Backwards Particles Motion

I´m trying to make a sort of “implosion”, how can i make that the particles go to the emitter

Every mesh has an IPO curve option called “Time.” It defines which frame of an animation will play at a given moment. You can make animations speed up, slow down, stop, or go backwards with a Time IPO. Particle systems are basically animations.

To make your particles go backward, select your emitter and open the IPO editor. Select Time in the right panel of the IPO window, then use ctrl-LMB in the IPO window to make a curve with a negative slope.

Cog describes the method in more detail in his Nebula tutorial at