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Concept
Mirror matter
Summary
In physics, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter.
Modern physics deals with three basic types of spatial symmetry: reflection, rotation, and translation. The known elementary particles respect rotation and translation symmetry but 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, to determine whether the electrons it emitted were radiated isotopically, like the two gamma rays. Wu performed this experiment in at the National Bureau of Standards in Washington, D.C. after nine months of work. Contrary to most expectations, in December of 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. The theory in its modern form was described in 1991, although the basic idea dates back further. Mirror particles interact amongst themselves in the same way as ordinary particles, except where ordinary particles have left-handed interactions, mirror particles have right-handed interactions. In this way, it turns out that mirror reflection symmetry can exist as an exact symmetry of nature, provided that a "mirror" particle exists for every ordinary particle. Parity can also be spontaneously broken depending on the Higgs potential.
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