by Anaswara.J.S.(2016-2019)
anaswarajs@gmail.com
“Most physicists work with equations using pen and paper, but because of his disability, Hawking found it easier to visualize things in his mind.” – Alan Lightman
Despite his profound disability, Stephen Hawking inspired millions around the world. But Hawking, who died on 14-March-2018, Wednesday at the age of 76, made his greatest contributions as a theoretical physicist. His books, papers, and lectures turned generations into armchair cosmologists and transformed our understanding of the universe — especially with regard to black holes .
The first black hole was discovered in 1971, and we now believe that 100 million or so are sprinkled across the universe. Most astronomers now believe that black holes lie at the center of most, if not all, galaxies, including our own Milky Way.
But at the time of Hawking’s birth in 1942, black holes were little more than a mathematical quirk — a prediction of Albert Einstein’s 1916 theory of general relativity . The term black hole itself wasn’t coined until the 1960s, when scientists began to realize that Einstein’s math actually described real objects — gaping abysses of raw gravitational force so powerful that they suck in dust, gas, and stars and stop light itself from escaping.
In the 1960s, Hawking and fellow British physicist Roger Penrose built on Einstein’s theories to describe the physical characteristics of black holes and showed that when a star collapses it forms an infinitely dense point called a singularity — the birth of a black hole.
Hawking also helped confirm the Big Bang theory. Drawing once again from Einstein’s equations, he and Penrose showed that 13.8 billion years ago the universe emerged violently from a single compressed point no bigger than an atom.
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. A black hole like that would radiate no energy, and no matter could escape from it. It would just… exist, cold, silent, and eternal.
When Hawking considered quantum mechanical effects in the mid-70s, he discovered that black holes should, in principle, radiate as if they were thermal objects with a temperature.
“If they radiate energy then their mass will decrease. And he found that as this happens, as they shrink, their temperature goes up and they radiate even faster.” Eventually, perhaps, the black hole would disappear entirely, or shrink to a little nubbin. Without fully reconciling relativity and quantum mechanics in a robust theory of “quantum gravity” (what physicists call a “theory of everything”), the final stage of that black hole evaporation remains a mystery.
The problem is that, according to his calculations, the radiation is perfectly thermal. It doesn’t retain any information about the state of the material that formed the black hole, and this would violate a fundamental rules in quantum mechanics.
INSPIRING BLACK HOLES
Whatever the truth, Hawking remained convinced that by attempting to understand the universe’s inner workings, humans can learn valuable lessons about themselves. As he explained in a 2015 lecture, black holes offer can their own form of inspiration.
“Black holes are not the eternal prisons they were once thought,” he said. “Things can get out of a black hole both on the outside and possibly come out in another universe. If you feel you are trapped in a black hole, don’t give up. There is a way out.”
BLACK HOLE PARADOX
Quantum physics requires that the whole future and past of every particle should be, in principle, possible to figure out and link through a series of chained, causal, probabilistic events. But if a black hole release an undifferentiated soup of particles with their information — their histories — unrecoverably erased, then that requirement is fundamentally broken.
The most dramatic late-career paper Hawking wrote suggested the black holes as they’ve classically been understood don’t exist at all.
In ” Information Preservation and Weather Forecasting for Black Holes ,” published in 2014, he suggested that the “event horizon” around black holes, the point beyond which even light could not escape, doesn’t really exist. Instead, he wrote, there’s simply an “apparent” horizon of trapped light which could fade away and allow the light to escape.
YET TO BE ANSWERED
“The absence of event horizons mean that there are no black holes — in the sense of regimes from which light can’t escape to infinity,” he wrote.
He also suggested some fundamental conceptual problems with a number of features physicists had attributed to black holes, like “firewalls” around their boundaries that destroy observers who try to enter.
In 2016, Hawking introduced ” Soft Hair on Black Holes .”
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The black holes are surrounded by “soft” or zero-energy particles , which he call hair. That hair, he wrote, stores the lost information of particles emitted by black holes on “holographic plates” beyond the black holes’ boundary regions. So the information, while displaced, is never truly lost.
In 1960, black holes were described not only by means of the general theory of relativity, but also methods of quantum mechanics. As a result it has become clear that to quantize the classical theory of gravitation in the same way as, for example, classical electrodynamics or mechanics, it won’t turn out. Hawking has gone some other way and has applied thermodynamics to black holes. He systematically applying thermodynamics to black holes, has removed an exact formula of entropy. Black holes radiate — owing to vacuum fluctuations. On the horizon of events couples of virtual particles are formed: one of them, with positive energy, departs from a black hole, another, with negative — falls in it, thereby reducing its weight. Hawking quantitatively calculated a thermal range of a black hole. For example, temperature of a black hole of solar weight — about one million kelvin. It is impossible to distinguish so small temperature from noise by modern astronomical methods.
R.I.P. Stephen Hawking
Syzygy 