Here is one more interpretation of verse 21:30
http://classicalislamgroup.com/index...er/s21-v30to33
The miraculous style of the Quran is that the words used by it may have different possibilities for interpretation, therefore, here as per one of these interpretations "ratq" means "to close" & "fatq" means "to open".
Different exegesists have explained differently the sense of the words "closing" and "opening", but the meanings which the companions of the Holy Prophet Sallallahu 'Alayhi Wasallam: Peace be upon him and the majority of the exegesists have adopted are that closing of sky and earth means shutting off rainfall from the sky and vegetation from the earth, and opening means the opening of these two i.e. the rainfall and vegetation.
So it seems 21:30 is talking about some different things not about big bang