Why do singularities either lie completely in the future or completely in the past? In his book "A Brief History of Time", Prof. Hawking goes on to state that singularities either lie completely in the future or in the past. 
What does that mean in layman terms and why does it so occur? 
I'm a UG math student so please bear with me.
 A: This statement when it comes to cosmology means the causal influence of the big bang or big crunch singularity is associated with the start and end of spacetime. This means there is no singularity at some region of space that generates or destroys particles or maybe more importantly is the emitter or absorber of information. This then means there is no naked singularity. This is not a proven statement, but is a conjecture called the chronology protection and cosmic censorship hypothesis. 
With black holes a similar situation does exist, where the singularity is in a sense to the future of an in-falling particle. This is the case for the Schwarzschild metric. The Kerr-Newman metric is a bit more nuanced, where there is a second horizon in the interior leading into a region where there is a timelike singularity. This is not regarded as that big of a problem because it is all cloaked by event horizons and not visible to the outside world.
A naked timelike singularity in spacetime would mean there are closed timelike curves. An orbit around a singularity would by virtue of a branch cut type of reasoning project you into parallel universes. It is similar to the existence of Riemann sheets connected by a branch cut. All sorts of odd things would take place. Time travel in a sense is similar to cloning quantum states, and the prevention of spacetime singularities makes some sense with respect to the no-cloning theorem of quantum mechanics.
As a result the cosmic censorship and chronology protection hypotheses make some measure of physical sense. It is likely however that a proof of this will in one way or the other involve a complete understanding of quantum gravity.
