# Does the second law hold at cosmic scales?

## TL;DR

This paper investigates whether the second law of thermodynamics applies at cosmic scales by analyzing the Hubble factor's history in homogeneous, isotropic universes without relying on specific cosmological models.

## Contribution

It provides a purely kinematic analysis to test the validity of the second law at large cosmological scales, independent of curvature or model assumptions.

## Key findings

- Supports the applicability of the second law at cosmic scales
- Shows the law holds regardless of spatial curvature
- Uses a model-independent, kinematic approach

## Abstract

The second law of thermodynamics is known to hold at small scales also when gravity plays a leading role, as in the case of black holes and self-gravitating radiation spheres. It has been suggested that it should as well at large scales. Here, by a purely kinematic analysis \textemdash based on the history of the Hubble factor and independent of any cosmological model \textemdash , we explore if this law is fulfilled in the case of homogeneous and isotropic universes regardless of the sign of the spatial curvature.