Why do we feel something? Why is there not only motion, reaction and calculation in a part of the universe, but also experience, qualia, self-awareness? Classical physics knows only cause and effect, computer science only knows input and output. But in consciousness, both seem to blur. This essay is based on the thesis: Consciousness arises where a recursive causal system loses the distinction between cause and effect of its own states. Based on concepts such as autocatalysis, information density, feedback and self-reference, we develop an interdisciplinary model of sensing – between physics, philosophy and artificial intelligence.