A Crack in Everything: How Black Holes Came in from the Cold and Took Cosmic Centre Stage

A CRACK IN EVERYTHING

ALSO BY MARCUS CHOWN

The One Thing You Need to Know

The Magicians/Breakthrough

Infinity in the Palm of Your Hand

Big Bang: A Ladybird Expert Book

The Ascent of Gravity

What a Wonderful World

Tweeting the Universe

The Solar System/Solar System for iPad

We Need to Talk About Kelvin

Felicity Frobisher and the Three-Headed Aldebaran Dust Devil

Quantum Theory Cannot Hurt You

The Never-Ending Days of Being Dead

The Universe Next Door

The Magic Furnace

Afterglow of Creation

A CRACK IN EVERYTHING

How Black Holes Came in from the Cold and Took Cosmic Centre Stage

MARCUS CHOWN

www.headofzeus.com

First published in the UK in 2024 by Head of Zeus Ltd,

part of Bloomsbury Publishing Plc

Copyright © Marcus Chown, 2024

The moral right of Marcus Chown to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act of 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of both the copyright owner and the above publisher of this book.

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

ISBN (HB): 9781804544327

ISBN (E): 9781804544303

Head of Zeus Ltd

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To my friend, Dave Hough. I miss you.

CONTENTS

Also by Marcus Chown

Title Page

Copyright

Dedication

Introduction

Author’s Note

1. An Impossible Thing Before Breakfast

2. Quantum Stars are Not Enough

3. I’m Spinning Around

4. Hole in the Sky

5. The Unbearable Whiteness of Black Holes

6. Big Black Hole Bonanza

7. Birth Cry of a Black Hole

8. The Gates of Hell

9. A Crack in Everything

10. Masters of the Universe

About the Author

Acknowledgements

Endnotes

An Invitation from the Publisher

INTRODUCTION

Of all the conceptions of the human mind from unicorns to gargoyles to the hydrogen bomb perhaps the most fantastic is the black hole: a hole in space with a definite edge over which anything can fall and nothing can escape; a hole with a gravitational field so strong that even light is caught and held in its grip; a hole that curves space and warps time.

Igor Novikov¹

Dwell on the beauty of life. Watch the stars, and see yourself running with them.

Marcus Aurelius

Black holes are extraordinary objects with extraordinary properties. Here is just one. If I were a black hole and you were in my vicinity and I turned on the spot through 360°, there would be nothing in the world you could do to stop yourself from being whirled around with me. It would not matter if you had the most powerful rocket or access to every last drop of energy in the universe. Space itself would appear glued to me and you would be unable to remain stationary. A black hole is exactly like that. It sits at the eye of an irresistible tornado of swirling space-time.

A black hole is a region of space from which nothing, not even light, can escape. Or, to put it more precisely, it is a bottomless pit in the fabric of space-time from which nothing, not even light, can climb out. The term was coined in 1967 by the American physicist John Wheeler, the research advisor of the famous physicist Richard Feynman. Before Wheeler popularised the term – he did not actually invent it – there was pretty much no research on black holes. Afterwards, interest exploded. It underlines just how important it is in science to coin a term that paints a striking picture in people’s minds. So vivid is the picture, in fact, that the term has entered everyday language and it is now common to talk of losing this or that item down a black hole.

Paradoxically, however, the term black hole does not paint an accurate picture of the objects astronomers have discovered in space. You would be forgiven for thinking that the two most striking features of black holes are that they are black and holes. But nothing could be further from the truth. Far from being black, black holes are some of the most prodigiously luminous objects in the universe. They appear white-hot. And far from being holes down which matter is inexorably sucked, their most striking feature is often immense jets of matter that stab outwards from their poles and extend for millions of light years across space.

