Complex sentence: This would act as ballast and would lead to a halt of the expansion, then as bodies attract and there is no matter beyond the maximum expansion point the matter would reverse the path, traveling back to the original explosion site.
Split into simpler sentences: This would act as ballast and would eventually lead to a halt of the expansion. Then as bodies attract and there is no matter beyond the maximum expansion point the matter would reverse the path, traveling back to the original explosion site.