Everything in the Universe bows down before Allah (SWT) i.e. obeys His orders or follows His laws known as ‘Laws of Nature’. In this sense even the infidels helplessly and involuntarily follow the laws of nature like being influenced by the gravity of the earth, urge to eat and drink etc though voluntarily they do not bow down to Him, 22:18. It’s a law of nature that opaque bodies cast shadows. In the evening the shadows lengthen to end in night and in the morning, they shorten giving rise to day.