The belief that all black holes would be black against the black of space, and so undetectable, is one reason for the lack of interest in these objects in the first half of the twentieth century. But a more fundamental reason is that they are the stuff of physicists’ nightmares. When a massive star at the end of its life runs out of fuel to generate the heat to push outwards against gravity, it shrinks catastrophically, its gravity intensifying until it literally vanishes from the universe. Wrapped in the invisibility cloak of an event horizon, the point of no return for in-falling light and matter, the star continues to shrink, its density skyrocketing to infinity. The appearance of such a singularity in a theory – in this case, Einstein’s theory of gravity – is a sign that it has been stretched beyond the point that it has anything sensible to say. No wonder Einstein never believed in black holes.

My own interest in black holes was sparked when my dad took me to a meeting of the Junior Astronomical Society at Alliance Hall in central London in 1972. The speaker, who walked to the lectern with a stick because of a childhood bout of polio, was Paul Murdin. Along with Louise Webster, he had recently discovered a blue supergiant star that every 5.6 days whirled around… absolutely nothing. Using Newton’s laws of gravity, Murdin and Webster deduced that the invisible object was at least four times, and possibly six times, the mass of the Sun. Only one kind of celestial body fit the bill: a black hole. Sitting there with my dad on that day and learning about the first black hole ever discovered blew my twelve-year-old mind.

A decade later, as a graduate student at the California Institute of Technology in Pasadena, I regularly walked by Maarten Schmidt in the entrance hall of Robinson Laboratory of Astrophysics. In the Junior Astronomical Society magazine, Hermes, I read how, in 1963, Schmidt discovered quasars, star-like points of light at the edge of the universe that were pumping out 100 times the energy of an entire galaxy of stars from a volume smaller than the solar system. There was only one possible source of such a phenomenal amount of energy coming from so small a volume: matter superheated to billions of degrees as it swirled down onto a black hole. But not a mere stellar-mass black hole. A black hole weighing billions or even tens of billions of times the mass of the Sun. The origin of such supermassive black holes remains to this day one of the great mysteries of cosmology.

I remember my Caltech supervisor, Tony Readhead, showing the first image of the galaxy Cygnus A, taken with the twenty-seven radio dishes of the Very Large Array in Socorro, New Mexico. The research group crowded around to see it and were stunned. From the tiny speck of the central galaxy there emerged oppositely directed, thread-thin jets of matter, which lanced outwards for millions of light years until they slammed into the intergalactic medium. The splashback, like water from a hose hitting a brick wall, created enormous twin radio-emitting lobes, which utterly dwarfed the central galaxy. Here was graphic evidence of a supermassive black hole projecting its enormous power across cosmic distances.

At this time, in 1983, it was widely believed that supermassive black holes were cosmic anomalies that powered only the 1 per cent of delinquent, or active, galaxies. Everything changed in 1990 with the launch of NASA’s Hubble Space Telescope. Orbiting above the turbulent atmosphere, its super-sharp eyesight was able to peer deep into the hearts of dozens of nearby galaxies. And, in every one, it saw stars whirling at tremendous speeds around an invisible but extremely massive object. Supermassive black holes were everywhere. Nevertheless, they are minuscule compared to their parent galaxies. It was still possible to believe that they were cosmic anomalies of only peripheral importance to the life of the cosmos.

That idea, however, was blown out of the water by the discovery of unexpected correlations between the masses of supermassive black holes and the motion of the stars in galaxies. To everyone’s astonishment, the growth of galaxies and supermassive black holes were intimately linked. In fact, supermassive black holes were the missing ingredient without which galaxies make absolutely no sense.

This is the story of how black holes, once thought to be so ridiculous as to not even be the preserve of science-fiction, have come in from the cold. This is the story of how, over the past century, these nightmare objects have journeyed from the periphery of the imagination into the very heart of science. This is the story of how we realised that black holes are not only the key to understanding fundamental physics, but also the key to understanding our universe – and maybe even why you are living on Earth and at this moment reading these very words.

London, 30 June 2023

AUTHOR’S NOTE

The stories I tell here are as factual as I can make them. If the scientists were alive, I interviewed them. If they were dead, I used historical facts, and especially oral histories, and dramatised the events around them. My hope is that, by doing this, I not only bring the events to life but also provide some idea of what the moment of discovery is like and how exhilarating it is to realise a profound truth about the world that no one has known before. For those interested in the history of science, I provide copious references.

