The precise measurement of the microwave background fluctuations by COBE, followed by the tour de force “concordance cosmology” results of the WMAP mission combined with decades of data on large scale structure, clusters of galaxies and distance ladder calibrations, up to and including type Ia supernovae, is one of the great pieces of modern complex physical science, and am endeavour which promises continued deep insight into the origin and properties of the universe, and the fundamental laws of physics.
Now with update and indirect word of WMAP reaction.
The current best estimate of the cosmological parameters is a bit strange, but has some intriguing aspects to it, which has kept hundreds of theorists busy while we wait for Planck data, which ought to settle some issues and deepen the strangeness of other.
Which is fun.
In particular, without worrying about nuances such as physics of reionization, or presence of non-zero curl in the microwave background, or the slowness of the evolution of early inflation, the WMAP results had interestingly large cosmic variance for the quadrupole and octopole, and an associated “axis-of-evil” – a possible preferred direction in space, associated with the orientation of the low order multipoles.
Now Sean points us to a new preprint, but only as a tweet/fb entry, not a blog.
So… since he made me go out and actually read the darned thing, I might as well make it blogfodder.
Paper is: Improved CMB Map from WMAP Data
by Liu and Li. on arXiv 17th July 2009, submitted to MNRAS
Abstract: “The cosmic microwave background (CMB) temperature maps published by the Wilkinson Microwave Anisotropy Probe (WMAP) team are found to be inconsistent with the differential time-ordered data (TOD), from which the maps are reconstructed. The inconsistency indicates that there is a serious problem in the map making routine of the WMAP team, and it is necessary to reprocess the WMAP data. We develop a self-consistent software package of map-making and power spectrum estimation independently of the WMAP team. Our software passes a variety of tests. New CMB maps are then reconstructed, which are significantly different with the official WMAP maps. In the new maps, the inconsistency disappeared, along with the hitherto unexplained high level alignment between the CMB quadrupole and octopole components detected in released WMAP maps. An improved CMB cross-power spectrum is then derived from the new maps which better agrees with that of BOOMRANG. Two important results are hence obtained: the CMB quadrupole drops to nearly zero, and the power in multiple moment range between 200 and 675 decreases on average by about 13%, causing the best-fit cosmological parameters to change considerably, e.g., the total matter density increases from 0.26 up to 0.32 and the dark energy density decreases from 0.74 down to 0.68. These new parameters match with improved accuracy those of other independent experiments. Our results indicate that there is still room for significant revision in the cosmological model parameters. ”
Like, wow, dude.
That is, academically speaking, a pretty serious calling out.
The claim is that the WMAP data reduction technique is formally correct, but must have been implemented incorrectly, because of claimed inconsistencies in the data.
There is also some comment on the use of “hot spot” data – mainly insufficiently harsh rejection of foreground structure from solar system and galactic objects. eg. Liu and Li require larger “avoidance zones” for the planets.
I will be interested in the WMAP analysis team response…
So, they’re basically claiming the quadrupole/octopole/alignment anomalies in the WMAP release are due to systematic errors in the data analysis, and that the actual cosmological parameters have more matter and less dark energy, though they do not claim qualitative changes in the cosmological parameters. Dark energy is still there, for example.
The discrepancies are at the 3-4σ level, kinda – actually the WMAP numbers they quote, for the matter density, for example, are not the current best fit WMAP numbers.
Liu and Li state 0.74 for ΩΛ, for example, while WMAP actually claims 0.72, which is closer (3 σ) to Liu and Li’s claim of 0.68.
This is a function of which prior one chooses in the WMAP matrix of results to get best estimated parameters (ie they compare WMAP5 alone instead of WMAP+BAO+SN).
The quadrupole is now, they claim, if anything, anomalously low; while the octopole becomes completely uninteresting, as does any alignment.
They also claim better agreement at high multipoles with BOOMERANG data.
Interestingly, they get higher τ and σ8.
But same ns and H0.
So… what do we make of this.
The WMAP team has some of the best data analysts in the world, with a large group and a formal process for error checking, consistency and verification of results.
Or there’s a couple of guys in China who redid the analysis, using the same methodology, but writing the code from scratch, who claim an inconsistency.
Well, I don’t know.
The structure they note in the differential time ordered data map may be a concern, I honestly can’t say, it might be something trivial that the people who stared at the data for 5 years will snort at.
Or, maybe a coding error introducing a subtle bias got through the process and the analysis is just off enough to be interesting, without having been qualitatively wrong.
I’m not sure a zero quadrupole is a good swap, metaphysically speaking, with a too large quadrupole…
What does this all mean.
Well, all the fun papers on cosmic variances, alignment of the sky, and hints of funky topologies or worse… irrrelevant, if Liu and Li are right.
The σ8 and τ are more annoying if those are wrong, a lot of detailed large scale structure simulations were then done using inadequate parameters and ought to be redone.
Jobs for the girls and boys, I suppose…
Theorists could now begin to obsess over the “overly rigid universe” implied by the low quadrupole, and start fantasizing about the implications for new, revolutionary physics.
Ultimately, Liu and Li will either be refuted, or confirmed, either by WMAP reanalysis or Planck data, or both. In the mean time the paper may either be ignored, or debated hotly, but it will probably not be quietly accepted without further discussion…
If correct, I think the new concordance parameters would be rather more boring.
But we are not done yet.
PS: I hear, second hand, that there is more to this.
1) the WMAP people think Liu and Li are wrong. Natch.
2) more than one of the Planck groups redid the WMAP analysis partly as warmup for Planck and partly as a fishing expedition, and they get results very consistent with the WMAP5 release
3) Liu and Li did talk to WMAP people, who asked L&L to do some tests on their technique to validate it, and WMAP people say L&L have failed to do this.
4) Liu and Li paper was previously rejected from another journal.
5) Most interestingly of all, I hear an experienced WMAP member sat down and actually tried to recreate Liu & Li’s analysis: I hear third hand that this person both found errors in how Liu and Li treated the hot pixels, and in how they filtered the time ordered data.
ie WMAP claims to understand the difference in the results and to have identifies explicitly the systematic errors in the analysis that Liu and Li are making, leading to the discrepant result.
So, right now, this tips very strongly to Liu and Li being wrong and we’re back to the slightly more exciting concordance cosmolgy, with preferred direction but low rigidity.
This could yet be a “teachable moment”…