The One Thing You Need to Know: The Simple Way to Understand the Most Important Ideas in Science

By Marcus Chown

From gravity to black holes, special relativity to global warming, this authoritative and entertaining book from bestselling author Marcus Chown breaks down complex science into manageable chunks, explaining the one thing you really need to know to get to grips with the subject.

Rather than trying to bend your mind around all the vast and confounding details of things such as gravitational waves, electricity and black holes, wouldn't it be easier to understand just one central concept from which everything else follows?

If you've ever found yourself fascinated by the idea of quantum computing but feel a little overwhelmed by the mindblowing subject of quantum mechanics or concerned by climate change but haven't been able to get to grips with the details of global warming, this book is for you. Let's take atoms, for example - what on earth are they? Well, if you start to think of them less like things you can't see with complex little nuclei and more like the alphabet of nature, which in different configurations can make a rose, a galaxy or a newborn baby, they might start to feel a little more understandable. Or gravitational waves - they sound poetic, but why are they creating so much excitement? Think of them as the voice of space, vibrations on the drumskin of space-time - before delving into all their complexities.

In twenty-one short and engaging chapters, Chown explains the one thing you need to know to understand some of the most important scientific ideas of our time. Packed full of astounding facts, scientific history and the entertaining personalities at the heart of the most pivotal discoveries about the workings of our universe, this is an accessible guide to all the tricky stuff you've always wanted to understand more about.

• Language: English
• Publisher: Michael O'Mara
• Release date: Feb 2, 2023
• ISBN: 9781789294828

Marcus Chown

Marcus Chown is an award-winning writer and broadcaster. Formerly a radio astronomer at the California Institute of Technology in Pasadena, he is a Royal Literary Fund Fellow at Brunel University. His books include Breakthrough, The Ascent of Gravity, which was the Sunday Times 2017 Science Book of the Year; Infinity in the Palm of Your Hand; What A Wonderful World; Quantum Theory Cannot Hurt You; We Need to Talk About Kelvin and Afterglow of Creation, both of which were runners-up for the Royal Society Book Prize. Marcus has also won the Bookseller's Digital Innovation of the Year for Solar System for iPad.

Book preview

THE

ONE THING

YOU NEED

TO KNOW

Also by Marcus Chown

Infinity in the Palm of Your Hand

The Magicians

The Ascent of Gravity

Quantum Theory Cannot Hurt You

What a Wonderful World

We Need to Talk About Kelvin

The Never-ending Days of Being Dead

Afterglow of Creation

The Universe Next Door

The Magic Furnace

Tweeting the Universe

Solar System

For children

Felicity Frobisher and the Three-headed Aldebaran Dust Devil

Apps

The Solar System for iPad

title

First published in Great Britain in 2023 by

Michael O’Mara Books Limited

9 Lion Yard

Tremadoc Road

London SW4 7NQ

Copyright © Marcus Chown 2023

All rights reserved. You may not copy, store, distribute, transmit, reproduce or otherwise make available this publication (or any part of it) in any form, or by any means (electronic, digital, optical, mechanical, photocopying, recording or otherwise), without the prior written permission of the publisher. Any person who does any unauthorized act in relation to this publication may be liable to criminal prosecution and civil claims for damages.

A CIP catalogue record for this book is available from the British Library.

This product is made of material from well-managed, FSC®-certified forests and other controlled sources. The manufacturing processes conform to the environmental regulations of the country of origin.

ISBN: 978-1-78929-480-4 in hardback print format

ISBN: 978-1-78929-482-8 in ebook format

Cover design by Ana Bjezancevic

Illustrations by Peter Liddiard

www.mombooks.com

To Eric, who, during the power cuts of the 1970s while working for the London Electricity Board, always turned Fulham’s electricity off after his partner’s favourite TV programme, Doctor Who, and to Mark, the New York computer wizard.

