What happened before Big Bang?
Hmm, the answer is not known yet, recent news articles indicate a new story on Big Bang.
as per below recent news article, it looks like the universe before Big Bang might not be a singularity.
It looks cosmic inflation is an increasingly agreed-to scenario before the Big Bang.
This is a deep topic, and explaining all the science behind is not our subject matter, hence the summary of the outcome is “We do not know what happened before Big Bang”.
Here below is the detailed article if you are really a science buff.