Chapter 1

Introduction

Every second, the Sun bathes the Earth in an immense stream of energy. A tiny fraction of that energy lands on rooftops, solar farms and portable panels around the world, where photovoltaic cells convert sunlight directly into electricity. It's easy to think of sunlight as ordinary. After all, the Sun has risen every morning for as long as humanity has existed. But every ray of sunlight has an extraordinary story.

Long before it reached a solar panel, it was created deep within the core of the Sun. Before the Sun existed, the atoms that make up our star drifted through space inside an enormous cloud of gas. Before those clouds formed, the matter itself was created during the earliest moments of the Universe.

The story of solar energy therefore doesn't begin with solar panels. It doesn't even begin with the Sun. It begins almost 13.8 billion years ago, with the birth of everything.

The Beginning of Everything

According to our best scientific understanding, the Universe began around 13.8 billion years ago in an event known as the Big Bang.

Despite its name, the Big Bang wasn't an explosion into empty space. In fact, there was no empty space at all. There was no centre of the Universe, no edge to expand into and no surrounding void waiting to be filled. Instead, the Big Bang marked the beginning of space, time, energy and matter themselves.

Before we go any further, there's one obvious question: what came before the Big Bang?

It's one of the biggest questions humanity has ever asked, and I wish we knew the answer. Understanding what, if anything, existed before the Universe began would completely change our understanding of reality and our place within it. But despite all our best efforts, the honest answer is that we simply don't know.

Several ideas have been proposed, including quantum fluctuations, cosmic inflation, cyclic universes and the multiverse, but we're very far off any concrete proof. For now, the origin of the Big Bang remains one of the greatest mysteries in science.

The Planck Epoch

The Planck Epoch refers to the period between time 0 and approximately 10⁻⁴³ seconds after the Big Bang. During this period, the region that would eventually become our observable Universe was roughly one Planck length across (another rabbit hole, but for our purposes it's unimaginably small) and had a temperature of around 10³² Kelvin. 

Our current understanding of physics has two theories that work remarkably well, but for very different things.

1. General Relativity - describes the behaviour of very large objects (planets, stars, black holes and galaxies).

2. Quantum Mechanics - describes the behaviour of extremely small objects (atoms, electrons, photons and quarks).

However, they both rely on very different assumptions. General Relativity assumes that space and time are perfectly smooth, rather like this:

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Whereas Quantum Mechanics suggests that nothing is perfectly smooth and that, at incredibly small scales, space and time look more like this:

---^--^^---^----^-^^--^---^-----

At the scale of planets and galaxies, quantum effects become so tiny that they can effectively be ignored. General Relativity is so accurate for describing large objects that, despite being over a century old, it continues to pass every experimental test we've been able to perform.

Quantum Mechanics, on the other hand, largely ignores gravity. At the subatomic scale, gravity is roughly 10⁴⁰ times weaker than the electromagnetic force, making its practical effect on individual particles virtually zero. As a result, Quantum Mechanics can accurately describe the behaviour of atoms and subatomic particles without needing to account for gravity.

The Universe is kind enough that almost every physical situation is dominated by one theory or the other. However, when it comes to describing the Universe during the Planck Epoch (or inside a black hole), where:

1. The object being described is unimaginably small.

2. Gravity is unimaginably strong.

...you cannot simply ignore gravity or quantum effects. Both theories become equally important.

To understand what really happened during those earliest moments, scientists believe we need a new theory of Quantum Gravity, something that remains one of the greatest unsolved challenges in modern physics.

So maybe the question we should try to answer first isn't "What happened before the Big Bang?" Maybe it's… "What the hell was happening during the Planck Epoch?"

Cosmic Inflation

Although we don't know exactly what happened during the Planck Epoch, scientists have a much better understanding of what happened next.

Between around 10⁻⁴³ and 10⁻³⁶ seconds after the Big Bang, the Universe remained unimaginably hot and dense while continuing to expand. Exactly what caused this initial expansion remains one of the biggest unanswered questions in cosmology. We can describe how the Universe expanded with remarkable accuracy, but we still don't know why it began expanding in the first place.

During this period, gravity separated from the other fundamental forces, becoming the distinct force we know today. The remaining forces were still united, and the Universe was far too energetic for atoms, protons or neutrons to exist.

