Light

I suppose everybody would agree that light is a very weird thing. Ask several physicists what light is, and none will give the same answer.
But I don't blame them. We just don't know what the hell light is. We pretend we do, but we don't. It's the big paradox, if you think about it. All of our knowledge of the world comes through our eyes, through light, and yet we don't know what light is. But then, how can we know that our knowledge has something to do with the real world? We can't, until we unveil light.