Facing Infinity

Prologue

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THE RING OF LIGHT AT THE
EDGE OF THE DARKNESS

The light blinds you.

You raise your hands to shield your eyes, letting fragments of light filter between your fingers. White, blue and red stars are shining brightly in the darkness.

You're floating in space. There's no up or down. There's nothing you can grip onto with your hands or push against with your feet. The only thing around you is a gaping expanse, a void. You are floating in it like a drop of water in the ocean.

Thick white gloves cover your hands. They are part of your spacesuit, your only protection from the deadly vacuum that surrounds you.

You lower your hands and squint. In the starfield in front of you, you see a darkness. There are no stars there. There's no light, nothing but cold, black emptiness: a black hole.

A black hole is a place in the universe with such strong gravity no light can escape it. That's why black holes are dark. But the darkness not only signifies the absence of light, it also represents a limit of knowledge. No particles, no radiation and no other information can exit a black hole. If you want to know what is going on in the darkness, you have to travel right into it.

You realize that the darkness in front of you has grown. You are falling towards it and there is nothing you can do to stop yourself. You have no spaceship, no rockets, no way to alter your course.

The darkness feels both menacing and alluring. Like the explorers of old, you are venturing into the unknown. You are going to find out what happens in one of the strangest places in the universe, a place no one else has ever visited.

But there's a difference between you and those adventurers: after they had explored far-away places, they could return home and describe what they had seen. You will not be able to travel back and tell your fellow humans what you've been through. Once you've fallen into the black hole, you can never turn back. Its gravitational pull is too strong. The darkness will swallow you forever.

'In space the universe grasps and swallows me like a point; in thought I grasp the universe.'1 These are the words of the seventeenth-century French philosopher Blaise Pascal. He imagined that humans, with their capacity for thought, could gain comprehension and understanding of how the universe works. But the darkness of the black hole is so compact that the human mind can barely comprehend it. So how can you and other humans understand what a black hole is?

Perhaps an analogy will help.2 Imagine you're floating in a river. It's night-time. The river is flowing towards a waterfall. With a flash of terror, you realize you must swim against the current to avoid being swept over the falls, but the closer you get, the faster the river flows. In the end, it's moving so fast you can't swim away. However hard you try, you are pulled inexorably towards and over the falls. The river is flowing too fast and you are swimming too slowly.

But let's assume there's someone else who can swim faster than you. At the point beyond which you're unable to escape the waterfall, this swimmer would be able to, though only to a certain point. At a certain distance from the falls, this swimmer too would be dragged along by the water's flow, because the water would be moving faster than they can swim away. There is, therefore, a boundary in the river, set by the highest speed a human can swim. Beyond this boundary, no human can swim against the direction of the river's flow. The boundary itself is invisible; there's nothing in the water to indicate where this boundary is.

Now imagine that the river is so wide you can't see its banks. It's also so deep you can't see the bottom. Because you're swimming at night, the stars are all you can see. Substitute space for the river, and the speed of light for the maximum swimming speed, and you'll find yourself in a situation similar to your fall towards the black hole. Instead of being swept along by the water in the river, you're now being conveyed by the movement of space. If you'd had a spaceship, you could have turned around and travelled away from the darkness. But just as it's impossible to swim upstream after a certain point in the river, there is a boundary around the black hole after which you cannot turn back. It makes no difference how powerful the spaceship's rockets are. In the end, space is flowing so fast towards the darkness that not even light can travel in the opposite direction.

The boundary after which light cannot escape forms the surface of the black hole. It is known as the event horizon, and it is a surface spun from space and time.

It might sound odd that space can flow as a river does. But Albert Einstein realized more than a hundred years ago that this is possible. He discovered that matter and energy can distort space and time. Far from being static arenas in which our lives play out, space and time are active participants in the drama of the universe. But we'll come to that later. Right now all your focus is on the darkness around you.

You're falling into an abyss of space and time that has an enormous gravitational pull. But falling in space is not the same as falling on planet Earth. On Earth you can feel the air rushing past your face and hear your clothes fluttering in the wind. In the emptiness of space, however, there is no air and no sound. All you can feel is your spacesuit bumping against your body, and all you can hear is your breath, though you start to perceive a thudding noise that has grown louder as the darkness has deepened. You realize it's the sound of your heart, beating harder and harder the closer you get to the black hole. It's as though your heart fears what you will meet in the darkness, as though it knows you will have to sacrifice something in order to see what is happening inside.

The idea that knowledge comes at a cost features in many myths. When Eve took a bite of the fruit of the tree of knowledge, she and Adam were driven out of the Garden of Eden. When Faust made a pact with the Devil to gain unlimited knowledge of worldly things, he was made to pay with his soul. And when the Norse god Odin sought knowledge of the world and the future, he had to sacrifice an eye, throw himself on his spear and hang himself from the tree Yggdrasil.

Knowledge comes at a cost. The greater the knowledge, the higher the price. To find out what happens in one of the darkest and most peculiar places in the universe, you will have to pay the highest price of all: your life.

The point at which this will happen depends on the size of the black hole. The larger it is, the longer you can survive. The black hole you are falling towards right now is almost as big as the solar system. You can pass through its surface painlessly, but after that, your life will be over in only a few hours.

Your field of vision is increasingly taken up by the dark sphere. As the darkness grows, the light around it seems to change. You see multiple copies of the light from the stars appear on either side of the black hole. At the same time, the stars' light seems to grow brighter, becoming compressed along the edge of the black hole. It occurs to you that the darkness is controlling the light. The black hole's powerful gravity is making the stars' light travel along peculiar paths that multiply its radiance. Phantom stars form in space, like mirages in the desert. These strange star-doubles disorient you. You want to tell your friends how the encroaching darkness fills you with terror, how the light of the stars is distorted and how helpless you feel. But even if you had a radio transmitter, you wouldn't be able to send your friends a message after you'd passed the event horizon. You will have to bear those final moments in the darkness alone.

Deep within the abyss, there is a point so extremely dense it is hard to wrap our minds around what goes on there. This point is called the singularity. In our river analogy, this is represented by the waterfall. As you were swept along by the river, you were unable to avoid the falls in the end. Similarly, everything that passes the event horizon will ultimately reach the singularity. There, all matter and all light will be concentrated in a state that is so distorted, even space and time seem to cease to exist.

You are gaining speed as you fall towards the darkness. There is nothing you can do to avoid it. You turn your head and look around you. The area of space behind you is growing darker and darker. You lose your ability to orient yourself. You cannot tell where you came from, or how far you are from the black hole. Are you already inside it? You don't know. There's no sign at the event horizon that says 'You are now passing the point of no return.'

The dark sphere seems to surround you in every direction. You flail your arms and legs in a desperate attempt to escape your journey towards the singularity, but it's pointless. There's no escaping the singularity. All that happens is that you start sweating.

You close your eyes, take a deep breath and think about what awaits you. When you travel feet-first towards a black hole, your lower body will feel a greater force than the upper body. You begin to be pulled apart. But it doesn't happen the same way as on a torture rack; instead, everything in your body is drawn out, from your skeleton, your tendons and your muscles, all the way...