From Chad Orzel, writing for Whatever:
Quantum mechanics is one of the most amazing theories in all of science, full of stuff that captures the imagination: zombie cats, divine dice-rolling, spooky actions over vast distances. Maybe the single most amazing thing about it, though, is that we think it’s weird.
That probably seems a strange thing to say, because quantum physics is so weird, but that’s exactly the point. These are the fundamental principles governing the behavior of everything in the universe, and yet they run completely counter to our intuition about how the world works. If these are the basic rules underlying everything, shouldn’t they make sense? How can the entire universe behave according to strictly quantum laws, and yet we’re not intuitively aware of it?
The answer is that quantum behaviors only become obvious when you’re looking at really small things: the behavior of electrons within atoms, say, or smallish groups of atoms moving slowly. As the things you’re looking at get bigger, their quantum-ness sort of blurs out, and we’re left with objects that, to an excellent approximation, behave according to the rules of Newtonian physics. The everyday, human-scale world, is just too big for us to see quantum physics in action.
At least, that’s what we think