Seeing as "eternity" isn't something that can be imagined, existence should, theoretically be eternal. However, we don't know that the universe doesn't just collapse/create itself in a continous cycle, and that it hasn't just been doing so eternally.

The problem with this whole disproving/proving God argument is that nothing can ever be proven 100%. If God came down right now and spoke to you, it is still entirely possible that you're in a coma and it's just your imagination. We can never prove anything, EVER. Even if you see a video of someone killing someone else, it is possible theoretically that "they" could just be a shapeshifting alien from a far away galaxy. Nothing is proveable.

For all we know, God could have been puffin on a J for a few bazillion years before creating us. Maybe we're the product of a haze induced trip. I hope so. That'd be so ironic. Imagine that shit, if Bush goes before God and God's like "Shit man, shoulda legalized maui, douche bag," - then throws him in the pit of flames.