It seemed to have been kicked into touch, but now the notion of a 鈥渂all-shaped鈥� universe is bouncing back, thanks to a look at the radiation left over from the big bang.
The idea of a balled-up universe was first proposed in 2003 by Jean-Pierre Luminet at the Paris Observatory, France, as a way to explain some odd patterns in the cosmic microwave background 鈥� the afterglow of the big bang. The CMB contains warmer and cooler splotches, which reflect the density variations of the universe in its youth. This fits nicely with cosmological models, except that if you blur the microwave map into big enough pixels, the splotches disappear and the map looks less random than you鈥檇 expect 鈥� and nobody can explain why.
Luminet and his colleagues suggested that this might be because the universe is finite, but is wrapped around on itself. This means that if a spaceship could cross the universe and 鈥渆xit鈥� through one side, it would still be in the same region of space but would 鈥渞e-enter鈥� from the opposite side of the universe. Because of this wrap-around effect, images of everything in the universe would appear to be repeated in the CMB. The best way to explain the data was if the universe is like a dodecahedron 鈥� a ball-like shape with a surface of 12 identical pentagons.
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鈥淎 spaceship could 鈥榚xit鈥� the universe through one side and suddenly find itself 鈥榬e-entering鈥� it from the opposite side鈥�
Last year, this shape of universe seemed to have been ruled out, when Andrew Jaffe and Anastasia Niarchou at Imperial College London performed a more detailed comparison between predictions for the size of the CMB splotches that would be visible in a dodecahedral universe and the actual splotches measured by the Wilkinson Microwave Anisotropy Probe (WMAP). The team found no match (快猫短视频, 7 December 2006, p 34).
But now Boudewijn Roukema, an astronomer at the Nicolaus Copernicus University in Poland, and his colleagues have reached the opposite conclusion, using a different method. Essentially, the team 鈥渃ut鈥� rings from a version of the WMAP data taken from opposite sides of the sky, twisted the cut-out rings relative to each other and looked for matches. They also considered variations in the orientation of the entire dodecahedron over the sky to ensure that some of their pairs of rings were cut from opposite flat sides of the dodecahedron instead of from its corners or edges.
They found that those rings were a close match if one ring was rotated by about 36 degrees around their perpendicular axis (see Diagram). Importantly, calculations for a dodecahedral universe predict that this is the angle you would see. 鈥淚 really didn鈥檛 expect to find anything like this,鈥� says Roukema. The team鈥檚 work has been submitted to the journal Astronomy and Astrophysics. ()
鈥淭he fact that they have found this 36掳 result as predicted is interesting and unexpected,鈥� says Jaffe. He adds that his own earlier analysis did not test the effect of rotating the orientation of the entire dodecahedron and that could explain the discrepancy between their results.
However, Roukema admits that there is still a 9 per cent possibility that the matches he found could have arisen by chance. He hopes that more detailed measurements of the CMB by the European Space Agency鈥檚 Planck satellite, due to be launched later this year, will help settle the question, though there is no guarantee that measurements taken from our restricted vantage point inside the universe could ever reveal the answer. 鈥淪adly, we may never have data good enough for us to know for sure,鈥� says Jaffe.
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