the era of supersonic travel?
I mean, sure, supersonic flight is /technically possible/ but it is exceedingly rare that the sound barrier is broken by traveling civilians.
My understanding is that the problem mostly has to do with air resistance increasing with the cube of speed; this could be overcome by going higher, above the atmosphere, but nobody has figured out how to do that at subsonic flight costs, either.
I mean, it is kind of sad; one of those technologies that we created, but that then turned out to not be as practical as the older stuff for everyday use.
Which is why countries and companies that don’t give a fuck about the environment are all over it. It took a long time to beat coal, but games over it won now it’s just a question of time.
However, replacing natural gas as peaking power that’s still in the works.