More than a century after the emergence of his first theory, scientists have completed Einstein’s homework on special relativity in electromagnetism.
Osaka University researchers have shown a relativistic contraction of an electric field caused by fast-moving charged particles, as predicted by Einstein’s theory, which may help improve radiation and particle physics research.
More than a century ago, one of the most famous modern physicists, Albert Einstein, proposed the revolutionary theory of special relativity. Most of everything we know about the universe is based on this theory, however, some of it has not yet been experimentally proven. Scientists from Osaka University’s Institute of Laser Engineering used ultrafast photoelectric measurements for the first time to visualize the contraction of the electric field surrounding a beam of electrons traveling at near the speed of light and demonstrate the generation process.
According to Einstein’s special theory of relativity, one must use a “Lorentz transform” that combines spatial and temporal coordinates in order to accurately describe the motion of objects passing in front of an observer at speeds close to the speed of light. He was able to explain how these transformations led to self-consistent equations of electric and magnetic fields.
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Illustration of the formation process of the planar electric field contraction that accompanies the propagation of a near-light-speed electron beam (shown as an ellipse in the figure). Credit: Masato Ota, Makoto Nakajima
Now, the research team at Osaka University has demonstrated this effect experimentally for the first time. They accomplished this feat by measuring the profile of the Coulomb field in space and time around a high-energy electron beam generated by a linear particle accelerator. Using ultrafast electro-optic sampling, they were able to record the electric field with extremely high temporal resolution.
It has been reported that the Lorentz transformations of time and space as well as those of energy and momentum were demonstrated by time dilation experiments and rest mass energy experiments, respectively. Here, the team looked at a similar relativistic effect called electric-field contraction, which corresponds to the Lorentz transformation of electromagnetic potentials.
“We visualized the contraction of an electric field around an electron beam propagating close to the speed of light,” says Professor Makoto Nakajima, the project leader. In addition, the team observed the process of electric-field contraction right after the electron beam passed through a metal boundary.
When developing the theory of relativity, it is said that Einstein used thought experiments to imagine what it would be like to ride on a wave of light. “There is something poetic about demonstrating the relativistic effect of electric fields more than 100 years after Einstein predicted it,” says Professor Nakajima. “Electric fields were a crucial element in the formation of the theory of relativity in the first place.”
This research, with observations matching closely to Einstein’s predictions of special relativity in electromagnetism, can serve as a platform for measurements of energetic particle beams and other experiments in high-energy physics.
Reference: “Ultrafast visualization of an electric field under the Lorentz transformation” by Masato Ota, Koichi Kan, Soichiro Komada, Youwei Wang, Truth C. Agulto, Valynn Katrine Mag-usara, Yasunobu Arikawa, Makoto R. Asakawa, Youichi Sakawa, Tatsunosuke Matsui and Makoto Nakajima, 20 October 2022,