Curious Kids is a series for children of all ages. If you have a question that you would like an expert to answer, send it to [email protected].
How could a big bang have been the beginning of the universe, since intense explosions destroy everything? – Tristan S., age 8, Newark, Delaware
Pretend to be a perfectly flat chess piece in a chess game on a perfectly flat and giant 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 take out your telescope and start exploring your universe, the chessboard….
What do you think? Your universe, the chessboard, is getting bigger. And even bigger over time! The board expands in all directions you can see. There’s nothing that seems to be causing this expansion, as far as you can tell – it just seems to be the nature of the chessboard.
But wait a minute. If it’s getting bigger and getting bigger, it means it must have been smaller and smaller and smaller in the past. Once, long, long ago, right in the beginning, it must have been so small it was infinitely small.
Let’s work on what happened next. At the beginning of your universe, the chessboard was infinitely small and then expanded, getting bigger and bigger until the day you decided to make some observations about the nature of your chess universe. All the stuff in the universe – the little particles that make up you and everything else – started very close together and then spread further apart as time went on.
Our universe works in exactly the same way. When astronomers like me observe distant galaxies, we see that they are all moving apart. It seems that our universe started out very small and has been expanding ever since. In fact, scientists now know that not only is the universe expanding, but the rate at which it is expanding. This mysterious effect is caused by something that physicists call dark energy, although we know little about it.
Astronomers also observe something called the cosmic microwave background radiation. It is a very low energy level that is present all over the room. We know from those measurements that our universe is 13.8 billion years old – much, much older than humans, and about three times older than Earth.
When astronomers look back completely at the event that started our universe, we call it the Big Bang.
Many people hear the name “Big Bang” and think of a gigantic explosion of stuff, 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 both space and time. Rather than an explosion, it was a very rapid expansion, the event that made the universe bigger and bigger.
This expansion is different from an explosion, which can be caused by things like chemical reactions or large impacts. Explosions cause energy to move from one place to another, and usually a lot. Instead, during the Big Bang, energy moved with space as it expanded, moving wildly, but more and more dispersed over time as space grew over time.
Back in the chessboard universe, the “big bang” would be the beginning of everything. It is the beginning of the board that gets bigger.
It is important to realize that there was no space and no time “before” the big bang. Going back to the chessboard analogy, you can count the amount of time on the game clock after the start, but there is no playing time before the start – the clock was not running. And before the game began, the chessboard universe did not exist, nor was there any chessboard space. You have to be careful when you say ‘earlier’ in this context, because time didn’t even exist until the big bang.
You have also wrapped your mind around the idea that the universe is not expanding “into” anything, since as far as we know the Big Bang was the beginning of both space and time. Confusing, I know!
Astronomers aren’t sure what caused the Big Bang. We just look at observations and see that this is how the universe came into being. We know it was extremely small and got bigger, and we know it started 13.8 billion years ago.
Where did our own chess game begin? That is one of the deepest questions anyone can ask.
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This article was republished from The Conversation, a nonprofit 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 would benefit from this article, and has not disclosed any relevant affiliations outside of their academic appointment.