What's the easiest way to understand the concept of "wavelength" as applied to a photon? This is one of those things that I've always assumed I knew until I thought about it more deeply. For example, if I had a photon with a wavelength of 100,000 km, then what does this actually mean?
I hope I'm right in assuming that my example photon is not actually smeared out over 100,000 km of space? Since I'm visualising some kind of weird particle (with wavelike properties) I find myself now struggling to grasp what wavelength is... and don't want to have to learn advanced quantum theory to seek resolution.