What is matter? In Quantum Mechanics, mass and form are imparted to energy. If you have seen my previous post, <98% of it is because of strong interaction and >2% by Higgs mechanism.
Yeah, everything is "stuff", as you said 'quark-gluon plasma'. Of course, we do not have all answers, the research is progressing. We do not know where from the 'quark-gluon plasma' arose. The possibility that it arose from 'absolute nothing' has not been denied by science. That is close to what RigVeda said 3,000 years ago, "Sages who searched with their heart's thought discovered the existent's kinship in the non-existent."
Hinduism: 1. THEN was not non-existent nor existent: there was no realm of air, no sky beyond it.
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