Cptera

Cptera, a hooded keeper of symmetries, holds three glowing violet orbs joined around a bright centre.

The Physics

Flip all charges (C), mirror space (P) and run time backwards (T), all at once, and any local, Lorentz-invariant quantum field theory looks exactly the same. This CPT theorem was worked out by Julian Schwinger (1951), Gerhart Lüders (1954) and Wolfgang Pauli (1955). It forces a particle and its antiparticle to have exactly equal mass and lifetime.

CPT: C × P × T is an exact symmetry

• C: charge conjugation, particle ↔ antiparticle
• P: parity, mirror reflection of space
• T: time reversal

The separate symmetries can break. In 1957 Wu showed P is violated, and in 1964 Christenson, Cronin, Fitch and Turlay found CP violation in neutral kaon decays (Phys. Rev. Lett. 13, 138). Because CPT holds, CP violation means T violation as well.

Honest caveat: CPT is a theorem about a class of theories, not a proof about nature; experiments test it, for instance by comparing kaon and antikaon or proton and antiproton masses, and so far it holds.

On the sticker

Cptera cups a bright point of light circled by three glowing violet orbs. Printed text: CPTERA with the line CPT. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.