With his1905 analysis, along with subsequent papers, Einstein showed that light can behave as a stream of particles; when it does, it knocks electrons out of the metal in the way a cue ball breaks a billiard rack.

• 在他1905年的分析及随后的论文里，爱因斯坦说明了光可以像是一束粒子流；如果这样，它会像撞球时母球撞开排好的球一样，将电子打离金属。