How Does Cosmology Series: The FLRW Universe and The Friedmann Equation Work?

The FLRW universe is like a giant balloon that’s slowly getting bigger, and it helps scientists figure out how our whole universe grows over time.

Imagine you're blowing up a balloon with dots on it, just like stars in the sky. As you blow more air into the balloon, all the dots move away from each other. This is similar to what happens in the FLRW universe, where space itself stretches, making everything seem like it's moving apart, even though nothing is actually moving through space.

The Friedmann equation is like a rulebook that tells us how fast the balloon (or our universe) grows. It depends on two main things:

1. How much stuff (like matter and energy) is inside the balloon.
2. How fast it's already growing.

If there’s more stuff, the growth slows down, just like when you blow up a balloon with lots of sand in it, it takes more effort to make it bigger. But if there’s less stuff, or even something that pushes everything apart (like dark energy), the balloon can grow faster and faster, kind of like a bubble that keeps expanding on its own.

So scientists use this rulebook to guess how old the universe is, or how fast it might keep growing forever. The FLRW universe is like a giant balloon that’s slowly getting bigger, and it helps scientists figure out how our whole universe grows over time.

Imagine you're blowing up a balloon with dots on it, just like stars in the sky. As you blow more air into the balloon, all the dots move away from each other. This is similar to what happens in the FLRW universe, where space itself stretches, making everything seem like it's moving apart, even though nothing is actually moving through space.