Cosmological Models with Varying Fundamental Constants

Cosmological models with varying fundamental constants explore the possibility that quantities traditionally regarded as immutable—such as the speed of light (c), Newton’s gravitational constant (G) and Planck’s constant (h)—may evolve over cosmic history. Such frameworks arise naturally in scalar-tensor theories, in which one or more scalar fields couple to the spacetime metric and influence effective coupling strengths. They also feature in scenarios of quantum geometry, where stochastic fluctuations of spacetime at microscopic scales induce time-dependent behaviours in macroscopic constants. Varying-speed-of-light (VSL) models seek alternative resolutions of the horizon and flatness problems by permitting c to change during a primordial epoch, while covarying-constant schemes adjust the cosmological constant Λ dynamically to account for late-time acceleration without invoking a pure vacuum energy. Observationally, these proposals are constrained by precision measurements of the cosmic microwave background, Big Bang Nucleosynthesis yields, the Hubble diagram of standard candles, spectroscopic determinations of fine-structure lines and the propagation of gravitational waves. Together, theoretical developments and multi-messenger observations form a coherent picture that tests fundamental symmetries, probes early-Universe chronology and informs prospects for unifying gravity with quantum field theory.

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Cosmological Models with Varying Fundamental Constants publication trend

The graph below shows the total number of articles in cosmological models with varying fundamental constants across all publications each year (not limited to Nature Index journals).

Technical terms

Fundamental constant: A physical quantity assumed invariant in standard cosmology, such as c or G, whose variation can alter cosmic evolution.

Scalar field: A field that assigns a single numerical value to each spacetime point, often invoked to drive dynamical constants.

Varying speed of light (VSL): A class of models in which the speed of light changes during early epochs to address standard cosmological puzzles.

Big Bang Nucleosynthesis (BBN): The process of light-element formation in the early Universe, sensitive to the expansion rate and G.

Standard candle: An astrophysical source with known intrinsic luminosity employed to measure cosmological distances.

Standard siren: A gravitational-wave event with predictable amplitude used as a distance indicator independent of the electromagnetic spectrum.

FLRW metric: The Friedmann–Lemaître–Robertson–Walker solution describing a homogeneous and isotropic expanding Universe.

References

1. Measuring the Speed of Light with Updated Hubble Diagram of High-redshift Standard Candles. The Astrophysical Journal (2023).
2. JWST early Universe observations and ΛCDM cosmology. Monthly Notices of the Royal Astronomical Society (2023).
3. The effect of the gravitational constant variation on the propagation of gravitational waves. Physics Letters B (2023).
4. Improved BBN constraints on the variation of the gravitational constant. European Physical Journal C (2020).
5. Effective cosmological constant induced by stochastic fluctuations of Newton's constant. Physics Letters B (2016).