Something that has fascinated me for as long as I have known about them: BLACK HOLES. I don't get it. How can space-time be... nothing? How can something that was there suddenly no longer be there (and I don't mean Apparating, I mean the real deal). The fundamental explanation of a black hole is that an area of space-time that is trapped by gravity. Nothing can escape. Not even light. The "event horizon" is the region from which escape is impossible. Meaning, once you have entered the event horizon, you have passed the point of no return (cue Phantom of the Opera music). Black holes are supposedly created - according to the theory of general relativity - when a mass is compact enough to actually become a black hole by deforming space-time. It is trippy thinking about space-time.... Now add deformed space-time into the mix? Not only that, but also space-time that defies so many other laws and theories about the universe? It's as though space-time really isn't a linear progression of cause to effect, but rather - when viewed from a non-linear, non-progressive standpoint - a... big ball of... wibbly wobbly... timey wimey... stuff.
Don't even get me started on space-time wormholes.