What is Friedmann-Lemaître-Robertson-Walker (FLRW) metric?

The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is like a special map that helps us understand how the universe grows or shrinks over time.

Imagine you have a balloon, and you draw little dots on it, each dot represents a galaxy. When you blow up the balloon, all the dots move away from each other, just like galaxies in our real universe. This is similar to what the FLRW metric describes: how space itself stretches or contracts as time goes by.

The FLRW metric uses math to describe the shape of the universe, whether it’s flat like a piece of paper, curved like a sphere, or even saddle-shaped like a horseback. These different shapes affect how things move and expand over time.

It also helps scientists predict what will happen in the future, will the universe keep growing forever, or will it eventually collapse back on itself?

Think of it as a recipe for the universe. Scientists use this recipe to understand the past (like the Big Bang) and guess at the future (will the universe keep expanding?). It’s not magic, it’s just a clever way of using math to describe something huge and ever-changing, like our universe itself!