From Atoms to Higgs Bosons

Voyages in Quasi-Spacetime

Chary Rangacharyulu, Christopher J. A. Polachic, Chary Rangacharyulu, Christopher J. A. Polachic

• Publisher: Jenny Stanford Publishing
• Year: 2019
• ISBN:
  9780429648397
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Astronomy & Astrophysics

The announcement in 2012 that the Higgs boson had been discovered was understood as a watershed moment for the Standard Model of particle physics. It was deemed a triumphant event in the reductionist quest that had begun centuries ago with the ancient Greek natural philosophers. Physicists basked in the satisfaction of explaining to the world that the ultimate cause of mass in our universe had been unveiled at CERN, Switzerland. The Standard Model of particle physics is now understood by many to have arrived at a satisfactory description of entities and interactions on the smallest physical scales: elementary quarks, leptons, and intermediary gauge bosons residing within a four-dimensional spacetime continuum.

Throughout the historical journey of reductionist physics, mathematics has played an increasingly dominant role. Indeed, abstract mathematics has now become indispensable in guiding our discovery of the physical world. Elementary particles are endowed with abstract existence in accordance with their appearance in complicated equations. Heisenberg's uncertainty principle, originally intended to estimate practical measurement uncertainties, now bequeaths a numerical fuzziness to the structure of reality. Particle physicists have borrowed effective mathematical tools originally invented and employed by condensed matter physicists to approximate the complex structures and dynamics of solids and liquids and bestowed on them the authority to define basic physical reality. The discovery of the Higgs boson was a result of these kinds of strategies, used by particle physicists to take the latest steps on the reductionist quest.

This book offers a constructive critique of the modern orthodoxy into which all aspiring young physicists are now trained, that the ever-evolving mathematical models of modern physics are leading us toward a truer understanding of the real physical world. The authors propose that among modern physicists, physical realism has been largely replaced—in actual practice—by quasirealism, a problematic philosophical approach that interprets the statements of abstract, effective mathematical models as providing direct information about reality. History may judge that physics in the twentieth century, despite its seeming successes, involved a profound deviation from the historical reductionist voyage to fathom the mysteries of the physical universe.

Chapter 1

The Reductionist Vision of Physics

Physics is, hopefully, simple. Physicists are not.

—Edward Teller
Conversations on the Dark Secrets of Physics (1991)

1.1 Reductionism

Let us begin with a bold but not very controversial claim: Reductionism is, and has always been, the scientist’s guide for investigating and understanding the physical world. This is the case because the reductionist vision is simply an instinct of our common sense. In unvarnished terms, reductionism is a metaphysical view that the behavior of a composite system can be fully understood from the combined behavior of its constituent parts and nothing more.

In physics, a reductionist view of nature can be applied in two ways, not unrelated to one another. First, physicists may seek a unified, underlying theoretical description of all natural phenomena, reducing higher-order rules and theories to a single, grand unified causal theory with (in principle) universal application. We might refer to this as theoretical reductionism. The other reductionist strategy of physical science, which we can call physical or ontological reductionism, has to do with the physical structure of matter.

Physical reductionists understand matter to be made of a hierarchical arrangement of increasingly small components, ending—perhaps—at some fundamental microscopic level. The two reductionist ambitions of physics intersect in that the behavior of the final building blocks may be governed by a single, consistent, underlying physical theory, perhaps in the form of a small number of elegant mathematical equations.

Before we go on, we should briefly acknowledge that there are alternatives to reductionist ways of understanding natural systems. In particular, the perspective of emergence asserts that complex systems sometimes give rise to phenomena that (somehow) become ontologically independent of their underlying cause, in the sense that these emergent properties cannot, even in principle, be fully explained in terms of the mechanical operations of a more basic underlying order. Along with this loss of physical dependency, emergence naturally precludes the possibility of the unifying framework of theoretical reductionism.

For those who have trained in the reductionist school of physics, emergence is a difficult view to embrace. Giving the problem careful consideration, the physicist may acknowledge that some macroscopic properties of physical systems appear to be ontologically disconnected from underlying mechanisms and can be described by macroscopic terms and rules that have no immediate reference to microscopic reality,¹ but it cannot be admitted that there is really such an ontological or theoretical disconnect between scales of matter.

