Do two photons approach each other at twice the speed of light, 2 c ? This popular question highlights the distinction between relative and closing speeds in Newtonian physics and their interpretation within the context of special relativity. In everyday Newtonian usage, when we mention that two cars are approaching each other at, say, 100 km/h, we typically refer to the closing speed, determined as the sum of the speeds of both cars. However, the relative speed is also calc