Muon's entourage

Muons owe their current fame to a quirk of quantum mechanics, the nonintuitive rules that underlie the atomic realm. Among other things, quantum theory holds that empty space is not really empty but is in fact boiling with “virtual” particles that flit in and out of existence.

“You might think that it’s possible for a particle to be alone in the world,” Dr. Polly said in a biographical statement posted by Fermilab . “But in fact, it’s not lonely at all. Because of the quantum world, we know every particle is surrounded by an entourage of other particles.”