TL;DR
This paper reviews the role of time in cosmology, discussing cosmic time, epochs, the initial singularity, and the arrow of time, highlighting fundamental issues and conceptual frameworks in understanding the universe's temporal aspects.
Contribution
It provides a comprehensive overview of how time is defined and understood within the current cosmological model, emphasizing conceptual and foundational issues.
Findings
Cosmic time is well-defined in standard models.
The initial singularity poses conceptual challenges.
The cosmological arrow of time relates to entropy increase.
Abstract
Time has always played a crucial role in cosmology. I review some of the aspects of the present cosmological model which are more directly related to time, such as: the definition of a cosmic time; the existence of typical timescales and epochs in an expanding universe; the problem of the initial singularity and the origin of time; the cosmological arrow of time.
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