The Jupiter Effect: “Is everything we know about the Universe wrong?”

Jupiter2storms_gemini Two recent results  suggest that the answer to the above question is “Quite possibly!” 

Utane Sawangwit and Tom Shanks of Durham University that the errors on the “gold standard” cosmic microwave background results from the WMAP satellite may be larger than previously supposed and that the mysterious dark energy and dark matter may not even exist.

The pattern of ripples detected by microwave background telescopes such as WMAP that underpin the idea that the Universe is composed of 22% dark exotic particles and 74% dark energy with the remaining 4% being the atoms in the ordinary material that we see around us. This model produces a largest ripple size of about 1 degree on the microwave sky and this is well matched by the ripples seen in the WMAP data. So these WMAP ripples have a size that is roughly twice the size of the Full Moon as they appear on the sky. 

Models that don’t have dark energy or dark matter tend to produce CMB ripples that are smaller, only about half the standard model size and so just about the size of the Full Moon.   

Sawangwit and Shanks have used point-like radio sources to test how much the WMAP telescope smoothes these CMB ripples and have found evidence that this ”beam smoothing” is much larger than suggested from WMAP’s observations of the planet Jupiter. 

The radio sources have the advantage that they are much closer in brightness to the CMB ripples that are being studied than Jupiter which is ~1000 times brighter. But their faintness is also a disadvantage which means that the Durham team have had to stack hundreds of the radio sources to get their result. If the WMAP CMB map is smoothed by as much as the radio sources appear to be then it may  make it more easy for other models without dark matter (or dark energy!) to fit the CMB data.

It will be fascinating to see if the new European PLANCK satellite, currently taking data, will confirm the WMAP results. The PLANCK telescope will also smooth the new CMB maps and again the radio source technique used by Sawangwit and Shanks can be used to help them judge how much. 

The same Durham team were also involved with international collaborators in another recent paper which suggested that an independent CMB check on the existence of dark energy might not be as “bullet-proof “ as previously thought. 

If dark energy exists it causes the expansion of the Universe to accelerate at late times. CMB photons have to pass through giant superclusters of galaxies on their way to be detected by telescopes such as WMAP. Normally a CMB photon gets gravitationally blueshifted as it enters a cluster and redshifted as it leaves and the two effects cancel. But if the cluster galaxies accelerate away from each other as the photon passes through then the cancellation is not exact and a trace is left in that slightly higher CMB temperatures should be observed in sightlines that pass near to galaxy superclusters. 

Previously claims have been made that this “ISW “ signal is seen at high significance when CMB-galaxy correlations are studied. But in a powerful new sample of ~1 million luminous red galaxies from the Sloan Digital Sky Survey no such effect is seen and when this result is included, the significances of the previous detections reduce to the point where they are as consistent with a null detection of dark energy as with the standard model prediction. 

If the same null result is seen in the Southern Hemisphere using WMAP and PLANCK CMB data coupled with millions of galaxies to be found in new Southern Surveys such as the ESO  VST ATLAS (PI T. Shanks) then again there will be a significant threat to the standard cosmological model in which dark energy plays a vital role. 

The identification of dark matter with exotic particles as yet undetected in the laboratory and the introduction of dark vacuum energy in an amount that is minute compared to the total energy of the Universe at early-times leaves many cosmologists feeling uncomfortable. 

The dark energy problem is particularly vexing– most theorists would prefer a zero cosmological constant because it might be hoped that it could be explained by some as yet unknown symmetry of nature. Indeed, if there had to be a cosmological constant then the string theorists of particle physics would actually prefer that it was negative which is the opposite to what is apparently observed in the supernova Hubble diagram. These problems frequently cause theorists to resort to the “anthropic principle” for an explanation. 

The standard model also has astrophysical difficulties. For example, in galaxy formation theories, as much “feedback” energy is now being used in preventing stars from forming as in forming them under gravity, seemingly at odds with the simplest “bottom-up” picture of galaxy formation.  

The evidence for dark matter is less strong than it was in the 1930’s when Fritz Zwicky first discovered the “missing mass” problem in the centres of rich galaxy clusters. The confirmation from X-ray satellites like Chandra and XMM-Newton that these galaxy clusters contain large amounts of hot gas as well as galaxies and stars has reduced the missing mass/dark matter discrepancy by a factor of 10-100! It remains to be seen whether the remaining factor or 4-5 merits the invoking of a cosmological density of exotic particles as required by the standard model.

The undoubted successes of the standard cosmological model therefore have to be balanced against the above problems. Much depends on the results from the “precision” Cosmic Microwave Background experiments. If these are correct then the standard model, with all its difficulties, will likely be correct. This is why tests of the CMB results such as those made by the Durham team and their collaborators are so important for cosmology. 

The effect of the WMAP telescope on the CMB ripples and the search for the signature of dark energy in the CMB-galaxy correlations are crucial for the survival of the standard model. 

Casey Kazan



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