I've been reading some cosmology papers lately and I'm just in awe at how clever an idea the cosmic distance ladder is. And I need to share that feeling!

So how do we know how fast the universe is expanding? Here is a thread on that. Sorry about the length Usually when doing science we use tools and equipment we understand and control to study things we don't. This broadly true whether you are measuring things with a ruler or studying particle physics with an accelerator.