A few billion years ago, in a galaxy not so far, far away, before humans even existed, the universe was created. Scientists posit that the universe was formed about 13 billion years ago. Imagine a black, empty void followed by a flaming ball of dust and debris forming our universe; this theory is called the “Big Bang.”
No one knows what matter initially created our solar system, but scientists infer that it was parts of a star explosion. Scientists also hypothesize that the Earth was created when gravity pulled stardust into a molten ball.
In this theory, the explosion from the Big Bang was so huge that to this day, there is matter flying through space. Astronomers can still sense the afterglow, or the “Cosmic Microwave,” as it's known, because this explosion was so strong.
Some scientists also theorize that the universe will never stop expanding. Others think that undetected dark matter will cause the universe to start shrinking, ultimately ending in the “Big Crunch.”
As for now, we can't be sure if the universe will expand infinitely or eventually shrink. Perhaps one day scientists will uncover the key to this mystery!
[Source: The Big Book of Knowledge]