Last article by Stephen Hawking: How to escape from a black hole

Cosmologist and popular science icon Stephen Hawking, who died last March for Einstein's birthday, recently expressed himself in front of the grave in the form of his latest scientific article. For a man on the other side, the document explains how to get out of a black hole.

Purified from its abstract mathematics, paper is an ode to memory, to loss and the oldest of human aspirations, the desire for transcendence. As Bruce Springsteen's convicted Atlantic City character says: "Everything dies, baby, it's a fact, but maybe everything that dies someday comes back."

Dr. Hawking was the manifestation of perseverance; suffering from Lou Gehrig's disease, he managed to conquer the world in a wheelchair. The fate of the material or information captured in a black hole is the one that has defined his career and which has become one of the deepest problems of physics.

Black holes are such dense objects that, according to Einstein's law of general relativity, even light can not escape. In 1974, Mr. Hawking returned these objects and the rest of the physics. He discovered, to his great surprise, that the random quantum effects that rule the microscopic world would cause black holes to leak and possibly explode and disappear.

In the fullness of time (which in many cases would be longer than the current age of the universe), all the mass and energy falling into the hole would come out. But, according to Einstein's classic equations, black holes are of a disturbing simplicity. their only properties are mass, electric charge and kinetic moment. All the other details about what falls in a black hole disappear from the memory banks of the universe. A black hole has no complications – no hair – says the proverb.

So the source of matter and energy coming out of a black hole would be random, Dr. Hawking pointed out in a 1975 paper. If you fall into the hole and come out, you will miss all the details you've created. : man or woman, blue or brown eyes, fan of Yankees or Red Sox. The equation describing this fate is written on Mr. Hawking's gravestone in Westminster Abbey, where it is likely to last a very long time.

It's a kind of reincarnation. If nature can forget you, she could forget everything – a fatal blow to the ability of science to reconstruct the past or predict the future. "It's the past that tells us who we are," said Dr. Hawking at a conference at Harvard a few years ago. "Without that, we lose our identity."

Indeed, Dr. Hawking asserted in his 1975 paper that the paradoxical quantum effects that Einstein once dismissed, claiming that God did not play dice, added an extra forgetfulness to nature. "Not only is God playing dice," Dr. Hawking writes, "but he often throws them where they can not be seen."

These were words that competed with other physicists; It was a fundamental principle that the proverbial film of history could be moved back to reconstruct what happened, for example, in the collision of a pair of subatomic particles in a collider. at high energy.

The last few years have brought a glimmer of hope. Andrew Strominger of Harvard has discovered that, from an exact mathematical point of view – that of a light ray directed to the infinite future – black holes are more complicated than we thought. They have what Dr. Strominger has called "soft hair," in the form of these imaginary rays of light, which can be wrinkled, caressed, twisted, or otherwise arranged by material entering the black hole. In principle, this hair could encode information on the surface of the black hole, recording all these details that Einstein's equations are supposed to be omitted.

In his recent posthumous report, Mr. Hawking and his colleagues tried to show how this optimistic idea could work. In addition to Dr. Hawking, the authors of the paper were Dr. Strominger, as well as Malcolm Perry and Sasha Haco from Cambridge University.

Last years The Pixar / Disney movie "Coco", which I had the opportunity to watch recently with my daughter, tells the story of a young Mexican boy who goes to the land of the dead to find an ancestor who can to help become a musician. Land of the Dead is a lively place, but its inhabitants can only stay there as long as someone remembers them. When memories disappear, animated skeletons disappear

Some astronomers now say that even this pale version of salvation could be in danger. A mysterious force called dark energy accelerates the expansion of the universe. One day, say these experts, if the expansion continues, causing the galaxies to fly faster and faster, the rest of the universe will definitely be out of our sight, and we'll be always. It would be as if we were surrounded by a black hole in which all our information and our memory disappeared.