A link between particle physics and gravity applies to Hawking radiation
Physicists have found a new way to investigate a long-standing enigma of black holes using the mathematics of particle physics.
Black holes are not entirely black. They emit a light fog of particles called Hawking radiationa concept central to the major puzzles swirling around black holes. But Hawking radiation is so weak that it is not possible to observe it directly.
Today, several teams of physicists have found a new angle on the phenomenon. They take advantage of a mathematical link between two seemingly distinct types of physics – a link known as double copying.
Theories of fundamental physics fall into two distinct camps: A theory called the standard model describes the physics of subatomic particles, while the general theory of relativity describes gravity. The double copy establishes a mathematical link between these two apparently distinct theories. This relationship can be used as a mathematical translation tool, moving a calculation from one “language” of physics to another. The exchange may facilitate calculations or reveal new information.
According to double copying, many phenomena in general relativity are mathematically equivalent to those of certain particles in the Standard Model, with one difference: in general relativity, there are two copies of a particular part of the equation. Since this relationship was discovered in 2010 and developed in the years since, it has become a useful tool for understanding various gravitational effects.
“It allows us to calculate things we’ve never been able to calculate before, just by recycling the results in an intelligent way,” says theoretical physicist Chris White of Queen Mary University of London.
Until now, scientists did not have an analogous standard model for Hawking radiation based on double copying. Finding one “is a major advance for these techniques,” says theoretical physicist Cynthia Keeler of Arizona State University in Tempe, who was not involved in the research. That’s because Hawking radiation connects the big and the small, with huge black holes emitting tiny particles. The finding shows that double copying can bridge both scales.
In an article accepted by the Journal of High Energy Physics, White and colleagues determined how Hawking radiation translates into the language of the Standard Model. In this language, the mathematical alter ego of Hawking radiation is a charged particle diffusing onto a spherical shell of charged matter collapsing in on itself. This is mathematically equivalent to the emission of a Hawking radiation particle.
Two other teams came mainly to the same conclusionfinding a mathematical analogue of Hawking radiation. Reported in February in Physical examination letters, These two papers show that the intrinsic physics of black holes is contained in the standard model of particle physics, explains theoretical physicist Anton Ilderton of the University of Edinburgh, co-author of one of the studies. “These papers have started to show how to extract this information from the Standard Model.”
Scientists thus hope to explore even more impenetrable characteristics of black holes. For example, researchers would also like to find a standard analog model for the event horizon of a black holethe boundary beyond which nothing that enters can escape. “That’s the big question we’d like to answer,” says theoretical physicist Uri Kol of Harvard University, who was not involved in the research. “These articles provide tools that can be used to answer this question.»
The Hawking radiation alone is intriguing enough for further study. After physicist Stephen Hawking conceived of radiation in 1974, physicists realized it involved a puzzle. When a black hole spews out particles, it shrinks and eventually fades away. Physicists don’t understand what happens to the information they have swallowed. According to quantum physics, information cannot be destroyed. Studying the characteristics of Hawking radiation translated into the language of the Standard Model can help shed light on what is happening.
Hawking radiation is a “Stone rosette” problem, says theoretical physicist John Joseph Carrasco of Northwestern University in Evanston, Illinois, co-author of one of the Physical Examination Letters papers. By studying it, physicists could better master the language of gravity.