The partial dissolution of the universe that takes place at the end of Brahmas day does not affect all the planetary systems. The planets of highly learned living entities like the sages Sanaka and Bhrgu are not affected by the dissolutions of the millenniums. All the planets are of different types, and each is controlled by a different kala-cakra, or schedule of eternal time. The time of the earth planet is not applicable to other, more elevated planets. Therefore, Vidura herein inquires about the duration of life on other planets.