Scientists use something called the Doppler Effect to see how the universe is getting bigger. They do this by looking at the light from faraway galaxies. Here’s how it works:

1. Redshift and Blueshift:

   • When a galaxy is moving away from us, its light changes to the red side of the color spectrum. This is called redshift.
   • On the other hand, if a galaxy is getting closer, its light changes to the blue side. This is called blueshift.

2. Calculating Speed:

   • The amount that the light shifts tells scientists how fast the galaxy is moving. They use a special formula to figure this out:

     $v = c \cdot \frac{\Delta \lambda}{\lambda_0}$

   • In this formula, $c$ is the speed of light, $\Delta \lambda$ is how much the light changes, and $\lambda_0$ is the original light before it changed.

3. Understanding Expansion:

   • By looking at many galaxies and their light shifts, scientists can get a better idea of how the universe is expanding. This helps them see how fast the universe is growing over time.