Space and Physics

Pear-Shaped Nuclei Explain Lack Of Antimatter And Make Time-Travel Impossible


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockJun 27 2016, 16:19 UTC
The shape of 224Ra deduced from the CERN measurements. ISOLDE/CERN

In physics sometimes proving the obvious is more complex than proving the difficult. The obvious, in this case, is why the universe is made of matter. From your loud neighbor to the furthest galaxy everything is made of matter, but the laws of physics are symmetrical so there should be just as much anti-matter. So why isn't there?


We haven’t got a full picture yet, but an international group of physicists might have found a very important clue. They discovered that some atomic nuclei aren’t symmetric, but are actually pear-shaped.

In a paper published in Physical Review Letters, researchers observed that the isotope Barium-144 is not spherical or oval shaped. In this short-lived atom, protons and neutrons end up distributed in an asymmetrical shape, with more mass at one end of the nucleus than the other. This finding is in contradiction with some nuclear theories, and it could even prove that time travel is impossible.

The pear-shaped distribution of particles violates the so-called CP-symmetry. CP stands for charge and parity. In C-symmetry, if you switch every particle for its antiparticle, they are expected to behave in the same way. Anti-hydrogen will behave like hydrogen, for example. The P-symmetry is about space: A system can be inverted, like in a mirror, and the physics should still be the same.

CP-symmetry suggests that for every particle spinning anticlockwise and decaying in a certain direction, there’s an antiparticle spinning clockwise and decaying in the opposite direction. Violation of C and CP symmetry are proposed and expected to explain the lack of antimatter in the universe, but so far only a handful of examples have been found.


This is the second atom discovered with an asymmetric shape and is another indication that there is more physics beyond what’s currently predicted by the Standard Model of particle physics.

As far as we know, the universe is symmetric under CPT (charge, parity, and time), which adds a time reversal condition. This implies that if CP is violated, then also the T symmetry must be violated so things don’t happen forward and backward in time. This is another example of an obvious thing at our level (broken eggs don’t jump back together) but not in fundamental physics. This discovery strongly indicates that time is indeed broken and it has a specific direction.

"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," co-author Dr Marcus Scheck told the BBC.


The experiment will now be repeated at CERN at its Isotope Separator On Line Detector (ISOLDE) facility in Switzerland, which can produce Barium-144 in huge amounts, in the hope of glimpsing what awaits us beyond the horizon of current physics.

[H/T: BBC News]

Space and Physics
  • antimatter,

  • symmetry,

  • CP violation,

  • Barium-144