The Big Bang: We came from heat
And in just one moment, from eternal night;
emerged it all, from color and light.
One of the most fundamental questions one can ask is, where did it all come from? Why are the things around me the way they are? Different cultures have come up with all sorts of wonderful and creative answers to that question. The creation story of many indigenous Australian tribes centers around a giant rainbow serpent, which was sleeping deep underground with all the animals in her belly. Then, when the time came, she awoke and spewed them forth onto the earth creating the land from her body. Ancient Egyptian equivalents involve a great pyramid emerging out of dark motionless water, symbolically representing the flooding of the Nile. They are all beautiful and poetic attempts to understand the world. And most probably weren’t believed as literally as we think (we’re a bit more rigid about these things in the modern world).
The Big Bang is the modern equivalent. The theory goes that the Universe was created all at once, in one moment, approximately 13.8 billion years ago. All matter, time, and space were condensed into a single point and then “exploded” creating the Universe we know today. The earliest version of the theory was proposed by Georges Lemaître, a catholic priest, in the late 1920s. It is now universally accepted by scientists, in the same category as gravity and evolution. That doesn’t mean it must be true, but it means it’s been thought about a lot, and the people who’ve studied it, almost all agree. Let’s dive in, to the Big Bang.
What is the Big Bang?
The Big Bang is easy to understand at a simple level, it’s… a “Big Bang”. On a deeper level, the idea that the Universe started with a “Big Bang” is weird and doesn’t make a lot of sense. What “went bang”? Where did the stuff that went “bang” come from? What happened “before” and why did it “go bang”?
This is where the term “Big Bang” gets a bit misleading. The Big Bang is not like the explosions we see in our life. And these sought of questions misunderstand what an “empty” universe is.
Imagine holding your hands up in the air in front of you. In normal conversation, you would probably say there is “nothing” in between them. The space is empty. But if you then think for a second you would realize, of course, there is air and dust and all sorts of random particles floating between them. So now imagine you took them away and you did the same thing far out in the vacuum of space. There would still be some particles, even space isn’t completely empty. But even ignoring that, in a perfect vacuum there would still be light and radiation and gravity waves and force fields interacting between your hands. So what if we imagine getting rid of all of that and hold our hands up again? Is the space between them empty then?
The answer is no. Even if you hold your hands up in the deepest of space, there is still something in between, even if all the matter and radiation is removed. There is the Universe itself. The blank canvas of space and time still continues to exist and flow in between your hands.
The Big Bang isn’t about explaining where the “stuff” in the Universe came from. It’s about explaining how the canvas came to exist. And so there wasn’t anything “before” the Big Bang that exploded. The Big Bang created time. To ask what was “before” the “Big Bang”, or what “caused” the Big Bang is like asking what is before the first page in a book – the question just doesn’t really make sense. That’s not to say it isn’t an interesting thing to think about. There are theories about what might have caused the Big Bang, generally around multiverses, but they are not particularly serious yet. The Big Bang is as early as we know how to go back.
So the Big Bang is the moment when all time, space, matter, and energy in the Universe was condensed into a single point, and then rapidly expanded. At this point, everything was so hot and dense that the normal laws of physics didn’t apply. In the same way, as you heat things up on earth they turn into fluids and gasses, after the Big Bang, everything was too hot to have any real form or structure. Afterward, over billions of years, the Universe cooled and clumped into galaxies and stars and the rest of history occurred. Before it, there was no time and no space.
How do we know the Big Bang happened?
Very early in the 21st century, it was obvious that the other galaxies in our Universe were moving away from Earth. This is pretty easy to work out. You point a telescope at the sky and find a galaxy. You then work out how far away the galaxy is and how fast it is moving. There are a bunch of different ways to do this, depending on how far away the galaxy is and what it is made of. However, once we did this we discovered that almost all the galaxies in the Universe were moving away from us. There were a variety of speeds, some moving much faster than others, but almost every single other galaxy was moving away from us. This is what people refer to as ‘the Universe expanding’. The things in the Universe are all getting further away from each other.
It’s pretty easy to work backward from here. Galaxies move in a very consistent way. They are not like tissues floating around in the breeze on Earth. They are massive and moving through space (so no air or breezes), so they almost always move in simple predictable ways. Therefore, if a galaxy is moving away from us, we just wind back time and we find that all galaxies were pretty much in the same spot billions of years ago. Working backwards, if we know how fast they are moving and how far away they are now, we can calculate how long ago that time was. And it was about 13.8 billion years.
This evidence gets you most of the way to the Big Bang. Even with this, it is clear that most of the stuff in the Universe was in the same place about 13.8 billion years ago. There are other pieces of evidence that give a bit more flavor, in particular the cosmic microwave background that gives you more information about how space and time were created (see our next post), but the general concept is the same. By observing what stuff looks like in the Universe, knowing some simple principles about how things in the Universe behave and going back in time, we can see without any doubt everything was very close together, very hot, and very dense about 13.8 billion years ago.
So what does this all mean?
The Big Bang is weird and wonderful. Perhaps just as weird and wonderful as a giant rainbow serpent spewing forth animals into the world. It answers the same question and raises the same questions about why and what happened before. Questions about the origins of the Universe always will.
There are many things to take away from the Big Bang. Firstly, to the best of our current understanding, the Universe had a start. And that start was a very long time ago. The Universe didn’t just spring forth fully formed as it was today, and it doesn’t seem to go around in loops or cycles. Secondly, when the Universe started, it looked very different from how it looks today. There were no stars or galaxies in the early Universe, it took billions of years for them to arrive (see our post here). It took even longer for the solar system and our Earth to evolve (see post) and for life on Earth to evolve even longer (see here).
Our current Universe has been the culmination of a slow process of evolution over billions of years. For much of it, there were no galaxies, no stars, no planets, and no life. And still, in most of the Universe, there are none of those things. It’s taken a very long while to get here. For us, here at The Universal Story, that makes us appreciate our Universe, even more.
