Electrons are absolutely round, and some physicists are unhappy with this.
The new experiment captured the most detailed images of electrons to date. Scientists have used lasers to detect evidence of particles surrounding the particles. By lighting molecules, the researchers were able to understand how subatomic particles alter the distribution of an electron's charge.
The symmetrical circular shape of the electrons suggests that the invisible particles are not large enough to change the shape of the electrons to oval. The results of the study reaffirm an old physical theory known as the Standard Model, which describes how particles and forces in the universe behave.
And at the same time, the new discovery could turn several theories of alternative physics that try to find missing information about phenomena that the Standard Model cannot explain.
Since subatomic particles cannot be observed directly, scientists learn about them through circumstantial evidence. By observing what happens in a vacuum around negatively charged electrons believed to be surrounded by clouds of as yet invisible particles, researchers can create models for the behavior of subatoms.
The Standard Model describes the interactions between all the building blocks of matter, as well as the forces that act on subatomic particles. For decades, this theory has successfully predicted how matter will behave.
However, there are several points that the model is unable to explain. For example, dark matter, a mysterious and invisible substance that is capable of gravitational attraction, but does not emit light. Also, the model does not explain gravity, as well as other fundamental forces that affect matter.
Alternative physics theories offer answers where the Standard Model fails. The Standard Model predicts that the particles surrounding the electron affect its shape, but on such an infinitesimal scale that it is almost impossible to detect using existing technology.
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But other theories say there are still undisclosed heavy particles. For example, the supersymmetric standard model states that every particle in the standard model has an antimatter partner. These hypothetical heavy particles can deform electrons to the point that researchers can see. To test these predictions, the new experiment looked at electrons at 10 times the resolution of a previous attempt in 2014.
Researchers were looking for an elusive and unproven phenomenon called the electric dipole moment, in which the spherical shape of an electron appears to be deformed - “crushed at one end and convex at the other,” DeMille explains. This form should be a consequence of the influence of heavy particles on the electron charge.
These particles would be “many, many orders of magnitude stronger” than the particles predicted by the Standard Model, so it would be “a compelling way to prove whether something is happening outside of the explanations of the Standard Model,” DeMille says.
For the new study, the researchers used beams of cold thorium oxide molecules at a rate of 1 million per pulse 50 times per second in a relatively small chamber in the basement of Harvard University. Scientists fired lasers at molecules and studied how light would be reflected from them; refraction in light would indicate an electric dipole moment.
But there was no distortion in reflected light, and this result casts doubt on physical theories that predict heavy particles swarming around electrons. These particles may exist, but are likely to differ from what is described in existing theories.
“Our result tells the scientific community to seriously rethink alternative theories,” says DeMille.
While the experiment evaluated the behavior of particles around electrons, it also provided important insights for the search for dark matter. Like subatomic particles, dark matter cannot be observed directly. But astrophysicists know it exists because they have observed its gravitational influence on stars, planets, and light.
“Much like us, astrophysicists look to where many theories have predicted a signal,” DeMille says. "And while they see nothing, and we see nothing."
Both dark matter and new subatomic particles that the Standard Model did not predict remain to be seen directly; yet a growing body of conclusive evidence suggests that these phenomena exist. But before scientists find them, it is probably worth discarding some old theories.
“Predictions about what subatomic particles look like are looking increasingly implausible,” says DeMille.
