The conception that the world can be represented as a system of levels of being can be traced back to the beginnings of European philosophy and has lost little of its plausibility in the meantime. One of the important modern conceptions of levels was developed by Nicolai Hartmann. It exhibits remarkable similarities and contrasts with the classification of the real developed by Werner Heisenberg in his paper Ordnung der Wirklichkeit (Order of Reality). In my contribution I will introduce these two (...) conceptions of levels and compare their salient features. I will discuss them as variants of a scientific worldview that attempts to forge a link to the perspective of the lifeworld. Then I will go on to argue that the shortcomings of these conceptions can be remedied by extending them with the level of the very small and that of the very large. The introduction of these ontologically fundamental levels is based on scientific knowledge that for the most part eludes he intuitively representable character of lifeworld experience. Historical changes in science and the lifeworld could lead to the notion that reality can be represented as a system of levels being challenged in future. (shrink)