Conformal cyclic cosmology (CCC) predicts that the Hawking radiation of supermassive black holes that evaporate in a previous aeon is concentrated, by conformal compression at the crossover between aeons, into point-like energy injections that imprint on the last-scattering surface small circular spots of raised temperature ('Hawking discs') with angular radius up to about 0.035 radians. An, Meissner, Nurowski and Penrose (2020) reported such spots in Planck and WMAP data at a claimed 99.98% confidence level while leaving open the quantitative mapping from previous-aeon black-hole energetics to the observed temperature increment and radial profile. Later independent analyses reach conflicting conclusions: Jow and Scott (2020) find the excess drops to about 87% confidence once the look-elsewhere effect is treated by marginalizing over the scanned search scales; Fernández-Cobos et al. (2020) find no strong evidence with radial-derivative filters; Bodnia et al. (2024), using a machine-learning search at full Planck resolution, find no significant signal once a few unusually bright or cold pixel spots are controlled; López et al. (2022) report an inconclusive excess at the 1% level. On the theory side, Meissner and Penrose (2025, preprint) derived a mass-energy conservation law across the crossover and estimated the spot amplitude at about 10^-3 in units of the CMB temperature, but the detailed radial profile and the particle physics of the transmitted radiation remain uncomputed. The open problem is to complete the quantitative CCC prediction of the Hawking-spot signature — amplitude, radial profile, angular size, and abundance — and to settle, by a statistically rigorous search on current or future CMB data, whether the signal is present, and what the answer implies for CCC versus the conventional inflationary picture.

Background

The cosmic microwave background (CMB) is the relic radiation released when the primordial plasma became transparent about 380,000 years after the Big Bang, at the last-scattering surface; its temperature fluctuations, of relative size about 10−510^{-5}, are the standard probe of very early universe physics. In the conventional account, an inflationary phase — a brief period of accelerating expansion — explains the observed flatness, isotropy, and near-scale-invariance of these fluctuations. A large literature searches the CMB for 'anomalies' that might point beyond this standard picture, and any such claim must confront the subtleties of statistical assessment on a single sky, in particular the look-elsewhere effect: if many candidate scales and directions are scanned, some apparent excess will arise by chance unless the significance is marginalized over the whole scanned parameter space.

Conformal cyclic cosmology (CCC), proposed by Roger Penrose, replaces inflation with an unending sequence of aeons, each ending in an exponential expansion driven by the cosmological constant, whose conformal infinity (the boundary reached by an indefinitely expanding space-time, rescaled so that infinity is brought to a finite 'distance') is joined smoothly, by a conformal rescaling of the metric (a position-dependent rescaling of distances that preserves angles and the causal light-cone structure), to the conformally stretched big bang of the next aeon; the common boundary is the crossover 3-surface. In each aeon, galactic clusters remain bound while superclusters disperse, so the far future is dominated by hugely massive black holes — up to perhaps 101410^{14} solar masses — which Hawking-evaporate completely (Hawking radiation being the thermal quantum radiation emitted by black holes, of temperature inversely proportional to mass). Although this evaporation takes of order 1010010^{100} years, the conformal compression of the remote future compresses the entire evaporation into what is effectively a single event just beneath the crossover: a Hawking point, whose energy — mainly photons — passes into the next aeon as a point-like injection just after its big bang. The injected energy then spreads, limited by the speed of light, and reaches the last-scattering surface as a small circular disc of raised temperature, centred on the Hawking point, of angular radius no greater than about 0.035 radians (about 2 degrees), with the temperature expected to fall off from the centre in a roughly Gaussian fashion; the theory thus predicts a sharp cutoff in spot diameter near 0.08 radians.

