It's often been said that we live in an uncertain world ... but certainly when we're talking about the quantum world, that's a true statement. The laws of quantum physics tell us about a world that is completely at odds with our classical understanding of reality.
Perhaps one of the most challenging concepts to our understanding of the universe is embodied in the Heisenberg uncertainty principle, which places fundamental physical limits (though small ones) upon the degree of precision that we an obtain about an object's physical state. The more precisely you try to measure the position of a particle, the less precisely you can measure that same position's momentum at the same time!
These relationships are shown in the equations to the left, but their physical meaning has implications about the limits of our notion of absolute time and space, because if we are unable to ever measure it, then there's a very real sense in which we're unable to know for sure what's ever happening there!