Some theories – such as string theory – that attempt to unify all known forces into a single "theory of everything" posit the existence of extra spatial dimensions beyond the three familiar ones.

But string theory has proven stubbornly resistant to experimental tests (although some physicists say it could be tested in the Large Hadron Collider scheduled to open by the end of 2007).

Now, Gary Shiu and Bret Underwood, both physicists at the University of Wisconsin in Madison, US, say the shape of the extra dimensions could leave an imprint in the afterglow of the big bang. This glow, called the cosmic microwave background, reveals the structure of the universe about 370,000 years after the big bang.