Quantum Gravity in a Nutshell1 Second Edition: Beyond Einstein, #9

By Balungi Francis

This second edition to the bestselling Quantum Gravity in a Nutshell1 is a good introduction to quantum gravity and has a lot of interesting history about the development of the theory since 1899. It's an informal introduction to a very difficult and doubtfully intelligible theory.- doubted even by its most ingenious contributors. The reader should expect that he/she will have to concentrate hard on what Balungi says but the rewards are significant. He is a talented physicist and a good writer. If you read it carefully and stop to think about the message as it unfolds then you will get a worthwhile if imperfect picture of what the theory is saying and how it was invented,It's buried treasure and you will have to do some digging. It is a really serious attempt to do all that can be done in an informal style. Balungi explains and re-defines Einstein's theory of general relativity, quantum mechanics, black holes, the complex architecture of the universe, elementary particles, gravity, and the nature of the mind. This wonderful and exciting book is optimal for physics graduate students and researchers. Not since Stephen W Hawking's celebrated best-seller Brief History of Time has physics been so vividly, intelligently and entertainingly revealed.
 

• Language: English
• Publisher: Bill Stone Services
• Release date: Jun 4, 2019
• ISBN: 9781393801337

Balungi Francis

Balungi Francis is a theoretical physicist and author of Quantum Gravity in a Nutshell, a book that explores the fundamental nature of space and time. He has a Bachelor's degree in Physics from Makerere University, where he developed his passion for understanding the mysteries of the universe. He has also published multiple books on topics such as gravitation, structure formation, theory of everything, and dark matter and energy. He is the founder of "Find yo Genius", an online library of over 1000 science and math eBooks and paperbacks by renowned physics and math geniuses. He is motivated by his curiosity and desire to share his knowledge with the world.

Book preview

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DEDICATION

To my wife W. Ritah for her constant feedback throughout and many long hours of editing​​​,

To my sons Odhran and Leander,

To Carlo Rovelli, Lee Smolin, Neil deGrasse Tyson and Sabine Hossenfielder, I say thank you for your astonishing suggestions.

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PREFACE

Today we are blessed with two extraordinarily successful theories of physics. The first is the General theory of relativity, which describe the large scale behavior of matter in a curved space time. This theory is the basis for the standard model of big bang cosmology. The discovery of gravitational waves at LIGO observatory in the US (and then Virgo, in Italy) is only the most recent of this theory’s many triumphs.

The second is quantum mechanics. This theory describes the properties and behavior of matter and radiation at their smallest scales. It is the basis for the standard model of particle physics, which builds up all the visible constituents of the universe out of collections of quarks, electrons and force-carrying particles such as photons. The discovery of the Higgs boson at CERN in Geneva is only the most recent of this theory’s many truimphs.

But, while they are both highly successful, those two structures leave a lot of important questions unanswered. They are also based on two different interpretations of space and time, and are therefore fundamentally incompatible. We have two descriptions but, as far as we know, we’ve only ever had one universe. What we need is a quantum theory of gravity.

There is a need for a book on a Quantum Theory of Gravity that is not directed at specialists but, rather, sets out the concepts underlying this subject for a broader scientific audience and conveys joy in their beauty. Balungi has written with this goal in mind, and has succeeded admirably. This wonderful and exciting book is optimal for physics graduate students and researchers. The physical explanations are exceedingly well written and integrated with formulas. Quantum Gravity is the next big thing and this book will help the reader understand and use the theory.

AUTHOR’S NOTE

Our search for ultimate understanding—the Quantum Theory of Gravity—has long been the quest of such great scientists as Aristotle, Newton, Einstein, Hawking and many others, and is expected to transform science, providing clarity and understanding that is unknown today, ideally via one single overlooked principle in nature. So far, this quest has produced theories such as Special Relativity, General Relativity and Quantum Mechanics, and such recent proposals as Dark Matter and Dark Energy in cosmology. Yet these all suffer serious internal problems and compatibility issues with each other, introducing even more questions, mysteries and paradoxes—and often even violations of our laws of physics upon closer examination. As a result, the Quantum Theory of Gravity continues to elude us, leaving a fractured and divided scientific community with no clear direction forward. This has also resulted in the mathematisation of physics which has resulted in the reduction of the cosmos to a mathematical entity, which has not only confused physicists but accounts for their worst and most distracting assertions. This book makes a first case for the latter, with clear discussions exposing the flaws in the above concepts and more, while stepping back to take a good look at the scientific legacy we have inherited.

We are probably asking the wrong questions at the moment, nevertheless it is impossible to resist the temptation to try. After all, the other fundamental forces – except gravity – fit very neatly with quantum mechanics.

Physics is an entity and therefore requires only one subject to describe it fully and this subject is quantum gravity.

Balungi Francis

PARTI FOUNDATIONS

1 GENESIS

The development of a quantum theory of gravity began in 1899 with Max Planck’s formulation of Planck scales of mass, time, and length. During this period, the theories of quantum mechanics, quantum field theory and general relativity had not yet been developed. This means that Planck himself had no idea about what he had just developed-behind the Black board. Planck was not aware of quantum gravity and what it would mean for physicists. But he had just coined in formula one of the starting point for the holy grail of physics.

