Nobel laureate Sir Roger Penrose explains one of the most iconic demonstrations of quantum physics: the double-slit experiment. This experiment shows how electrons can act like a wave and a particle. Electrons are fired through two slits and onto a screen. If you place a detector at the slits, you will see each electron act like a particle and travel through one of the slits and hit the screen at the back. But if you don't detect the electrons as they travel through the slits, the screen will sh