Primordial fluctuations

Imagine you are playing with a ball on a bouncy castle. The surface of the bouncy castle is not completely flat and smooth, but has tiny bumps and dips. When you bounce the ball, it follows the contours of these bumps and dips, creating little variations in the path it takes.

In the same way, when the universe was very young, it wasn't perfectly smooth and uniform. It had tiny variations in density and temperature, like the bumps and dips on the bouncy castle. These variations are called primordial fluctuations.

These fluctuations grew over time as the universe expanded and cooled, eventually leading to the formation of structures like galaxies and clusters of galaxies. Without these initial fluctuations, the universe would have been much more uniform and we wouldn't be here to talk about it!

Scientists study these primordial fluctuations by looking at the cosmic microwave background radiation, which is like a snapshot of the universe when it was just a baby. They use mathematical models and computer simulations to understand how these tiny variations grew and evolved into the universe we see today.