The black hole information paradox fascinated Hawking for decades, and is the subject of his latest research study.
When Stephen Hawking died in March at the age of 76, the world mourned a beloved and visionary scientist. But it's a comfort that Hawking's latest article was published in the pre-printed ArXiv journal, showing that, even in his final days, he was still with the epic cosmic questions that defined his career.
Titled "Black Hole Entropy and Soft Hair," the article was written by Hawking together with physicists Sasha Haco, Malcolm Perry, and Andrew Strominger.
"We are deeply saddened to lose our dear friend and collaborator Stephen Hawking whose contributions to the physics of black holes remained highly stimulating to the end," Haco, Perry and Strominger said on the second page of the newspaper. "This paper summarizes the state of our long-term project on large difeomorphisms, soft hair, and the quantum structure of black holes until the end of our time together."
The work is the third in a series by the team and addresses Hawking's famous creation: the black hole information paradox. Like many enigmas in physics, the paradox arises from the lack of coherence between quantum field theory and general relativity. On the smaller scales of matter, where atoms and quarks abound, there is a different and seemingly contradictory set of rules for the larger scale of matter, involving stars and galaxies. The search for a "theory of everything" that reconciles these two models is one of the holy grails of modern physics, and was a lifelong fascination for Hawking.
Black holes are notable flash points for this tension between quantum field theory and general relativity. According to the quantum rule book, it should be impossible for information about a particle - its spin, configuration, mass, and other characteristics - to be permanently removed from the universe. But what about the matter that falls into black holes, the objects with the reputation of not letting anything escape once it passes them? Can you clean the information inside black holes?
Hawking suggested that the information could be removed through "Hawking radiation," which is a type of theoretical radiation that can escape from inside a black hole. This process has never been observed empirically, but the radiation would supposedly remove all information about its original properties, and that would violate the rules of the universe as we know them.
In their latest paper, Hawking and his colleagues speculated that a phenomenon called "soft hair" could solve the black hole information paradox. The idea is that traces of light and gravity particles could circle the event horizon, and could store, at the very least, entropic information about the matter that fell into the black hole.
The paper does not solve the black hole information paradox, but it takes us one step closer to understanding some of the most important concepts in the known universe. Hawking's tireless dedication to these questions is a testament to his insatiable curiosity.
Original article (in English)