>it's not about the time dependence of the wave function. The uncertainty of position and momentum is fundamentally about the Fourier transform, and is definit

>it's not about the time dependence of the wave function. The uncertainty of position and momentum is fundamentally about the Fourier transform, and is definitely about the time dependence of the wave function. You don't even need a full description of quantum mechanics to get the uncertainty principle, "momentum is the Fourier transform of position" gets you there immediately. > This is not true, spreading out is due to dispersion. In this case, for a massive particle, the spreading out is due to the uncertainty principle. That uncertainty principle might be the cause of the dispersion, but you don't need to invoke anything else to get the spreading out. >Why you don't see particle like wave packets on water surface? Also dispersion. In fact you can create particle like waves on a guitar string, which is pretty much dispersionless. Also you can describe massless particles in QM which are also dispersionless. You can create particle like waves on water surface, on a guitar string (which IS dispersive, just not to first order), and in massless particles. They are called solitons, and are a pretty cool area of research.