ELI5: How big is the universe?

Imagine you have a balloon and you draw dots on it. Each dot is a galaxy, like our Milky Way, which has lots and lots of stars.

Now, start blowing up the balloon.

• Notice how the dots are getting farther apart from each other? That's kind of like how the universe is growing, or expanding.

Think about it this way:

• We can see light from very far away galaxies.
• But the light from some galaxies is so far away, it hasn't even reached us yet!
• That means there are galaxies out there that we can't even see.

But here's the tricky part:

• The universe might be even bigger than what we can see. It could go on forever!
• Or it could curve back on itself, like the surface of our balloon, but in a way we can't picture easily.