Researchers at Northwestern, Harvard and Yale universities have conducted a new study to examine the shape of an electron's charge, and have confirmed that - with unprecedented precision - it is perfectly spherical.
After conducting the study, the scientists claimed that if they'd found it had a slightly 'squashed' charge, it could have indicated unknown, hard-to-detect heavy particles in the electron's presence. This would have also raised questions over some of the fundamentals of modern physics.
The Standard Model as it stands cannot possibly be right because it cannot predict why the universe exists
"If we had discovered that the shape wasn't round, that would be the biggest headline in physics for the past several decades," said Gerald Gabrielse, who led the research at Northwestern.
"But our finding is still just as scientifically significant because it strengthens the Standard Model of particle physics and excludes alternative models."
The Standard Model is a longstanding theory where particle physics describes most of the fundamental forces and particles in the universe. It provides a model for a mathematical picture of reality, and no laboratory experiments performed so far have contradicted it.
However, this lack of contradiction has been puzzling physicists for decades.
Almost all of the alternative models say that the electron charge may well be 'squished'
"The Standard Model [of particle physics] as it stands cannot possibly be right because it cannot predict why the universe exists," said Gabrielse, the Board of Trustees professor of physics at Northwestern.
"That's a pretty big loophole."
Gabrielse and his colleagues have spent their careers trying to close this loophole by examining the Standard Model's predictions and then trying to confirm them through table-top experiments in the laboratory.
"Almost all of the alternative models say that the electron charge may well be 'squished', but we just haven't looked sensitively enough," added Gabrielse, who is also the founding director of Northwestern's new Center for Fundamental Physics.
The team fired a beam of cold thorium-oxide molecules into a chamber the size of a large desk. They then studied the light emitted from the molecules
"That's why we decided to look there with a higher precision than ever realised before."
To do this, the team fired a beam of cold thorium-oxide molecules into a chamber the size of a large desk. They then studied the light emitted from the molecules. Twisting light would indicate an electric dipole moment. When the light did not twist, the research team concluded that the electron's shape was, in fact, round, confirming the Standard Model's prediction.
No evidence of an electric dipole moment means no evidence of those hypothetical heavier particles. If these particles do exist at all, their properties differ from those predicted by theorists.
"Our result tells the scientific community that we need to seriously rethink some of the alternative theories," DeMille said.
The research teams plan to keep tuning their instrument to make more and more precise measurements. Until they find evidence to the contrary, the electron's round shape - and the universe's mysteries - will remain.
"We know the Standard Model is wrong, but we can't seem to find where it's wrong. It's like a huge mystery novel," Gabrielse said.
"We should be very careful about making assumptions that we're getting closer to solving the mystery, but I do have considerable hope that we're getting closer at this level of precision."
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