In “The Curious Case of Benjamin Button,” a story by F. Scott Fitzgerald and then a movie starring Brad Pitt, a man ages backward: He is born an old man, regresses over the years and dies an infant.

This is not typically seen in regular life. The question is, why not?

In what amounts to a technological triumph for the aspiring Benjamin Buttons of the virtual world, a team of quantum physicists reported earlier this year that they had succeeded in creating a computer algorithm that acts like the Fountain of Youth.

Using an IBM quantum computer, they managed to undo the aging of a single, simulated elementary particle by one millionth of a second. But it was a Pyrrhic victory at best, requiring manipulations so unlikely to occur naturally that it only reinforced the notion that we are helplessly trapped in the flow of time.

Most of us already sense that the atoms of a scrambled egg can’t be unscrambled back inside a pristine shell. Now it seems that, under general conditions, even a single particle probably can’t go backward without help and careful tinkering.