Fast Radio Bursts: Key to Solving Hubble Tension and Dark Energy ✛ ✎ ✦
Context
Back in 1929, Edwin Hubble discovered that galaxies are receding and formulated Hubble's law, and almost a century later Adam Riess and colleagues obtained the most precise local H0 estimates, exposing the problem. Earlier, Vera Rubin pointed to the existence of dark matter through her observations of galaxy rotation curves, without which the Universe's dynamics cannot be described. Today cosmology faces a major challenge: the two most accurate methods for measuring the Hubble constant yield incompatible results. Data from the cosmic microwave background, interpreted within the standard ΛCDM model, indicate H0 ≈ 67.4 km/s/Mpc, while local measurements using Type Ia supernovae and Cepheids give about 73.0 km/s/Mpc. This discrepancy, reaching 5σ, is known as the 'Hubble tension' and may hint at new physics. Meanwhile, data from the DESI spectroscopic survey suggest that dark energy is not a cosmological constant but evolves over time. To probe these mysteries, new independent tracers are essential, and fast radio bursts (FRBs) have emerged as one of the most promising, opening a window into the history of the Universe's expansion.
Methods
The principle of using FRBs in cosmology relies on dispersion: as radio waves travel through ionized plasma in the intergalactic and interstellar medium, different frequencies propagate at different speeds, causing a delay in the low-frequency signal. This delay, expressed as the dispersion measure (DM), is proportional to the total number of free electrons along the line of sight. The theoretical foundation is the Macquart relation, which links the average DM from the intergalactic medium (IGM) to cosmological parameters, including H0 and the baryon fraction. This relation derives from Friedmann's equations and the laws of electrodynamics. By determining the redshift of an FRB from its host galaxy, H0 can be recovered. Additionally, gravitational lensing is used: when a massive object along the line of sight creates multiple images of a burst, the time delay between them provides a purely geometric way to measure H0. Another method relies on the luminosity-rotation measure (L-RM) correlation for sources associated with compact radio sources. In all approaches, numerical simulations of baryon distribution in the IGM and host galaxies play a critical role, as does accounting for contributions from magnetars — the probable FRB sources.
Results
Analysis of 108 localized FRBs with known redshifts yielded an independent H0 estimate of 69.4 +2.1/-2.0 km/s/Mpc, placing it between the Planck and SH0ES results. Adding more than 500 unlocalized bursts with pseudo-redshifts improves precision to ~1%. The gravitational lensing method has not yet produced definitive results but is projected to achieve sub-percent precision with just a few dozen lensed systems. The L-RM correlation applied to four FRB-PRS systems gave H0 ≈ 86 +18/-15 km/s/Mpc, which currently has wide uncertainty but is free from systematics related to the IGM. Overall, FRB data are starting to constrain dark energy parameters: combined with other datasets, they hint at an evolving equation of state. Moreover, an analysis of all cosmological data reveals an intriguing trend: measured H0 values decline with increasing redshift, smoothing the tension between early and late epochs. This effect could be due to the dynamic nature of dark energy.
Implications
FRBs are becoming a full-fledged cosmological tool capable of resolving the Hubble tension without invoking new physical laws. Their independence from the distance ladder and sensitivity to baryon distribution open a path to directly test Friedmann's equations and Einstein's field equations in the late Universe. Joint analysis of FRBs, Type Ia supernovae, and cosmic microwave background data will accurately reconstruct the expansion history and determine whether dark energy is truly dynamic.
Future development
With next-generation instruments like SKA and DSA-2000 coming online, an avalanche of FRBs is expected — up to tens of thousands of localized events. This will not only reduce statistical errors to below 0.5% but also map baryon distribution in large-scale structure and, for the first time, detect hundreds of lensed systems. Already, FRBs are becoming a routine tool in cosmological simulations.
Impact
The results will influence fundamental cosmology, high-energy astrophysics, and plasma physics, as well as technologies for receiving and processing radio data.
