Is Time Linear?

    Whilst taking a walk to calm my overheating brain, this is actually the question that popped in my mind. And sent me into a tangle of pondering and mind racing.
    Is time linear?
    I mean, most people seem to operate under this assumption. Once something's done, it's done. Over.
    But is that true, or merely our perception?
    I think it was C.S. Lewis who wondered if all time is happening simultaneously - as in, St. Peter is always denying Jesus in that one period of time. Unfortunately, I can't find the original quote. But I find it an interesting possibility. Especially since if there is a God, He ought to be outside of time, which is not something I can exactly comprehend.
    Or is time circular? Are there infinite chances? When different choices change one thing, which changes another ... except if all of these things change, I wouldn't be me anymore. As much a some situations have sucked and my decisions have hurt, they're a part of my life. Not saying I wouldn't wish for something different, because in some cases I do, but they've still helped shape who I am, for better or worse.
    According to Wikipedia (don't deny you use it too), a lot of ancient cultures believes time was cyclical, but not Judaism of Christianity, since they believe that God created time.
    Then again, also according to Wikipedia, Kant proposed that time might just exist outside of the universe. As in, time is simply the way we process things, not real in itself. Don't ask me to comment more on that one. My head's not wrapping around it, though it's an interesting concept.
   And hey, according to Einstein and other crazy-smart people, space and time might just be the same thing: spacetime.
   Weird. And cool. And headache-inducing, but chock full of the potential to craft a good story.
   So, what about you? What do you think of this funny thing (if it is a thing) called time?

Love,
Kelley