Originally Posted by

**wogoga**
You either confuse longitudinal (temporal) coherence with spatial (transverse) coherence, and/or you confuse continuity of phase with continuity of frequency.

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.

Quote:

The only logical possibility of a stable continual drift in phase is a constant frequency.

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.