 Smolin hypothesizes that the laws of physics are not fixed, but rather evolve over time via a form of cosmological natural selection.In "The Singular Universe and the Reality of Time", co-authored with philosopher Roberto Mangabeira Unger, Smolin goes into more detail on his views on the physical passage of time.In contrast to the orthodox block universe view, Smolin argues that what instead exists is a "thick present" in which two events in the present can be causally related to each other.