opposite universe?

I read an article today about blackholes, whiteholes and wormholes. Apparently a whitehole is the exact opposite of a blackhole. Just as a blackhole sucks in everything, a white hole is supposed to spit everything out. But then the article went on to explain why whiteholes don't exist in our universe. [didn't quite grasp that...was speed reading]. The article ended with the theory that there might be an universe where everything is opposite. I'm trying to imagine that. It's odd. for everything to be opposite there has to be a default median. For instance if something is left, the opposite is right. But there has to be a line dawn in between otherwise u can't say where left stops and where right begins. A thing can only be 'left' in relation to a certain spot. That isn't an exact analogy but its the best I can do to explain my problem. If u try to imagine an universe exactly opposite to ours, u'll see what I mean.