As a journalist, as well as a former scientist, my first inclination is always to pick up a phone and get the story directly from the horse’s mouth. None of the scientists I talked to appear to have been contacted recently by anyone else writing a book on black holes. It is hard to convey the thrill of putting down the phone after an hour or two of conversation with a notebook filled with stories very probably nobody else knows. It was a thrill I first experienced researching the cosmic background radiation for Afterglow of Creation. Most of the people I interviewed on a whirlwind tour of the US are now dead so the book is now a unique historical account of one of the greatest cosmological discoveries of the twentieth century.

People working at the frontier of science are, by definition, extremely busy and hard to get hold of. I am therefore truly grateful to all those who generously gave up their precious time to talk to me.

- 1 -

AN IMPOSSIBLE THING BEFORE BREAKFAST

How a man dying in a First World War field hospital discovered that a star crushed into a tiny volume would warp space-time into a bottomless pit from which nothing, not even light, could escape.

Black holes are where God divided by zero.

Steven Wright

Curiously, black holes are very simple in that, like the back of the Moon, we cannot observe them.

Roy Kerr

MULHOUSE, ALSACE FRONT,

26 JANUARY 1916

So shocking was his mathematical result that his hands were shaking as he slipped his paper into an envelope and wrote on it: Prof A. Einstein, Kaiser Wilhelm Institute, Berlin. Somewhere out in the universe there could be holes in the very fabric of space and time, sealed off and cloaked forever from the rest of reality. On fastening the envelope, Karl Schwarzschild collapsed back, exhausted, in his cot, aware once again of the distant pounding of guns.

He had been woken by the latest bombardment 17 kilometres away at Hartmannswillerkopf.a As he screwed up his eyes against the winter sunshine streaming through a low window of the chapel, he was overcome with a deep depression. Not only was this awful war dragging on and on but it had been hard for him to get to sleep with all the pain and discomfort he was suffering from the blisters all over his body. But, no, he admonished himself, he must not succumb to self-pity. That way lay oblivion. At all costs, he must cling to the good things.

He glanced across at the wooden crate beside his cot – at the photograph of his wife, Else, in their beautiful garden back in Göttingen, and at the pages of esoteric calculations that, on waking, he had, for one terrifying moment, thought had been nothing but a dream. But, no, all was well. The letter to Einstein he had finished at 2.30 a.m. was exactly where he had left it. He had not been dreaming. His mathematical manipulations had revealed something extraordinary and scarcely believable about nature: it was possible for space and time to fold in on themselves, leaving a region of the universe forever shrouded in utter blackness.

The morning routine was exhausting. A sleep-deprived nurse with dried bloodstains on her white uniform came into his bay. She mopped at his ugly weeping blisters, rolled him over in his cot, changed the sheets, and rolled him back. She left him with a tray of soft bread and warm milk (though he would have preferred a beer).¹ As he chewed gingerly at the only food that did not further inflame his blistered mouth, he listened to the thud-thud of the distant guns and pondered the chain of events that had brought him to this field hospital in a half-demolished chapel on the Alsace Front.

When war was declared on 3 August 1914, there had been absolutely no need for him to volunteer. He was forty and the director of the Berlin Observatory, one of the most prestigious posts in German science. But antisemitism was on the rise in the German Empire and he was a Jew. He never mentioned it to anyone. In fact, in his Last Will and Testament, penned on the eve of joining the army, he strongly advised Else to withhold from his children, until they were at least fourteen or fifteen, the fact that he was Jewish.² But, though he did not attend synagogue or observe his religion in any way, he could not escape his Jewishness. What he could do, however, was demonstrate that Jews like him could be patriotic Germans. That was why, as ominous events unfolded across Europe over the summer of 1914, he resolved that, if it came to it, he would put his life on the line to defend the Fatherland.

The nightmare had begun in Sarajevo on 28 June 1914 when Gavrilo Princip, a nineteen-year-old Serbian nationalist, assassinated the Austro-Hungarian Archduke Ferdinand. International alliances clicked into place and, by the autumn, Germany and the Austro-Hungarian Empire were squaring up to England, France and Russia. The lamps are going out all over Europe, said British foreign secretary Sir Edward Grey. We shall not see them lit again in our life-time.

