaz thriller “The Box.”

The word “aporia” means an unresolvable dilemma, some situation that’s crated an impasse.

That’s what the characters here face as they ponder the possibilities, the ethics and the pitfalls of using “a machine that can (metaphorically) fire a bullet into the past” at the target of their choice. Well, kind of ponder.

We don’t learn about “the machine” until after we’ve met Sophie (Judy Greer), a struggling nurse and single-mom whose daughter (Faithe C. Herman) is getting kicked out of school for “not showing up.”

The fact that the school is calling and that Sophie is “there” even though they’re suspending for her skipping school is just the first unresolved puzzle facing us here.

Riley has been acting-out ever since her father died. In flasbhacks, we see how close she and Mal (Edi Gathegi) were and how much in love Sophie and Mal-short-for-Malcolm were.

But something happened, something that keeps dragging harassed Sophie back into court seeking justice. for Mal’s death.

Mal is gone, their daughter wants nothing to do with her mother and Mom is at her wit’s end.

Mal was a scientist living on disability after an on-the-job accident some years before his death. His best friend, the immigrant physicist-turned Lyft driver Jabir (Payman Maadi) is Sophie’s “rock,” the one she turns to in her many crises.

He’s the one who mentions this “machine” he and Mal had been working on. It hadn’t worked-out as a time travel device. But with a computer interface aimed at someone at a particular place at a very particular (very recent history only) time, it can engineer the death of the guy who killed Mal and bring the much-missed husband and fatehr back to life.

Smart filmmakers find ways to dodge “explaining” the means of delivering time travel. Sometimes, a DeLorean is all it takes. Writer-director Jared Moshe explains less than most — there’s this “abstract particle” — which is all well and good.

But there’s kind of cavalier, justify-this-as-it-goes improvisational feel to some of the many ethical and moral debates that the picture tries to introduce.

Jabir’s “What harm is there in trying?” flippancy comes before “There is no ‘undo’ button,” and before any consideration comes up about the morality of their actions.

They’re killing a guy, after all. We overhear enough about how he caused Mal’s death to wonder if this is defensible in the least.

But this being a movie, we know that A) Mal is going to find out what they did and B) there will be other calls to use that gadget — which uses car batteries and jumper cables in its design — to kill a mass shooter or school attacker, and tidy up lives that were dirsupted by that first “kill” intervention.

The stunning life make-over that bringing Mal back creates has Jabir and Sophie ecstatic, and unknowning Riley reborn, to say nothing about what it does for Mal. But unforseen consequences ripple away from that first killing.

Greer, in her best role in years, really sells that moment where Sophie morphs from angry, desperate skeptic with dashed hopes to wife who gets a cell phone call from the beloved-but-dead and much-needed partner and husband she lost eight months before.

It’s not Kathleen Turner answering a phone from her long-dead granny in “Peggy Sue Got Married,” but it’ll do. Greer give the nost nuanced performance here, and I didn’t feel much from any other actor’s effects.

I wasn’t nuts about the abrupt shifts in ethics and stumbling debates over taking this or that action in the middle acts. We never actually “see” the killings, which makes for an interesting series of ways to test if the outcome they sought turned out. Well, the first time we see that it’s “interesting.”

And the conclusion has a rough logic to its consequences, but seems arrived at abruptly. Big emotions we expect never quite arrive after that first “machining.”

Taking all this deathly serious has its own downside. There’s pathos and guilt we see but never raelly feel it.

If you’ve seen the several titles I mentioned at the outset — obvious sources of inspiraction here — this film’s big surprise or two will still land. But nothing outside of those third act twists feels fresh or as cleverly thought-out as the many antecedents to “Aporia,” several of which play better and challenge the viewer more than this version of a time-tested, time-honored genre.

Rating: R, profanity

Cast: Judy Greer, Edi Gathegi and Payman Maadi

Credits: Scripted and directed by Jared Moshe. A Well Go USA release.

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