Mirror matter

In theoretical physics, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter that mirrors the properties of ordinary matter but interacts with it only via gravity or weak interaction.

Overview

Modern physics deals with three basic types of spatial symmetry: reflection, rotation, and translation. The known elementary particles respect rotational symmetry and translational symmetry but some do not respect mirror reflection symmetry (also called P-symmetry or parity). Of the four fundamental interactions—electromagnetism, the strong interaction, the weak interaction, and gravity—only the weak interaction breaks parity.

Parity violation in weak interactions was first postulated by Tsung-Dao Lee and Chen-Ning Yang in 1956 as a solution to the τ-θ puzzle. In consultation with the experimental physicist Chien-Shiung Wu a number of possibilities were proposed to test whether the weak interaction was in fact invariant under parity. One of the group's suggestions involved monitoring the decay of cobalt-60,

27

60

Co

→

28

60

Ni

+

e

−

+

ν

¯

e

+

2

γ

{\displaystyle {}_{27}^{60}{\text{Co}}\rightarrow {}_{28}^{60}{\text{Ni}}+e^{-}+{\bar {\nu }}_{e}+2{\gamma }}

to determine whether the electrons it emitted were radiated isotropically, like the two gamma rays. Wu performed this experiment at the National Bureau of Standards in Washington, D.C. after nine months of work. Contrary to most expectations, in December 1956 she and her team observed anisotropic electron radiation, proving that the weak interactions of the known particles violate parity.

However, parity symmetry can be restored as a fundamental symmetry of nature if the particle content is enlarged so that every particle has a mirror partner.