The Big Bang Theory is the most widely accepted scientific explanation of how the universe formed. To understand this theory, start by picturing the universe expanding steadily. Then, reverse the direction of time, like pressing the “rewind” button on a video player. Now the universe is contracting, getting smaller and smaller. If you go far enough back in time, you will reach a point when the universe was squeezed into a very small volume.

According to the Big Bang theory, the universe began about 13.7 billion years ago, when everything in the universe was squeezed into a very small volume, as described above. There was an enormous explosion—a big bang—which caused the universe to start expanding rapidly. All the matter and energy in the universe—and even space itself—came out of this explosion.

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