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Book Review:
The Physics of Black Holes ... and more

Black Holes: The Key to Understanding the Universe

Brian Cox and Jeff Forshaw, 2022

For anyone interested in the physics of black holes, or in quantum entanglement ( "spooky action at a distance"), or in theoretical speculation regarding the idea of the cosmos as a hologram, I highly recommend this duo's book.


Cox is a professor at the University of Manchester and has been described by one reviewer as "Britain's best known physics professor" due to his involvement in numerous TV productions. Jeff Forshaw is a particle physicist at the University of Manchester and the co-author (with Cox) of "The Quantum Universe" and "Why Does E=mc2?"  Their book on black holes is unusual in that parts are written for an educated general audience (like myself) who lack advanced math skills and other parts for colleagues and other experts who have an in-depth understanding of particle physics and the mathematics that support quantum mechanics and general relativity. The book has much to offer both groups of readers. It is not light reading, but parts are fully accessible to non-experts.  


Chapter One, "A Brief History of Black Holes," contains much important and astonishing information: 

  • "Black holes lie where the most massive stars used to shine, at the centers of galaxies and at the edge of our current understanding." 

  • "The wonderful thing about the increasing number of black holes we have discovered ... is that each one is an experiment conducted by Nature that we cannot explain. This means we are missing something deep." 

  • In 1939, Einstein, whose theory of general relativity predicted that the collapse of massive stars would lead to a "black hole" which "will contain a singularity," asserted that black holes 'do not exist in physical reality.'  Einstein's illustrious contemporary, Arthur Eddington, put it in rather pithier terms: 'There should be a law of Nature to prevent a star from behaving in this absurd way.' Well, there isn't and they do." Einstein's theory also predicted "that there is a singularity in our past which constitutes, in some sense, a beginning to the universe."  

  • "We now understand that  black holes are a natural and unavoidable phase in the lives of stars a few times more massive than our Sun ...there are many millions of black holes." 

  • A typical neutron star has a radius of just a few kilometers and a mass 1.5 times that of the Sun. A million 'Earths' squashed into a region the size of a city."

  • "The gravitational pull at the surface of a neutron star is 100 billion times that of Earth."   

  • The galaxy, M87, which lies 50 million light years from Earth, "has a mass 6.5 billion times that of our Sun ..." 

  • The supermassive black hole at the center of our galaxy contains 4.31 million solar masses. 

  • Black holes occasionally collide. "In 2015, the LIGO gravitational wave detector registered the ripples in spacetime caused by the collision between two black holes that occurred 1.3 billion light years from Earth. The black holes were 29 and 36 times the mass of the Sun and collided and merged in less than two tenths of a second."

  •  Because "black holes affect the flow of time in their vicinity," viewed from the outside, nothing is ever seen to fall into a black hole, which means that an astronaut falling toward a black hole will remain frozen on the horizon (of the black hole) for eternity." The same idea applies to a star whose surface can never be seen to cross the horizon. "This is only one in a blizzard of apparent paradoxes." ( p. 11)   

  • Even though light cannot escape the gravity of a black hole, Stephen Hawking theorized that virtual particles known Hawking radiation steadily stream out into the universe "carrying a tiny fraction of the black hole's energy with them. Over unimaginable time scales ... a typical black hole will evaporate away and, ultimately, explode."  "Black holes, to use Hawking's famous phrase, ain't so black." 

  • " A typical solar mass black hole will have a lifetime of 1069 years, which is a very long time."  


According to these authors, there has been a long fruitful debate among physicists regarding whether the ultimate destruction of black holes through quantum fluctuations means that all information regarding the matter that was captured by a black hole has been destroyed. If so, some physicists (including Hawking) believe the principle of determinism in physics would be undermined. As the authors explain in an unsatisfying way, "information is not destroyed and physics is safe." They add: "Today, the study of black holes appears to be edging us in a new direction, toward a language more often used by quantum computer scientists. The language of information. Space and time may be emergent entities that do not exist in the deepest description of Nature. Instead, they are synthesized out of entangled quantum bits of information in a way that resembles a cleverly constructed computer code." ... black holes are cosmic Rosetta Stones ..." On the next to last page of the book, the authors ask "Are we living in a giant quantum computer? The evidence is mounting that it may be so." They go on to add that they do not believe "we are virtual creations living inside the computer game of a super-intellect."    


