A Survey through Conformal Time

Tahereh Aeenehvand; Ahmad Shariati

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arXiv · 2604.06120

A Survey through Conformal Time

Tahereh Aeenehvand·Ahmad Shariati

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Abstract

We revisit conformal time $\eta$ in a spatially flat Friedmann--Robertson--Walker universe and use a $1+1$-dimensional setting as a technically transparent pedagogical arena. Our purpose is to clarify the relation among cosmic time $t$, conformal time $\eta$, and the scale factor $a(t)$, and then to follow how this relation governs the geodesics of freely moving particles and the curvature of the corresponding manifold. The radiation-dominated, matter-dominated, and exact vacuum-only de Sitter cases are treated separately, because each of them produces a distinct conformal-time dependence and therefore a distinct geodesic structure. We then write the affine-parameter formalism in a form that is genuinely general for any spatially flat conformal metric, and we record the straightforward extension to the spatially flat $3+1$ case. The presentation remains elementary in spirit, but the notation, the curvature formulas, and the de Sitter interpretation are kept explicit.

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Tahereh Aeenehvand, Ahmad Shariati. 2026-04-07. A Survey through Conformal Time. https://arxiv.org/abs/2604.06120

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