Chapter 15: The Whole Story in One Working Day

Night 178: Packing to Go Home

Mission day 178 was Noor's last full day on the station. The next day, she, Tomás and Ade would climb into the small spacecraft that had brought them there, close the hatch and begin the journey home. A new crew had arrived a few days earlier, and the station was fuller and noisier than usual. Every corner seemed to have someone in it, learning where things were kept, asking questions and laughing at the way the new people bumped into walls, as Noor had in her first week.

Most of Noor's day was spent packing and handing over. There is very little room in the spacecraft for personal things, so she had only a small bag. Into it went a few photographs, a letter from Sami, a notebook full of small drawings of the Earth and the soft cloth she had used to wipe the large window. Everything else she left for the new crew or packed into cargo for later return. She spent two hours with the newest flight engineer, showing her the experiments, the tricky latch on one cupboard and the place where the water system makes a strange sound that is completely normal.

Late in the afternoon, Noor took her last photographs of the Earth. She had taken thousands during her stay, of oceans, deserts, rivers, ice and the lights of towns at night. That day she did not try to make good pictures. She simply wanted to remember. She watched one more sunrise spread along the edge of the planet, then one more sunset, and she noticed that after six months, she still could not describe the colours properly. Perhaps nobody can.

She also did her exercise, as she had every day. It mattered even more now. After six months in weightlessness, her body had grown used to floating. Her bones and muscles had weakened a little, in spite of all the work on the treadmill and the lifting machine. Back on Earth, she would need weeks of careful exercise to feel at home in gravity again. The first days would be hard. Many astronauts say that, for a while after landing, even their own head feels heavy.

In the evening, the old crew and the new crew ate together. Tomás played music. Ade gave a short speech that was mostly jokes. Then, one by one, people drifted away to sleep. Noor went to the large window for the last long look of her stay. The Earth turned below her, blue and white and dark, and the stars shone above the thin line of air.

Earlier that day, Sami had sent a message. "Last night up there," he wrote. "You have told me so many stories. Can you tell me the whole thing at once? From the beginning until now. I have a short break tonight." Noor thought about it for a while. Then she decided to tell it in a way that a working person would understand: as a single working day.

Midnight to Morning

Imagine that the whole history of the universe, about 13.8 billion years, is squeezed into one day of 24 hours. The universe begins at midnight, and the present moment is the next midnight. On this scale, one hour is about 575 million years, one minute is about 9.6 million years and one second is about 160,000 years. Everything we have talked about over these fifteen nights fits into this one day.

At midnight, the universe is extremely hot and dense, and it begins to expand and cool. Whatever happened at the very first instant, we do not know; as we have seen, our physics cannot yet describe it. If inflation happened, it was over in a tiny fraction of the very first moment. Within the first fraction of a second, the building blocks of protons and neutrons came together. Within the first few minutes, helium and a little lithium were made. On our clock, all of this happens in far less than the first second after midnight, a time too short to notice.

A little less than two and a half seconds after midnight, the fog clears. This is the moment, about 380,000 years after the beginning, when atoms form and the oldest light begins its long journey. That light is still arriving at our telescopes today, stretched into microwaves. Then the cosmic dark ages begin. For a while, there are no stars at all, only gas slowly gathering into clumps under gravity, guided by the invisible pull of dark matter.

Probably within the first half hour or so after midnight, the first stars light up. We do not yet know exactly when, and we have not yet seen the very first stars with certainty. Many of them are probably huge and short-lived, and their light slowly clears the dark again. By the early hours of the morning, galaxies are forming, growing and merging. The tiny ripples seen in the oldest light are becoming the great web of galaxies.

It is worth saying that this clock is a picture, not an exact timetable. Some of its times are known very well, for example the age of the universe, the moment of the oldest light and the age of the Sun and the Earth. Other times, such as when the first stars lit up or when life began, are still being studied, and they may move a little as new measurements arrive. But the general shape of the day is clear, and it has been checked in many independent ways.

Through the rest of the night and the whole morning, the universe is busy. Galaxies grow, including our own Milky Way. Generations of stars are born and die. Big stars explode and scatter carbon, oxygen, iron and other elements. Neutron stars collide and make heavy elements such as gold. Each generation leaves the clouds between the stars a little richer than before. By noon, the universe has already been working for half its life, and still there is no Sun and no Earth.