During his eighteen months in the Kaiser’s army, Schwarzschild had run a weather station in Belgium and calculated shell trajectories with an artillery battery in France.³ Finally, his artillery brigade had been posted to Mulhouse, a shell-damaged city in Alsace, the only mountainous region on the 700-kilometre-long Western Front.b

For France, the declaration of war with Germany had been seen as a golden opportunity to snatch back Alsace and part of Lorraine, which had been ceded to Germany after the Franco-Prussian War in 1871. From August 1914, bloody battles had ensued in which positions were repeatedly taken, lost and retaken. In 1915 alone, the strategically important 956-metre-high rocky spur of Hartmannswillerkopf had changed hands four times.⁴

It was at Mulhouse that Schwarzschild started to feel unwell. On 22 December 1915, he wrote to Else: I don’t know how to name or define it, but it has an irrepressible force and darkens all my thoughts. It is a void without form or dimension, a shadow I can’t see, but one that I can feel with the entirety of my soul.⁵

Schwarzschild, lying alone in his cot, looked down at his chest and the blisters beneath his unbuttoned pyjamas, some scabbed over and some still weeping. He shut his eyes tight and instead thought of the letter now on its way to Berlin – the second of two letters he had sent to Einstein at the Kaiser Wilhelm Institute in Berlin. Had he made a mistake in his calculations? Did his astonishing result hold up? There had been nobody to talk it over with. The new theory of gravity was so fresh that he was one of the first people, if not the very first, to understand and master it. Apart from, of course, its genius creator.

*

Albert Einstein’s path had crossed Schwarzschild’s on only a handful of occasions and they had exchanged nothing more than pleasantries. Whereas the Kaiser Wilhelm Institute was in the Berlin suburb of Dahlem, the Berlin Observatory was outside the city in Potsdam. Despite this minimal contact, Schwarzschild had followed Einstein’s decade-long struggle to find a theory of gravity that was compatible with his revolutionary special theory of relativity of 1905 with burning interest.⁶

The problem with special relativity is that it contradicts Newton’s theory of gravity in several ways. For instance, Einstein’s theory maintains that nothing can travel faster than light whereas Newton’s assumes that the gravity of a body like the Sun is felt everywhere instantaneously, which is tantamount to saying that gravitational influence propagates at infinite speed.

Newton was very aware that such instantaneous action at a distance is nonsensical and that between the Sun and the Earth there must be some kind of medium that transmits gravity. But he was unable to come up with a credible explanation of how it might work. And he had little incentive given that his universal theory of gravity was so brilliant at explaining everything from the motion of the planets to the periodic rise and fall of the tides in the ocean.

Fast-forward to the early nineteenth century. When the English physicist Michael Faraday held a piece of iron close to a magnet, he could actually feel the magnetic force of attraction reach out across space and grab it. He was sure there was something in the air around the magnet and he imagined an invisible field of force. A magnet creates such a field, he guessed, and it is the field that applies a force to the piece of iron.

Faraday was ridiculed for his concept of the magnetic field by other physicists wowed by the successes of Newton’s theory of gravity and supposing, wrongly, that Newton believed in instantaneous action at a distance. Only one physicist took the idea seriously: the Scot James Clerk Maxwell. In 1820, the Danish physicist Hans Christian Ørsted found that a wire carrying an electric current deflected a nearby compass needle, and so acted as a magnet, revealing a surprising connection between electric and magnetic fields. In a mathematical tour de force, Maxwell obtained a description of this electromagnetic field and discovered, to his amazement, that the speed of a disturbance propagating through the field is the speed of light. Not only is there a connection between electricity and magnetism, there is a connection between electricity, magnetism and light. Light is an electromagnetic wave.

But, if an electromagnetic field mediates the electromagnetic force between electric charges, Faraday wondered, could there be a gravitational field that mediates the force between masses? Maxwell thought it a serious possibility. Unfortunately, he died, aged only forty-eight, before he could explore the idea.

