Expansion of the Universe

The expansion of the universe refers to the gradual increase in distance between galaxies over time. This phenomenon is based on the observation that galaxies are moving away from us, particularly those that are farther away, which indicates that the universe is expanding uniformly. This expansion can be likened to dots on a balloon that moves apart as the balloon inflates. It suggests that the universe began from an extremely hot and dense state, known as the Big Bang, about 13.8 billion years ago, and has been growing ever since.