Here is an interesting podcast with Matt Christman from Chapo Trap House about 9/11's impact on pop culture, especially music. They focus more on the political angle -- what things must or must not be said in pop music in the wake of 9/11, did the culture of fear kill off aggressive rock music from the late '90s, and so on.
Characterizing music of the early 2000s, they identify the zeitgeist of numbness, sadness, schmaltizness, etc. as 9/11's cultural impact. My take has always been the opposite, and now that I've figured out the 15-year cultural excitement cycle, it's possible to separate what 9/11's effect was, and what would have already happened with or without a major terrorist attack.
The early 2000s were a vulnerable phase, a refractory period after the manic climax of the late '90s, and before energy levels had recovered to baseline during the late 2000s. So anything that typifies a vulnerable phase will be unremarkable to find during the early 2000s. Namely the soft, ethereal, numb, emo, schmaltzy trends that also characterized pop music of the late '80s and early '70s -- which were hangovers after the previous manic phases of the early '80s and the late '60s.
What made the post-9/11 zeitgeist feel so different was the social and cultural unity that it brought out of people from all walks of life, both normie and indie, teenagers and geezers. It was not as socially unifying as a steadily rising crime rate, as experienced during the '60s through the '80s, but it was of a similar kind, if lesser in degree (a one-time spectacle, not decades of constant crime stories).
And when people perceive an imminent risk of massive violent attack, they tend to discount the future, live more in the present, and want to party with others and enjoy their company while it's still possible.
So, 9/11's cultural impact would be something that looked unusual for an otherwise soft, numb, emo period -- one which, as the podcast hints at, was already under way before 9/11. (See the year-end charts for 2001 for reference.) It would be unusual in being more socially bonding and party-centered, relative to the backdrop of a vulnerable phase culture where people want to be left alone and sleep under a pile of blankets / sink to the bottom of the sea.
In two recent posts, I identified dance-punk and crunk as two such signatures of 9/11. I'd thought of them in that way since the 2000s, but these recent posts detail how they are clearly not what was to be expected given their backdrop (a vulnerable phase). Those posts are brief, so I won't rehearse them any more here. They're relevant to today since we've been in another vulnerable phase since 2015, and yet there's been no such trends this time around (since there's been no 9/11), while there is plenty of soft, numbing, emo music all over again.
Instead, I'll end with a real deep cut from the dance-punk craze of the first half of the 2000s, in honor of 9/11's enduring cultural influence. I was living in Barcelona when this was out, and got turned on to them by the long-term housemate who I was renting a room from. It was his friend's band. Nothing replaces face-to-face recommendations -- you couldn't hear this after reading some centralized website, no matter how obscure their branding. You had to get out, interact, and listen to what other people had to say.
"NYCgaps" by Delorean (2004):