Why does the Qur'an say the mountains become "a mirage" on the Day of Judgment (78:20)?

Answer

Surah An-Naba 78:20 says "the mountains are set in motion and become a mirage" (sarāban). The image works on two levels, both noted by the classical mufassirūn. First, on that Day the mountains—the most fixed and immovable features of the earth—are torn from their foundations and driven along, then pulverized into scattered dust. Al-Ṭabarī and Ibn Kathīr explain that what remains is so insubstantial that an observer looking toward where a mountain once stood sees only something resembling shimmering water in the distance: a sarāb, a mirage, which appears to be something real but is in fact nothing. Second, the comparison powerfully conveys impermanence: the things humans treat as the very symbols of permanence and strength turn out to be illusions before Allah's command. This complements other verses describing the mountains on that Day as being made to pass away "like clouds" (27:88), as "carded wool" (101:5), as "a heap of sand poured out" (73:14), and as "scattered dust" (56:5-6). The unifying point is theological, not geological forecasting: the seemingly eternal earthly order is dismantled, and only Allah remains. The mirage image leaves the reader with a vivid sense of emptiness where solidity once stood.