Cosmology explores the origin, structure, evolution, and ultimate fate of the universe. It seeks to understand the large-scale distribution of matter and energy, the dynamics of cosmic expansion, and the processes underlying the formation of galaxies and larger structures—all grounded in physical and mathematical principles.

Modern physical cosmology is primarily based on Einstein’s theory of General Relativity (GR), formulated in 1915. Within this framework, the standard model of cosmology—commonly referred to as the ΛCDM model—describes a universe that is, on large scales, homogeneous and isotropic, and has been expanding since its origin in a hot big bang approximately 13.8 billion years ago.

The ΛCDM model posits that the universe underwent a brief but dramatic phase of early accelerated expansion (inflation), followed by radiation-dominated and matter-dominated epochs, and is currently experiencing a phase of late-time accelerated expansion. Presently, the energy content of the universe is estimated to be composed of ~70% dark energy, ~30% matter (of which approximately 80% is dark matter), and a negligible amount of radiation.

The research focus of the Cosmology Group at CSR lies in the interface between gravitation and cosmology, with particular emphasis on modified gravity as a framework to address fundamental questions about the nature of dark matter and dark energy—components that remain poorly understood within standard GR.

Our work includes:

• Investigating extensions and generalisations of General Relativity, such as f(R), f(T), and f(Q) gravity models, examining their implications for both background cosmological evolution and large-scale structure formation. 
• Studying alternative matter models, including scalar fields and Chaplygin gas cosmologies, as well as interacting dark-fluid models that seek to unify or explain both early-time dark matter and late-time dark energy effects.
• Performing theoretical analyses of the background field equations and linear perturbations to assess the internal consistency and physical viability of these models. 
• Employing observational and simulated data to constrain model parameters and test deviations from the standard ΛCDM paradigm.

Through this work, the Cosmology Group aims to contribute to a deeper understanding of the universe’s structure and dynamics, and to the ongoing effort to uncover the fundamental laws governing its evolution.

Researchers: Prof Amare Abebe, Thato Tsabone,  Olebogeng Tlhapane 

Current postdocs: David Figueruelo, Renier Hough, Shambel Sahlu
Current students:
MSc: Carissa de Klerk, Edmund Kyazze, Jaydon Durow, Moemedi Mmutle, Olebogeng Tlhapane, Rethabile Thubisi, Robert Rugg

PhD: Dumiso Mithi, Edmund Kyazze, Ritesh Pandey, Thato Tsabone