Why there is more matter than its mirror image, antimatter, in the Universe has long baffled physicists. If the two components were more evenly distributed, they would cancel out, leaving nothing but a dull glow in the great nothingness of space. Something fundamental in the way the Universe operates shifted at some point, giving more weight to the mirrored state – or parity – of one type of “stuff” than the other. Without much success, scientists have looked for traces of this crucial period in the cosmic microwave background and gravitational waves left over from the Big Bang.
Three American astronomers from the University of Florida and the Lawrence Berkeley National Laboratory have now identified either a breathtakingly obvious signal of such asymmetry shortly after the beginning of time, or an impossibly specific random error. In addition, their results may finally put to rest the question of whether or not the Universe underwent a phase of inflation shortly after its precipitous creation.
“Since parity violation can only be imprinted on the Universe during inflation,” says Zachary Slepian, an astronomer at the University of Florida, “if what we found is true, it provides smoking-gun evidence for inflation.”
Artistic symmetry and physical symmetry are not so dissimilar. If you turn a square around 90 degrees, you’ll get back the original square. This rotational symmetry makes sense intuitively, yet it should be noted that transformation is not limited to a simple shift in position. Symmetries in physics can be described in terms of time, charge, and parity, which all involve a strict ordering of coordinates (think of translations between your right and left hand). The development of physical forces, in particular the weak force, can be easily explained by a breakdown of the symmetry of parity. In this situation, weak interactions only include the left-handed parts of particles and the right-handed parts of antiparticles. However, the weak force is insufficient to explain our asymmetry because it could not have swayed any preponderance of matter over antimatter.
Jiamin Hou, an astronomer at the University of Florida, and his colleagues were able to find an asymmetry in parity on a much broader scale by studying the orientations of groups of four galaxies across our skies. Since a tetrahedron (a triangle pyramid) is the most basic shape with both left and right sides, it was naturally utilized in sets of four. It is “the simplest shape that cannot be rotated into its mirror image in three dimensions (3D),” as the researchers described it.
If the universe were perfectly symmetrical, we would see an equal number of “left-handed” and “right-handed” galaxy orientations in tetrahedral patterns. However, when researchers used a supercomputer and advanced mathematical models to trace tetrahedrons between a staggering million trillion groups of four brilliant red galaxies, they came to a different conclusion. Both data sets Hou and her team tried were skewed, with only one yielding statistically significant results. Sigma probabilities are used to determine how likely it is that an alternative explanation for the data is correct. At the five sigma level, scientists are extremely certain that their results are not due to random chance alone. A sigma of 7 was assigned to the group’s findings.
Despite finding no evidence of this in their testing, Hou and team warn that an underestimating of noise within their databases could have added spurious galaxy detections that may not correctly reflect the real Universe. With the larger and more precise galaxy data that our new, more capable telescopes, such as the Dark Energy Spectroscopic Instrument (DESI), will give, they aim to redo their calculations. In an episode of Cosmology Talks, Shaun Hotchkiss, a cosmology researcher at the University of Auckland, says that an individual anomaly like this can turn out to be a fluke, but when multiple anomalies link together, it’s more likely that there’s something to it. In this situation, parity violation was recently discovered in cosmic birefringence, where the polarity of a light wave causes it to move differently. However, the certainty of this result is significantly lower. f the result holds up, the next obvious issue is what caused the shift. It could have resulted from a previously unknown force or quantum phenomenon when the compact Universe suddenly expanded.
Big puzzles regarding the cosmos have long intrigued me. Where did everything that exists come from? How do we know the laws by which it develops? Slepian questions why there is anything at all. “This piece of work deals with those fundamental issues.”
