How can an explosive big bang be the birth of our universe?

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No one knows what kicked off the big bang that eventually caused the stars to start forming. Adolf Schaller for STScI, CC BY

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How can a big bang be the beginning of the universe, since intense explosions destroy everything? – Tristan S., 8 years old, Newark, Delaware

Suppose you are a perfect chess piece in a game of chess on a flat and human chessboard. One day you look around and ask: How did I get here? How did the chessboard get here? How did it all start? You pull out your telescope and start exploring your universe, the chessboard …

What do you think? Your universe, the chessboard, is getting bigger. And over time, even bigger! The board expands in all directions you can see. There is nothing that can cause this expansion as far as possible – it just seems to be the nature of the chessboard.

But wait a minute. As it gets bigger, and it gets bigger and bigger, it means in the past that it should have been smaller and smaller and smaller. At a certain time, long, long ago, at the very beginning, it must have been so small that it was infinitely small.

Let’s work ahead of what happened then. At the beginning of your universe, the chessboard was infinitely small and then expanded, it got bigger and bigger until the day you decided to make observations about the nature of your chess universe. All the things in the universe – the small particles that make up you and all the others – started very close to each other and then spread over time.

Our universe works in exactly the same way. When astronomers like me make observations of galaxies in the distance, we see that they are all moving apart. It seems like our universe started very small and has since expanded. In fact, scientists now know that the universe is not just expanding, but that the speed at which it is expanding is increasing. This mysterious effect is caused by something physicists call dark energy, although we know very little about it.

Astronomers also observe something called cosmic microwave background radiation. It is a very low level of energy that exists everywhere in space. From the measurements we know that our universe is 13.8 billion years old, much older than humans and about three times older than Earth.

When astronomers look back completely on the event that started our universe, we call it the big bang.

Many people hear the name “Big Bang” and think of a giant explosion of things, like a bomb going off. But the big bang was not an explosion that destroyed things. It was the beginning of our universe, the beginning of space and time. Instead of an explosion, it was a very rapid expansion, and the event that made the universe grow bigger.

This expansion is different from an explosion, which can be caused by things like chemical reactions or major impacts. Explosions cause energy to move from one place to another, and usually a lot of it. Instead, during the Big Bang, energy moved with space as it expanded and moved wildly, but spread more and more over time as space grew over time.

Back in the chessboard universe, the ‘big bang’ would be like the beginning of everything. This is the beginning of the board that gets bigger.

It is important to realize that there was no space and time before the big bang. If you go back to the chessboard analogy, you can count the time on the game clock to the beginning, but there is no playing time before the start – the clock does not run. And before the game started, the chessboard universe did not exist and there was no chessboard space. You have to be careful when you say ‘before’ in this context, because time only existed before the big bang.

You also have to think about the idea that the universe does not “expand” at all, because as far as we know, the big bang was the beginning of space and time. Confusing, I know!

Astronomers do not know what caused the big bang. We just look at observations and see that’s how the universe started. We know it was extraordinarily small and got bigger, and we know it kicked off 13.8 billion years ago.

What started our own chess game? This is one of the deepest questions anyone can ask.

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This article was published from The Conversation, a non-profit news site dedicated to sharing ideas from academic experts.

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Michael Lam does not work for, consult, own shares in or receive funding from any company or organization that benefits from this article, and has not disclosed any applicable commitments outside of their academic appointment.

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