Then, around 10⁻³⁶ seconds after the Big Bang, something remarkable happened.

As the Universe cooled, the strong nuclear force separated from the remaining forces. Scientists believe this sudden change released an enormous amount of energy, triggering one of the most extraordinary events in the history of the Universe: Cosmic Inflation.

For a tiny fraction of a second, the Universe expanded at an astonishing rate, doubling in size roughly every 10⁻³⁷ seconds. During this brief period, the region that would eventually become our observable Universe grew from something unimaginably small to an estimated diameter of just a few metres.

That might not sound particularly impressive, but the speed of this expansion is almost impossible to comprehend. If you started with just one cent and doubled your money at the same rate the Universe expanded during Cosmic Inflation, by the end you would have a number with more than 30,000 digits. For comparison, the estimated total global wealth is around $500–600 trillion, a number with a mere 15 digits. If the entire global wealth was represented by a single dollar bill, the wealth generated by this thought experiment would form a stack stretching roughly 20 light-years (120 trillion miles) into space, enough to reach Proxima Centauri, the nearest star beyond our Sun, and back, twice.

Cosmic Inflation helps explain why the Universe looks so remarkably uniform in every direction. Regions of space that are now billions of light-years apart were once close enough to share the same conditions before being stretched across the cosmos. Although inflation has never been observed directly, it successfully explains many of the features we see in the Universe today, making it the leading explanation for what happened during these earliest moments.

A Universe That Never Stopped Growing

Inflation eventually came to an end, but the expansion of the Universe didn't. While the rate of expansion slowed dramatically, the amount by which the Universe grew became far, far greater. In just one second, the region that would eventually become our observable Universe expanded from just a few metres across to roughly 15–16 light-years in diameter.

One of the greatest discoveries in modern astronomy is that the Universe is still expanding.

Imagine drawing dots on the surface of a balloon. As the balloon inflates, every dot moves away from every other dot, not because the dots are travelling across the surface, but because the surface itself is stretching. The Universe behaves in much the same way.

Every galaxy is moving away from every other galaxy because space itself is expanding between them. In fact, the most distant galaxies are moving away so quickly that their light is stretched into longer, redder wavelengths, a phenomenon known as redshift. It was this discovery that first revealed that our Universe is expanding.

As the Universe expanded, it became larger, less dense and, most importantly for our existence, cooler. That gradual cooling changed everything. In the unimaginably hot conditions immediately after the Big Bang, particles collided with such enormous energy that stable matter simply couldn't exist. The Universe was more like an unimaginably hot soup of energy than anything we would recognise today.

Only once it had cooled sufficiently could the first stable particles begin to form, laying the foundations for every atom, star, planet and living thing that would eventually exist.

The First Ingredients

As the Universe continued to expand, it continued to cool. Within the first millionth of a second, temperatures had fallen enough for quarks (the fundamental building blocks of matter) to combine and form the first protons and neutrons.

Over the next few minutes, the Universe cooled even further. About three minutes after the Big Bang, conditions were finally right for these protons and neutrons to join together and form the first atomic nuclei. This brief period is known as Big Bang Nucleosynthesis, and although it lasted for only around twenty minutes, it determined the chemical recipe for almost the entire Universe.

Almost all ordinary matter consisted of just three elements:

• Hydrogen

• Helium

• Tiny traces of lithium

At this stage there were still no complete atoms. The Universe remained so hot that electrons couldn't settle into orbit around atomic nuclei. That wouldn't happen for another 380,000 years, as we'll discover in the next chapter.

These simple atomic nuclei may not sound particularly impressive, but they became the raw materials for everything that followed. Every star. Every planet. Every ocean. Every mountain. Every tree. Every person who has ever lived. The sugar you may, or may not, put in your coffee and even the silicon inside a modern solar panel ultimately traces its origins back to these first ingredients.

Looking Ahead

The Big Bang had created the first ingredients needed to build everything that would eventually exist. Atomic nuclei had formed. The Universe was still expanding and cooling. But there was still one problem. There were no stars. No galaxies. No planets. No sunlight. The Universe was still completely dark. The first lights of the cosmos were yet to ignite.