| Antimatter is matter composed of antiparticles, such as positrons, antineutrons and antiprotons. |
| Antiparticles have opposite charges and certain other quantum properties of opposite sign. |
| It follows that somewhere antiworlds consisting of antiparticles are bound to wander. No traces of these antiworlds have as yet been found. |
| Antiprotons, the relatively exotic antiparticles of the proton, are difficult to create and were not to be squandered. |
| Note that subatomic particles sometimes have antiparticles, with opposite charge and spin, that are the same ones going backwards in time. |
| Positrons, antiprotons and other antiparticles can be routinely created at particle accelerator labs and can even be trapped and stored for days or weeks at a time. |
