time is on my side

whenever i read fiction about time travel, i can't help but get lost in my own thoughts about how it happens. how come we can go back to a past or forward to a future that is ever-continuing and ever-happening? doesn't time flow just once, or does it have a cycle, much like water?

is there a sub-dimension for every moment that allows it to happen forever, so that we can go to it with some sort of time travel mechanism and alter it? if not for each moment, for each period, decade, or era?

what about the possibility of fractured time? about the difference of time's movement in certain areas? that would make time a dimension, wouldn't it?

but really... is time linear, or not?

(time spiral, i want you now.)