Key takeaway
Quran 6:125 likens the chest of someone who rejects guidance to one made "tight and constricted as though he were climbing into the sky." At high altitude air pressure falls, less oxygen reaches the lungs, and climbers feel breathlessness and chest tightness. The physiology of this hypoxia was worked out in detail in the 19th century.
The verse
فَمَن يُرِدِ ٱللَّهُ أَن يَهْدِيَهُۥ يَشْرَحْ صَدْرَهُۥ لِلْإِسْلَـٰمِ ۖ وَمَن يُرِدْ أَن يُضِلَّهُۥ يَجْعَلْ صَدْرَهُۥ ضَيِّقًا حَرَجًا كَأَنَّمَا يَصَّعَّدُ فِى ٱلسَّمَآءِ ۚ كَذَٰلِكَ يَجْعَلُ ٱللَّهُ ٱلرِّجْسَ عَلَى ٱلَّذِينَ لَا يُؤْمِنُونَ ١٢٥
So whoever Allāh wants to guide - He expands his breast to [contain] Islām; and whoever He wants to send astray - He makes his breast tight and constricted as though he were climbing into the sky. Thus does Allāh place defilement upon those who do not believe.
Key Arabic terms
| Arabic | Transliteration | Meaning |
|---|---|---|
| ضَيِّقًا حَرَجًا | ḍayyiqan ḥarajan | tight and extremely constricted |
| يَصَّعَّدُ | yaṣṣaʿʿadu | climbs with effort and strain, step by step (intensive form of ṣaʿida, to ascend) |
A spiritual simile
The verse is first about guidance: Allah opens the heart of the one He guides to Islam, while the heart that turns away feels constricted. The simile compares that state to the strain of climbing upward into the sky. The intensive verb yaṣṣaʿʿadu conveys laborious, effortful ascent.
What happens at altitude
As altitude increases, atmospheric pressure drops. At about 5,500 m it is roughly half its sea-level value, so each breath carries less oxygen. The result, hypoxia, causes shortness of breath, a racing heart, headache and a feeling of tightness, and at extreme heights it can be fatal. The French physiologist Paul Bert showed in 1878 that these effects come from the low partial pressure of oxygen.
Balanced assessment
Moderate A reasonable, accurate correspondence; the words have other valid meanings or the fact was partly known before.
People in mountainous regions surely felt breathless when climbing, so the experience was not unknown. What is notable is that the simile is framed as ascent "into the sky" rather than up a mountain, and that the physical effect it describes is accurate. It is an apt, scientifically sound comparison, offered for spiritual reflection.
Frequently asked questions
What does Quran 6:125 say about climbing into the sky?
It says the one Allah leaves astray has a chest made "tight and constricted as though he were climbing into the sky," which matches the breathlessness caused by low oxygen at altitude.
References
Quran
- Quran 6:125, Saheeh International translation (Quran.com)
Science & history
Classical exegesis is summarized from the standard commentaries (e.g. al-Ṭabarī, Ibn Kathīr, al-Qurṭubī). See our methodology.
Cite this page
Quran Scientific Miracles. “Breathlessness at Altitude.” https://quranscientificmiracles.com/topics/oxygen-and-altitude/ (reviewed 2026-10-20).