(Credit: Associated Press)
Stephen Hawking, who died March 14, leaving behind a huge legacy of the work of an astrophysicist, science communicator, activist, and the figure of the pop-culture admiration. And on the day of his death, a question that he raised and worked until the last years of his life remains unanswered: Can the information really be lost from the universe?
Hawking is the most famous paper, “Black Hole Explosions?,” published 44 years ago, in 1974, took an axe to the whole idea of black holes as physicists had already understood. And it was Hawking’s first whack on that fundamental question.
“Classically, a black hole should be “perfectly cold” in the sense that it absorbs everything, but emits nothing. This is how they were understood in the early 1970s,” Robert McNees, a physicist at Loyola University in Chicago, wrote in an e-mail. [Stephen Hawking’s Most Intriguing statements about Humanity, Aliens, and Women]
A black hole like that would radiate no energy and no matter could escape. It would just… exist, cold, silent, and eternal. Hawking is paper made of the black holes in life — and perhaps mortal.
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“When Stephen is regarded as the quantum mechanical effects in the middle of the’ 70s, he discovered that the black holes should, in principle, radiate, as if they were thermal objects with a temperature,” McNees told Live Science. “As they exude energy than their mass will decrease. And he found that if this happens, as they shrink, the temperature is going up and blasting them even faster.”
Eventually, perhaps, the black hole would disappear, or shrink to a small nubbin. Without fully reconcile relativity and quantum mechanics in a robust theory of “quantum gravity” (what physicists call a “theory of everything”), the final stage of black hole evaporation remains a mystery.
“The problem is that, according to his calculations, the radiation is perfectly thermal. It does not store any information about the state of the material that formed the black hole, and this would be contrary to a fundamental rule in quantum mechanics,” McNees wrote.
Quantum physics requires that the entire future and the past of each particle should be, in principle, possible to figure out and the link by means of a series of consecutive, causal, probabilistic events. But if a black hole shows an undifferentiated soup of particles with their information — their history — unrecoverably deleted, then that claim is fundamentally broken. [Stephen Hawking is the Most Far-Out Ideas About Black Holes]
“[Physicists call this], the black hole information paradox, “and attempts to solve it have driven much of the work in the quantum gravity since it was first organized, the” McNees wrote.
Hawking, who was already an accomplished physicist by 1974. And a lot of short biographies imply that, after the publication of his 1988 popular science book “A Brief History of Time” his most important scientific work was behind him. Hawking continued to produce important and controversial scientific articles, most recently in this decade, a conflict with the paradox he introduced decades earlier.
The most dramatic late-career paper Hawking wrote proposed that the black holes as they have classically understood, does not exist.
In “Information Preservation and weather forecasting for Black Holes”, published in 2014, he proposed that the “event horizon” around the black hole, the point beyond, where not even light can escape, does not really exist. Instead, he wrote, there is just an “apparent” horizon of the trapped light that can disappear and let the light to escape.
“The absence of event horizons means that there are no black holes-in the sense of regimes from which light can’t escape to infinity,” Hawking wrote.
He also suggested a number of fundamental conceptual problems with some of the features physicists had been attributed to black holes, such as “firewalls” to their limits to destroy the observers who are trying to enter.
That was not Hawking’s latest word of the science. As recently as 2016, Hawking published a paper with the Cambridge University physicist Malcolm Perry and Harvard University physicist Andrew Strominger “Soft Hair on Black Holes.”
The research team found that black holes are surrounded by “soft” or zero-energy particles, which they call her. That to her, that she wrote, saves the lost information of particles emitted by black holes to “holographic boards” beyond the black holes’ border regions. So the information, while moving, is never really lost.
“A full description of the holographic plate and the resolution of the information paradox remains a challenge, which we have presented new and concrete tools to address,” they wrote.
Even at the end of his life, He remained very much a working scientist, presenting ideas that advanced the field, and ideas of his colleagues rejected.
“It is my impression that the 2014 paper is not generally accepted. In 2016, the paper, on the other hand, that is working with Perry and Strominger, is a direction that people are still actively working on,” McNees wrote.
“The black hole information paradox is one of the most important questions for people who work on quantum gravity. And, if it remains unanswered, I think it remains the most interesting question that [Falconry] increased.”
Originally published on Live Science.