From my perspective, one of the strongest parts of this book is the discussion of quantum entanglement contained in pages 191-225. Those of you who have read my discussions of polarity in cosmology, biological evolution of mind, social anthropology, history and psychology will not be surprised by my interest in a discussion that applies polarity principles to the quantum realm. The authors assert: "We should emphasize that, as far as we can tell, all of Nature is quantum mechanical, "not only our understanding of atoms and molecules and all of chemistry and nuclear physics, but also modern day electronics. ... the semi-conductor in is modern electronic devices is an inherently quantum mechanical device.  We live in a quantum universe." 


The authors explain that "the vacuum of empty space is not empty. ... Roughly speaking, the vacuum is to humans as water is to a fish, an ever present  backdrop to our everyday experience, " and "quantum theory describes a sea that always ripples."  Further, "virtual  particles emerge from the vacuum in pairs," one with positive energy and the other negative energy."  "Vacuum fluctuations tickle the black hole, causing it to lose energy by emitting particles." These ghostly particles flicker in and out of existence, such that "the total energy of the vacuum remains unchanged on the average."  


Cox and Forshaw state that the physics of a singularity is unknown, but the physics of Hawking radiation is well understood by quantum physics. A pair of particles which emerge from the quantum vacuum are entangled; they add, "Of all the the bizarre aspects of quantum physics, none is perhaps quite so bizarre as the notion of entanglement," the "intellectual resource (and physical) that underpins the nascent quantum computers programmed and studies in many research laboratories." Entangled particles that are very far apart 'feel' each others influence because they should be viewed as a single connected system." To explain entanglement, the authors introduce the concept of a quantum bit, or 'qubit'. "An ordinary bit is like a switch; it can only have two values, which we might call 'on' or 'off'. Qubits are a far richer resource because they can be both 0 and 1 at the same time." Imagine that measuring the value of a qubit is like tossing a coin: there is a 50/50 chance of the qubit having a value of 0 or 1. "And yet, if the coins were quantum coins entangled in this way, if one of the coins came up heads, we would know for certain that the other came up tails," regardless of the distance between the coins. This duality cannot be the result of causality as defined in the usual way, because the process is instantaneous. Once the value of one quantum "coin" is measured, the value of the coin with which it is entangled can be known with complete certainty, re of distance. The authors assert:  "There are electrons in your hand and electrons in the Andromeda galaxy, separated by over two million light years, linked through quantum entanglement." ( p. 210) 


 The most difficult and challenging part of the book for me is the chapter, "The World As A Hologram." The authors assert that there is strong evidence that "The inside of a black hole somehow 'the same' as the outside. This idea has become known as the holographic principle." Cox and Forshaw refute the idea that it is possible to make an identical copy of  some unknown quantum state as something falls through a black holes event horizon, a conclusion they assert is justified "if we want to respect the foundations of both quantum theory and general relativity. Their argument appears to follow the underlying principles of entanglement, i.e., entangled particles might be both inside and outside an event horizon and therefore must exhibit complementarity. This is an involved complex discussion that requires a much better understanding of particle physics than I possess. 

However, I do grasp the radical implications: "Holography .. is a perfect example of complementarity in action. There are two entirely equivalent descriptions of anything and everything, and this is an essential feature of all of nature and not just black holes."  Black holes are the Rosetta Stone, which  introduced us to a new language, an entirely different yet equivalent description of physical reality. One description resides on the boundary of any given region of space, and the ither resides more conventionally in the space internal to the boundary. The implication is that our experience can be described with absolute fidelity in terms of information stored on a distant boundary, the nature of which we do not yet understand. This sounds utterly bonkers, but clinching evidence comes from the most highly cited high energy physics paper of all time," i.e., a paper by Juan Maldecena, published in 1997. According to the authors, this paper, "The Large N Limit of Superconformal Field Theories and Supergravity," has "changed the face of theoretical physics over he past 25 years, It is also the paper that provides the strongest evidence supporting the idea that the holographic principle is true." The authors believe "holography is here to stay" in physicists' deepening understanding of black holes.   

-- Dee Wilson

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