The Robertson–Walker metrics are presented as the simplest candidates for the models of our observed Universe. The Friedmann solutions of the Einstein equations (which follow when a R–W metric is taken as an ansatz), with and without the cosmological constant, are derived and discussed in detail. The Milne–McCrea Newtonian analogues of the Friedmann models are derived. Horizons in the R–W models are discussed following the classical Rindler paper. The conceptual basis of the inflationary models is critically reviewed.

In this essay, Iaddress some preliminary considerations surrounding different notions of “peace” and peacebuilding and the appropriate methodologies to study the same.I place emphasis on the adoption of a moral epistemology that is overtly value-oriented and normatively ambitious without being oblivious to the structural characteristics of collective political behavior that tend to privilege the self at the expense of the other, such as that used by the World Order Models Project (WOMP). Rather than relying on one standard definition of “cosmopolitanism,” I advocate for a pluralistic conception that acknowledges different cosmopolitanisms. I provide a framework for peacebuilding assessment that frames inquiry around different “horizons” of aspirations (feasibility, necessity, desperation, desire), and I lay out my version of cosmopolitanism, which centers on the importance of peacebuilding objectives that are necessary and desirable. In so doing, I compare my perspective toother paradigmatic perspectives, concluding that cosmopolitanismis concerned with reconciling unity with difference, through mutual understanding of otherness.