>>38
How to make something out of "nothing", and then back again.
Large amount of massless energy ==> small amount of mass
Particle/antiparticle collision ==> return to original state.

It's not like He (or bigger) atoms are popping up randomly, it's opposing pairs of small particles and their antiparticles who only make something positive or negative when permanently separated from each other (like if one gets sucked into a black hole or something)