By focusing on processes, I realized I could address the question of why we exist by describing what had to happen at each stage of our universe’s history as one entity on my list transformed into the next. The mechanisms, in contrast to the process, describe how each transition happened rather than why. One reason for skipping over much of the how is that mechanisms can become fiendishly complicated and difficult to write about in a non-technical way. For example, a mechanistic description of developmental biology, a topic I discussed in the last chapter, would require covering how DNA is unzipped, copied and translated into chains of amino acids, how proteins fold, and how different proteins run chemical reactions that play key roles in the construction of our bodies. The subject is fascinating but complex, and a mechanistic description of how you developed from a single cell would run to hundreds of thousands of words, many of which would be technical with very specific meanings. If this book has piqued your interest in any aspects of the science I have summarized, I list some books in the appendix that provide descriptions of the mechanisms that I do not describe.
As I started to plan this book, I delighted in researching and reading about the processes, and the challenge I had set myself became more manageable. I started to gain some understanding of how a simple, minuscule pinprick of extraordinarily hot energy could transform itself over billions of years into you and me, extremely complex organisms built from trillions of cells working together. Yet there were still choices on what to, and what not to, describe. One early challenge was whether to deal with the three laws of thermodynamics. The first states that energy can neither be created nor destroyed but it can be transformed between different forms, the second that systems tend to become more disorganized and less ordered over time, and the third that the level of disorganization eventually settles down to a specific value (I’m not going to explain the value) as the temperature gets close to absolute zero, the coldest temperature that matter can obtain, or −273.15 degrees Celsius. The second law is the most bewildering, given that clearly you and I are highly ordered beings and we have arisen from a point of intense energy over the course of 13.77 billion years. We are not just a random set of molecules that happen to be in the same place at the same time. The history of Earth and of you and me appears to contradict this second law, yet all reputable scientists accept it as correct.
The apparent paradox between the second law of thermodynamics and our existence is that the law does hold if we consider the entire universe. On average, the universe is becoming less ordered, but there are corners of it, such as Earth, that have become more organized over time. Averages are useful, but they do not always explain what is happening in a particular location. While Earth has become more ordered, with atoms assembling themselves into you and me, other parts of the universe have become much more disordered than average. These bits of space will have become colder, contain very little matter, are much less structured, and simpler. If we could examine the history of every cubic inch of the universe, we would find that on average they have become less ordered, but there is a distribution of change in how ordered things are, with each bit of the universe having a different history.
The second law of thermodynamics holds because, on average across the universe, the degree of disorganization, or entropy to give it its scientific name, is increasing. I have written this book focusing on Earth. If I had chosen a point in deep space, somewhere beyond our solar system but before another star system starts, the history would be rather less exciting. I would have described a history of space cooling, the density of energy and matter thinning, and not a lot happening. The book would have been easier to write, shorter, but (I hope) not as interesting to read.
I chose not to introduce the laws of thermodynamics early in the book as I wanted to tell the history of our neck of the cosmic woods, and I wanted to avoid getting into discussions of some of the scientific conundrums scientists have grappled with, or those they still work on. But as I near the end of the book and turn to the questions of why we exist, and whether our existence was inevitable or not, I need to consider some of the hardest questions that scientists, and philosophers, are trying to solve. One of the questions that motivated the book is whether our universe’s history was predetermined from its birth, or whether randomness has played a role.
If our universe is deterministic it would develop in exactly the same way each time my repeat universe experiment described at the start of the book was run, as long as the starting conditions were identical. Each universe would end up with identical histories. If the initial starting conditions were to differ between two runs, even by just a tiny amount, the resulting universes would be different. We would consequently be inevitable in a deterministic universe with the same starting conditions as ours. In such a universe, scientists would, hypothetically at least, be able to exactly predict the history of every single particle in our universe from its inception until its demise. Such a feat is technologically impossible with today’s computers and is likely beyond the wit of any advanced civilization.
Some scientists argue that the universe is deterministic because they can accurately predict the behaviour of many things, such as the orbits of the planets, and have become better and better at doing so as various scientific breakthroughs have been made. Science progresses and as it does so it increases our understanding. There is only one direction of traveclass="underline" ever better predictions. For example, 500 years ago we were poor at predicting many celestial events. But today, using equations discovered by Isaac Newton and Albert Einstein, astronomers can very accurately predict the return of comets to our night skies decades into the future, the trajectories of spacecraft, and the orbits of planets around our sun. Similarly, physicists can predict how magnetism will move objects, and chemists can predict what will happen when some types of chemicals are mixed in beakers, in ways that were unimaginable even a century or two ago. Many bits of the natural world are now predictable, and that gives some scientists hope that the future of our universe might be perfectly predictable.
There are many things that we still cannot predict. I can’t tell you when my teenage son will get out of bed at the weekend with any accuracy, we can only predict the weather in my hometown of Oxford a day or two ahead with any confidence, and we cannot predict when volcanoes will erupt or earthquakes will shake the ground on which we stand. Given our inability to predict many things, why do some scientists think the universe might be deterministic? Their argument is that we are yet to identify the mathematical equations that would allow us to perfectly predict the currently unpredictable, but that these equations do exist, and it is only a matter of time before we discover them. Scientists have improved our ability to predict all sorts of things, from the way that proteins fold to the existence of new fundamental particles such as the Higgs boson. Scientists will continue to improve predictions, but that does not mean the universe is deterministic.