i once heard some theory (not naming who's in case i'm wrong) that said that the universe is constantly expanding. of course this is due to the heat of everything being so close and hot (ie: galaxies heat the space between them and expand, a bit like steel train tracks). like steel train tracks, as they cool, they shrink back together, making the universe have a pulse (in a way...but very, very, very slow).
this theory also suggested that as the universe cools and contracts, time reverses, making everything go backwards. perhaps de ja vu is us remembering things that have already happened, and that those who are capable of making accurate predictions are better at remembering (like nostradamus, who predicted an evil tyrant called 'hissler'.....any guess who that might be?)