Exactly in what way are photons wave-like? With respect to what property or metric? For example, we often hear the wave-like nature of photons compared to waves in water. Well, wave behavior in water can be measured or observed in respect to mechanical displacement - crests and troughs which can be seen in the Z and other axes. Water waves can be quickly recognized to oscillate the observed/measured height of the water. What property exactly is being oscillated by the wave-like behavior of photons? What most obvious physical property would I look at first to immediately identify that the photon is in fact wave-like? We often use the example of the slit diffraction experiment to show that light is wave-like, as exhibited by the interference pattern. But so that interference pattern is identifiable by its variations in brightness, where brightness at any particular point is the result of number of photons landing there. So since photons arriving at a particular point is due to motion or trajectory, are we saying that it's specifically in their motion or trajectory that photons are wave-like?