If there is no such thing as the future because it hasn't happened yet, how can someone travel back in time to where we are..? How could we travel forward in time when that time doesn't exist..? It hasn't happened yet. On top of that, there is no past either and we could never travel there because of that very reason. We only think of the past because our brains remember what was the present. There is no past and there is no future. The Sex Pistols said it so well
;)