CONTENTS

FOREWORD

1GRAVITY

Every piece of matter exerts an attractive force on every other piece of matter

2ELECTRICITY

By exploiting a force 10,000 billion billion billion billion times stronger than gravity we power the world

3GLOBAL WARMING

Molecules like carbon dioxide absorb heat radiated by the Earth’s surface and trap it in the atmosphere

4WHY THE SUN IS HOT

It contains a lot of mass

5THE SECOND LAW OF THERMODYNAMICS

There are many more ways for things to be disordered than ordered, so if each is equally likely, order will gradually morph into disorder

6PLATE TECTONICS

The Earth’s crust is fractured like crazy paving into plates, which rising magma causes to jostle with each other

7QUANTUM THEORY

Particles can behave as waves and waves can behave as particles

8ATOMS

They are the alphabet of nature and, by arranging them in different ways, it is possible to make a rose or a galaxy or a newborn baby

9EVOLUTION

Traits which enable organisms to compete successfully for scarce food resources, and so survive to reproduce, become more common with each successive generation

10 SPECIAL RELATIVITY

Light is uncatchable

11 THE BRAIN

The principal activities of brains are making changes in themselves

12 GENERAL RELATIVITY

Gravity is acceleration

13 HUMAN EVOLUTION

Three words characterize humans and their ancestors: migration, migration, migration

14 BLACK HOLES

A sufficiently concentrated mass creates a bottomless pit in space-time from which nothing, not even light, can escape

15 THE STANDARD MODEL

The complexity of the world stems from the permutations of just three fundamental building blocks glued together with three fundamental forces

16 QUANTUM COMPUTERS

They either exploit copies of themselves in parallel universes or behave as if they do

17 GRAVITATIONAL WAVES

They are vibrations of the drum skin of space-time – the voice of space

18 THE HIGGS FIELD

The basic building blocks of matter have no intrinsic masses but acquire them by interacting with the Higgs

19 ANTIMATTER

A photon has zero charge so, when it changes into an electron, the charge of the electron must be cancelled out by a particle with opposite charge: an antiparticle

20 NEUTRINOS

Though fleeting ghosts that barely haunt the physical world, they are the second most common particle in the universe

21 THE BIG BANG

The universe began in a hot, dense state and has been expanding and cooling ever since

ACKNOWLEDGEMENTS

GLOSSARY

ENDNOTES

INDEX

FOREWORD

‘I am the wisest man alive, for I know one thing, and that is that I know nothing.’

SOCRATES

‘I was born not knowing and have only had a little time to change that here and there.’

RICHARD FEYNMAN

Recently, I was asked to give a talk to a law firm about quantum computers. Warned that I could not assume any scientific knowledge in my audience, I thought: ‘What is the one thing you need to know to understand quantum computers – the one thing from which everything else follows?’ As I put together my presentation, it occurred to me that I could do exactly the same for a myriad other scientific concepts and that, in a world where most people are time-poor, telling them the one thing they need to know to understand a topic, and showing how everything else follows as a logical consequence, might be a novel and fun way to communicate a lot of deep stuff in a compact and digestible form. Einstein’s special theory of relativity is a consequence of the fact that a beam of light is uncatchable. Similarly, much of quantum theory is a consequence of the extraordinary fact that the ultimate building blocks of matter – atoms and their constituents – can behave both as localized particles and spread-out waves. The Standard Model of particle physics – the high point of 400 years of physics – is a result of nature’s mysterious obsession with enforcing local gauge symmetry (admittedly, that’s a bit more of an esoteric thing!). Of course, not all subjects are as clear-cut as this, and, with complex subjects like human evolution and the brain, not everything quite follows from one single thing. But, with this proviso, I have tried my best to provide a way in to twenty-one topics, from global warming to the Higgs particle, from electricity to the big bang, from black holes to evolution by natural selection. I hope you enjoy it!

Marcus Chown

1

GRAVITY

Every piece of matter exerts an attractive force on every other piece of matter.

‘I can calculate the motion of heavenly bodies, but not the madness of people.’

ISAAC NEWTON

Gravity is a ‘universal’ force of attraction, which means that it acts between every chunk of matter and every other chunk of matter. There is a force of gravity, for instance, between you and someone passing you on the street. And there is a force of gravity between you and the coins in your pocket. You do not notice either of these things, however, because gravity is such a phenomenally weak force. It probably does not seem so. After all, it is hard to jump more than a metre in the air before being pulled back down to the ground. Nevertheless, gravity is puny. Hold your arm out horizontally. The gravitational force of the entire Earth – countless quadrillions of tonnes – cannot pull your arm down.

