Simple water waves or simple sinusoidal EM wave (such as AM radio waves) display interference. Both are classical objects because their g^(2) > 1. You can look

Simple water waves or simple sinusoidal EM wave (such as AM radio waves) display interference. Both are classical objects because their g^(2) > 1. You can look at, for instance, the g^(1) function to determine how nicely a particular wave interferes with itself. Second order correlations directly test for the bosonic nature of photons. In quantum light, photons clump together because they are bosons, while in classical light photons are independent of each other and any clumping that happens is purely probabilistic. The g^(2) function tests this degree of clumping.