Observations describe a pattern, processes chronicle why the pattern happens and mechanisms explain how processes occur. For example, the observation that hydrogen and oxygen atoms combine to form water molecules is a pattern; why the atoms behave like this is because the oxygen and hydrogen atoms have opposing electric charges that attract them to one another to form a molecule; and how they bond together is because the atoms share particles called electrons. A detailed understanding of why a pattern is observed requires knowledge of both process and mechanism.
Some mechanisms are extremely complex, especially those involved in complex life forms. The emergence of the two separate lineages that would eventually result in chimpanzees and humans from a shared common ancestor that lived between 6 and 8 million years ago is a pattern; the processes that caused the diverging lineages is evolution by natural selection; while the mechanisms that resulted in separate chimp and human lineages are errors, or mutations, in the genetic code that impacts the way individuals of each species develop. These contrasting developmental trajectories involve different genes being turned on and off at different times in the growing embryo, different proteins being produced in some of our cells, and these proteins impacting whether we grow up looking like a person or a chimp. In this case, the pattern is well characterized, the process is well understood, and bits of, but by no means all, the developmental mechanisms have been characterized. Descriptions of the details of complex mechanisms quickly become very complicated, and in this book I largely avoid them. Instead, I focus on the processes that led from the Big Bang to me and you, giving overviews of the mechanisms only when this does not require technical detail.
Sometimes as science progresses there can be multiple interpretations of patterns. When this happens, and while researchers strive to collect more data that might allow one of a set of competing hypotheses to be supported with others rejected, most scientists turn to Occam’s razor to decide which hypothesis to favour. William of Ockham was an English theologian and philosopher born in the village of Ockham in Surrey in 1287. His razor states that when there are multiple explanations for a phenomenon, go with the simplest. That is the approach I take when equally plausible explanations have been proposed, and in particular I use this philosophy in the final chapter when I answer the question of whether our existence was inevitable or down to chance.
As well as answering that question, I want this book to convince you of science’s remarkable achievements. I can only summarize a tiny fraction of scientific understanding, but it is sufficient to provide a history of why we exist. Many people are wary of science, but they should not be. The history and workings of our universe are worth understanding, for they are both remarkable and beautiful. The scientific method should not be feared, it should be embraced, for the knowledge it has uncovered through the hard work of millions of scientists is breathtaking. Let’s begin exploring the history of why we exist.
The Beginning
I have always been an avid reader. My parents would have to tell me to stop reading and to go outside to play, so the opposite of any normal kid, and I would hide under my covers with a torch and a book after being told to go to bed. I can’t remember the first science book I read, but I would go to the mobile library that visited our village and borrow books on any aspect of science I could find. The best reads were often about physics, and particularly those that revealed secrets of the universe, although books on dinosaurs came a close second. I remember hoping scientists might even discover dinosaurs living on other planets.
Although I loved reading about physics at home, it was taught in a fabulously dull way at school. The curriculum required us to learn about the differences between potential and kinetic energy for what seemed like weeks on end, yet we were never taught about exciting things like supernovae. We would work out the angle a ball would bounce off a wall, but we never learned about particles such as quarks or photons. At home I would read about how time slowed down as objects neared the speed of light, but in the classroom the most exciting thing we did with light was to build a pinhole camera.
My teachers strove hard to make the lessons exciting, but they fought a losing battle, for whoever had designed the curriculum was on a mission to make an interesting subject boring. Physics is the science that explains why the universe behaves like it does. It describes how fundamental forces work, how energy and matter (anything that can be weighed and takes up space) are related, and why particles interact with one another in the way they do. It now seems remarkable that my classmates and I weren’t wowed with mind-bending knowledge. I was left nonplussed but undeterred. I continued to read about the exciting bits of physics at home, and soon came to realize that the inanimate world could be fascinating, and even kinetic and potential energy could be interesting. Nonetheless, for those readers who suffered the same physics curriculum as I did, that is the last you will hear of these types of energy in this book.
For you and me to exist, the universe had also to exist, but how did it come to be? We take it for granted that our universe has the right characteristics to harbour life, but was it inevitable that the universe would turn out this way at its birth? Could a universe have formed in which it was impossible for life to evolve? Scientists have found that if some of the characteristics of our universe were just a little bit different, then atoms, stars, planets, you and I could not exist. The first steps in our history will take us from a minuscule point of intense energy from which our universe grew, to fundamental particles, to the first atoms, and then to the first stars. There is still much to learn about the early days of our universe, but scientists have an astonishing understanding of the particles, energy and forces that determine how our universe behaves, and how these laid the foundations for life on Earth. Before we start this journey, I will introduce a few facts about our universe.
Today our universe is truly massive. No one knows quite how big, but scientists have estimated that it may well be over 7 trillion light years across. It would take a beam of light 7,000,000,000,000 years to travel that vast distance. One light year is just under 6 trillion miles – that’s how far light can travel in a year – which makes the universe 42 trillion trillion miles across. From Earth, we can see only a fraction of this, and scientists call this the observable universe. It is a mere 93 billion light years across, but it is getting bigger. Later in the chapter I explain why, along with why we can’t see all of the universe.
Distances that are measured in billions of miles don’t make much sense given our daily experience on Earth. One of the longest non-stop flights you can take is from London, England, to Perth, Australia. It takes 17 hours, and the plane travels 9,000 miles. That is 0.0000000015 of a light year. Light can make the journey in less than 1/20th of a second. The Boeing 787-9 Dreamliner that makes the London–Perth journey has a top speed of 690 miles per hour, which is very sluggish compared to light. It is also slow compared to our fastest machines. NASA’s Parker Solar probe is the fastest object humans have produced. It achieved 0.05 per cent of the speed of light when it hit a speed of 330,000 miles per hour as it passed close to the sun, but that is still only 1/2,000th of light speed. Light is very fast, and our universe truly vast.