Human judges can show mercy. But against the laws of nature, there is no appeal.

Clarke contrasts human legal systems—where judgment can be tempered by compassion, discretion, or extenuating circumstances—with the impersonal regularity of physical reality. “Mercy” belongs to social institutions; nature’s “laws” operate without intention, sympathy, or exception. The line underscores a recurring Clarke theme: technological ambition and moral hope do not suspend constraints like gravity, entropy, radiation, or biological limits. It can be read as a warning against wishful thinking (expecting the universe to bend to our desires) and as an ethic of humility: progress depends on understanding and working within natural law rather than pleading against it.