We are born. We live. And then we die. It’s a shame but it’s true: those few moments we call our own can be summed up in three short sentences. Still, life lingers. It stirs. It goes on again. That’s our history. Tell us about it. Tell us yours. Write a chronology of your life to date.
Last week I wrote a personal essay; this week I’m going to live up to my promise and do some science writing. I’ve decided to interpret this week’s topic in a very broad way. The short history of me starts first with the history of life on Earth. Life on Earth wouldn’t be possible without Earth and the Sun. The Sun only exists as a product of galaxy formation. You probably guessed what’s next: the galaxy is only one small part of the Universe. What follows is my understanding (backed up by a few university courses on the topic, an insatiable curiosity, and the handy-dandy Internet) of the origins of Life, the Universe, and Everything.
Scientists think our universe started with a Big Bang. People tend to throw around the words “Big Bang” and it is often conceptualized as an explosion. While this is a useful analogy, the Big Bang refers to a time in the Universe’s history when everything was very hot and dense. In the first instants of the universe, everything was so hot that even quarks couldn’t stick together for long enough to form the protons, neutrons and electrons of matter like we know it. There was so much energy in such a small space that the space could no longer stay small and so the universe underwent Inflation. This weird and wonderful period is characterized by the faster-than-light growth of space itself.
If you didn’t have to re-read that last sentence and your mind isn’t blown, you’re doing it wrong.
“But, but, but…. nothing can travel faster than the speed of light! E=mc^2! Einstein! ” True. Anything with mass or momentum cannot exceed the speed of light. Luckily, the fabric of space has neither mass nor momentum and so is not constrained by this ultimate speed limit. They only sort of lied to you in physics class.
During Inflation, the universe cooled down tremendously. This makes sense; water stays warmer longer in a kettle than in a puddle on the ground. In puddle form, the water is much more spread out. In a similar way, the particles of the universe spread out, collided less, and effectively cooled down. Eventually quarks slowed enough to stick to each other with the Strong Force. This created protons, neutrons, and electrons. There were also all sorts of photons and neutrinos bouncing around in that early-universe soup as well. The soup was still too hot for the protons to capture electrons. All the light (photons) continued to deflect off of the ionized particles like a flashlight on a foggy night. When the universe cooled some more and protons could finally trap electrons, the foggy universe suddenly became transparent and the photons could travel unimpeded. If we look far enough away (and so far enough back in time) with our telescopes, we can see this baby picture of the universe. We call it the Cosmic Microwave Background Radiation.
When a proton captures an electron, we call it a Hydrogen atom. When 4 Hydrogen atoms collide, Helium is formed. When a Helium and a Hydrogen collide, we get Lithium. In the early universe, only these three atoms were created. About 90% of the universe was Hydrogen, 10% was Helium, and there was a very small fraction of 1% that was Lithium. These are basically still the abundances of atoms in the universe, but we (and by we I mean the stars) managed to create some new and exciting elements along the way. Why did the early universe stop at Lithium? Because the universe cooled too quickly. There was a sweet-spot in time where the universe was cool enough to allow atoms to hit each other without flying off in opposite directions, but still hot enough to allow them to hit. This sweet spot lasted only for a couple minutes and then everything was too cold to create bigger atoms.
This is where stars come in. Everything cooled down, but there were slight gravitational imbalances. Some places in the universe had slightly more atoms than others. Over time, slightly denser regions became dense regions because of gravity. When an area becomes very dense, the gas collapses and a star is born. Stars are basically big balls of burning gas (mostly Hydrogen for most of their lives). But they are not burning in the typical ‘oh did someone drop a piece of dried spaghetti on the burner again’ way. They are burning Hydrogen through fusion. Gravity has managed to get enough Hydrogen atoms in the same place that they get very hot and hit each other very fast and fuse together, creating Helium. This fusion releases a metric shit-ton of energy because of the c in E=mc^2. Two Hydrogen atoms weigh slightly more than one Helium atom. This extra mass hasn’t disappeared, it’s simply turned into energy. And because c=300 000 000 m/s, the small difference in mass becomes a huge amount of energy. Stars eventually run out of Hydrogen to turn in to Helium, so they start fusing Helium into heavier elements. This is good because we are made of heavier elements. If a star is especially heavy, it will fuse elements all the way to Iron and then burst in a spectacularly terrifying explosion known as a supernova. Supernovae are great because they spread heavy elements (like Carbon) across the Universe.
Supernovae allowed the Earth to form with enough Carbon and water to support life. And thank goodness it did. Being alive is great!
Next week, find out how life came to exist on this third chunk of rock from the Sun.