A GIANT knot may have been found in the fabric of space-time 鈥� almost a decade after cosmologists abandoned the idea that such objects might exist.
Known as 鈥渢opological defects鈥�, such esoteric entities were first proposed in the 1970s, when physicists realised that the processes that gave rise to particles and forces in the early universe could also fracture space, creating twists and knots, dubbed textures, or 鈥渃osmic strings鈥� that stretch across the universe.
The idea attracted attention because Neil Turok at the University of Cambridge, and others, showed that such defects could help form galaxies by acting as gravitational seeds, pulling matter towards them and building a web of galaxy clusters.
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But there was a rival concept, based on the idea that the early universe went through a rapid period of expansion known as inflation, giving rise to regions of relatively dense matter that could also act as seeds for galaxies. By the late 1990s, precise measurements of the cosmic microwave background (CMB) 鈥� the radiation left over from the big bang 鈥� tilted the balance in favour of inflation. 鈥淭hat鈥檚 when everybody fled the defects field,鈥� says cosmologist Carlo Contaldi of Imperial College London.
But now it seems that cosmologists may have turned their back on defects prematurely. String theorists have recently discovered a small selection of models predicting that topological defects exist and could leave imprints on the CMB. 鈥淔inding evidence of defects will really help us rule out a vast number of our models,鈥� says string theorist Renata Kallosh of Stanford University in California.
Just such evidence may now have been found. Even more precise measurements of temperature fluctuations in the CMB by NASA鈥檚 WMAP satellite have revealed a perplexingly large 鈥渃old spot鈥�. Marcos Cruz at Cantabria University in Spain and colleagues calculated the probability of the spot occurring by chance as less than 2 per cent. The team then noticed that in 1989 Turok had predicted that a space-time texture would produce a cold spot of exactly this size, and so they joined Turok to create computer models to show how the texture could indeed create such a cold spot as it unravels. Turok presented the findings at a conference on particles, strings and cosmology at Imperial College London last week.
鈥淭urok had predicted that a space-time twist would produce a cold spot of exactly this size鈥�
Turok knows it will take more than just one cold spot to convince cosmologists that textures exist. His calculations suggest that there should be other, smaller cold spots, created by smaller textures, but unfortunately these are too small to show up in the WMAP data. So Turok is calculating texture signatures that could be measured by ESA鈥檚 Planck satellite, due to be launched in 2008.
鈥淭urok鈥檚 idea is really cool,鈥� says Hiranya Peiris, a member of the WMAP collaboration at the University of Chicago in Illinois. But she cautions that the cold spot could just be a blip in the WMAP data. 鈥淚鈥檓 glad Turok鈥檚 making predictions for Planck. He鈥檚 making an extraordinary claim and it will take extraordinary evidence to support it.鈥�
