“The whole world was seen as the divine activity welling up from the mysterious being of Brahman, which was the inner meaning of all existence. The Upanishads encouraged people to cultivate a sense of Brahman in all things. It was a process of revelation in the literal meaning of the word: it was an unveiling of the hidden ground of all being. Everything that happens became a manifestation of Brahman: true insight lay in the perception of the unity behind the different phenomena.”
‘A History of God: The 4000-Year Quest of Judaism, Christianity, and Islam’ by Karen Armstrong
In other words – Brahman = the laws of physics, atoms, whatever you want to call the underlying fabric of the cosmos.