Much of this déjà entendu dancepop is exciting in its crass, energy-drink-blast kind of way. So why does the aural overfamiliarity matter? Well, up until the 2000s pop decades always had epoch-defining sounds. Two or three (sometimes more) genres would emerge to achieve dominance or, at the very least, prominence in the mainstream. Musical styles usually build on the past to some degree, but these genres always took their sources in striking and fresh directions, and they often wrapped the music up in subcultural garb, with a distinct fashion element, new rituals and dance moves, and so forth.

The ’70s generated heavy metal, punk, disco, reggae and more. The ’80s spawned hip-hop, synthpop and Goth. The ’90s had grunge and the techno/rave/electronic explosion. But the decade and a bit that followed the turn of the millennium has produced — well, what exactly? Hip-hop and R&B have built incrementally, at times imperceptibly, on where they were at during the ’90s. Emo is a tuneful and melodramatic merger of pop-punk and Goth. True, if you venture into the musical left field, you will find various underground genres that can claim at least relative freshness: grime and dubstep in Britain, the post-indie sounds of Animal Collective and similar bands in America. But their effects on mainstream pop music has been minimal.

Those who don’t have much personal investment in the idea that popular music should always be pushing forward probably won’t be especially troubled by the current pop scene’s muddled mix of stasis and regression. But those whose expectations have been shaped by growing up during more fast-moving and ever-changing pop decades — which is basically all of them to date except for the 2000s — are likely to be perplexed and disheartened by these developments. In particular the innovation-obsessed ’60s and the cyber-optimistic ’90s instilled an ideal of pop music as herald of the future, a vanguard sector of the culture that was a little bit ahead of the rest of society.

The fading of newness and nowness from pop music is mystifying. But in the last couple of years a concept has emerged that at least identifies the syndrome, even if it doesn’t completely explain it. Coined by the co-founders of cyberpunk fiction William Gibson and Bruce Sterling, “atemporality” is a term for the disconcerting absence of contemporaneity from so much current pop culture. This curious quality can be detected not just in pop music but in everything from fashion to graphic design to vintage chic.