Atoms of
antimatter and matter are perfect mirror images, even when weird quantum phenomena
come into play.
The
energy levels of antihydrogen atoms — the antimatter opposites of hydrogen
atoms — are altered by a quantum effect called the Lamb shift, just as hydrogen atoms are, physicists report February
19 in Nature.
Hydrogen
atoms can exist in several states of higher and lower energy, known as energy
levels. Some subtle quantum effects slightly alter those energy levels. One such
tweak — the Lamb shift — surprised physicists when it was reported in hydrogen atoms in 1947. That discovery helped scientists
form the theory of quantum electrodynamics, which describes how light interacts
with electrically charged particles. The Lamb shift results from flighty
particles that, according to quantum electrodynamics, appear and disappear constantly, even in empty space (SN: 12/9/16).
Now, the
Lamb shift has been spotted in antihydrogen atoms too. The energy shift is
about the same size as in hydrogen atoms, report researchers with the ALPHA experiment (SN: 12/19/16). Located at
the particle physics lab CERN in Geneva, ALPHA also revealed a tweak known as
fine-structure splitting. That effect occurs in hydrogen, too, and results from
spin-orbit coupling, an interaction between the electron’s movement within the
atom and a quantum property called spin.
According
to physicists’ current understanding, matter and antimatter atoms should have
the same energy levels, based on a principle called charge-parity-time, or CPT,
symmetry. This symmetry means that physics would remain the same if the
universe were reflected in a mirror, all antiparticles swapped with particles,
and if time ran backward.
So far, physicists
have never discovered a case where CPT symmetry is violated. But, says
physicist Jeffrey Hangst of Aarhus University in Denmark, spokesperson for the
ALPHA collaboration, “you can never be sure until you actually check.”