I understand that the big bang theory is based on the observation that stars and other galaxies are moving away from us and it's thought that all matter started off in an incredibly dense small space before rapidly expanding.
I'm not sure if I've understood this correctly but I'm under the impression that it wasn't so much of a 'bang' and rather a sudden expansion of matter.
If that is the case then why is this theory not relevant on a quantum level? Why is it only what we see in telescopes moving away from each other and not an expansion of matter itself?