This entry examines the oath "by the sky which sends back" (as-sama' dhat ar-raj') in Surah at-Tariq 86:11, and the modern readings that find in it the water cycle, the ionosphere's reflection of radio waves, and other "returning" functions of the sky. The classical rain reading is primary here, and the multi-phenomenon extension is treated with caution.
The source text
وَٱلسَّمَآءِ ذَاتِ ٱلرَّجْعِ
“By the sky which sends back”
Qur'an 86:11 · Saheeh International
What was understood in the seventh century
Classical Arabic lexicons record raj' as an existing name for rain, and the early exegetes explained the oath as referring to rain because the sky "returns" it again and again; some added that clouds return the water first drawn up from the earth. Desert Arabs were acutely aware of rain's cyclical return — their lives depended on it — though the physical mechanism of evaporation and condensation was not quantitatively understood anywhere in the seventh century. The oath is paired in the next ayah with "the earth which splits," a coupling classical readers heard as rain and the plants it raises: a complete and familiar cycle of provision.
The modern correspondence
The hydrologic cycle — ocean evaporation, atmospheric transport, condensation and precipitation returning water to the surface — was first quantitatively demonstrated by Pierre Perrault and Edme Mariotte in seventeenth-century France and is now textbook science, summarized by the USGS Water Science School.
Twentieth-century atmospheric physics added further senses in which the sky "returns." The ionosphere reflects radio waves back to the ground, exploited since Marconi's 1901 transatlantic transmission and explained by Appleton in the 1920s; the ozone layer turns back harmful ultraviolet radiation by absorption and scattering; and the magnetosphere deflects charged particles. Modern commentators cite some or all of these as layers of meaning in the single word raj'. None of these later senses was available to the seventh century; the question is whether the verse intends them.
Considerations and counterpoints
Skeptics observe that raj' already meant rain to the Qur'an's first hearers, so the oath conveyed familiar knowledge; the seasonal return of rain required no science to notice. They further argue that stacking additional referents — radio waves, ultraviolet, charged particles — illustrates the elastic, post-hoc character of the genre: the sky is credited with "returning" whatever physics later discovers, which renders the claim unfalsifiable. A fair presentation, adopted here, keeps the classical rain reading primary and treats the rest as modern homiletic extension rather than evidence. The case here is accordingly weak as a knowledge-claim, though the aptness of a word of "return" to later discoveries is what keeps the item in circulation.
Credibility rating: Tier 3 · Contested — Rain's cyclical return was the verse's plain seventh-century meaning per the classical lexicons, and the multi-phenomenon modern reading is post-hoc accumulation.