Einstein, however, was in no doubt that a theory of gravity that would simultaneously supplant Newton’s and be compatible with his special theory of relativity must be a field theory. If there existed a gravitational field, it would take time for a gravitational influence to propagate through the field. Einstein’s maximum speed limit of the speed of light would therefore be incorporated naturally. Whereas Newton’s theory predicted that, if the Sun were to suddenly vanish, the Earth would notice immediately and fly off to the stars, Einstein’s theory predicted that, before doing so, the Earth would orbit the Sun for a further eight and a half minutes: the time it would take for news of the Sun’s absence to propagate through the gravitational field at the speed of light.

The gargantuan task Einstein set himself was to find a field theory of gravity. He started out by addressing a 400-year puzzle.

The seventeenth-century Italian scientist Galileo Galilei reportedly dropped different masses from the top of the Leaning Tower of Pisa and observed that they hit the ground at the same time. This observation is perplexing. To understand why, imagine two identical sledges on an ice rink: one empty and one carrying a child. If each is pushed with the same force, the sledge with the child, on account of having more mass, or inertia, will be more reluctant to move and so will not change its velocity, or accelerate, as much as the empty sledge. In short, the same force applied to two different masses results in different accelerations.

Contrast this with two different masses that are acted on by the force of gravity. They categorically do not accelerate at different rates. As Galileo demonstrated, they accelerate, or fall, at the same rate.c Peculiarly, the force of gravity appears to adjust itself to any mass, so that, for instance, the force on a body twice as massive as another is twice as big, the force on a body ten times as massive is ten times as big, and so on. By perfectly compensating for their masses in this way, the force of gravity ensures all bodies accelerate at the same rate.

Einstein’s genius was to realise that, actually, no adjustment is needed. Because there is one circumstance in which all bodies, no matter what their mass, automatically appear to accelerate at the same rate.

Imagine an astronaut in a spacecraft far from any source of gravity such as the Earth. Imagine also that the spacecraft is accelerating at 1g so that the astronaut’s feet are pinned to the floor of the cabin, exactly as if he were standing on the Earth’s surface. If, furthermore, the windows are blacked out and the cabin is perfectly insulated from the vibration of the engines, for all the astronaut knows, the cabin could truly be on the surface of the Earth.

Now, imagine that the astronaut holds out two masses at the same height in front of him – say, a hammer and a drawing pin – and lets go of them. They appear to fall under gravity, hitting the floor simultaneously. But this is not really what has happened. Because the spacecraft is far from any source of gravity, the hammer and drawing pin have actually hung, weightless, in mid-air. What has happened is that the floor has accelerated upwards at 1g to meet them. It struck them simultaneously because, well, how could it not?

According to Einstein, therefore, Galileo’s observation that all masses fall at the same rate under gravity has a trivial explanation. Gravity is acceleration. Not realising that we are accelerating, we have made sense of our world by inventing a force called gravity.

Think of the astronaut again. Imagine he shines a laser horizontally from the left-hand wall of his cabin to the right-hand wall. He notices that the spot on the right wall is slightly lower than on the left wall. This is because, during the time the light is in flight across the cabin, the floor has accelerated upwards. (Of course, this is only a very tiny effect because the speed of light is huge – 300,000 kilometres a second – but this is only a thought experiment.) The astronaut, however, believes he is experiencing gravity. He believes gravity has bent the beam of light so that it curves downwards.

But what has actually happened? Light is well known for taking the shortest path between any two points. On the Earth’s surface, this would be a straight line – but only if the ground is flat. If the ground is hilly, the shortest path is curved. Since the path of the beam of light is curved, the unavoidable conclusion is that space too is curved. And, since gravity and acceleration are indistinguishable, gravity must be curved space.

Here, then, is the explanation of how we can be accelerating while not noticing: space, though we are unaware of it, is curved, or warped. We think there is a force of gravity, like an invisible tether, that extends from the Sun to the Earth and keeps the Earth trapped forever in orbit around the Sun. But this is