Far out cosmology: Stephen Hawking and black holes (Introduction)

by David Turell , Tuesday, June 18, 2024, 16:30 (81 days ago) @ David Turell

Not theoretical anymore:

https://aeon.co/essays/a-brief-history-of-stephen-hawkings-greatest-equation?utm_source...

" we’re still waiting for experimental evidence to support the implications of his equation, which he called ‘my most surprising discovery’, one that casts black holes in a whole new light. As Hawking put it, ‘black holes ain’t so black’: they glow....

"In his biographical note in Hawking’s Order of Service, Penrose acknowledged that the equation was Hawking’s most important contribution: ‘[H]e was able to provide the one clear-cut physical implication, that we know of, which brings together the two great revolutions of 20th-century physics, namely general relativity and quantum mechanics …’ We have already encountered general relativity, a theory of gravity, which shapes the large-scale structure of the Universe. Quantum mechanics, which Einstein also had a hand in, explains how extremely small objects simultaneously, and paradoxically, act like both particles and waves.

"Yet these great theories seem at first glance to be incompatible, with one describing the subatomic realm as a domain of individual particles, or quanta, where there are sudden jumps, and the other ruling the grandest stage of all, the Universe, in terms of smooth distortions, undulations and warps of spacetime. Uniting them meant more than trying to reconcile languages as dissimilar as Morse Code and whalesong, however: while general relativity is deterministic, quantum mechanics is couched in terms of chance.

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"...according to Kip Thorne, his old friend at Caltech in the US, where Hawking was a frequent visitor. In his Westminster Abbey tribute, Thorne described how Hawking ‘manipulated, in his mind, images of geometric shapes: of ribbons, curves, cubes and spheres, and topological images, like a coffee cup deforming into a donut. His flowing mental images gave him insights nobody else could find.’

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"Using tools developed by Penrose, Hawking ‘defined what we call the event horizon’, a veil that shrouded the inner workings of a black hole.

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"A key scientific property called entropy, which broadly represents the degree of disorder, also always rises, according to the second law of thermodynamics,...Thermodynamics shows how, just as a watermill harnesses falling water to produce work, so work can be drawn from a steam engine as steam ‘falls’ from a higher temperature to condense into water. But, according to the second law, not all heat can be converted to work because of a rise in unusable energy, or entropy.

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"Hawking’s results suggested the opposite. By December 1973, he realised that not only did black holes radiate heat, but also that they did so by the amount required if the area of their event horizons was indeed a measure of their entropy.

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"The mathematical expression shows the temperature of Hawking radiation given off by a black hole that is not rotating:

T=ℏc3/8πGMk
T stands for temperature; ℏ for Planck’s constant, used in quantum mechanics; c is the speed of light, used in relativity theory; 8π helps us to grasp the black hole’s spherical nature; G is Newton’s constant to introduce gravity; M stands for the mass of the black hole, and k for Boltzmann’s constant, used in thermodynamics to relate energy to temperature for individual particles....

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"At an event horizon, a black hole’s gravitational point of no return, Hawking realised that a pair’s virtual particles can be separated, with one sucked in, and the other released, so the black hole loses a little of its energy, and therefore some of its mass (mass and energy are of course related by Einstein’s most famous equation E = mc2). As a result, the black hole sheds mass, evaporates and shines. Over its finite lifespan, it rots from the outside in.

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"No matter what you toss into a black hole, from a rocket to a pile of books of the same mass, its Hawking radiation will stay the same, as if the black hole is oblivious to what it has consumed. Moreover, as the black hole evaporates as it gives off Hawking radiation, it eventually disappears, along with all the information it once carried.

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"Farmelo added: ‘Stephen was first to understand clearly that information flow in the region of a black hole poses a fundamental challenge to our understanding of the laws of physics. In doing this, he set the agenda for one of the important problems in physics for decades.’

"When Hawking’s ashes were interred in the Scientists’ Corner at Westminster Abbey in June 2018, his Caithness slate gravestone depicted a black hole as a swirl of rings surrounding a darker central ellipse. Intersecting lines showed the dimensions of space and time and, of course, there in all its glory was his little equation that showed black holes don’t live forever."

Comment: this tribute to Hawking allows us to dip into the mathematical quagmire of astrophysical theoretical explorations. A giant article worth reading all of it. Note the human mind is capable of unlocking the universe's secrets. When I say God designed it, dhw will ask why did God make it so big and complex. Why should the issue of God change the way we look at the universe? The atheist views it and accepts it as a natural result of chance events. From both viewpoints the universe simply is what it is.