Why you have always said your age wrong, according to astrophysicists

How old are you? It is a simple question that we have all been asked at some point. But the answer is not that simple; In fact, it is surprising if we stop to think about where we come from. The key is to realize that the elements that make up our body are older than we think, even older than our planet.

This is the explanation: it is often said that we are stardust; very nice, very heard already, but it is not so true. If we ask ourselves how old our bodies are, we must analyze what a human body actually is. Well, our bodies are composed, for the most part, of water (around 60% by mass). That is H₂O, two atoms of hydrogen for each one of oxygen, which means that most of the approximately 7,000 quadrillion atoms that make up us are hydrogen, about 62% by number. And how old are those hydrogen atoms? The answer is not simple again. Hydrogen atoms are made up of one proton and one electron. Well, protons appeared in the Universe, according to our most recent calculations, a little less than 13,813 million years ago, with an error of 38 million years up or down.

Specifically, the protons of virtually all hydrogen atoms that exist today appeared from the first second after the Big Bang and in the first 3 minutes counted from that moment 13,813 million years ago. From the first second of our universe, quarks, which previously dominated the entire cosmos, disappeared to form protons and neutrons. Also in that remote time (but it happened here next door, in the same place from where you read this article -and anywhere else-), electrons were already quite oldformed between one millionth and one billionth of a second after the Big Bang.

But electrons and protons didn’t come together to form hydrogen until about 380,000 years after the Big Bang. So 62% of the atoms in my body and yours (which constitute 8% of its mass) have a whopping more than 3 times the age of formation of our planet, meaning the moment at which created that ball where we live. And this leads us to say that we are not as stardust as is often said; Our atoms were, rather, conceived, for the most part, shortly after the Big Bang.

Returning to our composition in terms of molecules and their atoms, we had left oxygen hanging. Furthermore, this element is very important, because although hydrogen is the most abundant atom in our body, if we look at the mass, oxygen dominates, which is about 16 times heavier than that proton and electron that we were talking about. 65% of our mass is oxygen.

And how old is that oxygen that dominates what we see on the scale? There are astrophysicists who have been wondering about this for decades and searching for oxygen, which the truth is that it is easy to find in the universe, in more and more distant galaxies. Oxygen has been seen when the universe was less than 3% of its current age. Observing distant galaxies means looking back in time, since they are so far away that it takes almost an eternity for light to reach us. And that delay allows us travel in space-time. Our studies tell us that three quarters of the oxygen existing in the universe today was formed in the first half of the history of the cosmos, and the other quarter later. Further in space, and earlier in time, 50% of the oxygen we have here today was formed in the first quarter of the history of the universe, in the first 3.5 billion years after the Big Bang, when there were still about 5 billion years left. of years for the Sun and Earth to appear, which in turn are another 4.5 billion years old. We do not give more data on the formation of oxygen, although there is some, and we conclude that, on average, our oxygen may be about 10.5 billion years old. We’re as old as that.

We are oxygen, carbon and hydrogen

If we keep asking ourselves how old we are by counting when the elements that make up us were formed, we must go to the next type of atom in mass contribution to our scale measurement. That element is carbon, which accounts for almost 20% of our mass. Carbon, more oxygen, more hydrogen already add up to 93% of our body mass. Carbon is somewhat more difficult to observe, but with a radio telescope we can go almost as far and as early in the history of the universe as in the case of oxygen.

Up to this point it is enough for us, more or less, to calculate the real age of our bodies. We leave the formation of the other elements (nitrogen, calcium and phosphorus are the next in bascular interest) as a small correction that we do not want to get into. Nor do we stop at the fact that any atom, in reality, comes from that primordial hydrogen that appeared in the first second of our universe, mixed in lunchboxes stellar, with the help of other very ancient particles such as photons (which were not always there).

For the planet we could make a similar account taking into account its atoms and where they come from and when they appeared. How does our age compare to that of our planet, in terms of how old our atoms are? A third of the Earth’s mass is iron, a little less is oxygen, and another third is dominated by silicon and magnesium, almost 15% of the mass each, leaving only room (or rather, mass) for a little sulfur, nickel, cadmium, etc.

When was the iron or silicon that we have on our planet formed? Well, it is much more difficult to give an answer than in the case of oxygen. Iron can be detected in very distant objects, although it is extremely difficult. We have detected iron and silicon in the vicinity of supermassive black holes that existed when the universe was 5% of its current age, but these elements surely appeared much more slowly than oxygen: we need to continue investigating to confirm this.

We leave here this journey through the history of our bodies. We don’t get into when the matter, which has been dancing through the universe for eons, came together in that way and acquired something that philosophy and religion have been trying to explain for a few millennia. Bits of our bodies already filled part of the cosmic void long before, and they will return to it, although each time they fill it a little less.

Cosmic Void It is a section in which our knowledge about the universe is presented in a qualitative and quantitative way. It aims to explain the importance of understanding the cosmos not only from a scientific point of view but also from a philosophical, social and economic point of view. The name “cosmic vacuum” refers to the fact that the universe is and is, for the most part, empty, with less than one atom per cubic meter, despite the fact that in our environment, paradoxically, there are quintillions of atoms per meter cubic, which invites us to reflect on our existence and the presence of life in the universe. The section is made up Pablo G. Pérez Gonzálezresearcher at the Astrobiology Center, and Eva VillaverDirector of the Space and Society Office of the Spanish Space Agency, and Research Professor at the Institute of Astrophysics of the Canary Islands.

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