How at the beginning of this universe the fields as proposed in quantum fields theory get excited?? How exactly these fields originated?
4$\begingroup$ This sounds like a physics question more than Astronomy, and I'm not sure it's an answerable physics question either. $\endgroup$– userLTKAug 6, 2018 at 9:12
$\begingroup$ Because it was possible? This could even become a metaphysical question... $\endgroup$– J. ChomelAug 6, 2018 at 12:30
Unfortunately, this question is one which is under active -- and so far fruitless -- investigation by the theoretical physics community. Anyone who could answer it would have the choice of publishing here and getting +450 reputation or so, and a couple of badges. Or they could publish in Nature of Phys Rev and get at least one Nobel Prize.
Bottom line: No one knows yet.