September 20, 2002 | David F. Coppedge

How Precise Is “Precision Cosmology”?

When data from the Wilkinson Microwave Anisotropy Probe (WMAP) came in, cosmologists heralded it as the era of “precision cosmology” and immediately began to make claims that resulting data map confirmed some cosmological theories and falsified others (see 02/14/2003 headline).  Two papers in the Astrophysical Journal, however, are discounting the precision of the data and questioning its usefulness for confirming cosmological models.
    Erickson et al.1 studied the method used by the WMAP science team to analyze the data and make cosmological conclusions.  They concluded that it had the potential to inform models, but cautioned that “great care must be taken both in implementation and in a detailed understanding of limitations caused by residual foregrounds, which can still affect cosmological results.”  They concluded that the sky map used by the science team was “not clean enough to allow for cosmological conclusions.  Alternative methods must be developed to study these issues further.”
    David L. Larson and Benjamin D. Wandelt also studied the WMAP data and concluded that the “hot spots” were too cool and the “cold spots” too warm to confirm an assumption made by the science team that the Cosmic Microwave Background (CMB) is an isotropic, Gaussian random field.  “A question of fundamental importance to our understanding of the origins of these primordial seed perturbations is whether the CMB radiation is really an isotropic and Gaussian random field, as generic inflationary theories predict,” they note.  Yet they compared the actual field to a Monte Carlo simulation of a Gaussian field and were able to rule out Gaussianity in the WMAP data to the 95% confidence level at both the north and south hemispheres.  This casts doubt on the theoretical statements based on the data, they say:

We find the WMAP data to have maxima that are significantly colder and minima that are significantly warmer than predicted by Monte Carlo simulation.  For almost all simulations, we have 95% confidence that the mean of the WMAP hot spots or cold spots is in a 5% tail of the Monte Carlo distribution.  In one case, we are 99% confident that the maxima statistic is in a 1% tail.  Since we find the same lack of extreme temperature when we use the directly measured WMAP power spectrum, we are not simply restating that the WMAP power spectrum has a lack of power at large angular scales.  The effect is independent of the galactic mask or power spectrum used….
    Our results may not be a detection of primordial non-Gaussianity.  They could still be an effect of the WMAP instrument or data pipeline not modeled in our simulations or an as yet undiscovered foreground.  Our result is still highly significant.  We have detected something, whether it is primordial non-Gaussianity or some other effect in the data.  Having anomalous mean temperature values for the maxima and minima in both the north and the south ecliptic hemispheres is unlikely to occur if the WMAP data were consistent with theoretical expectations.
  (Emphasis added in all quotes.)


1Erickson, Gorski and Lilje, “On Foreground Removal from the Wilkinson Microwave Anisotropy Probe Data by an Internal Linear Combination Method: Limitations and Implications,” The Astrophysical Journal, 612:633-646, 2004 September 10.
2Larson and Wandelt, “The Hot and Cold Spots in the Wilkinson Microwave Anisotropy Probe Data Are Not Hot and Cold Enough,” The Astrophysical Journal Letters 613:L85-L88, 2004 October 1.

Always read the fine print after the bluffing whirlwind of hot air has subsided.  Evolutionary theories, both biological and cosmological, are like dust devils.  They attract attention for awhile, but perceptive readers examine what material was weighty enough afterwards to remain on solid ground.

(Visited 43 times, 1 visits today)
Categories: Cosmology

Leave a Reply