Afternoon and Evening

In the afternoon, something changes in the background. For the first part of the day, the expansion of the universe has been slowing down, braked by the gravity of all the matter in it. But as space stretches and matter thins out, the mysterious dark energy begins to take over. Some time in the afternoon, the expansion begins to speed up. It is still speeding up when the day ends.

At about four in the afternoon, in one ordinary galaxy, a cloud of gas and dust collapses. It is full of elements made by many earlier stars. At its centre, the Sun begins to shine. Around it, a spinning disc forms planets, and one of them is the Earth. Soon after, something large crashes into the young Earth, and the Moon is born from the debris. The Earth is hot, battered and without oceans at first. But it cools, and water gathers on its surface.

At around six in the evening, or perhaps a little earlier, the first known signs of life appear on the Earth. They are tiny and simple, and scientists still discuss exactly when and how they began. For hours of our clock, life stays small. Through the evening, it slowly changes the oceans and the air. Late in the evening, larger living things appear, and later still, plants and animals spread onto the land.

At about seven minutes before midnight, a large body from space strikes the Earth, and the age of the dinosaurs comes to an end. Mammals, which had lived alongside the dinosaurs as mostly small animals, begin to spread and change. In the last minute of the day, the ancestors of people appear.

Modern humans arrive only about two seconds before midnight. All of written history, every book and every working day that anyone has ever recorded, fits into a tiny fraction of the very last second. The first astronomers who carefully recorded the positions of stars, the people who measured the speed of light, the woman who studied pulsing stars on photographic plates, the engineers who heard the hiss of the oldest light, and Noor looking out of her window tonight, all live in that last flash of time.

It is a humbling picture, but it need not feel sad. In that last fraction of a second, a part of the universe, made of hydrogen from the first minutes and of elements from many stars, has become able to look back and understand where it came from. We are latecomers to the day. But we are latecomers who can read the clock.

What Comes Next

Sami's message asked about the story "until now". But a working day is followed by another one, and the universe also has a future. What can we say about it? Some things are well understood. Others are not known at all.

The Sun is in the middle of its life. In about 5 billion years, it will run low on hydrogen in its core. It will swell into a red giant, much larger and cooler than it is today, and the inner planets will be scorched or swallowed. Later, it will gently push its outer layers into space and become a small, slowly cooling white dwarf. This is the normal life of a star like the Sun, and astronomers can see stars at each of these stages elsewhere in the galaxy.

In about 4 to 5 billion years, the Milky Way and the Andromeda galaxy are expected to come very close to each other, although their exact paths are still being measured. As we saw on an earlier night, even if they meet, the stars themselves will almost never collide, because the spaces between them are so large. Over a long time, the two galaxies may merge into one larger galaxy. If anyone is watching the sky from a planet at that time, the night will look very different, with new bands and clouds of stars.

The far future of the whole universe is less certain. If dark energy stays as it seems to be now, the expansion will keep speeding up. Galaxies far beyond our own group will move away faster and faster, and over very long times, their light will fade from view. Stars will continue to be born for a very long time, but the gas they need will slowly run out. In the extremely distant future, the universe may become dark and cold. But all of this depends on the nature of dark energy, which we do not understand. So it is more honest to say that the far future is an open question than to describe it as a certain ending.

The Pleasure of Open Questions

Over these fifteen nights, we have met many open questions. What happened at the very first moment, and was there anything before it? Did inflation really happen? Why was there a little more matter than antimatter? What is dark matter? What is dark energy? Why do two careful ways of measuring the expansion give different answers? How large is the whole universe? How did life begin on the Earth, and is there life anywhere else? None of these questions has a final answer today.

This may seem like a disappointing way to end a book. But the history of the subject suggests another way of seeing it. A little more than a hundred years ago, many astronomers believed that the Milky Way was the whole universe. Nobody knew that space was stretching. Nobody knew what made the Sun shine. Nobody had heard the oldest light or knew where the elements in their bodies came from. Each of those questions was answered by people at work, measuring, calculating, checking and arguing, often for years.

