ELI5: Explain Like I'm 5

Principal bundle

Okay, so imagine you want to go to a fun playground, but it's too far away for you to walk there. Luckily, your parents have a car! The car has a driver (your mom, for example) and a bunch of seats for you and your friends to sit in. You and your friends are like the people who want to go to the playground, and the car is like a "principal bundle."

What's a bundle, you ask? A bundle is like a bunch of things all together. In this case, it's a bunch of seats in a car, or a bunch of points on a circle, or a bunch of arrows on a plane. These things are all grouped together in a bundle.

Now, a "principal bundle" is a special kind of bundle where every point has a special property. For example, imagine your mom's car is a special car that only takes people to the playground. Every seat in the car has the same special property - they all take people to the playground! That's what a "principal bundle" means - every point in the bundle has a special property that's the same.

In math, we use principal bundles a lot to help us understand things like gravity and electricity. Just like your mom's car takes you to the playground, a principal bundle helps us "transport" things like electric charges or particles of light from one place to another. It's like a special kind of "transportation system" that makes it easy for us to study these things.

So there you have it! A principal bundle is like a special car that takes us to a fun playground, and it helps us study things like electricity and gravity.