Why Is Infinite Velocity Characteristic of Diffusion Processes?

[fisico30]

Hello everyone,

a wave propagates at a speed (group of phase speed), less than the speed of light, no matter what type of wave we are dealing with (electromagnetic, mechanical,...).

Why is infinite velocity characteristic of a diffusion process? What does that mean?
For something to diffuse it always take some finite amount of time..


thanks!

 

[Mapes]

The diffusion model assumes infinite propagation speed to make the equations easier. In practice, the propagation speed is usually much faster than the diffusion speed (though not infinite), so the idealization works pretty well. Consider heat conduction through a metal: the diffusion speed might be on the order of mm/s, while the propagation speed is related to the speed of sound, which may be >100 m/s.