Originally Posted by wogoga
I have done nothing of the sort. Shifting the phase is the same thing as shifting the frequency. If you remain at the same frequency, the phase is stable.
A constant-rate phase shift is exactly the same as being at a slightly shifted (but constant) frequency. But the drift is not
stable. The phase change is random, and it's caused by random fluctuations in the frequency. It's only constant in the sense that it's always changing, not in the sense that its rate of change is constant.
Plus, you're wrong about superpositions decohering over a distance. They don't. The longitudinal wave profile of plane-wave radiation traveling through a vacuum, whether it's monochromatic or not, will not
change as it propagates, because a vacuum is non-dispersive. You have a fundamental misunderstanding of wave mechanics.