Why the Universe is Flat I The Great Courses?

The universe is flat like a pancake, and we can tell just by looking around.

Imagine you're on a really big balloon. If the balloon is deflated, it feels flat, but if you blow it up, everything curves around you. Now think of the whole universe as that balloon. If it's very large, it looks flat, like a pancake, even though it might be curved in ways we can’t see.

Flatness means the universe doesn't bend or curve much, it’s just mostly straight. Scientists use something called cosmic microwave background radiation, which is like the "echo" of the Big Bang, to measure this flatness. It's like taking a picture of the whole universe and seeing if it looks straight or bent.

Scientists did experiments with light from very far away, kind of like looking at stars that are super old. They saw that everything was just right for the universe to be flat, like how your desk is flat even though you can’t see its edges.

It’s not magic, it's just a really big pancake that we live on! The universe is flat like a pancake, and we can tell just by looking around.

Imagine you're on a really big balloon. If the balloon is deflated, it feels flat, but if you blow it up, everything curves around you. Now think of the whole universe as that balloon. If it's very large, it looks flat, like a pancake, even though it might be curved in ways we can’t see.

Flatness means the universe doesn't bend or curve much, it’s just mostly straight. Scientists use something called cosmic microwave background radiation, which is like the "echo" of the Big Bang, to measure this flatness. It's like taking a picture of the whole universe and seeing if it looks straight or bent.