Sean Carroll - The Biggest Ideas in the Universe: Space, Time and Motion

Praise for Sean Carroll

As a ten-year-old physics enthusiast, I would have loved The Biggest Ideas in the Universe. With this book, Sean Carroll rejects traditional elitism in physics and welcomes in anyone who knows only a little algebra but wants to understand the whole universe.

Chanda Prescod-Weinstein, author of The Disordered Cosmos: A Journey into Dark Matter, Spacetime, and Dreams Deferred

Sean Carroll is a wizard of empathy. In this short book, the first of three on The Biggest Ideas in the Universe, he anticipates whats always confused you about physics and then gently guides you to enlightenment and ultimately, to newfound wonder.

Steven Strogatz, author of The Joy of X and Infinite Powers

No-nonsense, not-dumbed-down explanations of basic laws of the universe that reward close attention.

Kirkus

Sean Carrolls greatest gift isnt that hes an expert on the fundamentals of physics, which he is, but that he never speaks down to his reader. He assumes that anyone, even the uninitiated, can learn to understand the formulae that underlie complicated concepts like space and time. It is a pleasure to read his work, a greater pleasure still to get a world-class education from such a witty, thoughtful teacher.

Annalee Newitz, author of The Future of Another Timeline

Carroll has the remarkable ability of putting the reader utterly at ease with his lucid and addictive prose.

Jim Al-Khalili

Sean Carroll is a fantastically erudite and entertaining writer.

Elizabeth Kolbert

ALSO BY SEAN CARROLL

Something Deeply Hidden

The Big Picture

The Particle at the End of the Universe

From Eternity to Here

A Oneworld Book

First published in Great Britain, the Republic of Ireland and Australia by Oneworld Publications, 2022

This ebook edition published 2022

Copyright Sean Carroll, 2022

The moral right of Sean Carroll to be identified as the Author of this work has been asserted by him in accordance with the Copyright, Designs, and Patents Act 1988

All rights reserved

Copyright under Berne Convention

A CIP record for this title is available from the British Library

ISBN 978-0-86154-288-8

eISBN 978-0-86154-289-5

Image of hyperbolic space courtesy of Wikimedia Commons.

All other illustrations by Jason Torchinsky and Sean Carroll.

Oneworld Publications

10 Bloomsbury Street

London WC1B 3SR

England

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To Jennifer

My dream is to live in a world where most people have informed views and passionate opinions about modern physics. Where you knock off after a hard day at work, head down to the pub with friends, and argue over your favorite dark-matter candidate, or competing interpretations of quantum mechanics. A world where, as kids are running around at a birthday party, one parent says, I dont see why anyone thinks there should be new particles near the electroweak scale, and another immediately replies, Then how in the world are you going to address the hierarchy problem? People have opinions, after all, about supply-side economics or critical race theory. Why not inflationary cosmology and superstring theory?

Thats not quite the world in which we live. Even more than most other academic disciplines, physics is a field by and for specialists. Practitioners talk to one another in a highly specialized jargon, one that is dominated by mathematical concepts most people have never heard of, much less mastered. There are sensible reasons why this is the case, but it doesnt have to be this way. The situation is due in large part to the ways in which physicists tend to share their knowledge with the rest of the world.

If you are a non-expert interested in learning about modern physics, you have basically two options. One is to remain at a popular level of explanation, where you can learn about some of the relevant concepts without digging into the technical or mathematical details. You can read books, go to lectures, watch videos, listen to podcasts. The good news is that we do have a vibrant ecosystem of such resources, and its possible to learn quite a bit, albeit in a somewhat haphazard way. But at the end, you know youre not getting the real stuff. What you get are images and metaphors, rough translations of the underlying mathematical essence into ordinary language. You can go an impressive distance down this route, but something vital will always be missing.

The other route is to become a physics student. That could be literally at a university, or by assembling the right textbooks and online resources. Along the way you will need to become proficient at quite a bit of mathematics: calculus and differential equations most importantly, but also aspects of vector analysis, complex numbers, linear algebra, and more. The journey will be rewarding, but frustratingly slow. It typically takes at least a year of introductory courses before a student ever hears about relativity or quantum mechanics. And most physics students can get an undergraduate degreeor even go all the way to obtain a PhDwithout learning about particle physics, black holes, or cosmology. Those goodies are reserved only for specialists in particular subfields.

The gap between learning physics as an interested amateur, relying on metaphors and murky translations, and becoming a credentialed expert, comfortable with pushing around equations of intimidating complexity, is wide but not unpassable. Just because I dont want to be a professional race-car driver doesnt mean I shouldnt be allowed to drive at all. Surely there is a way to engage with some of the authentic essence of modern physicseven if that means looking at a few equationswithout slogging through years of a standard curriculum.

Youve come to the right place!

The Biggest Ideas in the Universe is dedicated to the idea that it is possible to learn about modern physics for real, equations and all, even if you are more amateur than professional and have every intention of staying that way. It is meant for people who have no more mathematical experience than high school algebra, but are willing to look at an equation and think about what it means. If youre willing to do that bit of thinking, a new world opens up.

Here is the thing about equations: They are not that scary. They are just a way to compactly summarize a relationship between different quantities. Its one thing to be told that, according to Einsteins theory of general relativity, mass and energy cause spacetime to curve. It is quite another to be given Einsteins equation:

The English-language sentence gives you a kind of feeling for what general relativity is about, but the equation tells you what is really going on, in precise and unambiguous terms. You can read all of the words you like, but until you understand this equation, you wont really understand Einsteins theory.

The problem is that this equation is utterly opaque if you dont know what the symbols mean. Its gibberish. To wrap your head around it, you need to understand the individual roles of all the numbers and letters, including the subscripts and , which are from the Greek alphabet, for goodness sake. There are good reasons why typical physics students take years to make it that far.