What is the Big Bang?
The Big Bang is not an explosion in space, but rather an expansion of space itself. It describes how the entire universe started from an incredibly small, hot, and dense point and has been expanding outward for nearly 14 billion years. Everything we see today, including all stars, planets, and galaxies, came from this initial event. Scientists call the starting point a singularity, which is hard to imagine because it contains all the matter and energy that would ever exist, compressed into something smaller than an atom.
How Did Scientists Discover This?
In the 1920s, astronomer Edwin Hubble observed that galaxies were moving away from each other, suggesting the universe was expanding. Later, scientists discovered leftover radiation from the Big Bang called the cosmic microwave background, which fills all of space. This radiation is like the afterglow of the Big Bang and provides strong evidence that the theory is correct. These discoveries convinced most scientists that the Big Bang actually happened.
What Happened During the Big Bang?
The Big Bang did not happen at a single location in space. Instead, space itself began expanding from the singularity. In the first fraction of a second, the universe was unimaginably hot and packed with energy. As it expanded, it cooled down. Within the first few minutes, the first atomic particles formed. After several hundred thousand years, atoms combined to form the first gases, which eventually gathered into the first stars and galaxies.
Is the Universe Still Expanding?
Yes, the universe continues to expand today. Galaxies are moving away from each other, and the space between them is growing. Scientists have discovered that this expansion is actually speeding up due to something called dark energy, which is a mysterious force that makes up most of the universe. This means galaxies will continue moving apart forever.
What Came Before the Big Bang?
Scientists do not yet know what came before the Big Bang, or if the question even makes sense. Time itself may have started with the Big Bang, so asking what came before is like asking what is north of the North Pole. Current physics cannot answer this question, and it remains one of the biggest mysteries in science. 
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