With production overrunning on Martin Scorsese’s passion project The Irishman, the director admitted this month he had misgivings about the “youthification” technology he was employing to smooth out his actors.

The film focuses on Frank Sheeran, played by Robert De Niro, a union leader and mobster, and his involvement in the disappearance of Jimmy Hoffa, a former leader of the Teamsters union, played by Al Pacino. As such, the first half finds the two actors playing young versions of their characters, with their wrinkles and jowls obliterated by CGI.

Speaking to the British director Joanna Hogg, the film-maker known to everybody who has met him once as “Marty”, said that there was a problem with keeping his actors’ eyes expressive, adding: “Does [the technique] change the eyes at all? If that’s the case, what was in the eyes that I liked? Was it intensity? Was it gravitas? Was it threat? And then how do we get it back? I don’t know.”

Facebook Twitter Pinterest Raw material … Robert DeNiro and Al Pacino as they are now. Photograph: Kevin Mazur/Getty Images for Tribeca Film Festival

In this, he isn’t alone. While the technology is doubtless impressive, there have been complaints about the “uncanny valley” effect of digitally de-ageing actors, from such critics as Manohla Dargis of the New York Times (who has written about the “weird, disrupting digital facelift” that Kurt Russell had in Guardians of the Galaxy Vol 2), or The Ringer’s Andrew Gruttadaro, who observed that “as an audience member [watching Russell, or Robert Downey Jr in Captain America: Civil War] you get the creeping feeling that you’re not watching a person, but an entity imitating a person”. Similar reservations have been heard about Anthony Hopkins being de-aged in TV’s Westworld. Later this year, Ang Lee’s Gemini Man will appear, starring Will Smith as an assassin who meets his younger self. Also played by Smith. The problem is that everybody who grew up with The Fresh Prince of Bel-Air knows what Will Smith looked like as a younger man, and it wasn’t this buff colt. (A film where a solemn Will Smith from 2019 met a goofy Will Smith from 1990 might hold more interest.)

To quote Dr Ian Malcolm from Jurassic Park: “Your scientists were so preoccupied with whether or not they could, they didn’t stop to think if they should.” De-ageing technology gives us the dazzling impression rather than the effect of youth, as a younger actor would. More goes into the ageing process than mere looks; it betrays a thin understanding of psychology to expect otherwise. For instance, when De Niro was young, he gave off the magnetic hunger of somebody who cared about his career, which is more than you can say for his Warburtons-shilling persona of 2019. Actors can be made to look younger, but can they be made to look bothered?