Earlier CCC searches had looked for concentric low-variance circles in the CMB, attributed to supermassive black-hole encounters in a previous aeon (Gurzadyan and Penrose 2013), and for ring-type structures (An, Meissner and Nurowski 2018); the statistical significance of those claims was repeatedly disputed in independent re-analyses, and the same statistical issues recur for the Hawking points. An, Meissner, Nurowski and Penrose (2020) searched Planck 70 GHz maps for annuli with large negative radial temperature slope (temperature decreasing outwards, as expected for a hot central spot), comparing the tails of the cumulative distribution of slopes against 10,000 Gaussian simulations, against 1,000 FFP8.1 simulations (the Planck collaboration's end-to-end mock skies including beam, noise, scanning strategy and gravitational lensing), and against the data of the independent WMAP (Wilkinson Microwave Anisotropy Probe) satellite, finding the five strongest Planck locations also among the strongest in WMAP. They reported an excess at the claimed 99.98% confidence level for annuli of inner radius 0.01 radians and widths 0.02 or 0.03 radians. The paper itself records what it does not establish: the actual radial temperature profile 'depends on the detailed particle physics involved' and is not computed; residual systematics and foregrounds are excluded only to the extent represented by the FFP8.1 simulations and the WMAP cross-check; the relation of these small hot spots to the earlier claimed large-scale CCC features (and to the pronounced anisotropic clustering of earlier ring-claim centres into three sky regions) is deferred; and the compatibility of the observed sharp angular-size cutoff and central peaking with conventional inflation is left unresolved — the authors note it is 'hard to see' a natural inflationary explanation.

Subsequent independent work reshaped this landscape. Jow and Scott (2020) reproduced the per-scale excess but showed that marginalizing over the scanned annulus scales — the look-elsewhere effect — raises the probability to exceed to 13% (about 87% confidence, roughly 1 sigma), and found neither anomalous clustering of the strongest candidate points nor any polarization counterpart. Fernández-Cobos, Marcos-Caballero and Martínez-González (2020) applied radial-derivative filters with FFP10 simulations (a later version of the same Planck end-to-end mock skies) and found no strong evidence for CCC-type circular patterns. Bodnia et al. (2024) searched about fifty million sky centres at full Planck resolution with a ResNet18-based neural network (a deep 18-layer residual convolutional network) trained on Gaussian-amplitude Hawking-spot models, and found no statistically significant Hawking points once a handful of unusually bright or cold few-pixel spots — which also generate spurious families of low-variance circles — are accounted for. On the theory side, Meissner and Penrose (2025) proved, using 2-spinor and twistor methods (spinor- and light-ray-based reformulations of space-time geometry), a mass-energy conservation law across the crossover surface and estimated the central temperature rise of a Hawking spot from the mass of the pre-crossover galactic cluster, obtaining a relative rise of order 10−310^{-3}, in claimed agreement with the 2020 observational estimate; they also introduced a gravitational-wave epoch at the crossover to explain why the observed angular diameter is about twice the naive causal expectation. This is an order-of-magnitude amplitude argument, not the detailed particle-physics and radiative-transfer computation of the radial profile; it has not engaged the statistical critiques, and it exists so far only as a preprint.

Problem Statement

The problem is to make the CCC Hawking-point prediction quantitative and to settle whether it is present in the CMB, with three jointly linked components serving one objective — turning the Hawking-point idea into a quantitative, decisive test of physics before our Big Bang. (1) Theoretical prediction: starting from the Hawking evaporation of supermassive black holes in a previous aeon, with the total evaporated mass set by the host galactic cluster (of order 101510^{15} solar masses), and from the conformal matching across the crossover 3-surface, compute the signature imprinted on the last-scattering surface: the central temperature increment ΔT/T\Delta T/T as a function of the source mass, the radial temperature profile (functional shape and angular width) — including the particle physics of the extremely blueshifted transmitted Hawking radiation and its radiative transfer through the radiation-dominated early aeon — the characteristic angular diameter with its predicted sharp cutoff near 0.08 radians, and the expected number of such spots on the sky. (2) Observational decision: test this prediction against the CMB with a search whose statistical significance is evaluated with full marginalization over the search parameters (annulus radii and widths, or the equivalent profile parameters) — i.e. with the look-elsewhere effect properly treated — and with explicit control of few-pixel bright and dark spots and astrophysical foregrounds, thereby resolving the standing disagreement between the claimed 99.98 percent confidence excess of An et al. (2020) and the independent null results of Jow and Scott (2020), Fernández-Cobos et al. (2020) and Bodnia et al. (2024); either a detection at stated confidence, or a quantitative upper bound on the Hawking-spot amplitude and abundance for the predicted profile family, is an admissible outcome. (3) Interpretation: state what the outcome implies for CCC and for the conventional inflationary picture, in particular whether the sharp angular-size cutoff and the central temperature peaking of the spots can, or cannot, be accommodated within standard inflation. Components (1) and (2) are inseparable in practice: the search is only well-defined against the predicted profile family, and the prediction is only tested by the search; an answer that supplies one without confronting it with the other does not settle the question.