Despite its fundamental weakness, gravity has the property that it gets bigger the more matter there is. Unlike nature’s electromagnetic force, which can be both attractive and repulsive so that in all normal matter it cancels out, gravity comes in only one form, which is always attractive (see Chapter 2 on electricity). Consequently, gravity’s effect is cumulative: the more matter there is, the more gravitational attraction. This is why gravity plays no discernible role on the scale of the coins in your pocket or of people passing you in the street, but is significant for large bodies such as planets, stars, galaxies and the universe as a whole.

In fact, it is possible to deduce the threshold size at which gravity becomes dominant. Take an atom, which consists of a positively charged nucleus about which negatively charged electrons orbit (see Chapter 8 on atoms). It is the repulsion between the orbiting electrons of one atom and the next that keeps them apart and keeps matter stiff. In the simplest atom, hydrogen, which consists of a single proton orbited by an electron, the gravitational force between them is about 10⁴⁰, or 10,000 billion billion billion billion, times weaker than the electromagnetic force. Consequently, when a body contains more than about 10⁴⁰ atoms, the force of gravity beats the electromagnetic force.

For a body made of rock, 10⁴⁰ atoms corresponds to a diameter of about 600 kilometres and, for a body made of ice, which is easier to squeeze, the equivalent diameter is about 400 kilometres. If the force of gravitational attraction is dominant, it will pull all the matter into the most compact form possible, which is a sphere. So, the prediction is that all rocky bodies in the solar system bigger than about 600 kilometres across will be spheres, while all that are smaller than this will be potato-shaped. For an icy body, the corresponding threshold is about 400 kilometres. And, sure enough, looking out across the solar system this prediction is indeed borne out.

The original template for the force of gravity was actually magnetism. In 1600, the English scientist William Gilbert experimented with naturally magnetized chunks of magnetite. He found that the greater the mass of such a ‘lodestone’, the greater the attraction it exerted on a piece of iron. He also showed that the attraction is mutual – that is, the force of attraction exerted by a lodestone on a piece of iron is exactly as strong as the force of attraction exerted by the iron on the lodestone. On the basis of this, Gilbert suggested that magnetism might be the force holding the solar system together.

Robert Hooke, Isaac Newton’s greatest rival, was much taken by Gilbert’s findings. However, he realized that the force holding the planets in the grip of the sun could not be magnetism since bodies, when heated, lose their magnetism, and the sun is clearly very hot. Hooke, nevertheless, saw magnetism as a model for the force that is orchestrating the motion of the bodies of the solar system. Like magnetism, gravity reaches out from one mass across empty space and grabs another mass. Like magnetism, the bigger the force, the bigger the masses involved. And, like magnetism, it is a mutual force.

The clues to the detailed behaviour of gravity lay in the planetary laws of Johannes Kepler. Between 1609 and 1619, the German mathematician pored over precise naked-eye observations of the planets made by Danish astronomer Tycho Brahe from his observatory on the island of Hven. Eventually, after a gargantuan effort, he deduced three laws that govern the behaviour of the planets.

Kepler’s second law of planetary motion recognizes that a planet travels more quickly when nearer the sun and more slowly when further away. More precisely, it states that an imaginary line joining a planet to the sun sweeps out equal areas in equal times. This area is proportional to the speed of a planet times its distance from the sun, a quantity in modern parlance known as its orbital angular momentum. This quantity is constant, Newton realized, only if the force on a planet is directed solely towards the sun, and there is no component whatsoever along the path of a planet.

Consider for a moment how extraordinary this is. Before Newton, almost everyone who had ever wondered about the motion of the planets imagined a force actually pushing them around in their orbits, provided perhaps by angels flying alongside the planets and blowing them along or chivvying them with their beating wings. Newton, however, saw the message in Kepler’s second law: no force is driving the planets around in their orbits. Instead, they are in motion solely because of their inertia: the tendency of a body in motion to stay in motion. It was something Newton encapsulated in his first law of motion: ‘A body stays at rest or moves at constant speed in a straight line unless acted upon by a force.’ (On Earth, there is always a force acting on any body, such as the friction slowing a kicked football, but in the absence of such a force, the football would carry on in a straight line for ever.) Armed with his insight, Newton was able to pin down exactly what the force of gravity, directed always towards the sun, does to a planet’s trajectory: it continually drags it away from its natural straight-line path. And in doing so, it traps it in eternal solar orbit.

