How does light 'know' the shortest path?

The video begins by posing a thought experiment: if you're at point A on a beach and need to reach a friend struggling in the water at point B, which path should you take to minimize travel time? It highlights that running on the beach is faster than swimming. A straight line path might be shortest in distance, but it involves more swimming. Running down the beach to minimize swimming distance increases the overall distance. The optimal path lies somewhere in between, dependent on the relative speeds of running and swimming. This scenario is then linked to Snell's law, which governs how light bends when passing between different mediums. The video explains that light, too, takes the path of least time, a principle famously articulated by Fermat. Instead of simply refracting at an interface, light is presented as exploring all possible paths simultaneously, and the path we observe is the one that takes the least time. This principle is described as one of the greatest illusions in physics, as it implies a form of 'knowledge' or 'intention' in light's behavior.