Published: July 6, 2023

Illustration of multiple molecules made up of two atoms represented by blue and red spheres

Illustration showing the electrons in a cloud of hafnium fluoride ions. (Credit: Steven Burrows/JILA)

In the first moments of our universe, countless numbers of protons, neutrons and electrons formed alongside their antimatter counterparts. As the universe expanded and cooled, almost all these matter and antimatter particles met and annihilated each other, leaving only photons, or flashes of light, in their wake. 

And if the universe were perfectly symmetrical, with equal amounts of matter and antimatter, that would be the end of the story—and we would never have existed. But there must have been an imbalance—some leftover protons, neutrons and electrons— that formed atoms, molecules, stars, planets, galaxies and eventually, people. 

“If the universe had been perfectly symmetrical, then there would be nothing left but light. This is a hugely important moment in history. Suddenly there is stuff in the universe, and the question is, why?” said Eric Cornell, a fellow of the National Institute of Standards and Technology (NIST) and JILA. “Why do we have this asymmetry?”

The mathematical theories and equations that explain our universe call for symmetry. Particle theorists have refined these theories to tackle the presence of asymmetry. But without evidence, those theories are just math, Cornell explains, so experimental physicists including his group at JILA have been looking at fundamental particles such as electrons for signs of asymmetry. 

Now, the JILA group has made a record-breaking measurement of electrons, narrowing down the search for where this asymmetry came from. Its findings have been published in Science.

JILA is jointly operated by NIST and CU Boulder.

Read the full story from NIST