References

  1. Daniel An, Krzysztof A. Meissner, Paweł Nurowski, Roger Penrose (2020), 'Apparent evidence for Hawking points in the CMB Sky', Monthly Notices of the Royal Astronomical Society 495, 3403-3408, DOI: 10.1093/mnras/staa1343, https://doi.org/10.1093/mnras/staa1343 (preprint arXiv:1808.01740, https://arxiv.org/abs/1808.01740)
  2. Dylan L. Jow, Douglas Scott (2020), 'Re-evaluating evidence for Hawking points in the CMB', Journal of Cosmology and Astroparticle Physics 2020(03), 021, DOI: 10.1088/1475-7516/2020/03/021, https://doi.org/10.1088/1475-7516/2020/03/021 (arXiv:1909.09672, https://arxiv.org/abs/1909.09672)
  3. R. Fernández-Cobos, A. Marcos-Caballero, E. Martínez-González (2020), 'Radial derivatives as a test of pre-big bang events on the Planck data', Monthly Notices of the Royal Astronomical Society 499, 1300-1311, DOI: 10.1093/mnras/staa2844, https://doi.org/10.1093/mnras/staa2844 (arXiv:2004.14435, https://arxiv.org/abs/2004.14435)
  4. Eve Bodnia, Vlad Isenbaev, Kellan Colburn, Joe Swearngin, Dirk Bouwmeester (2024), 'The quest for CMB signatures of conformal cyclic cosmology', Journal of Cosmology and Astroparticle Physics 2024(05), 009, DOI: 10.1088/1475-7516/2024/05/009, https://doi.org/10.1088/1475-7516/2024/05/009 (arXiv:2208.06021, https://arxiv.org/abs/2208.06021)
  5. M. López, P. Bonizzi, K. Driessens, G. Koekoek, J. A. de Vries, R. Westra (2022), 'Searching for ring-like structures in the cosmic microwave background', Monthly Notices of the Royal Astronomical Society 519, 922-930, DOI: 10.1093/mnras/stac3485, https://doi.org/10.1093/mnras/stac3485 (arXiv:2105.03990, https://arxiv.org/abs/2105.03990)
  6. Krzysztof A. Meissner, Roger Penrose (2025), 'The Physics of Conformal Cyclic Cosmology', arXiv:2503.24263, https://arxiv.org/abs/2503.24263 (preprint submitted 31 March 2025; no journal reference)
  7. V. G. Gurzadyan, R. Penrose (2013), 'On CCC-predicted concentric low-variance circles in the CMB sky', The European Physical Journal Plus 128, 22, DOI: 10.1140/epjp/i2013-13022-4, https://doi.org/10.1140/epjp/i2013-13022-4 (arXiv:1302.5162, https://arxiv.org/abs/1302.5162)
  8. Daniel An, Krzysztof A. Meissner, Paweł Nurowski (2018), 'Ring-type structures in the Planck map of the CMB', Monthly Notices of the Royal Astronomical Society 473, 3251-3255, DOI: 10.1093/mnras/stx2299, https://doi.org/10.1093/mnras/stx2299