Brandenberger–Vafa mechanism

In string theory, the Brandenberger–Vafa mechanism is an argument for why the observable universe has one macroscopic timelike and three macroscopic spacelike dimensions. Its importance stems from the fact that string theory contains additional dimensions rolled up in Planck scale, as described by Kaluza–Klein compactification. In simple terms, the argument connected with brane cosmology claims that strings and branes wrapped around compactified dimensions cause an energy barrier, which permits their unfolding. The Brandenberger–Vafa mechanism is named after Robert Brandenberger and Cumrun Vafa, who first described it in 1989.