''"on the request of your grandfather, you went back in time using a time machine made by your grandfather to kill said
grandfather with a knife given by you by the same grandfather in the present. so yeah, who are you again?"''
"So...uh, don't you ever worry 'bout paradox?"
"Naw, I've got a topical cream for that."
A paradox can be paradoctored.
"I hate time travel."
"One of the major problems encountered in time travel is not that of accidentally becoming your own father or mother. There is no problem involved in becoming your own father or mother that a broadminded and well-adjusted family can't cope with. There is also no problem about changing the course of history...the course of history does not change because it all fits together like a jigsaw. All the important changes have happened before the things they were supposed to change and it all sorts itself out in the end."
— Hitchhiker's Guide
, The Restaurant At The End Of The Universe
"No matter what, you can't die, because would mean that I would cease to exist, right? But, I was here before when I was you. I'm so confused!"
"See? Five minutes before I shall place it there, it is there!"
His other colleague frowned at the cube. "But," he said, "what if, now that it has already appeared five minutes before you place it there, you should change your mind about doing so and not place it there at three o'clock? Wouldn't there be a paradox of some sort involved?"
"The best way to deal with temporal paradoxes is not to think about them."
Dr. Emmett 'Doc' Brown: ...the encounter could create a time paradox, the result of which could cause a chain reaction that would unravel the very fabric of the space-time continuum and destroy the entire universe! Granted that's a worst case scenario. The destruction might in fact be very localized, limited to merely our own galaxy.
"Anyone who has not gotten a headache contemplating the paradoxes of time travel has never really understood the concept."
Sisko: "No, no, not at all."
Agent #1: "Good."
Agent #2: "We hate those."
Future Shego: Listen, we don't have a lot of time. Ok, actually, we do. Well... we will.
Present Shego: When you want to make sense, just let me know.
Future Shego: Grab the Time Monkey.
Present Shego: Why?
Future Shego: You need the Time Monkey.
Present Shego: Can't I just use yours?
Future Shego: No, this is mine! OK, well, actually it's yours too. I mean, well, it's the one you're gonna to steal, so technically...
"If nature abhors a vacuum, nature loathes, abominates, and despises a paradox, and I haven't much stomach for them myself."
"This next test may involve trace amounts of time travel, so, word of advice, if you meet yourself on the testing track, don't make eye contact. Lab boys tell me that'll wipe out time. Entirely. Forward and backward...."