Beside implosion and reverse time what are best theoretical ways to reverse waves?

>>16706514 (OP)
Bound the propagation domain so the wave gets reflected back.

>>16706514 (OP)
for em waves, employ materials with negative index of refraction and wait until the system reaches steady state. wave crests go one way, energy the other.

>>16706514 (OP)
Generate a wave with a phase shift, respective to the first wave, of 18 degrees.

>>16706652
180* degrees

>>16706652
>first wave
>phase shift 180'
that just shifts the phase of the combined wave, which has the same frequency

>>16706661
sin(ax)+sin(bx+180)=a-b

>>16706662
I fucked up because retarded:
A*sin(X)+B*sin(X+180)=A*sin(X)-B*sin(X)...
You get the point I was making...

>>16706514 (OP)
Mirrors

program a non-Newtonian fluid to ensure elevated energy states in each molecule converge instead of diverge

>>16706514 (OP)
there are metamaterials which do this (reflect waves back to their point of origin, and optionally amplify them as well) but iirc it's all in the military domain