A history of the universe in eight hundred words
I’ve been meaning to write today’s post for a long time. I prepared to tell it for a Moth story on stage, but didn’t get to, so I’ll share it with you. It’s the story of how you got here from the beginning of the universe, at least as far back as we can trace it.
As you know, I like both physics and being able to make complicated things simple. I hope I convey both here.
The history of the universe in a few paragraphs
As far we can project back, everything seems to have explode out from a small volume. We can’t figure out before then since nothing we can see today gives us any clue about what happened then, which makes sense since it seems to have happened about fourteen billion years ago. Since then, as far as we can tell, with a few questions unanswered (which could be more important than we realize, like what are dark matter and energy), everything followed the same patterns as we see today — gravity, electricity and magnetism, and so on.
First, everything being so packed and dense made it hot–everything was bouncing off each other so much nothing meaningful could stay together, so it was just fundamental particles in a hot, dense fluid. As everything expanded, things bounced off each other less. One by one, different particles could interact more with different other particles. For example, by about a second after the big bang, protons and neutrons had formed from the particles that make them up. So for a while there were a lot of protons and neutrons bouncing around with all the other particles still around. Most other particles decoupled from each other similarly, with differences depending on the properties of the particles and their interactions.
About three minutes later, as the protons and neutrons kept mostly moving apart, they hit each other rarely enough that they could form those chemical nuclei, although only the lightest ones, like helium, which you might also remember from chemistry or physics class has one of the lightest nuclei. About three hundred thousand years later, the electrons stopped bouncing around so much that they could stick to the nuclei and form full atoms. When that happened, light could start to pass through this fluid and space became mostly clear, like it looks today.
At this stage there was lots of hydrogen, helium, a bit of other atoms, and some other particles in a big ball of gas. If it was denser in some places, gravity would get the atoms around it to fall in, forming stars, galaxies, and many of the stable structures we see in telescopes today.
We’re not done yet, though. Just having hydrogen and helium isn’t enough to make the Earth or us, since we’re made of heavier chemicals, like carbon and oxygen. After all this time of the universe getting less dense, some places started getting dense again–inside stars. Inside stars protons and neutrons got close enough to stick together, which made heavier combinations of them, which is to say, they formed heavier nuclei, as happens in fusion nuclear weapons. So inside early stars formed all the matter we’re made of. Stars balance the pressure from the nuclear fusion pushing them apart with gravity pulling them in. Many stars, depending on their properties, like their mass, suddenly hit certain reactions that cause them to explode suddenly more than gravity can keep them in.
One of those early stars exploded and send its inside all over space, making the gas around that area have a lot of heavier elements (I did some of my PhD work in an area like this). Just like that first star formed from gas falling together, a new star formed out of that new heavy-element-rich gas, only this time some of that gas didn’t make it into the star because it was spinning around. Eventually that heavy-element-rich gas clumped into chunks, many of which would look like asteroids, but nine of which formed bigger clumps, one of which we call Earth.
We’re getting close to home now, but we’re still about four billion years ago. Actually, you know the rest pretty well. At first everything was hot and the atmosphere poisonous. As things cooled, larger and more fragile molecules formed. Some larger molecules moved in ways that replicated themselves. Others formed membranes that enclosed some fluid. Eventually the replicating molecules replicated inside the enclosed fluids and caused new enclosures to form, which we call cells.
Variations in the replicated cells caused them to respond differently to different environments leading to some cells reproducing more than others, leading to some cell patterns growing and others shrinking and disappearing, a process that continues today. In fact, some of those cells formed at least two groups that formed patterns that could encode everything written in this post–specifically, a group called Joshua Spodek who typed it and another group called whatever your name is, who hasn’t yet finished reading it.
You reading these words is the most recent event in the fourteen-billion year history of the universe.
I’m curious to see what happens next.
(EDIT: for a more detailed account of the same story, “Before There Were Stars,”Â by Daniel Wolf-Savin, who was a post-doc in my group when I got my PhD.)
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