MAPS of the oldest light in the universe underpin some of cosmology鈥檚 most prized theories. Now some astrophysicists are saying that certain features in these maps may be artefacts caused by some unknown property of our solar system, throwing into question the data鈥檚 relevance and accuracy.
The all-sky maps of the faint microwave radiation left over from the big bang 鈥� measured by a spacecraft called the Wilkinson Microwave Anisotropy Probe (WMAP) 鈥� were released with great fanfare in 2003. They supported a bizarre model of the universe dominated by dark energy and dark matter and also backed the popular idea that the universe went through a period of rapid 鈥渋nflation鈥� just after the big bang.
Now, astrophysicist Glenn Starkman from Case Western Reserve University in Cleveland, Ohio, and his colleagues are casting doubt on the interpretation of the data and, in turn, on some of the models that spring from it. 鈥淭here is overwhelming evidence of weird things going on,鈥� he says.
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Starkman鈥檚 team has found that certain patterns in the temperature maps, known as quadropoles and octopoles, line up with the special directions in the solar system (Physical Review Letters, vol 93, p 221301). For instance, the quadropoles, which are arrangements of four alternating hot and cold spots, can be described by two vectors, and the plane of these vectors is nearly perpendicular to the plane of the solar system and to the direction of the solar system鈥檚 motion through the universe. Similar vectors that describe the octopoles also line up with these local features.
鈥淭aking all these things together makes you very suspicious that this is not cosmology but some local observations,鈥� says Dominik Schwarz, a team member from CERN, the European particle physics lab in Geneva, Switzerland. 鈥淲e have absolutely no idea what is causing this effect, but a stupid first guess is that maybe there is some component of dust in the solar system not discovered yet.鈥� This dust could absorb or scatter radiation.
鈥淭aking all these things together makes you suspect that this is not cosmology but some local observations鈥�
It might also be due to some quirk of the WMAP probe itself. But Gary Hinshaw, a member of WMAP鈥檚 science team, says: 鈥淲e are pretty confident there is nothing in the instrument. We鈥檝e looked pretty carefully at this.鈥� He admits however, that the WMAP data was heavily processed, and this might have affected the maps.
Starkman is not the only one to have found such oddities. Another team had already spotted that the quadropoles and octopoles were aligned with each other, while others discovered that the temperature maps were noisier in the southern skies than in the northern skies. And puzzlingly, the octopoles and quadropoles are fainter than predicted by the inflation model of the universe.
鈥淭here are lots of tantalising clues,鈥� Hinshaw says. But he adds that these are not significant enough to really worry the WMAP team at this time. 鈥淏ut if it turns out the large scale really is local, then yes we would have been fooled by the data. But it would also mean the universe is even more bizarre than we thought.鈥