ELI5: What is dark matter?

Imagine space is like a big playground with a roundabout. We see stars and galaxies like kids on the roundabout.

We know how heavy each kid is (their mass) and how fast the roundabout should spin based on that weight. But when we look at real galaxies, they spin way too fast! The kids (stars) should fly off!

That means there's something else there, something we can't see, holding everything together. It's like a grown-up is secretly pushing the roundabout to keep the kids on. This secret pusher is dark matter.

• We can't see it with our telescopes. It doesn't shine or block light like stars do.
• But we know it's there because of its gravity. Gravity is like the grown-up's push - it keeps things from flying apart.

• Maybe it's made of tiny particles we haven't discovered yet. Think of them like super-small, invisible pebbles.
• Maybe our understanding of gravity is wrong, and we need a new code for how things work in space.

1. We see galaxies spinning super fast.
2. We know visible matter (stars, planets) isn't enough to hold them together.
3. There must be extra, invisible "stuff" (dark matter) providing extra gravity.