“We are stardust reflecting on stars .” This iconic phrase spoken by Carl Sagan is not a mere poetic expression, but has a scientific basis: our atoms and those of everything that exists are made from the debris of ancient stars that died in the remote past of the universe.
Thirteen thousand eight hundred million years ago, it is believed that a brutal explosion began to expand matter, giving rise to the universe. This hypothesis is known as the Big Bang Theory, from which all matter that exists, that has existed, and that will never exist could come. Apparently, from an infinitely small and dense point, all matter began to expand. Today scientists know that our universe still continues to expand, thanks to contemporary instruments, which give us access to very precise analyzes of the first moments of the universe, such as microwave background radiation.
The first type of matter that could exist had to be, necessarily, elementary particles. According to this model, from the first second to three minutes after the initial explosion, the so-called Nucleosynthesis stage took place: the one in which the first atomic nuclei begin to form, through the combination of protons (hydrogen ions) and neutrons.
Hydrogen is one of the most fundamental elements in the universe, and probably the oldest element. Hydrogen is the fuel for stars: that is, they fuse hydrogen atoms in their nucleus to obtain helium, which gives rise to energy in the form of light and heat (what we perceive of our Sun from Earth). But the stars are not eternal. At the end of their lives, the most massive explode in the form of supernovae; others simply turn into white dwarfs, little stellar corpses. The point is that, most of them, they leave behind a nebula, and after their disintegration complex chemical reactions take place that give rise to new elements, such as carbon or silicon. Carbon, for example, is the basis of the life forms we know on Earth. This means that our entire being, our atoms and the atoms of all living things that populate, populate, or will ever populate the Earth are made of the debris of ancient stars that died thousands of years ago (perhaps hundreds or billions of years). This is, in short, the premise that matter is neither created nor destroyed, but is transformed. That is, as Carl Sagan, probably the most famous scientific popularizer of the 20th century, said, we are all (and everything) literally stardust , in our era, reflecting on stars.
