Firmamento translates to "firmament" or "sky". It's a more poetic and grand word for the sky, evoking a sense of vastness and cosmic scale.
In "Big Bang," Amaral sings, "Cuando estalle el firmamento" (When the firmament explodes). This imagery connects to the song's title and theme, suggesting a powerful, universe-altering event that will reveal hidden truths and feelings. It's a striking word that adds a dramatic flair to the lyrics.
'Big Bang' spends its first verses turning down every role that would put her beneath someone else. 'Y no soy tu princesa' [And I'm not your princess], 'Ni quiero ser tu reina' [Nor do I want to be your queen], and 'Ni voy a ser tu geisha' [Nor will I be your geisha] reject three different fairy tales about pleasing a man, one right after another. What she asks for instead is plainer and harder to fake: 'Sólo quiero jugar' [I just want to play], someone to meet her as an equal instead of worshipping her from a pedestal.
The song locates the real power somewhere else: 'Está en la mente, mi amor' [Is in the mind, my love]. That line sets up the title's central image, because from here on the song talks about desire like it's a creation event. The hook, 'Justo en el comienzo del big bang' [Right at the beginning of the big bang], repeats four times in a row to close the song, so the chorus doesn't build toward that moment so much as sit inside it, echoing like the aftershock of the explosion itself.