The reductionist vision is the framework that has successfully and usefully guided the arrow of scientific discovery since antiquity. Physical reductionism, in particular, is a powerful, intuitive idea and arguably a simple matter of common sense.

1.2 Our View of the World

Human beings are sensory beings. Our everyday sense perceptions provide us with data about the physical world. They are the natural starting point for a scientific description of nature.

The data obtained from our senses are all bound to a certain scale of physical reality: the macroscopic world of everyday-sized objects moving slowly enough that we can take notice and perform measurements. At this scale, our sensory data inform our reasoning about nature along three fundamental physical lines: spatial extension, time, and interaction. We observe a physical world composed of spatially extended objects that interact with one another by various means—usually, but not always, through physical contact—and which experience changes in their relative position and composition according to a certain ordering, which is congruent with a subjective sense of time passing. Our reductionist theories of physics have been necessarily expressed in these terms, because these are the basic categories that appear to define the world in which we live.

Our natural observation of macroscopic physical systems makes it evident to us that material objects have composite structure. This is clear from the fact that apparently continuous material substances can be divided into smaller pieces. A volume of liquid can be separated into an arbitrarily large number of containers, and a large solid object can be broken by force into smaller components, each of which can be further reduced. Air around us is separated by the passage of a body moving through it. Even though our senses are unable to perceive objects smaller than a certain size, this pattern of reducible composition at larger scales suggests our everyday thinking that even below the limit of perception, this pattern should go on further.

At each scale of matter, these fragments should have the same properties of (progressively reduced) spatial extension, location, and motion relative to other bodies, all evidently describable in terms of the conservation of certain parameters of the system such as energy and momentum, and identifiable rules of interaction among the physical entities. Reducibility is simply an observed fact of macroscopic objects. The inference that reduction continues into microscopic scales of the physical world may not be strictly logical (in the sense of provable), but it is a natural extrapolation in the absence of contrary evidence.²

Science has been divided into disciplines that operate at these different scales. The biological scale of life can, in part, be understood reductionistically in terms of structural elements called cells. Types of cells differ in form and function but share some common characteristics and have tremendous internal complexity. They are reducible to biochemical structures constituted by organic molecules of various sizes, compositions, and functions. But the incredible, dynamic variety of the molecular world is itself reducible to a relatively compact set of elemental atoms categorized in the periodic table of elements. If this view of the physical world is correct (and physics operates on the assumption that it is), then (in principle) if we could³ fully describe the behavior of the atoms, we could work our way up to a complete physical description of the cells.

The reduction of molecules to the atomic scale is a significant step in simplification and organization of our knowledge of matter. About 100 chemical atomic species form the underlying structure of our visible, everyday world. The properties of these atomic constituents can be described by a conceptually simpler set of more fundamental building blocks. The essential structure of every atom is the combination of mutually interacting protons, neutrons, and electrons—three species of bricks forming the larger whole. The protons and neutrons are held together in the nucleus by the strong nuclear interaction, and the electrons bind to the protons via electromagnetic attraction. Three kinds of particles and two interactions combine in various stable configurations to build up the larger world in all its complexity, as individual atoms interact with one another through their electrons. The result is a physical, macroscopic world of gases, liquids, and solids. Understand the properties of the former scale, and you should, in principle, understand the larger. This is the power of reductionist vision.

The relatively small number of entities—three!—involved in the structure of atoms irresistibly suggests that the remaining journey to the fundamental level of matter may be short. The enterprise of nuclear physics has pursued this dream since the discovery of the neutron in 1932. Scientists have employed high-energy collisions of atomic constituents to try to break apart the nuclei. These efforts, rather than resulting in clear evidence of a lower level, instead produced an astonishing variety of exotic, short-lived particle-like states with properties similar to those of protons and neutrons.

