Here's the breakdown:
* The Universe is expanding: The space between galaxies is stretching, causing them to move further apart.
* Hubble's Law: Edwin Hubble discovered that the farther away a galaxy is, the faster it appears to be moving away from us. This relationship is linear, meaning the speed increases proportionally with distance.
* Redshift: As galaxies move away, the light they emit is stretched, shifting towards the red end of the spectrum (hence "redshift"). The amount of redshift is directly related to the galaxy's speed.
Important Note: It's crucial to understand that galaxies aren't *actually* moving through space *faster* than nearby galaxies. The expansion of space itself is what causes them to appear to be moving faster. It's like dots on a balloon being stretched apart as the balloon inflates – the dots aren't moving, but their distance from each other increases.
This concept is fundamental to understanding the age and size of the universe, and it's a key piece of evidence supporting the Big Bang theory.