Many of those people were not famous in their own time. Some were employed to do patient, repetitive work, like measuring the brightness of stars on glass plates. Some were trying to solve an ordinary problem, like a noise in an antenna, and found something extraordinary instead. Some did their most important thinking alongside other duties, such as teaching. The beginning of the universe was not discovered in one flash of genius. It was pieced together over a century by many working people, each adding a part.

Today, the same kind of work continues. There are telescopes in space and on the ground, instruments that sense ripples in space itself, and machines on Earth that recreate tiny drops of the early universe's heat. Somewhere tonight, people are checking data, repairing equipment and writing careful notes. Some of today's open questions will be answered in your lifetime. Others may wait for people who are not yet born. That is not a failure. It is how a long piece of work is done.

There is a kind of pleasure in this that many working people will recognize. The best days at work are not always the days when everything is finished. Sometimes they are the days when a difficult problem finally begins to make sense, or when you see a new way to approach it. Astronomy has many such days ahead. A question that has no answer yet is not a closed door. It is work that is still waiting for someone, and that is a hopeful thing.

The Last Message to Sami

Noor wrote her message slowly, floating by the window, with the Earth turning beneath her. She tried to make it short enough for a break between deliveries.

"Here is the whole story as one working day," she wrote. "At midnight, the universe begins, hot and dense, and starts to stretch. In the first second, the first elements are made. In the first half hour or so, the first stars light up. All morning, stars and galaxies grow and die and make new elements. At about four in the afternoon, the Sun and the Earth are born from a cloud of old star dust. At about six in the evening, the first signs of life appear. At seven minutes before midnight, the dinosaurs end. People arrive two seconds before midnight. And right now, at the very end of the day, a truck driver and his sister are talking about all of it. See you soon. Keep looking up."

At three in the morning, on a quiet road far below, Sami parked for his break. He read the message slowly. Then he stepped out of the cab, stretched his tired back and looked up. Between the clouds, a few bright stars were shining. Somewhere up there, hidden in the Earth's shadow at that hour, a station was crossing the sky with his sister inside. He wrote back only three words: "Come home safely."

Noor read his reply just before she slept, curled in her sleeping bag for the last time on the station. The next day there would be the hatch, the long fall through the atmosphere, the heat outside the small windows, the parachutes and finally the heavy, wonderful pull of the Earth. That night, there was only the soft hum of the fans and the memory of a hundred and seventy-eight days of sunrises. She closed her eyes.

Now the story turns to you. Tomorrow, or on any clear evening after work, step outside for a few minutes. You do not need a telescope or a dark mountain. Look up at whatever you can see: the Moon, a few bright stars, perhaps a planet. Remember that the light reaching your eyes has travelled for seconds, minutes or years to meet you. Remember that the atoms of your body were made in the first minutes of the universe and in the hearts of stars. And remember that people are still working, night after night, to understand the rest. You are part of the story too, in the last second of a very long day.

Common Misunderstandings

Many people think that astronomy and astrology are the same thing, or two sides of one subject, because both look at the stars and planets and both have similar names. Long ago, the two were often practised by the same people. But today they are completely different. Astronomy is the science that studies what the stars, planets and galaxies are and how they work, and it tests its ideas against careful measurements. Astrology claims that the positions of the planets and stars shape people's characters and lives, and these claims are not supported by evidence. Some people read horoscopes for fun, and that is their own choice, but astrology is not part of astronomy.

Many people also think that the universe will end soon, or that its end is something to worry about. Sometimes dramatic films and headlines give this impression. In fact, the changes described tonight take place over billions of years and more. The Sun has about 5 billion years of steady life still ahead of it. Any meeting with the Andromeda galaxy is billions of years away. Whatever the far future of the universe will be, it is so distant that it has nothing to do with the life of anyone alive today, or of their children or grandchildren.

Finally, some people think that science has finished the story of the universe, or, on the other hand, that because there are still open questions, science knows nothing at all. Neither is true. Some parts of the story are known very well: the universe is about 13.8 billion years old, it is expanding, it was once hot and dense, the oldest light fills the sky and the lightest elements were made in the first minutes. Other parts, such as dark matter, dark energy and the very first moment, are still unknown. Knowing some things well and other things not yet is the normal state of a living science. The story is still being written, and every clear night, it is waiting above your head.