Quantum Ripples in a Particle Stream
Throw a stone into a pond, and ripples spread across the water. Throw two stones nearby, and the ripples intersect, creating a pattern of reinforced and canceled waves. That's interference.
Causality: Why It Can't Be Measured
The quantum world plays a strange game with causality. If in everyday life salt is always added to soup before serving, here the ingredients end up in the bowl at the same time, and the chef doesn't remember the order. Physicists asked: can we measure this 'recipe'? The answer is no.