Yes. The expansion of the universe is extremely well documented. BTW, the average density of the universe is roughly 5.9 protons per cubic meter. This does not take dark matter or dark energy into account, mind you.
I was talking about the mass of the Universe expanding, which may not even be true
The mass of the universe is not increasing.
You said 'space' expands. If it expands, what is it expanding into, and how would you go about measuring that ?
It's not expanding "into" anything.
https://www.universetoday.com/1455/podcast-what-is-the-universe-expanding-into/
BTW, the average density of the universe is roughly 5.9 protons per cubic meter.
Where was that measurement taken ?
The mass of the universe is not increasing. How would we know whether it was or not ? We don't even know how 'big' it is, or if it is infinite.
It's not expanding "into" anything.
To help clarify, you are using 'space' and 'universe' interchangeably, correct ?