Stephen Hawking never stopped trying to unravel the mysteries surrounding black holes — in fact, he was still working to solve one of them shortly before his d…
Stephen Hawking never stopped trying to unravel the mysteries surrounding black holes — in fact, he was still working to solve one of them shortly before his death. Now, his last research paper on the subject is finally available online through pre-publication website ArXiV, thanks to his co-authors from Cambridge and Harvard. It’s entitled Black Hole Entropy and Soft Hair, and it tackles the black hole paradox. According to Hawking’s co-author Malcolm Perry, the paradox « is perhaps the most puzzling problem in fundamental theoretical physics today » and was the center of the late physicist’s life for decades.
The information paradox arose from Hawking’s theoretical argument back in the 1970s that black holes have a temperature. As such, they’re bound to evaporate over time until there’s nothing left, releasing energy now called the » Hawking Radiation. » See, it’s believed that when an object enters a black hole, its information gets preserved on its surface forever even if it vanishes from sight. If a black hole evaporates, though, then so will that information. That creates a paradox, because according to the rules of quantum physics, information can never be destroyed.
The new paper shows how that information can be preserved by photons called « soft hair » surrounding the edge of black hole, which you might know as the event horizon. According to Hawking, Perry, Andrew Strominger and Sasha Haco, a black hole’s temperature changes when you throw an object (say, a planet’s atoms) into it. The hotter it gets, the more its entropy (its internal disorder) rises. That entropy is what’s preserved in a black hole’s soft hair.
Perry said he called Hawking a few days before he passed away to discuss their work. « It was very difficult for Stephen to communicate and I was put on a loudspeaker to explain where we had got to. When I explained it, he simply produced an enormous smile. I told him we’d got somewhere. He knew the final result, » he told The Guardian. The scientists admit that there’s a lot of work to be done, though: « It’s a step on the way, but it is definitely not the entire answer, » Perry said. « We have slightly fewer puzzles than we had before, but there are definitely some perplexing issues left. »
You can read the paper in full in its pre-published state. Earlier this year, Hawking’s last paper on the multiverse theory was also published in the Journal of High Energy Physics, in case that’s more up your alley.
