Proposed in the early 1860s, Maxwell’s theory of electrodynamics helped elucidate the properties of electromagnetic fields and is used to accurately describe the properties of electricity, magnetism, and light.
Despite its undeniable success, this theory does have limitations. For example, when it is used to calculate the mass of a charged particle, the answer the theory provides is infinite. From experiments, we know that the mass of any particle is finite (otherwise, it would take an infinite force move them), which means that Maxwell’s theory can’t be used to fully explain the properties of subatomic particles.
In the 1930s, two physicists from the University of Cambridge named Max Born and Leopold Infeld proposed a modification to Maxwell’s theory now known as Born-Infeld electrodynamics, in which calculated particle masses becomes finite.
Since then, many alternatives to Maxwell’s theory of electrodynamics have been put forward, but the problem all these theories faced is that their predictions typically deviate significantly from Maxwell’s only for strong fields, such as the electromagnetic field around a black hole. As a result, these theories cannot be tested as these fields cannot be replicated in a lab, leaving scientists without concrete answers.
To shed light on this issue, a team of physicists from Italy and Turkey led by Amodio Carleo of Università di Salerno and Osservatorio Astronomico di Cagliari proposed studying electromagnetic fields that exist not on Earth, but in space, where extreme phenomena, such as black holes and neutron stars or supernova explosions and gamma-ray bursts, can generate very powerful fields.
In a study recently published in Annalen der Physik, they used modifications to Maxwell’s theory of electrodynamics to analyze two types of electromagnetic waves: radiation from matter orbiting a black hole (also known as an accretion disk) and the cosmic microwave background radiation.
Although this microwave background radiation is currently very weak, its properties can provide clues as to what happened during those first moments following the Big Bang, when electromagnetic fields were strong enough for Maxwell’s theory to be reasonably compared to other candidates to test how well it holds up against the alternatives.
To compare the results of their theoretical study with observation, the team has used data collected from space-based telescopes, such as the Planck Observatory. They found that the spectrum of the microwave background as we observe it today is in agreement with Maxwell’s theory and sharply contradicts the predictions made by many of the alternatives, indicating that the true theory of electromagnetism may be very similar to Maxwell’s theory.
Regarding black holes, a “super strong” electromagnetic field is generated by their accretion disks. In the current study, the researchers’ analysis determined that the calculated properties of accretion disk radiation using Maxwell’s theory indeed differs from those predicted by alternative theories, as was expected. The authors didn’t compare their calculations with observations but noted that the future experiments will be another way to find out which theory is the true theory of electromagnetism.
While these results are promising, the scientists need to do more research and compare their results with observations. For example, their calculations are valid for slowly rotating black holes, but many black holes rotate very quickly, and so future research will need to investigate the properties of radiation in these cases.
Only experimental studies may help to find the final answer to the question of the true theory of electromagnetism. To validate any theoretical calculations, it is necessary to more accurately measure the radiation intensity of the accretion disk of a black hole and the parameters of the cosmic microwave background. Hopefully, the necessary methods and instruments will become available in the near future.
Reference: Amodio Carleo, Gaetano Lambiase, and Ali Övgün, Non-Linear Electrodynamics in Blandford–Znajek Energy Extraction, Annalen der Physik (2023). DOI: 10.1002/andp.202200635.
Feature image credit: NASA