Stephen Hawking, who died earlier this year, is one of the most-respected names in modern physics. Hawking’s final paper has now been published in the pre-print journal arXiv by colleagues who worked on the research with him. The team finished the research study just a few days before the famous scientist passed away.
Hawking’s final paper was the third in a series of papers looking at black holes, a concept he spent decades studying, particularly the black hole information paradox. As explained by Live Science, black holes are very dense, to the point that they are capable of warping space and time. They are formed when two stars collide or when massive stars collapse onto themselves.
Scientists believe nothing can really escape a black hole, and in the 1970s, Hawking suggested that black holes could have temperatures of their own and could even leak quantum particles. This is known as the “Hawking radiation” effect, which says black holes evaporate over time, leaving a vacuum that looks the same for each black hole, no matter what it sucked in during its lifetime.
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Still, there was a problem with that idea. Black holes pull in a lot of celestial objects during their lifespan, but scientists do not know where those objects go. The laws of physics suggest no material can be destroyed and that it can only change its shape. Thus, if there used to be some kind of information, even in the shape of large celestial objects, we should be able to recover it. Hence, the idea creates a paradox.
In Hawking’s final paper, he and his colleagues wrote about a mechanism they say uses some yet-unproven assumptions.
“It agreed with the famous formula now inscribed on Stephen’s headstone,” senior author Andrew Strominger told Live Science via email.
That formula is also known as “Hawking’s equation,” and it describes how black holes can emit Hawking radiation.
For example, when a black hole swallows some object, its temperature should change, theoretically, as should its entropy — the inability of the system to convert its thermal energy into mechanical work, causing the disorder of its particles. In higher temperatures, the particles will move around at a faster pace, meaning more disorder. The study suggests something known as “soft hair” can really record the entropy of a black hole, as explained by The Guardian.
Malcolm Perry, a co-author on the study and professor of theoretical physics at the University of Cambridge, told The Guardian that Hawking “knew the final result” of their study before he died. He also said that when he tried to explain the results of the study to Hawking a few days before his death, “he simply produced an enormous smile.”
“This is excellent progress, but we have much work yet to do,” Strominger told Live Science.