The Universe In Your Hands

In Cosmology by Brian Koberlein1 Comment

Take a look at your hands.

Have you ever thought about where your hands came from? Naturally, you got your hands from your parents. They gave you the DNA which determined the size and shape of your hands. All the muscles, bones and tendons in your hands were honed by natural selection to the form you have today. Your DNA traces its lineage through the entire history of life on earth from its early beginnings more than 3.5 billion years ago to the present day. It is a profound concept when you think about it, but that is just part of the story.

Your muscles, tendons and DNA are all made up of oxygen, carbon, iron, and a dozen other chemical elements. Where did they come from? It turns out that oxygen, carbon and iron all trace their origin to nuclear fusion within the hearts of stars. Long before our solar system formed, ancient stars burned brightly, their cores fusing hydrogen and helium into all the useful elements we see around us. But as with all things, their life came to an end. When large stars die, they rip themselves apart in what are called supernovae. All that carbon, oxygen, iron and more are cast out into space, creating large regions of gas and dust called nebula.

About 5 billion years ago, a humble star we call the Sun formed within such a nebula. The Earth and all the other planets of the solar system formed from the dust left over from the Sun’s formation. Your hands are made of stardust, formed in the hearts of long-dead stars. All the atoms and molecules from which you are made were created long before the Sun shone its first light.

But where did those long-dead stars come from? The earliest stars formed within galaxy-sized clouds of hydrogen and helium. The hydrogen and helium were formed about 13.8 billion years ago. At that time the universe was much more dense, and much hotter than it is today. We think of space as being cold and empty, but at that time the entire universe was about as hot and dense as the surface of the Sun. We still see the remains of that period as the cosmic background radiation. This radiation has cooled over time as the universe expanded, until now it is a weak echo of its former intensity. Everything you see around you, from your hands to the most distant galaxy traces its origin to that ancient fireball.

When you look at your hands, you are looking at atoms which are billions of years old, some of which are among the oldest atoms in the universe. They have been a great many things, from stars to planets. They have been living things and ancient stones. Before they became a part of you, these atoms were most likely wheat, or apples, or chickens. That is, until you ate them, and they became a part of you. These ancient elements will eventually continue on their way, leaving you to continue on yours.

But for now, they are your hands.

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