hindu-cosmosWe're still mapping where this idea was first discussed. Key passages and related ideas below.
Tattva 32 — Space (Ākāśa)
Space itself: the subtlest great element, the open room in which all things exist.
Ākāśa is the gross element of space (or 'ether') — the first and subtlest of the five great elements that make up the physical world. It is the all-pervading openness in which everything else has room to be, and the medium that carries sound. As the most rarefied of the elements, it stands at the top of the material world, unfolding from the subtle element of sound.
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Bṛhadāraṇyaka Upaniṣad 3,8.7↗explains
Bṛhadāraṇyaka Upaniṣad · Vedic Revelation (śruti)
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