I already know that the pattern created by non coherent sources will constantly change ( from the other answers). I want to understand why this is so
My explanation (which I want to confirm): suppose 2 waves with different frequencies meet perfectly in phase at a point p at time t1. The amplitudes add. Now suppose that in the time one of the waves completes one cycle , the other covers half a cycle(different frequency) . This now creates complete destructive interference at the same point. This can happen for different combinations. Thus the pattern is not observable. Am I missing something?