If you shine light on a wall, what will be seen is a "patch" with constant intensity. However, if light is viewed as a wave, then it is oscillations of the electromagnetic field changing from 0 to the amplitude and back really fast. So my question is, if I were able to look at the world at extreme slow motion, a quadrillion times slower or so, and I shined a beam of light at a wall, will I see a "patch" with oscillating intensity, with maximum brightness at the peaks of the wave and minimum when the field is 0? If so, is the constant brightness seen normally just our puny mortal eyes capturing only the average of this oscillating brightness?
[Physics] Does light intensity oscillate really fast since it is a wave
electromagnetic-radiationintensityvisible-lightwaves
Best Answer
You would need a coherent beam, because in waves it is not only intensity but also phase that makes a difference. In an incoherent beam, as sunlight, you would not get any changes in this thought experiment, because the average intensity would hold even at wavelength distances.
In a coherent laser beam you should see in your thought experiment what is shown towards the end of this youtube video,(at 2' 09") the sinusoidal in time pattern of impinging intensity . The video draws the oscillating electric field E, and the intensity left on the screen will be $=E^2$, which will also be oscillating in time.
After all, mathematics allows us to materialize thought experiments as this one.