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The regime previous to the Hot Big Bang that naturally explains the super-horizon correlations of the Cosmic Microwave Background is denoted by Cosmic Inflation. The physics of this epoch lies at the interface between quantum mechanics and gravity. This early period of rapid expansion in the universe offers a unique window into the fundamental workings of the universe, where the principles of quantum mechanics influence gravitational forces at the largest scales. Understanding this interplay not only provides insights into the origins of the universe but also helps in unifying the theories of the very small and the very large.
For more visual insight, check out this from Swagat Saurav Mishra
$G_{\mu\nu} + \Lambda g_{\mu\nu} = \frac{8\pi G}{c^4} T_{\mu\nu}$