biological tissue right so we don't have first of all we don't have a guys there how do we solve that problem in biological tissue well let me illustrate the time reversal concept using this cartoon let's say we have a tiger this there's a bottle of liquid right that's gonna cause way front distortion so if you have plane wave way from very nice way from on this side as a propagates through this bottle it becomes this wavy way from right this wave wave wave away from if it's reflected by this standard mirror like the mirror you use every