DANIEL: I’ve studied relativistic physics my entire life. Jack, I’ve spent years just staring at equations. One thing emerged over and over. One simple rule: No matter what, you can’t change the past. You can’t do it. Whatever happened, happened. In laymen’s terms....
[Daniel tosses a small stone in the creek]
DANIEL: The creek keeps washing over any pebble thrown into it. A pebble represents a change. A small change. The creek is time. Okay now, after Charlotte died I left the Island, I used the DHARMA facilities in Anne Arbor to recreate my entire life’s work. For three years I stared at these equations again and again and again. And then I finally realized, I’ve been spending so much time focused on the constants I forgot about the variables. Do you know what the variables in these equations are, Jack?
JACK: [smiles] No. No I don’t.
DANIEL: Us. We’re the variables. People. We think, we reason, we make choices, we have free will, if we ... if we accept that we can't ... can’t change the past, can’t do anything about it then we don’t even bother trying. But, if we decide, if we believe that we can change the past ... then we don’t use pebbles, Jack.
[Daniel picks up a big rock]
DANIEL: We use boulders.
[Daniel throws the rock in the creek]
DANIEL: See? If you drop a big enough rock into a creek you create a dam, right? And then that creek ... changes.