As far as we know, the Universe in which we live arose from the sudden explosion of a point of infinite density, the Big Bang, just over 13.7 billion years ago, and then began to expand. An expansion that continues to occur today and that we could compare to a balloon that continues to inflate and grow in all directions.
However, something is wrong with this story. And the best proof of this is that physicists cannot agree on exactly what the expansion rate of the Universe is, that is, how fast it is growing. It is enough to use different measurement methods so that the results, instead of