Attempting to classify these new species, particle physicists settled on a reductionist model of quarks to describe the underlying structure of many of these new discoveries in the subatomic world. The theory of this quark model suggests a new, more basic level for the physical world below the triplicate foundation of electrons, protons, and neutrons. Do quarks provide a final answer to an ancient metaphysical question: “What is the bottom level to physical reductionism?” As we will argue in detail in this book, the answer should not be an unqualified “yes” because it is not at all clear that the quark model has continued along, rather than deviated from, the trajectory of the reductionist enterprise at the heart of physics.

1.3 Democritus’ Atoms

The hunt for the foundational stuff of matter, both philosophically and experimentally, is an old one. Thales of Miletus opined that all substances in nature could be understood as different, complex forms of an underlying fundamental substance, namely water. Leucippus of Thracian Abdera, in the fifth-century BCE, mused whether the apparent continuity of the Aegean water was merely an illusion of scale, the substance being like the sand of the seashore, divisible.

But how far divisible? If a volume of water be divided into parts, can those parts be divided again, and then further divided, ad infinitum? Here, Leucippus’ disciple Democritus concluded that common sense must prevail: There must be some smallest level of division at which the process stops—a fundamental unit with non-separable parts, which Democritus characterized as uncuttable, or a-tomon in Greek, from which our word atom is derived.

Democritus was a fifth-century BCE philosopher, also from Abdera. He was among the Greek natural philosophers who carefully applied their powers of reason to understand the rules and structures of nature, long before an experimental method had developed in the advent of modern science. None of Democritus’ three dozen or so books on the natural sciences, mathematics, and medicine have survived down to today, except as fragments. However, his basic ideas were reiterated by later authors whose works do survive. Within the large body of quotations and commentary in the writings of Epicurus, Simplicius, and Aristotle, we have today a good sense of Democritus’ hypotheses. For a man whose original writings no longer survive, he has attained a reputation as the archetype for ontological reductionism.

The basic stuff of matter, Democritus postulated, can be understood as eternally existing, small bodies, infinite in number. These atoms occupy empty space, the void, which has two characteristics: its emptiness and its infinite extent. The defining property of atoms is their indivisibility, which follows necessarily from reason: If there exists some substance of finite mass that is divisible into smaller parts at every point within its mass, then if all possible divisions were made it would be divided into points without spatial dimension. How much of the total mass would each point then contain? Can the recombination of points with no magnitude produce a larger macroscopic object of definite extension and finite mass? Democritus’ answer was “no;” rather, the ultimate composition of matter must have some finite form and size and cannot be forever reducible. There is a necessary bottom layer to physical reality: the Democritian atoms.

It is important to notice that these atoms, while fundamental and microscopic, are not necessarily simple: Indivisibility does not require simplicity of structure. Democritus understood that the rich variety of complex structures in the macroscopic world requires some variety of form among the atoms, and thus different atomic species. Atoms, he thought, must have spatial extension—they are not points in space—and their different shapes and sizes allow interaction with one another without loss of individuality. They entangle and grasp one another, forming larger structures that can be broken apart by the application of a sufficient force to undo their bonds. This diversity of atomic species yields all the complex behaviors and bulk properties of matter. From the perspective of a modern high school or college education in the natural sciences, this ancient description of matter is beginning to sound very familiar.⁴

Democritus’ physical reductionism offers no compromise for emergent phenomena: “The atoms,” wrote Aristotle, interpreting Democritus’ view,

struggle and are carried about in the void because of their dissimilarities and the other differences mentioned, and as they are carried about they collide and are bound together in a binding which makes them touch and be contiguous with one another but which does not genuinely produce any other single nature whatever from them; for it is utterly silly to think that two or more things could ever become on...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• Introduction
• 1. The Reductionist Vision of Physics
• 2. Quasirealism
• 3. Space, Time, and Relativity
• 4. Mathematical Spaces
• 5. Mass
• 6. Quantum Physics
• 7. When Is an Atom?
• 8. Elementary Quanta
• 9. What Is a Photon?
• 10. Symmetries, Conservation Laws, and Gauge Bosons
• 11. Higgs Boson
• Epilogue
• Appendix: Epitaph for All Photons
• Index