Next steps
Key tasks: improving models of electron distribution in host galaxies and the IGM, developing robust Bayesian methods for joint analysis of heterogeneous data, and identifying the nature of FRB central engines.
Key open problems
FRBs are directly linked to the Hubble tension problem, the nature of dark energy, the search for 'missing baryons' in the Universe, and the possible evolution of fundamental constants.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The paper reviews the use of fast radio bursts as a cosmological tool. The author examines the relationship between dispersion measure and redshift, methods for measuring the Hubble constant, including gravitational lensing and the luminosity–rotation measure correlation, and provides an estimate of H0 = 69.4 +2.1/-2.0 km/s/Mpc based on 108 localized FRBs.
Where its strength is
The strength of the work lies in systematizing several independent methods for using FRBs in cosmology and demonstrating their current competitiveness, especially in the context of the Hubble tension.
Where it could go next
- It might be interesting to see how the machine learning methods described in the paper on a universal neural network for FRB search could speed up data processing for future surveys and increase the sample of localized events with known redshifts.based on: Cosmic Calligraphy: A General-Purpose Neural Network Catches Fast Radio Bursts arXiv:2607.07382
- A related approach uses FRBs to measure the distribution of missing baryons in the intergalactic medium; it could be applied to refine systematic uncertainties in the Macquart relation, which is critical for the accuracy of H0.based on: Cosmic Lightning: How Fast Radio Bursts Illuminate Hidden Baryons arXiv:2607.04106v1
- A possible direction is to compare FRB results with independent H0 estimates from gravitational waves, to check the consistency of methods and better understand systematics.based on: Gravitational waves measure the expansion rate of the universe arXiv:2605.27227
Worth trying
- Test the neural network classifier from paper 2607.07382 on CHIME data to select FRB candidates, aiming to increase the number of localized events with known redshifts.
- Use the correlation between dispersion measure and baryon excess from paper 2607.04106v1 to model the contribution of galactic halos to DM and reduce systematics in the H0 estimate.
- Check joint constraints on H0 and dark energy parameters by combining FRBs with gravitational wave data, as in paper 2605.27227.
Why this may matter
Advances in FRB cosmology could provide an independent way to resolve the Hubble tension and refine the equation of state of dark energy, which is fundamental to understanding the evolution of the Universe.
Nearby works in our archive
- Cosmic Radio Bursts: A Mystery a New Telescope Will Unravelsimilarity 0.72
- Cosmic Calligraphy: A General-Purpose Neural Network Catches Fast Radio Burstssimilarity 0.68
- Magnetic Echolocation: Measuring the Cosmic Cocoons of Fast Radio Burstssimilarity 0.67
- A Polygraph for Flashes: How the Pincus–Lyapunov Diagram Uncovers FRBssimilarity 0.67
- Radio bursts help measure the expansion of the Universesimilarity 0.66
- Gravitational waves measure the expansion rate of the universesimilarity 0.66
- Cosmic Lightning: How Fast Radio Bursts Illuminate Hidden Baryonssimilarity 0.65
The archive is crowded around this work: 8 reviews nearby, closest at 0.72. This ground is well walked — and there is plenty to compare against.
The energy of a typical FRB is equivalent to the Sun's output over several days, packed into a burst lasting just a few milliseconds.
In science fiction, fast radio bursts were once considered possible signals from extraterrestrial civilizations — much like in Carl Sagan's novel 'Contact,' where characters tried to decode an alien message.
Key numbers
- Number of localized FRBs (Gao et al. 2025): 108
- H0 (FRBs, localized): 69.4 +2.1/-2.0 km/s/Mpc
- H0 (SH0ES, 2022): 73.04 ± 1.04 km/s/Mpc
- H0 (Planck, 2020): 67.4 ± 0.5 km/s/Mpc
- H0 precision from unlocalized FRBs: ~1%