A ‘defect’ in spacetime may be one of the most curious findings of the data collected from the Wilkinson Anisotropy Probe. What WMAP gave us is the earliest image of the cosmos we have in our repertoire, showing temperature changes across the microwave background thought to be the aftereffect of the Big Bang. When Marcos Cruz (Instituto de Fisica de Cantabria) and colleagues found a cold spot in the data, they launched an investigation to determine what in heaven could be causing it.
A random fluctuation in the data? Possibly, but the Spanish and British team studying the cold spot think the odds on that are only about one percent. A cosmic defect would be quite a find, evidence of exotic phase transitions in the infant universe involving the breaking of symmetry between particles. A cooling universe would see a phase transition when quarks, for example, became distinct from electrons and neutrinos. A homely analogy is to a kitchen freezer, where the defects in ice cubes show how irregularly matter behaves when it undergoes phase change.
Neil Turok (Cambridge), a co-author on the study, explained how such defects should form in the 1990s, pointing out that some of them might be visible in the cosmos today. He describes phase changes this way:
“Imagine a large crowd of people with everyone standing. To any person in it, the crowd looks roughly the same in all directions. Now tell them all to lie down. People would tend to lie in the same direction as their neighbours, but over large distances the direction chosen would vary. In some places, people would be unable to decide which was the best direction to lie in: if everyone lies down pointing directly away from you, you are forced to stand. You are now a defect in the symmetry, a texture.”
A cosmic defect, of course, would have occurred at high temperatures and at enormous energy levels for the particles involved, providing useful indicators of fundamental particles and forces as the cosmos evolved. Turok notes that defects called ‘textures’ could have formed as particles separated from the earliest hot plasma. Turok calls a texture “…a three-dimensional object like a blob of energy,” but adds that “…within the blob the energy fields making up the texture are twisted up.”
Further studies will be required to confirm that what the team has found is indeed a texture, but other hypotheses — scattering of the CMB by large galaxy clusters, for example — are looking less likely. Thus a cold spot in the WMAP data, plausibly a defect in the structure of the vacuum, will surely be a hot topic in upcoming research. The paper is Cruz et al., “Feature in the Cosmic Background Radiation Consistent with a Cosmic Texture,” to be published today on Science Express (abstract).