Galaxies are moving away from each other, showing that the universe is actively expanding.

Back in 1929, an astronomer named Edwin Hubble made a massive discovery. He noticed that almost all galaxies are moving away from us. Think of it like dots drawn on a balloon. As you blow up the balloon, the dots stretch farther apart. Since everything is moving away now, it means if we play the tape backward, everything must have started packed tightly together in one tiny spot.