The song’s name is God Only Knows. What a fitting name for the anime of it’s origination? Of course, someone planned it that way and they use the “God only knows…” portion of the song during the true OP. Youtube offers a special full version that will no doubt be deleted eventually.
Seriously, the best part is the flowing repetition of “God only knows”. While being in English, sometimes the words are hard to make out. That gives it the illusion of being regular japanese music — it’s not. It’s special.
A few more words on The Golden Age: the main character erases some of his memories. While doing so, everyone tells him that it is simply better to forget them and not bother to pursue them. The song speaks of increasing one’s abilities, exploring possibilities and satisfying curiosities. That is exactly what the main character’s desire is and I found the song quite fitting with the book. Ultimately, it does better with this book than the anime it belongs too.