After P.Bridgman’s disapproval of Planck’s units in 1922, Albert Einstein having published the General Relativity theory, a few months after its publication he noted that to the intra-atomic movement of electrons, atoms would have to radiate not only electromagnetic but also gravitational energy if only in tiny amounts, as this is hardly true in nature, it appears that quantum theory would have to modify not only Maxwellian electrodynamics, but also the new theory of gravitation. This showed Einstein’s interest in the unification of Planck’s quantum theory with his newly developed theory of Gravitation.

Then in 1933 came Bronstein’s cGh-plan as we know it today. In his plan he argued a need for Quantum Gravity. In his own words he stated: After the relativistic quantum theory is created, the task will be to develop the next part of our scheme that is, to unify quantum theory (h), special relativity (c) and the theory of gravitation (G) into a single theory. Thus the theory of quantum gravity is expected to be able to provide a satisfactory description of the microstructure of space time at the so called Planck scales, at which all fundamental constants of the ingredient theories, c (speed of light), h ( Planck constant) and G ( Newton’s constant), come together to form units of mass, length and time.

The need for the theory of quantum gravity is crucial in understanding nature, from the smallest to the biggest particle ever known in the universe. For example, we can describe the behavior of flowing water with the long- known classical theory of hydrodynamics, but if we advance to smaller and smaller scales and eventually come across individual atoms, it no longer applies. Then we need quantum physics just as a liquid consists of atoms. Daniel Oriti in this case imagines space to be made up of tiny cells or atoms of space and a new theory of quantum gravity is required to describe them fully.

The demand for consistency between a quantum description of matter and a geometric description of spacetime, as well as the appearance of singularities and the black hole information paradox indicate the need for a full theory of quantum gravity. For example; for a full description of the interior of black holes, and of the very early universe, a theory is required in which gravity and the associated geometry of space-time are described in the language of quantum physics. Despite major efforts, no complete and consistent theory of quantum gravity is currently known, even though a number of promising candidates exist.

For us to solve the problem of quantum gravity (QG) we need to address and understand in detail the situations where the general theory of relativity (GR) fails. That is; General relativity fails to account for dark matter, GR fails to explain details near or beyond space-time singularities. That is, for high or infinite densities where matter is enclosed in a very small volume of space.  Abhay Ashtekar says that; when you reach the singularity in general relativity, physics just stops, the equations break down.

2GRAVITY

Gravity is the branch of physics relating to the very big. The histroy of gravity began with the following people; Archimedes and Vitruvius the architect both of Greco-Roman world, Aryabhata of ancient India and Galileo Galilei. Gravity is most accurately described by the general theory of relativity which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing not even light can escape once past the black hole's event horizon.

However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force which causes any two bodies to be attracted to each other, with the force proportional to the product of their masses and inversely proportional to the square of the distance between them.

Gravity is the weakest of the four fundamental forces of physics, as a consequence, it has no significant influence at the level of subatomic particles. In contrast, it is the dominant force at the macroscopic scale, and is the cause of the formation, shape and trajectory of astronomical bodies. For example, gravity causes the Earth and the other planets to orbit the Sun, it also causes the Moon to orbit the Earth, and causes the formation of tides, the formation and evolution of the Solar System, stars and galaxies. The earliest instance of gravity in the Universe, possibly in the form of quantum gravity, supergravity or a gravitational singularity, along with ordinary space and time, developed during the Planck epoch, possibly from a primeval state, such as a false vacuum, quantum vacuum or virtual particle, in a currently unknown manner. Attempts to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything) with the other three forces of physics, are a current area of research.

In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. In his own words,

Ideduced that the forces which keep the planets in their orbs must [be] reciprocally as the squares of their distances from the centers about which they revolve: and thereby compared the force requisite tomkeep the Moon in her Orb with the force of gravity at the surface of the Earth; and found them answer pretty nearly.

Newton's theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the general position of the planet, and Le Verrier's calculations are what led Johann Gottfried Galle to the discovery of Neptune.

A discrepancy in Mercury's orbit pointed out flaws in Newton's theory. By the end of the 19th century, it was known that its orbit showed slight perturbations that could not be accounted for entirely under Newton's theory, but all searches for another perturbing body (such as a planet orbiting the Sun even closer than Mercury) had been fruitless. The issue was resolved in 1915 by Albert Einstein's new theory of general relativity, which accounted for the small discrepancy in Mercury's orbit. This discrepancy was the advance in the perihelion of Mercury of 42.98 arcseconds per century.

Although Newton's theory has been superseded by Einstein's general relativity, most modern non-relativistic gravitational calculations are still made using Newton's theory because it is simpler to work with and it gives sufficiently accurate results for most applications involving sufficiently small masses, speeds and energies.

In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force. The starting point for general relativity is the equivalence principle, which equates free fall with inertial motion and describes freefalling inertial objects as being accelerated relative to non-inertial observers on the ground. In Newtonian physics, however, no such acceleration can occur unless at least one of the objects is being operated on by a force.

Einstein's theory has important astrophysical implications. For example, it implies the existence of black holes— regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an endstate for massive stars. There is ample evidence that the intense radiation emitted by certain kinds of astronomical objects is due to black holes. For example, microquasars and active galactic nuclei result from the presence of stellar black holes and supermassive black holes, respectively. The bending of light by gravity can lead to the phenomenon of gravitational lensing, in which multiple images of the same distant astronomical object are visible in the sky. General relativity also predicts the existence of gravitational waves, which have