Past Gas

Sometimes I wonder whether the past still exists. I seem so sure of it, and I define myself (and my self-esteem) largely by what I've done (what I remember doing). But does the past exist at all (outside of memory)? I mean metaphysically; how can it exist? If all that is is now then then 'that stuff ain't real'. It's not just that it's a nice idea to strive to 'live in the now'; it's that there is nothing but now. So live.