Understanding the Universe

The Physics of the Cosmos from Quasars to Quarks

Andrew Norton

• Publisher: CRC Press
• Year: 2021
• eBook ISBN: 9781000383959
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Science History

Understanding the Universe: The Physics of the Cosmos from Quasars to Quarks explores how all areas of physics, from the very smallest scales to the very largest, come together to form our current understanding of the Universe. It takes readers on a fascinating journey, from the Big Bang and how the Universe has evolved, to how it appears now, and the possibilities for how it will continue to evolve in the future.

It also explores the latest exciting developments in the area and how they impact our understanding of the Universe, such as quantum chromodynamics, black holes, dark energy, and gravitational waves. Equally importantly, it explains how we have come to know all of this about the Universe and details the limitations of our current understanding.

This book is accessible to all introductory undergraduate students interested in the physical sciences. It prioritises a non-mathematical approach so it can be understood by all students, with only two algebraic equations in the book and any numerical calculations shown are limited to simple arithmetic.

Key Features:

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• Combines current understanding of quantum physics and cosmology, and includes the latest exciting developments from the field.

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• Provides an accessible introduction to the topic, focusing on a non-mathematical presentation.

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• Presents a comprehensive narrative on the subject and a coherent story.

1  Quasars to Quarks

This book’s title is very ambitious, but the intention is indeed to show how physics allows us to understand the way in which the Universe operates, from the very large scale of quasars to the very small scale of quarks, and everything in between. Almost by definition, the rules of physics that have been discovered over the last 400 years or so allow us to understand the Universe and so explain how it works on all scales. In order to explore the Universe, I will therefore tell the story of its entire history, from its origin 14 billion years ago to the present day, and examine both the smallest objects and the most distant structures that comprise it. Along the way, many of the fundamental principles of physics will be encountered, and by the end of the book you will have met the key ideas of two specific areas of science, namely cosmology and particle physics.

To set the scene for this incredible journey it’s convenient to begin by looking at the various sizes of things, and the various distances to objects, that comprise the Universe. In scientific terms, these sizes and distances are jointly referred to as length scales (Figure 1.1). The journey from one extreme of length scale to the other might be summed up by the phrase “quasars to quarks.” Although the words “quasar” and “quark” are adjacent to each other in the index to this book, the objects they refer to are as far apart as it’s possible to be in terms of the length scales of the Universe. Quasars represent the most distant astronomical objects it is possible to observe and are up to one hundred million billion billion metres away. This distance may be written as 100 000 000 000 000 000 000 000 000 m or more compactly as 10²⁶ m, where the positive superscript value of “26” represents the “number of tens” that must be multiplied together to get the specified value. In contrast, quarks are the fundamental constituents of matter and are smaller than one-tenth of a billionth of a billionth of a metre in size. This size may be written as 0.000 000 000 000 000 000 1 m or more compactly as 10^–19 m, where this time the negative superscript value of “–19” indicates the “number of tens” multiplied together that must be divided into “1” to get the specified value. The distance to a quasar is therefore 45 factors of 10 greater than the size of a quark; in other words it is 45 orders of magnitude larger. These two length scales – separated by a factor of a billion, billion, billion, billion, billion – conveniently represent the extremes of human comprehension of the Universe.

FIGURE 1.1 Length scales in the Universe. Quarks (10^–19 m) are a billion times smaller than atoms (10^–10 m), which are a billion times smaller than apples (10^–1 m), which are themselves a billion times smaller than Jupiter (10⁸ m). The distances to the nearest stars (10¹⁷ m) are a billion times larger than the size of Jupiter, and quasars are a billion times further away (10²⁶ m) than nearby stars.

In science, prefixes to indicate multiples of units are often used to avoid having to write such large or small numbers. Ones you may be already familiar with include nano- (n, 10^–9), micro- (µ, 10^–6), milli- (m, 10^–3), kilo- (k, 10³), mega- (M, 10⁶), and giga- (G, 10⁹). You may have seen these in units such as nanometres (nm), microseconds (µs), millilitres (ml), kilograms (kg), megayears (My), and gigajoules (GJ), for instance.

Before beginning our exploration of the Universe, it’s worth pausing for a moment to try to appreciate the sheer range of length scales implied by the simple phrase “quasars to quarks.” A factor of a billion (10⁹) spans nine orders of magnitude. In terms of sizes that we can more easily comprehend, this is equivalent to going from, say, the size of the planet Earth (to the nearest order of magnitude this is 10,000 km, or 10⁷ m, in diameter) down to the size of a marble (about 10 mm, or 10^–2 m, in diameter). But there are five such steps, each requiring a decrease in size by a factor of a billion, in going from quasars to quarks!

Understanding the Universe throughout this range of length scales is necessarily the most wide-ranging subject that can be addressed by science. Other scientific issues, such as climate change or genetic engineering, certainly have more immediate relevance to everyday lives, but when it comes to fundamental questions such as:

• How does the Universe behave on small and large scales?
• What rules does the Universe follow?
• How does the Universe change with time?

there are none that are larger in scope. Answers to questions like these are to be found in the fields of cosmology and particle physics. Scientists who work in these two apparently unrelated areas of science – one concerned with the infinitely large, the other with the unimaginably small – now work together in an attempt to explain the universal processes that occur throughout time and space.

1.1 Cosmology and Particle Physics

In this book I will explore the physics of both the very large and the very small to take you on a journey from quasars to quarks. Along the way, many other components of the Universe will be encountered, and I will introduce you to the key ideas of modern physics, developed over the last century, that now form the fundamental basis for understanding the Universe.

