FRB 20240304B reaches redshift 2.148, when the Universe was about 3 billion years old, extending localized FRB studies across roughly 80% of cosmic history. Its propagation signatures reveal structured magnetized plasma across the sightline and help inventory diffuse ionized baryons, but one burst cannot determine the universal baryon fraction.
Two lenses on the same evidence. Source weight and the primary source ratio show what each rests on.
Alternative
Source weight 54%
Lens adapted to this topic: Cautious reading of the signal
A more skeptical interpretation treats FRB 20240304B primarily as a proof of reach, not a clean measurement of early-universe magnetism or baryon completeness. The observed signal combines source, host, foreground-group, cluster, and intergalactic contributions. Existing FRB work also shows that assumptions about plasma phase, turbulence, and sample construction can materially affect inferred magnetic limits and baryon fractions.
The event's complex sightline is scientifically useful but makes attribution difficult: magnetic and dispersion signatures need not originate mainly in the diffuse early intergalactic medium.
A single sightline cannot establish the strength, coherence, or cosmic evolution of primordial or intergalactic magnetic fields.
FRB scattering studies show that conclusions about small-scale intergalactic magnetism depend on assumptions about turbulence and warm-hot gas; one analysis derives upper limits of 10–30 nG at z around 1–2.
Baryon-fraction estimates are model-sensitive: a large-sample analysis reports about 86% in diffuse ionized intergalactic gas, but its review flags sample-description and likelihood issues.
The burst demonstrates that high-redshift ionized-baryon measurements are possible, not that the missing-baryon inventory or early magnetic-field origin has been uniquely solved.