Samuel John Wilson
Samuel John Wilson


In the Beginning

If you wish to make an apple pie from scratch, you must first invent the universe.

Carl Sagan

The Pillars of Creation, Eagle Nebula: Clouds of hydrogen gas and dust in the process of forming stars. Credit: NASA, ESA, Hubble Heritage Team, J. Hester and P. Scowen (Arizona State University)

It seems appropriate that my inaugural post should start at the start, so I will begin at the truest start we are aware of, the Big Bang. In fact, discussing time before the Big Bang may be nonsensical. Many scientists think that the Universe erupted from a singularity. In this context, a singularity refers to a location where density and gravity are infinite. This particular singularity contained everything that our Universe comprises; all of the mass, space-time, and energy were contained within a single point. As this singularity contained absolutely everything in the Universe, time as we know it likely did not exist until that primordial singularity was rent asunder. Even in attempting to write about what came before the Big Bang, I find that the English language is insufficiently descriptive. Words like before, until, precedingoccurred, or previously all refer to time; how exactly does one discuss or describe the state that precedes the existence of time? I find that when confronted by incredible concepts that challenge my primate brain—as so often happens when I read about physics and cosmology—I feel the urge to laugh. Trying to imagine the absence of time rarely fails to generate a chuckle, or at least a bemused smile.

Before I continue I will mention an important caveat regarding this site: what you read here may not be correct. I will certainly try to ensure that all of the information I put forth is correct, and I do spend a lot of time reading about the topics that I will discuss. However, you may encounter errors in my understanding, gaps in my knowledge, or outright ignorance of new ideas. I may also oversimplify complex subjects. I welcome corrections to any errors I make. Additionally, the concepts I write about could be overturned at any time. If I were writing 1000 years ago, I would be confidently discussing the stationary Earth around which the rest of the Universe rotates. Today I am discussing what came before our Universe, and there's a chance that this theory is just as wrong as the geocentric model of the Universe. With all that in mind, current models of the Universe suggest a primordial singularity containing all space-time exploded about 13.8 billion years ago, and discussing what came before that may be very difficult for our puny ape-brains.

After the Big Bang there were a series of cosmological epochs. I won't go into them all right now, as that tangent would take us too far from the point I am hoping to make. Suffice it to say that some very weird and interesting things were going on in the heady days of our Universe's youth. We will skip ahead to a point where stars have already formed, and I'll address some of those weird and interesting things in another post. We all know that the star nearest to us is the Sun. You may have heard the Sun described as a giant flaming ball of gas, which might have led you to believe that the energy it releases is from burning gas. Well, stars are not actually gas, they're plasma, and their energy does not come from burning, it comes from nuclear fusion. Plasma is a form of matter created from gas heated to a very high temperature, as in lightning strikes or within stars. Nuclear fusion is a process wherein atomic nuclei are brought together with sufficient force to cause them to fuse. Fusion is able to release massive amounts of energy from matter, because it can release the binding energy that holds atoms together. The amount of energy in any given amount of matter is described by the world's most famous equation:

`E = mc^2`

where the energy of a system (`E`) is equal to its mass (`m`) multiplied by the speed of light squared (`c^2`). This is known as mass-energy equivalence; mass and energy are two sides of the same coin. I will note that the speed of light is around 300,000,000 meters/second, so the speed of light squared is 90,000,000,000,000,000 `m^2`/`s^2`. As you can imagine, this means that even small amounts of matter contain enormous amounts of energy. This is part of why stars can can exist for billions of years without running out of fuel. But while stars can exist for billions of years, they are not eternal, a fact which brings us back to our story approximately 100 million years after the Big Bang. Around this time the Universe was almost entirely composed of hydrogen and helium, the two simplest elements. In their most common forms, hydrogen is composed of 1 proton and 1 electron, and helium is composed of 2 protons, 2 neutrons, and 2 electrons. Just to give you an sense of how simple hydrogen and helium are, the most common form of uranium has 92 protons, 92 electrons, and 146 neutrons. When matter began to form after the Big Bang, about 75% of the total matter was hydrogen, and about 25% was helium. The reason that hydrogen and helium dominated the early Universe is because their constituents were simply floating around in space; as soon as conditions became favourable, the fundamental forces pulled the constituent parts together and formed the simplest stable elements. Large clouds of hydrogen dominated the Universe for quite some time (similar to those pictured at the top of this post). As with any massive body, these clouds were attracted to one another via gravity. Over time they would coalesce into larger and larger clouds. When a cloud became sufficiently large and dense, the gravity of the system would initiate its collapse into a star. These first stars are known as Population III stars.

