Antiworld

But possibly there is an antiworld in which, in addition to matter, time is also negative. […] In such an antiworld man would grow younger with time and a broken glass would come together from its fragments.

It follows that somewhere antiworlds consisting of antiparticles are bound to wander. No traces of these antiworlds have as yet been found.

There could be whole antiworlds and antipeople made out of antiparticles. However, if you meet your antiself, don't shake hands!