Cosmology is the branch of science that involves the study of the Universe as a whole. The research tools of cosmologists include powerful telescopes that can detect galaxies out to the furthest reaches of the Universe (Figure 1.2). It may seem strange that people working in this field should count those who work on particle physics amongst their closest allies. The research tools of particle physicists include giant particle accelerators in which high-energy beams of subatomic particles are smashed together, enabling details of exotic reactions to be investigated and understood. But this is the key to the union of these two subjects. For only in particle accelerators are scientists able to recreate the high-energy conditions that once existed in the Universe during the first moments of its creation. When particle physicists study these reactions, they can provide cosmologists with a window on the Universe when it was only one-thousandth of a billionth of a second old.

FIGURE 1.2 (a) Telescopes on Mauna Kea, Hawaii and (b) part of the Large Hadron Collider particle accelerator at CERN, on the Swiss/French border.

An example of the interplay between these two areas of study concerns the fundamental particles known as neutrinos, which will feature later in the book. Some years ago, cosmologists studying reactions that occurred in the early Universe announced that there can be no more than three types of neutrino. If there were, say, four types of neutrino then they calculated that there would be more helium in the Universe than is actually observed. Particle physicists, studying decays of exotic particles in high-energy accelerators, were also able to calculate how many types of neutrino there are in the Universe. The answer the particle physicists arrived at was also three – if there were more, or fewer, types of neutrino, the particles they were studying would have decayed at a different rate. So, it is highly likely that there really are only three types of neutrino in the Universe – whether the problem is tackled from the large or the small scale.

1.2 Understanding How the Universe Works

The big questions outlined at the start of Chapter 1 will now be used as themes for what follows. To begin with, Chapter 2 summarizes some of the key ideas that form the foundations of physics. This includes information about atoms, motion, energy, and light that are central to understanding the world around us. Material in this chapter is your toolkit for understanding what follows and will highlight the importance of these tools for understanding the Universe.

In the first part of the book, comprising Chapters 3 to 7, the topics are the overall structure and composition of matter on the smallest scales. The branch of science that describes how the smallest particles of matter behave is known as quantum physics. To begin with, the two key features of quantum physics that control the behaviour of matter and energy at a fundamental level – quantized energy and indeterminate positions and velocities – are explored. Taking the world apart, you’ll examine the structure of atoms before moving on to look at how atomic nuclei behave, and finally you will look inside the protons and neutrons to discover quarks – the fundamental building blocks of the Universe. This is quite an itinerary for your journey into the heart of matter. You will be working in the tiny, subatomic domain and will be coming to terms with ideas that are almost unbelievable in the context of the everyday world. Most people are awe-struck by spectacles such as mountain scenery here on Earth or an exploding star in outer space. Prepare yourself to encounter phenomena that are much too small to be seen but that are none the less just as rich in fascination and mystery.

The second part of the book, comprising Chapters 8 to 10, turns to the science of cosmology and examines the overall properties of the Universe on the largest scales. After exploring just how astronomers observe the Universe using telescopes that operate across the electromagnetic spectrum, you will see that observations of quasars hold the key to understanding the distant Universe – by which is meant distant in both time and space. You will discover that the Universe is not static: it was different in the past to how it is now, and it will be different again in the future. Understanding this evolution relies crucially on two pieces of evidence: first, evidence that the Universe is expanding and, second, evidence that the Universe is cooling. Each of these is considered in turn to complete the picture of the Universe’s large-scale behaviour. Once again, you will be dealing with concepts that lie completely outside those of everyday experience.

Any attempt to chart the history of the evolving Universe must take account of the laws that govern all physical processes. So, the third part of the book, comprising Chapters 11 to 15, contains accounts of the distinctive features of the four types of interaction of matter and radiation: electromagnetic, strong, weak, and gravitational forces. You will see that these four interactions underlie all processes, at all scales, everywhere in the Universe. Then the question is raised of whether the four interactions are actually distinct or whether there might be bigger and better theories, that unify some of the four interactions.

Bringing together the information from the earlier chapters, the final part of the book, comprising Chapters 16 to 18, begins by presenting a history of the Universe from the Big Bang to the present day. It then explores the galaxies, stars, and planets that are observed in the Universe today, and finally considers what the future of the Universe may have in store.

Some of the ideas discussed in this book may challenge the view of the world that you currently hold, and throughout history such challenges have been one of the hallmarks of scientific progress. Apart from the intellectual excitement of topics in cosmology and particle physics, they also serve to illustrate the way in which scientists continually strive to push back the boundaries of knowledge, extrapolating from what can be measured in the laboratory to realms that are impossible to study directly. However, it’s important to note that these subjects are, nonetheless, relevant to everyday lives – for instance, the current technological age could not have come about were it not for the underpinning science of quantum physics. You will also encounter some rather bizarre ideas in the following pages. These will include particles that appear out of nothing, gravitational waves that permeate the entire Universe, and a remarkable theory of an 11-dimensional spacetime! Prepare for some mental exercise as you embark on a journey to the frontiers of physics and an exploration of the processes that allow us to understand the Universe.

2 The Physical World

Physics is the science that provides the rules for understanding the Universe, and many of the underlying ideas of physics are probably familiar to most people, whether they rea...

Table of contents

• Cover
• Half-Title
• Title
• Copyright
• Dedication
• Contents
• Author
• Chapter 1 Quasars to Quarks
• Chapter 2 The Physical World
• PART I The Small-Scale Universe
• PART II The Large-Scale Universe
• PART III Universal Processes
• PART IV The Universe through Time
• Book Summary
• Acknowledgements
• Appendix: A Timeline for Understanding the Universe
• Index