You, reader, we send into space; but not now, but within 5 billion years. It makes you witness the death of the Sun in an explosion that incinerates the Earth as if it were a simple cigarette butt. It is a transcendental vision because it confronts you with an inevitable reality. The countdown of the Earth and everything on it does not stop, and although the future seems distant, it is a certainty. Galfard makes a statement of principles right out of the gate. “Of all the possible futures that exist, (…) only one path will allow humanity to survive the inevitable death of the Sun and almost any other catastrophe. That path is that of knowledge, that of science. A journey that is only within the reach of the human being. A journey you are about to embark on.” On this journey we will discover what the universe is made of, what is beyond Earth, how far one can look, what has been the history of the universe. Let’s start with the closest, our natural satellite.

Moon Four billion years ago our young planet was struck by another planet the size of Mars, ripping off a considerable chunk of its mass and launching it into space. Over the ensuing millennia, the debris from that collision compacted into a single sphere that orbited our world. The result of that process was the Moon; the first stop on your odyssey.

The moon brought us the tides and a pale “sun” that illuminates the night. Without our brother star, life as we know it would not exist on Earth. It also protects us quite well from asteroids and comets that come close to our planet. You are inside a large crater looking at the sky. You see the stars and the rest of the planets with total clarity because the Moon has no atmosphere. Craters like the one you rest in that dot the Moon’s surface are a good reminder of that. Hundreds of thousands of mountain-sized boulders have been battering at her since her birth. Sun Our powerful Sun shines 150 million kilometers away. If humans were able to capture all the energy that our star radiates in one second, it would be enough to sustain the needs of the entire planet for the next 500 million years. The Sun is much smaller than when you saw it in that vision of his death, but next to the Earth it is a titan.

Hydrogen and helium make up 98% of the universe. Before they were almost all that existed, but the stars created heavier elements such as oxygen or silver As you get closer to the Sun you see huge flares of plasma (not fire) erupt from its surface. The heat is scorching, and the star takes up half of your vision. You enter inside thanks to your immunity to heat. Advantages of traveling with thought. The nucleus is a jumble of hydrogen atoms that have been stripped of their electrons (cations) due to the enormous surrounding energy. Strong gravity causes these nuclei to fuse to form heavier nuclei. As they rise toward the star’s surface, they trap electrons and transform into larger atoms such as nitrogen or carbon. Those nuclear fusion reactions are what differentiate stars from planets. The Earth, Mars or Uranus are not large enough to cause enough pressure in their core for fusion reactions to take place. In the fusion process, the resulting mass of the new atom is less than that of hydrogen and helium separately. The rest does not disappear, but is converted into energy, a lot of energy. To calculate how much, you only need a formula.

E = mc2

The energy released by the fusion is to blame for the stars shining and for compensating the gravitational force of the stars, preventing the collapse of the star. When there are not enough hydrogen and helium nuclei left inside, gravity wins the day and the stars die. When they die, they expel the heavy atoms from their interior, creating clouds of star dust. Perhaps in the future, that dust will be the seed of new stars and planets. The author thus narrates the end of our star: “The Sun will shrink and gain density until a new nuclear fusion reaction is unleashed, but this time farther from the nucleus, closer to the surface. This reborn reaction will not balance gravity, but will overcome it, and the surface of the Sun will be forced outwards, with which the star will grow.

It’s overwhelming to realize that all the atoms that make up your body, the air you breathe, and the apple you’re eating were created inside stars billions of years ago.