haah. that's nice, isn't it? isn't that nice? hey, how come the center of the eye is black? there's no reason for that. everyone got black pupils. why black pupils? because they absorb. because they're like this. they're absorbing. they're absorbing. how much light that goes into your eye that are bouncing around. how much do you think goes back out again? how much light that comes in here and they'll go through all these multiple reflections comes back out the hole? not very much. so the hole to you looks black. okay? because there's what-- this is a net absorber. however, if i put fire in here, made it very, very bright, then you'll see that hole very, very bright, then it would be a net emitter. we call this a black body. a body that absorbs all the radiation that hits it appears black to the eye. we call that a black body. there's a whole science of black body radiation. we won't be getting into that. we talked about this temperature up here. how about like this with-- this is to say if frequency is directly proportional to temperature, then if you double the temperature