Hawk­ing sheds new light on black holes

China Daily (USA) - - WORLD - By EARLE GALE in Lon­don earle@mail.chi­nadai­lyuk.com

The sci­en­tific pa­per oc­cu­py­ing the mind of Bri­tish physi­cist and cos­mol­o­gist Stephen Hawk­ing when he died in March aged 76 has been fin­ished by col­leagues from Cam­bridge and Har­vard and pub­lished on­line.

Mal­colm Perry, a pro­fes­sor of the­o­ret­i­cal physics at Cam­bridge and a co-au­thor of Black Hole En­tropy and Soft Hair, told The Guardian news­pa­per that its sub­ject, known as “the in­for­ma­tion para­dox”, was “at the cen­ter of Hawk­ing’s life” for 40 years.

“The dif­fi­culty is that if you throw some­thing into a black hole, it looks like it dis­ap­pears,” the pa­per quoted Perry as say­ing. “How could the in­for­ma­tion in that ob­ject ever be re­cov­ered if the black hole then dis­ap­pears it­self ?”

The quandary be­gan with Al­bert Ein­stein who, in 1915, pub­lished his the­ory of gen­eral rel­a­tiv­ity, de­scrib­ing how grav­ity arises from the space­time-bend­ing ef­fects of mat­ter and ex­plain­ing why plan­ets cir­cle the sun. Ein­stein also said black holes can be de­scribed by only three things: Their mass, their charge, and their spin.

In Hawk­ing’s fi­nal pa­per, he and his col­lab­o­ra­tors add to Ein­stein’s the­o­ries about black holes by try­ing to un­der­stand what hap­pens to in­for­ma­tion when ob­jects fall into black holes, the so-called in­for­ma­tion para­dox. The anal­y­sis was com­pleted days be­fore Hawk­ing’s death and Perry said Hawk­ing was de­lighted with the con­clu­sion.

“It was very dif­fi­cult for Stephen to com­mu­ni­cate and I was put on a loud­speaker to ex­plain where we had got to,” Perry said. “When I ex­plained it, he sim­ply pro­duced an enor­mous smile. I told him we’d got some­where. He knew the fi­nal re­sult.”

In the pa­per, the team says black holes should be de­scribed by four at­tributes, not three, be­cause they also have a tem­per­a­ture, and it is the fact that hot ob­jects lose heat into space that means black holes are des­tined to evap­o­rate out of ex­is­tence.

How­ever, the rules of the quantum world say in­for­ma­tion can never be lost and Hawk­ing and his col­leagues con­tend that at least some in­for­ma­tion may be recorded by pho­tons known as “soft hair” that sur­round the black hole’s event hori­zon, which is the point at which light can­not es­cape the in­tense grav­i­ta­tional pull.

Physi­cists who worked on the pa­per in­cluded Sasha Haco from Cam­bridge and An­drew Stro­minger from Har­vard.

Perry said the pa­per is an im­por­tant step in un­der­stand­ing black holes but that “a lot more work” needs to be done.

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