What Actually Expands In An Expanding Universe?

The universe is getting bigger, and everything in it is moving apart, like when you blow up a balloon.

Imagine you have a balloon, and you draw some dots on its surface. When you blow air into the balloon, it stretches out, and all the dots move away from each other. This is like what happens in the expanding universe, space itself is stretching, and everything in it (like stars and galaxies) moves apart as a result.

The space between things is expanding, not the things themselves. So if you think of the universe like a balloon, the dots are like galaxies, and the rubber of the balloon is like space. As the balloon stretches, the distance between the dots increases, even though the dots themselves don’t get bigger.

This means that galaxies are moving away from each other because the space around them is stretching, just like how your drawing on a balloon gets stretched out as it expands. It's not magic, it's just space growing, like the floor of a room getting bigger, and everything on it moves apart with it. The universe is getting bigger, and everything in it is moving apart, like when you blow up a balloon.

Imagine you have a balloon, and you draw some dots on its surface. When you blow air into the balloon, it stretches out, and all the dots move away from each other. This is like what happens in the expanding universe, space itself is stretching, and everything in it (like stars and galaxies) moves apart as a result.