WR124: A Wolf-Rayet star in the constellation Sagitta. The bright central point is the star, while the orange cloud is a nebula of intensely hot hydrogen being expelled as the star begins to use helium as fuel. Credit: Judy Schmidt,

Some scientists hypothesize that the average Population III star was several hundred times larger than our Sun. Inside these giant first stars the temperature and density were sufficient to fuse hydrogen into helium. Hydrogen continued to fuel the stars for billions of years, until most of the hydrogen was depleted. At this point, a star would begin to use helium as its fuel source, producing carbon, oxygen, and nitrogen. After the source of helium was depleted, carbon would be used as fuel, followed by oxygen, neon, and finally silicon. However, when a star begins to use silicon as fuel, the reaction produces iron in its core. Stars cannot extract energy from the fusion of iron, causing the temperature of the core to drop. Once a sufficient amount of inert iron has been produced, nuclear fusion ceases and the outer layers of the star fall inward on the collapsing core. The material falling inward from the outer layers bounces off of the iron core at speeds up to 30,000,000 `m`/`s`. This event is known as a supernova, and it ejects much of the star's stellar mass. Along with the elements that have been created over the star's lifetime, new elements created during the supernova event explode out into the Universe. This is another moment when the English language seems insufficiently descriptive; to say that the star simply explodes doesn't convey the true sense of the event. The explosive energy of a supernova is predicted to be comparable in scale to the energy our Sun will produce over the course of its multi-billion year lifetime. There was a recent supernova, known as ASASSN-15lh, that was 600 billion times brighter than the Sun. If that doesn't sound amazing enough, consider that it was 20 times brighter than all of the stars in our entire galaxy combined.

The Crab Nebula: The remnant of a supernova that occurred in 1054 CE. It is composed of helium, hydrogen, carbon, oxygen, nitrogen, neon, and sulfur. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University),

There are 94 elements that have been found in nature and 23 that have been synthesized by humans. Of the naturally occurring 94 elements, only 3 were present in the early Universe. The remaining 91 elements were forged in the hearts of ancient stars or in cosmic explosions that exceeded the luminous intensity of neighbouring galaxies. The culmination of this story—and the part I find more incredible and beautiful than any creation story or fiction that I have read—is that you and I are composed of long dead stars. In fact, everything around us is composed of stardust from giant celestial bodies that exploded billions of years ago. Your body is approximately 10% hydrogen by mass, with the remaining 90% composed of elements that were generated deep in the heart of a dying star. In the words of Carl Sagan, "The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff." When troubled by this mortal coil, I find it deeply reassuring to contemplate the genuine connectedness that exists between all things in our Universe. My problems somehow feel less worrisome knowing I trace my ancestry to ancient stars.

Part of the reason I began with this subject is because our genesis is among my favourite subjects to marvel at. We trace our lineage to the hydrogen clouds that followed the Big Bang. The stars that formed from those clouds generated all the remaining elements that compose our Universe. Our solar system was born from those stars, and lifeless stardust eventually formed primitive life here on Earth. Billions of years of evolution yielded increasingly complex life forms. Then somewhere on the plains of Africa, a humble primate species began to codify guttural grunts into a protolanguage. Today, our most complex or abstract thoughts can be clearly conveyed to others. Consider that our vocal cords, the neurons in our brains, the small bones of the ear, and the very air through which sound waves propagate, are each derived from the hydrogen clouds of the early Universe. I have quoted Sagan twice already in this post, and I will close by quoting him once more. In his popular science program Cosmos, Sagan is discussing the nature of our existence as living beings, born out of lifeless atoms created in lifeless stars, when he declares, "We are a way for the cosmos to know itself." Our existence allows the Universe to contemplate its own existence. If that doesn't make you want to laugh, I don't know what will.

Thanks for reading.

Samuel WilsonComment