h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I really need some coffee.

Hey, I was reading last month's Scientific American today. Anyone read that article on how to build your own time machine? Pretty interesting stuff. I hate physics, I only like the stuff that challenges the current scientific paradigm. Anyway, the author showed this this problem using pool balls: If you shot a pool ball into your time-wormhole, what if it came out in the past just in time to knock itself out of place, causing itself to never enter the wormwhole in the first place? In that case, the existance of the "second" ball doesn't make any sense. The author holds that the situation would still have to adhere to the rules of logic, so somehow, the "second" ball would wind up knocking the "first" ball into the wormhole. Well, it makes no sense to me, but I figure you have to end up with one of two outcomes: either you get infinite energy, or a real nifty way to get a whole bunch of pool balls.