Newton now had to identify the precise character of the force of gravity: how it varied in strength with distance from a massive body like the sun. He was able to do this because of his guess that gravity is universal – in other words, that the force that acts on a planet is the same force that acts on an apple detached from a tree. Such a proposal was radical and courageous because it flew in the face of the Church’s teaching that the heavens were not only made of a different essence to the Earth, but also danced to the tune of different laws. But it enabled Newton to directly compare the strength of the Earth’s gravity acting on a falling apple with the strength of the Earth’s gravity acting on the moon. Knowing how far away the apple was from the centre of the Earth and how far away the moon was from the centre of the Earth, he could then determine how the force of gravity changed with distance.

At first glance, it appears impossible to compare the force of the Earth’s gravity on an apple and the moon because the apple is falling and the moon is not. However, it was Newton’s genius to recognize that appearances are deceptive and the moon is in fact falling.

Newton imagined a cannon firing a cannonball horizontally. As it flies through the air, it is pulled downwards by gravity and hits the ground after travelling, say, half a kilometre. He then imagined a larger cannon that fired a cannonball even faster, so that it hit the ground after travelling, say, 5 kilometres. Finally, he imagined a super-cannon that shot a cannonball at 18,000 kilometres an hour. At this enormous speed, as fast as the cannonball falls towards the Earth, the Earth’s surface curves away from it. So it never hits the ground! In fact, it falls forever in a circle. The moon is doing precisely this. It is falling towards the Earth as surely as an apple falls from a tree. The surprising answer to the question ‘Why do the moon and Earth-orbiting satellites not fall down?’ is therefore that they are falling down. It is just that they never reach the ground.

Newton estimated the acceleration of the apple by timing its fall and he estimated the acceleration of the moon from how far it fell towards the Earth in the same time. He compared the two and, knowing the distance of both the apple and the moon from the centre of the Earth, deduced that gravity weakens according to an inverse-square law. In other words, if two massive bodies are moved twice as far apart, the force of gravity between them is four times as weak; if they triple their separation, gravity becomes nine times as weak, and so on.

For his next trick, Newton demonstrated that a planet experiencing a centrally directed inverse-square law of gravity orbits the sun in an ellipse. It was Kepler who had discovered that the paths of the planets around the sun are ellipses and not circles as the Greeks had believed. He had enshrined this in his first law of planetary motion: ‘A planet travels in an ellipse with the sun at one focus.’* Newton turned his mind to explaining Kepler’s first law in August 1684 when Edmund Halley visited him at Cambridge, hoping to settle a dispute between his friends Robert Hooke and Christopher Wren. Hooke maintained, without proof, that if the force of gravity was directed towards the sun and obeyed an inverse-square law of gravity, then the path of a planet would be an ellipse, as Kepler had found.¹ Newton told Halley that he had obtained a proof that it was indeed an ellipse. However, despite searching high and low in his rooms at Trinity College, he could not find his calculations. Halley’s visit not only prompted him to redo his calculations, but also spurred him to embark upon a two-year write-up of decades of his unpublished work on gravity and motion, in what would become one of the towering achievements of science: the Principia.

Newton in fact proved that bodies under the influence of centrally directed inverse-square law of attraction move not in an ellipse but more generally in a conic section. Think of a cone standing on its base and a sharp knife slicing clean through the cone. If the knife simply cuts through the cone from one side to the other, the exposed cross-section is elliptical (and if the slice is parallel to the base, it is a circle, which is a special case of an ellipse). If the knife cuts down through one side of the cone and out through the base, parallel to the other side of the cone, the exposed cross-section is an open-ended parabola. And if the knife cuts down through one side of the cone and out through the base vertically, the result is an open-ended hyperbola.

The three types of path correspond to three different physical situations. If a body has insufficient speed – or energy – to escape the sun, it will be trapped forever in an elliptical orbit, as the planets are. However, if it has sufficient energy to escape, it will follow a hyperbola, flying off to the stars. The parabola is the path of a body that sits on the knife-edge between being bound and unbound. It can escape the sun’s gravitational tyranny only by putting an infinite amount of distance between it and the sun, which would take an infinite amount of time.

Conic cuts: three ways of slicing through a cone expose a parabola (left), an ellipse (middle), and a hyperbola (right). All are possible paths of a body under the sun’s gravity.

Armed with his law of gravity, Newton