can you elaborate on this? sorry if it's a dumb question but like space? mass-wise? i thought the universe was mostly empty space? so what exactly is growing? dumb question i know but i'm a dumb person
No such thing as a dumb question.
Studying the electromagnetic spectrum shows us that energy is represented in different ways.
Focusing on observable light, we see a red tint in many objects observed. Through certain measurements, we can determine the red shift along the spectrum. Using mathematical models, this information shows us that celestial bodies are moving away from each other at an increasing rate.
Our universe is thought to have borders which are expanding. Imagine pouring pancake mix in a pan. The near-empty space expands. It is hard to visualize, but space is not a perfect vacuum, not perfectly empty.
The Law of Conservation of Mass says that mass cannot be created nor destroyed. That being said, it is believed that the universe does not contain enough mass to reach the level of gravity necessary to pull the borders back in. In other words, our universe will not retract into another big bang. So imagine pouring an infinate amount of mix on the floor.
All of that to say, objects are moving away from each other, so we think space itself is expanding.
I love this stuff! Amazing isn't it?