Astronomical data from 2019 demonstrated a positive spatial curvature of the Universe
the verdict
CONTESTED
contested - evenly split
refutedsupported
the weight of evidence
3 sources for · 3 against
Astronomical literature from 2019 and 2020 documents that Planck data analyses found a preference for positive spatial curvature at high confidence levels, though combining these observations with other datasets like baryon acoustic oscillations continues to be a subject of intense debate and differing conclusions.
The recent Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in cosmic microwave background power spectra compared with that predicted in the standard Λ cold dark matter model, where Λ is the cosmological constant. A closed Universe can provide a physical explanation for this effect, with the Planck cosmic microwave background spectra now preferring a positive curvature at more than the 99% confidence level. Here, we further investigate the evidence for a closed Universe from Planck, showing that positive curvature naturally explains the anomalous lensing amplitude, and demonstrating that it also removes a well-known tension in the Planck dataset concerning the values of cosmological parameters derived at different angular scales. We show that since the Planck power spectra prefer a closed Universe, discordances higher than generally estimated arise for most of the local cosmological observables, including baryon acoustic oscillations. The assumption of a flat Universe could therefore mask a cosmological crisis where disparate observed properties of the Universe appear to be mutually inconsistent. Future measurements are needed to clarify whether the observed discordances are due to undetected systematics, or to new physics or simply are a statistical fluctuation. The standard cosmological model assumes a flat Universe, but some model inconsistencies appear when curvature is allowed, as supported by the latest Planck Legacy 2018 power spectra. Is it time to consider new physics?
The question of whether cosmic microwave background (CMB) temperature and polarization data from Planck favor a spatially closed universe with curvature parameter ΩK < 0 has been the subject of recent intense discussions. Attempts to break the geometrical degeneracy combining Planck data with external data sets such as baryon acoustic oscillation (BAO) measurements all point toward a spatially flat universe at the cost of significant tensions with Planck, which makes the resulting data set combination problematic. Settling this issue requires identifying a data set that can break the geometrical degeneracy while avoiding these tensions. We argue that cosmic chronometers (CCs), measurements of the expansion rate H(z) from the relative ages of massive early-type passively evolving galaxies, are the data set we are after. Furthermore, CCs come with the additional advantage of being virtually free of cosmological model assumptions. Combining Planck 2018 CMB temperature and polarization data with the latest CCs, we break the geometrical degeneracy and find ΩK = −0.0054 ± 0.0055, consistent with a spatially flat universe and competitive with the Planck+BAO constraint. Our results are stable against minimal parameter space extensions and CC systematics, and we find no substantial tension between Planck and CC data within a nonflat universe, making the resulting combination reliable. Our results allow us to assert with confidence that the universe is spatially flat to the level, a finding that might possibly settle the ongoing spatial curvature debate and lends even more support to the already very successful inflationary paradigm.
The curvature parameter tension between Planck 2018, cosmic microwave background lensing, and baryon acoustic oscillation data is measured using the suspiciousness statistic to be 2.5 to 3$\sigma$. Conclusions regarding the spatial curvature of the universe which stem from the combination of these data should therefore be viewed with suspicion. Without CMB lensing or BAO, Planck 2018 has a moderate preference for closed universes, with Bayesian betting odds of over 50:1 against a flat universe, and over 2000:1 against an open universe.
# Did we really determine a positive curvature of the Universe in 2019?
Tags: general-relativity, cosmology, universe, curvature, cosmic-microwave-background
- Score: 21
- Views: 5271
- Answers: 2
- Answered: yes
- Asked by: peterh (1 rep)
- Asked: 2021-08-16
- Edited: 2021-08-19
- Site: physics
## Question
This arXiv paper says:
The recent Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in CMB power spectra compared to that predicted in the standard $\lambda$CDM model. A closed universe can provide a physical explanation for this effect, with the Planck CMB spectra now preferring a positive curvature at more than 99% confidence level.
If I understand it well, this question might be already obsolete - there is a little deviation from a completely flat Universe into a positive direction. How is it possible? As far I know, there were no recent Planck (or similar) measurements.
How believable is this new development? If it is believable (99% CL in an arXiv paper looks for me strong), what is the estimated radius of the Universe, if we assume a small, constant, positive curvature and spherical topology?
## Answers
### Answer by Allure (sco
The concordance of the $\Lambda$CDM cosmological model in light of current observations has been the subject of an intense debate in recent months. The 2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power spectrum measurements appear at face value to favour a spatially closed Universe with curvature parameter $\Omega_K<0$. This preference disappears if Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to break the geometrical degeneracy, although the reliability of this combination has been questioned due to the strong tension present between the two datasets when assuming a curved Universe. Here, we approach this issue from yet another point of view, using measurements of the full-shape (FS) galaxy power spectrum, $P(k)$, from the Baryon Oscillation Spectroscopic Survey DR12 CMASS sample. By combining Planck data with FS measurements, we break the geometrical degeneracy and find $\Omega_K=0.0023 \pm 0.0028$. This constrains the Universe to be spatially flat to sub-percent precision, in excellent agreement with results obtained using BAO measurements. However, as with BAO, the overall increase in the best-fit $\chi^2$ suggests a similar level of tension between Planck and $P(k)$ under the assumption of a curved Universe. While the debate on spatial curvature and the concordance between cosmological datasets remains open, our results provide new perspectives on the issue, highlighting the crucial role of FS measurements in the era of precision cosmology.
Interacting dark energy models are widely renowned for giving an explanation to the cosmic coincidence problem as well as several observational issues. According to the recent observational data, and so far we are concerned with the literature, the choice of the interaction function between dark matter and dark energy is always questionable since there is no such underlying theory that could derive it. Thus, in this work we have raised this issue by proposing two new non-linear interaction functions and constrain them using cosmic microwave background (CMB) from Planck 2018, baryon acoustic oscillations (BAOs), dark energy survey and a measurement of the Hubble constant H0 from Hubble Space Telescope (HST) 2019. The dark energy equation of state is considered to be constant throughout the work and the geometry of the universe is assumed to be homogeneous and isotropic with zero spatial curvature. Our analyses report that a non-zero interaction is always allowed by the observational data and the dark energy equation of state is bent towards the phantom regime. In particular, when H0 from HST is added to Planck 2018+BAO, we find an evidence for a non-zero coupling at more than 2σ confidence level. Our analyses also report that for both the models, H0 is close to its local measurements and thus alleviating the H0 tension. In particular, one of the interacting models perfectly solves the H0 tension.
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