Extra dimensions present a new flatness problem
Extra dimensions present a new flatness problem
There is no known fundamental reason to demand as a cosmological initial condition that the bulk possess an $\mathrm{SO}(3,1)$ isometry. On the contrary, one expects bulk curvature terms that violate the $\mathrm{SO}(3,1)$ isometry at early epochs, leading to a violation of Lorentz invariance on our brane. Demanding that the Lorentz …