The Story of the Universe and Me: Where Did I Come From?

By NASA & ESA [see page for license], via Wikimedia Commons

Part 1: The Universe

Everything that makes up my body was once packed into a single point, along with all the other energy that has ever existed. That includes everything that makes up the planet Earth, every star in the sky, and you, dear reader. Of course, it was in a much different form than as you currently see it. It wasn't matter or atoms yet; in fact it didn't take any recognisable form as far as we know.
All of this compressed into one place made for a very hot, very dense point. In fact, if one can grasp such mathematical aberrations, it would have had infinite density and infinite temperature. At least, that's what we think; but our understanding of the universe tends to break down when you force the whole thing into the space of an atom.
Then, about 13.8 billion years ago (give or take), this energy couldn't stand its own company any more, and it burst. We tend to think of what happened as an explosion, and that's accurate to a degree. But instead of a chemical reaction, propelling matter into the surrounding space, space itself expanded, taking the matter with it. Space exploded into being, and brought time along with it.
After a trillionth of a second, the laws of physics as we know them settled into place, and the universe was allowed to begin cooling down. It was still growing at a phenomenal rate, but now there was more space for its energy to inhabit. Energy transformed into fundamental particles, quarks and gluons. These cooled down even further as the universe swelled and were able to join together as protons and neutrons. All of this happened within a second of the initial explosion.

A few minutes later, they themselves joined together to become hydrogen and helium nuclei. This was only possible because the universe was still very hot and very dense. Just no longer infinitely so. After some three hundred and seventy-seven thousand years, the nuclei were cool enough to capture electrons and become atoms. The atoms continued away from each other with some speed, as the universe continued to grow.

After 150 million years, gravity finally overcame the force with which these particles were flung. The matter wasn't quite evenly spread; it was ever so slightly lumpy. Bits of it were a little bit closer than other bits, and their mass began to pull at each other. Ever so slowly, these atoms fell toward each other, condensing first into loose clouds of dust, and then into hotter balls of gas called protostars. As these protostars collapsed under their own weight, they heated up. The potential energy from the distant association of atoms became thermal energy as they all crushed in together. Finally, the heat and pressure inside these protostars pushed hydrogen atoms at their core together so hard that they fused together, transmuting neatly into deuterium (an isotope of hydrogen), and then into helium. This repeat nuclear fusion gave off huge amounts of light, heating up the protostars even further and transforming them into fully-fledged stars.
This was the first generation, lighting up the universe for the first time in millions of years. The gravity of these stars pulled them into huge collections, known as galaxies, orbiting each other and a common centre.
As these first stars aged, they collected enough helium at their cores to fuse helium and hydrogen into carbon and oxygen. When helium ran out, they moved on to even heavier elements, crafting new nuclei that had never existed before. Once their cores were heavy with iron, which, instead of emitting light when fused, absorbs it, they could burn no longer. They expired, one by one.

Smaller stars simply swelled for a time, and then threw their layers off until only the embers remained. That will be the fate of the star that graces our daytime sky.

Stars that were large enough exploded in furious displays of raw power, echoes of the distant past, and with such force that the explosions created even heavier elements. Left behind were their hearts, the densest objects in infinity: neutron stars or, in the wake of the greatest behemoths, black holes.

Just as those first stars were born from the material cast off in the primordial boom, so too did their ejections give rise to new stellar nurseries, protostars, and stars. And the cycle continued. Every supernova enriched the stellar nurseries with more heavy atoms, and every generation of stars grew from more metallic gas. Rocky planets were now able to form from their parent stars’ leftovers, gathering from the discs that swirled around the bright, young globes.

Around five billion years ago, an average-sized white star swelled from the dust. It was orbited by a swarm of smaller bodies, from gas giants to tiny, rocky worlds. One of these worlds was to become our home.

To be continued!

Part 2: The Solar System

Author's note: I hope no-one reading takes offence to any poetic liberties I may have taken with the grand story of our universe. I've striven for accuracy, but it's difficult to convey all of the complexities of physics in an accessible way (particularly when I'm no expert in the first place). So hopefully you can enjoy it for all its flaws.