i read brian greene's book 'the fabric of the cosmos' a long while ago, and i remember being surprised by the notion that one's 'now slice' of reality can angle toward the past OR the future of someone else's. (toward past if moving away, toward future in moving toward someone who is 'stationary'). this doesn't seem to mesh with my understanding of special relativity, because i thought time dilation occurred the same regardless of what direction you were moving-- just as long as you are moving relative to someone else. hence, the whole twin's paradox, which includes a trip away from earth, then a trip back. i would think that 'now slices' should always angle toward the past as someone moves through spacetime. i just watched the nova program (based on the book), and this cognitive dissonance has been reawakened in me. could some please explain, in layman's terms, how this is so? i don't question the truth of brian greene's statements, i just want to fully understand them. thanks.