Physicists probe why the Universe exists and has matter

A new study rocks prevailing theories on antimatter in the early Universe.

Physicists probe why the Universe exists and has matter

Big Bang and expansion in early Universe.

NASA
  • Scientists from around the world teamed up to study the properties of neutrons.
  • They were able to achieve extremely precise measurements of electric compasses in neutrons.
  • The results challenge current theories of why antimatter and matter didn't destroy each other in the early Universe.

When expressed in physics terms, one of the most important human questions of "Why do I exist?" can be expressed as "Why is there more matter than antimatter?" In other words, during the Big Bang, a tremendous amount of antimatter was created, which could have cancelled out the matter. So why didn't it? In a newly published study, scientists came closer to understanding the answer by measuring properties of neutrons with unprecedented precision.

The team looked at whether a neutron, a fundamental particle of the Universe, can act as an "electric compass" by measuring its EDM (Electric Dipole Moment). This property results from the somewhat asymmetrical shape of a neutron, which is slightly positive at one end and slightly negative at the other, making it like a bar magnet, as explains the press release from the University of Sussex.

The team discovered that the measured EDM of the neutrons was much smaller than the theories predicted, pointing to the possibility that they need to be improved or replaced.

Big Bang and early Universe expansion.

Credit: NASA

Explanations related to matter left over after the Big Bang predict the existence of such "electric compasses" in neutrons, and understanding this phenomenon is essential to figuring out why matter didn't just disappear.

As explained by CERN, the Big Bang was supposed to create an equal amount of matter and antimatter, and yet obviously the things we see around us now are very much made of matter.

Where is the antimatter? Why is there such an asymmetry between matter and antimatter, whose particles are produced in pairs? If ever they were to come in contact, they would destroy each other, leaving only pure energy behind. And yet that's not what ultimately seems to have happened.

Apparatus for Measuring the Neutron's EDM.

Credit: University of Sussex

Professor Philip Harris of the University of Sussex, who led the EDM group, said that their results were a culmination of more than two decades of work by numerous scientists, while their particular experiment took measurements over two years.

"We've found that the "electric dipole moment" is smaller than previously believed," he pointed out. "This helps us to rule out theories about why there is matter left over - because the theories governing the two things are linked."

He also pointed out that their team "set a new international standard for the sensitivity of this experiment." The asymmetry they were able to pinpoint is extremely tiny but their experiment measured it "in such detail that if the asymmetry could be scaled up to the size of a football, then a football scaled up by the same amount would fill the visible Universe," he added.

To achieve this precision, the scientists upgraded an apparatus that has held the world's sensitivity record from 1999 till now. The measurements they achieved were so accurate that they'd compensate even for such factors as a truck driving by their institute, which would disturb the magnetic field enough to affect their experiment.

In total, the scientists measured over 50,000 bunches, each containing more than 10,000 ultracold neutrons, which move relatively slowly.

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Dr. Clark Griffith, who lectures Physics at the University of Sussex, expounded on the multi-disciplinary components involved in the findings:

"This experiment brings together techniques from atomic and low energy nuclear physics, including laser-based optical magnetometry and quantum-spin manipulation," he shared.

These tools allowed the scientists to probe "questions relevant to high-energy particle physics and the fundamental nature of the symmetries underlying the universe," said Dr. van der Grinten.

The scientists hope their search will lead to a "new physics" that would expand upon the Standard Model. Previous developments in measuring EDMs, which stared in the 1950s, resulted in such technology as atomic clocks and MRI scanners.

The team included scientists from the UK's University of Sussex, the Science and Technology Facilities Council's (STFC) Rutherford Appleton Laboratory in the UK, the Paul Scherrer Institute (PSI) in Switzerland, with 18 organizations involved overall.

Their results were published in the February 28, 2020 issue of the journal Physical Review Letters.

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