An international team of physicists has confirmed the existence of a new, asymmetrical shape of atomic nuclei, a finding that challenges foundational assumptions about the laws of nature and may hold clues to two of cosmology's deepest puzzles: the dominance of matter over antimatter and the one-way direction of time.
The research, published in the journal Physical Review Letters, verifies that the isotope Barium-144 exhibits a pear-shaped configuration, where the nucleus is denser at one end than the other. This is the second isotope known to possess such a shape; the first, Radium-224, was identified at CERN in 2013.
For decades, nuclear physics recognized only three symmetrical shapes: spherical, discus, and rugby ball. These forms align with the principle of CP symmetry, which posits that the laws of physics should remain unchanged if particles are swapped with their antiparticles (charge conjugation) and spatial coordinates are inverted (parity). The newly confirmed pear shape, however, breaks this symmetry, indicating that matter can be distributed unevenly within a nucleus.
“This violates the theory of mirror symmetry and relates to the violation shown in the distribution of matter and antimatter in our Universe,” said Marcus Scheck, a physicist at the University of the West of Scotland and a co-author of the study, in a statement.
The connection to matter-antimatter asymmetry is significant. In the early universe, the Big Bang should have produced equal amounts of matter and antimatter, which would have annihilated each other, leaving a cosmos devoid of matter. Yet, matter clearly prevailed. Physicists have long suspected that a violation of CP symmetry could explain this imbalance, but the known violations are too small to account for the observed surplus.
Astrophysicist Brian Koberlein, who was not involved in the study, explained the potential implication: “It’s been proposed that a violation of CP symmetry could have produced more matter than antimatter, but the currently known violations are not sufficient to produce the amount of matter we see. If there are other avenues of CP violation hidden within pear-shaped nuclei, they could explain this mystery after all.”
The pear-shaped nuclei also offer a novel perspective on the nature of time. Because the uneven mass distribution gives the nucleus a distinct orientation in space, the team suggests this may be linked to a fundamental direction in time.
“We’ve found these nuclei literally point towards a direction in space. This relates to a direction in time, proving there’s a well-defined direction in time and we will always travel from past to present,” Scheck told BBC News.
While the time-travel implication is speculative, it raises intriguing questions about whether the arrow of time is an intrinsic property of the universe rather than an emergent phenomenon. The discovery, if it holds up to further scrutiny, could open new avenues in theoretical physics, prompting a re-evaluation of the symmetries that underpin our understanding of the cosmos.
For now, the confirmation of pear-shaped nuclei stands as a reminder that the universe may be more complex than current models suggest, and that the search for a complete theory of physics is far from over.
