We investigate topology change in 3D. Using Morse theory and handle decomposition we find the set of elementary cobordisms for 3-manifolds. These are: (i) Ø ↔ S 2 ; (ii) Σ g ↔ Σ g+1 ; (iii) Σ g 1 ⊔ Σ g 2 ↔ Σ g 1 +g 2 , and they have appealing physical interpretations, e.g. Big Bang/Big Crunch, wormhole creation/annihilation and Einstein-Rosen bridge cre-ation/annihilation, respectively. This de...

We show that the dynamics of a spatially closed Friedmann Robertson Walker Universe conformally coupled to a real, free, massive scalar field, is chaotic, for large enough field amplitudes. We do so by proving that this system is integrable under the adiabatic approximation, but that the corresponding KAM tori break up when non adiabatic terms are considered. This finding is confirmed by numeri...

In spherically symmetric charged dust, just like in neutral dust, two kinds of singularity may be present: the Big Bang/Crunch (BB/BC) singularity, and shell crossings. Quite unlike in neutral dust, the BB/BC singularity may be avoided. When the charge density ρe and the mass-energy density ǫ obey |ρe| < De def = √ Gǫ/c2, the conditions that allow the model to avoid the BB/BC singularity necess...

In spherically symmetric charged dust, just like in neutral dust, two kinds of singularity may be present: the Big Bang/Crunch (BB/BC) singularity, and shell crossings. Quite unlike in neutral dust, the BB/BC singularity may be avoided. When the charge density ρe and the mass-energy density ǫ obey |ρe| < De def = √ Gǫ/c2, the conditions that allow the model to avoid the BB/BC singularity necess...

The null-brane background is a simple smooth 1/2 BPS solution of string theory. By tuning a parameter, this background develops a big crunch/big bang type singularity. We construct the DLCQ description of this space-time in terms of a Yang-Mills theory on a time-dependent space-time. Our dual Matrix description provides a nonperturbative framework in which the fate of both (null) time, and the ...

We show that a class of 3+1 dimensional Friedmann-RobertsonWalker cosmologies can be embedded within a variety of solutions of string theory. In some realizations the apparent singularities associated with the big bang or big crunch are resolved at non-singular horizons of higher-dimensional quasi-black hole solutions (with compactified real time); in others plausibly they are resolved at D-bra...