And this is seen in space when light travels from the sun, the hot object to the Earth, the cooler object, the waves travel in a vacuum in the absence of molecules. And that's because waves, electromagnetic waves, are actually energy bundles that carry themselves from a hot object to a cool object, okay? And it is radiation that heats the Earth. When we spoke earlier about conduction, we also mentioned rate of energy transfer. Here we can also talk about a similar concept, rate of energy transfer. But the formula here, it's different.